Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 6560 insertions, 0 deletions

diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
new file mode 100644
index 0000000000..83fe205e35
--- /dev/null
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -0,0 +1,6560 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CanvasRenderingContext2D.h"
+
+#include "mozilla/gfx/Helpers.h"
+#include "nsXULElement.h"
+
+#include "nsMathUtils.h"
+
+#include "nsContentUtils.h"
+
+#include "mozilla/intl/BidiEmbeddingLevel.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/SVGImageContext.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/FontFaceSetImpl.h"
+#include "mozilla/dom/FontFaceSet.h"
+#include "mozilla/dom/HTMLCanvasElement.h"
+#include "mozilla/dom/GeneratePlaceholderCanvasData.h"
+#include "nsPresContext.h"
+
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsIFrame.h"
+#include "nsError.h"
+
+#include "nsCSSPseudoElements.h"
+#include "nsComputedDOMStyle.h"
+
+#include "nsPrintfCString.h"
+
+#include "nsRFPService.h"
+#include "nsReadableUtils.h"
+
+#include "nsColor.h"
+#include "nsGfxCIID.h"
+#include "nsIDocShell.h"
+#include "nsPIDOMWindow.h"
+#include "nsDisplayList.h"
+#include "nsFocusManager.h"
+
+#include "nsTArray.h"
+
+#include "ImageEncoder.h"
+#include "ImageRegion.h"
+
+#include "gfxContext.h"
+#include "gfxPlatform.h"
+#include "gfxFont.h"
+#include "gfxBlur.h"
+#include "gfxTextRun.h"
+#include "gfxUtils.h"
+
+#include "nsFrameLoader.h"
+#include "nsBidiPresUtils.h"
+#include "LayerUserData.h"
+#include "CanvasUtils.h"
+#include "nsIMemoryReporter.h"
+#include "nsStyleUtil.h"
+#include "CanvasImageCache.h"
+#include "DrawTargetWebgl.h"
+
+#include <algorithm>
+
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/Array.h"  // JS::GetArrayLength
+#include "js/Conversions.h"
+#include "js/experimental/TypedData.h"  // JS_NewUint8ClampedArray, JS_GetUint8ClampedArrayData
+#include "js/HeapAPI.h"
+#include "js/PropertyAndElement.h"  // JS_GetElement
+#include "js/Warnings.h"            // JS::WarnASCII
+
+#include "mozilla/Alignment.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/CheckedInt.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/dom/CanvasGradient.h"
+#include "mozilla/dom/CanvasPattern.h"
+#include "mozilla/dom/DOMMatrix.h"
+#include "mozilla/dom/ImageBitmap.h"
+#include "mozilla/dom/ImageData.h"
+#include "mozilla/dom/PBrowserParent.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/dom/TypedArray.h"
+#include "mozilla/EndianUtils.h"
+#include "mozilla/FilterInstance.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Tools.h"
+#include "mozilla/gfx/PathHelpers.h"
+#include "mozilla/gfx/DataSurfaceHelpers.h"
+#include "mozilla/gfx/PatternHelpers.h"
+#include "mozilla/gfx/Swizzle.h"
+#include "mozilla/layers/PersistentBufferProvider.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/RestyleManager.h"
+#include "mozilla/ServoBindings.h"
+#include "mozilla/StaticPrefs_gfx.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "nsCCUncollectableMarker.h"
+#include "nsWrapperCacheInlines.h"
+#include "mozilla/dom/CanvasRenderingContext2DBinding.h"
+#include "mozilla/dom/CanvasPath.h"
+#include "mozilla/dom/HTMLImageElement.h"
+#include "mozilla/dom/HTMLVideoElement.h"
+#include "mozilla/dom/SVGImageElement.h"
+#include "mozilla/dom/TextMetrics.h"
+#include "mozilla/FloatingPoint.h"
+#include "nsGlobalWindow.h"
+#include "nsDeviceContext.h"
+#include "nsFontMetrics.h"
+#include "nsLayoutUtils.h"
+#include "Units.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+#include "mozilla/ServoCSSParser.h"
+#include "mozilla/ServoStyleSet.h"
+#include "mozilla/SVGContentUtils.h"
+#include "mozilla/layers/CanvasClient.h"
+#include "mozilla/layers/WebRenderUserData.h"
+#include "mozilla/layers/WebRenderCanvasRenderer.h"
+#include "WindowRenderer.h"
+
+#undef free  // apparently defined by some windows header, clashing with a
+             // free() method in SkTypes.h
+
+#ifdef XP_WIN
+#  include "gfxWindowsPlatform.h"
+#endif
+
+// windows.h (included by chromium code) defines this, in its infinite wisdom
+#undef DrawText
+
+using namespace mozilla;
+using namespace mozilla::CanvasUtils;
+using namespace mozilla::css;
+using namespace mozilla::gfx;
+using namespace mozilla::image;
+using namespace mozilla::ipc;
+using namespace mozilla::layers;
+
+namespace mozilla::dom {
+
+// Cap sigma to avoid overly large temp surfaces.
+const Float SIGMA_MAX = 100;
+
+const size_t MAX_STYLE_STACK_SIZE = 1024;
+
+/* Memory reporter stuff */
+static Atomic<int64_t> gCanvasAzureMemoryUsed(0);
+
+// Adds Save() / Restore() calls to the scope.
+class MOZ_RAII AutoSaveRestore {
+ public:
+  explicit AutoSaveRestore(CanvasRenderingContext2D* aCtx) : mCtx(aCtx) {
+    mCtx->Save();
+  }
+  ~AutoSaveRestore() { mCtx->Restore(); }
+
+ private:
+  RefPtr<CanvasRenderingContext2D> mCtx;
+};
+
+// This is KIND_OTHER because it's not always clear where in memory the pixels
+// of a canvas are stored.  Furthermore, this memory will be tracked by the
+// underlying surface implementations.  See bug 655638 for details.
+class Canvas2dPixelsReporter final : public nsIMemoryReporter {
+  ~Canvas2dPixelsReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    MOZ_COLLECT_REPORT("canvas-2d-pixels", KIND_OTHER, UNITS_BYTES,
+                       gCanvasAzureMemoryUsed,
+                       "Memory used by 2D canvases. Each canvas requires "
+                       "(width * height * 4) bytes.");
+
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(Canvas2dPixelsReporter, nsIMemoryReporter)
+
+class CanvasConicGradient : public CanvasGradient {
+ public:
+  CanvasConicGradient(CanvasRenderingContext2D* aContext, Float aAngle,
+                      const Point& aCenter)
+      : CanvasGradient(aContext, Type::CONIC),
+        mAngle(aAngle),
+        mCenter(aCenter) {}
+
+  const Float mAngle;
+  const Point mCenter;
+};
+
+class CanvasRadialGradient : public CanvasGradient {
+ public:
+  CanvasRadialGradient(CanvasRenderingContext2D* aContext,
+                       const Point& aBeginOrigin, Float aBeginRadius,
+                       const Point& aEndOrigin, Float aEndRadius)
+      : CanvasGradient(aContext, Type::RADIAL),
+        mCenter1(aBeginOrigin),
+        mCenter2(aEndOrigin),
+        mRadius1(aBeginRadius),
+        mRadius2(aEndRadius) {}
+
+  Point mCenter1;
+  Point mCenter2;
+  Float mRadius1;
+  Float mRadius2;
+};
+
+class CanvasLinearGradient : public CanvasGradient {
+ public:
+  CanvasLinearGradient(CanvasRenderingContext2D* aContext, const Point& aBegin,
+                       const Point& aEnd)
+      : CanvasGradient(aContext, Type::LINEAR), mBegin(aBegin), mEnd(aEnd) {}
+
+ protected:
+  friend struct CanvasBidiProcessor;
+  friend class CanvasGeneralPattern;
+
+  // Beginning of linear gradient.
+  Point mBegin;
+  // End of linear gradient.
+  Point mEnd;
+};
+
+bool CanvasRenderingContext2D::PatternIsOpaque(
+    CanvasRenderingContext2D::Style aStyle, bool* aIsColor) const {
+  const ContextState& state = CurrentState();
+  bool opaque = false;
+  bool color = false;
+  if (state.globalAlpha >= 1.0) {
+    if (state.patternStyles[aStyle] && state.patternStyles[aStyle]->mSurface) {
+      opaque = IsOpaque(state.patternStyles[aStyle]->mSurface->GetFormat());
+    } else if (!state.gradientStyles[aStyle]) {
+      // TODO: for gradient patterns we could check that all stops are opaque
+      // colors.
+      // it's a color pattern.
+      opaque = sRGBColor::FromABGR(state.colorStyles[aStyle]).a >= 1.0;
+      color = true;
+    }
+  }
+  if (aIsColor) {
+    *aIsColor = color;
+  }
+  return opaque;
+}
+
+// This class is named 'GeneralCanvasPattern' instead of just
+// 'GeneralPattern' to keep Windows PGO builds from confusing the
+// GeneralPattern class in gfxContext.cpp with this one.
+class CanvasGeneralPattern {
+ public:
+  using Style = CanvasRenderingContext2D::Style;
+  using ContextState = CanvasRenderingContext2D::ContextState;
+
+  Pattern& ForStyle(CanvasRenderingContext2D* aCtx, Style aStyle,
+                    DrawTarget* aRT) {
+    // This should only be called once or the mPattern destructor will
+    // not be executed.
+    NS_ASSERTION(
+        !mPattern.GetPattern(),
+        "ForStyle() should only be called once on CanvasGeneralPattern!");
+
+    const ContextState& state = aCtx->CurrentState();
+
+    if (state.StyleIsColor(aStyle)) {
+      mPattern.InitColorPattern(ToDeviceColor(state.colorStyles[aStyle]));
+    } else if (state.gradientStyles[aStyle] &&
+               state.gradientStyles[aStyle]->GetType() ==
+                   CanvasGradient::Type::LINEAR) {
+      auto gradient = static_cast<CanvasLinearGradient*>(
+          state.gradientStyles[aStyle].get());
+
+      mPattern.InitLinearGradientPattern(
+          gradient->mBegin, gradient->mEnd,
+          gradient->GetGradientStopsForTarget(aRT));
+    } else if (state.gradientStyles[aStyle] &&
+               state.gradientStyles[aStyle]->GetType() ==
+                   CanvasGradient::Type::RADIAL) {
+      auto gradient = static_cast<CanvasRadialGradient*>(
+          state.gradientStyles[aStyle].get());
+
+      mPattern.InitRadialGradientPattern(
+          gradient->mCenter1, gradient->mCenter2, gradient->mRadius1,
+          gradient->mRadius2, gradient->GetGradientStopsForTarget(aRT));
+    } else if (state.gradientStyles[aStyle] &&
+               state.gradientStyles[aStyle]->GetType() ==
+                   CanvasGradient::Type::CONIC) {
+      auto gradient =
+          static_cast<CanvasConicGradient*>(state.gradientStyles[aStyle].get());
+
+      mPattern.InitConicGradientPattern(
+          gradient->mCenter, gradient->mAngle, 0, 1,
+          gradient->GetGradientStopsForTarget(aRT));
+    } else if (state.patternStyles[aStyle]) {
+      aCtx->DoSecurityCheck(state.patternStyles[aStyle]->mPrincipal,
+                            state.patternStyles[aStyle]->mForceWriteOnly,
+                            state.patternStyles[aStyle]->mCORSUsed);
+
+      ExtendMode mode;
+      if (state.patternStyles[aStyle]->mRepeat ==
+          CanvasPattern::RepeatMode::NOREPEAT) {
+        mode = ExtendMode::CLAMP;
+      } else {
+        mode = ExtendMode::REPEAT;
+      }
+
+      SamplingFilter samplingFilter;
+      if (state.imageSmoothingEnabled) {
+        samplingFilter = SamplingFilter::GOOD;
+      } else {
+        samplingFilter = SamplingFilter::POINT;
+      }
+
+      mPattern.InitSurfacePattern(state.patternStyles[aStyle]->mSurface, mode,
+                                  state.patternStyles[aStyle]->mTransform,
+                                  samplingFilter);
+    }
+
+    return *mPattern.GetPattern();
+  }
+
+  GeneralPattern mPattern;
+};
+
+/* This is an RAII based class that can be used as a drawtarget for
+ * operations that need to have a filter applied to their results.
+ * All coordinates passed to the constructor are in device space.
+ */
+class AdjustedTargetForFilter {
+ public:
+  using ContextState = CanvasRenderingContext2D::ContextState;
+
+  AdjustedTargetForFilter(CanvasRenderingContext2D* aCtx,
+                          DrawTarget* aFinalTarget,
+                          const gfx::IntPoint& aFilterSpaceToTargetOffset,
+                          const gfx::IntRect& aPreFilterBounds,
+                          const gfx::IntRect& aPostFilterBounds,
+                          gfx::CompositionOp aCompositionOp)
+      : mFinalTarget(aFinalTarget),
+        mCtx(aCtx),
+        mPostFilterBounds(aPostFilterBounds),
+        mOffset(aFilterSpaceToTargetOffset),
+        mCompositionOp(aCompositionOp) {
+    nsIntRegion sourceGraphicNeededRegion;
+    nsIntRegion fillPaintNeededRegion;
+    nsIntRegion strokePaintNeededRegion;
+
+    FilterSupport::ComputeSourceNeededRegions(
+        aCtx->CurrentState().filter, mPostFilterBounds,
+        sourceGraphicNeededRegion, fillPaintNeededRegion,
+        strokePaintNeededRegion);
+
+    mSourceGraphicRect = sourceGraphicNeededRegion.GetBounds();
+    mFillPaintRect = fillPaintNeededRegion.GetBounds();
+    mStrokePaintRect = strokePaintNeededRegion.GetBounds();
+
+    mSourceGraphicRect = mSourceGraphicRect.Intersect(aPreFilterBounds);
+
+    if (mSourceGraphicRect.IsEmpty()) {
+      // The filter might not make any use of the source graphic. We need to
+      // create a DrawTarget that we can return from DT() anyway, so we'll
+      // just use a 1x1-sized one.
+      mSourceGraphicRect.SizeTo(1, 1);
+    }
+
+    if (!mFinalTarget->CanCreateSimilarDrawTarget(mSourceGraphicRect.Size(),
+                                                  SurfaceFormat::B8G8R8A8)) {
+      mTarget = mFinalTarget;
+      mCtx = nullptr;
+      mFinalTarget = nullptr;
+      return;
+    }
+
+    mTarget = mFinalTarget->CreateSimilarDrawTarget(mSourceGraphicRect.Size(),
+                                                    SurfaceFormat::B8G8R8A8);
+
+    if (mTarget) {
+      // See bug 1524554.
+      mTarget->ClearRect(gfx::Rect());
+    }
+
+    if (!mTarget || !mTarget->IsValid()) {
+      // XXX - Deal with the situation where our temp size is too big to
+      // fit in a texture (bug 1066622).
+      mTarget = mFinalTarget;
+      mCtx = nullptr;
+      mFinalTarget = nullptr;
+      return;
+    }
+
+    mTarget->SetTransform(mFinalTarget->GetTransform().PostTranslate(
+        -mSourceGraphicRect.TopLeft() + mOffset));
+  }
+
+  // Return a SourceSurface that contains the FillPaint or StrokePaint source.
+  already_AddRefed<SourceSurface> DoSourcePaint(
+      gfx::IntRect& aRect, CanvasRenderingContext2D::Style aStyle) {
+    if (aRect.IsEmpty()) {
+      return nullptr;
+    }
+
+    RefPtr<DrawTarget> dt = mFinalTarget->CreateSimilarDrawTarget(
+        aRect.Size(), SurfaceFormat::B8G8R8A8);
+
+    if (dt) {
+      // See bug 1524554.
+      dt->ClearRect(gfx::Rect());
+    }
+
+    if (!dt || !dt->IsValid()) {
+      aRect.SetEmpty();
+      return nullptr;
+    }
+
+    Matrix transform =
+        mFinalTarget->GetTransform().PostTranslate(-aRect.TopLeft() + mOffset);
+
+    dt->SetTransform(transform);
+
+    if (transform.Invert()) {
+      gfx::Rect dtBounds(0, 0, aRect.width, aRect.height);
+      gfx::Rect fillRect = transform.TransformBounds(dtBounds);
+      dt->FillRect(fillRect, CanvasGeneralPattern().ForStyle(mCtx, aStyle, dt));
+    }
+    return dt->Snapshot();
+  }
+
+  ~AdjustedTargetForFilter() {
+    if (!mCtx) {
+      return;
+    }
+
+    RefPtr<SourceSurface> snapshot = mTarget->Snapshot();
+
+    RefPtr<SourceSurface> fillPaint =
+        DoSourcePaint(mFillPaintRect, CanvasRenderingContext2D::Style::FILL);
+    RefPtr<SourceSurface> strokePaint = DoSourcePaint(
+        mStrokePaintRect, CanvasRenderingContext2D::Style::STROKE);
+
+    AutoRestoreTransform autoRestoreTransform(mFinalTarget);
+    mFinalTarget->SetTransform(Matrix());
+
+    MOZ_RELEASE_ASSERT(!mCtx->CurrentState().filter.mPrimitives.IsEmpty());
+    gfx::FilterSupport::RenderFilterDescription(
+        mFinalTarget, mCtx->CurrentState().filter, gfx::Rect(mPostFilterBounds),
+        snapshot, mSourceGraphicRect, fillPaint, mFillPaintRect, strokePaint,
+        mStrokePaintRect, mCtx->CurrentState().filterAdditionalImages,
+        mPostFilterBounds.TopLeft() - mOffset,
+        DrawOptions(1.0f, mCompositionOp));
+
+    const gfx::FilterDescription& filter = mCtx->CurrentState().filter;
+    MOZ_RELEASE_ASSERT(!filter.mPrimitives.IsEmpty());
+    if (filter.mPrimitives.LastElement().IsTainted()) {
+      if (mCtx->mCanvasElement) {
+        mCtx->mCanvasElement->SetWriteOnly();
+      } else if (mCtx->mOffscreenCanvas) {
+        mCtx->mOffscreenCanvas->SetWriteOnly();
+      }
+    }
+  }
+
+  DrawTarget* DT() { return mTarget; }
+
+ private:
+  RefPtr<DrawTarget> mTarget;
+  RefPtr<DrawTarget> mFinalTarget;
+  CanvasRenderingContext2D* mCtx;
+  gfx::IntRect mSourceGraphicRect;
+  gfx::IntRect mFillPaintRect;
+  gfx::IntRect mStrokePaintRect;
+  gfx::IntRect mPostFilterBounds;
+  gfx::IntPoint mOffset;
+  gfx::CompositionOp mCompositionOp;
+};
+
+/* This is an RAII based class that can be used as a drawtarget for
+ * operations that need to have a shadow applied to their results.
+ * All coordinates passed to the constructor are in device space.
+ */
+class AdjustedTargetForShadow {
+ public:
+  using ContextState = CanvasRenderingContext2D::ContextState;
+
+  AdjustedTargetForShadow(CanvasRenderingContext2D* aCtx,
+                          DrawTarget* aFinalTarget, const gfx::Rect& aBounds,
+                          gfx::CompositionOp aCompositionOp)
+      : mFinalTarget(aFinalTarget), mCtx(aCtx), mCompositionOp(aCompositionOp) {
+    const ContextState& state = mCtx->CurrentState();
+    mSigma = state.ShadowBlurSigma();
+
+    // We actually include the bounds of the shadow blur, this makes it
+    // easier to execute the actual blur on hardware, and shouldn't affect
+    // the amount of pixels that need to be touched.
+    gfx::Rect bounds = aBounds;
+    int32_t blurRadius = state.ShadowBlurRadius();
+    bounds.Inflate(blurRadius);
+    bounds.RoundOut();
+    if (!bounds.ToIntRect(&mTempRect) ||
+        !mFinalTarget->CanCreateSimilarDrawTarget(mTempRect.Size(),
+                                                  SurfaceFormat::B8G8R8A8)) {
+      mTarget = mFinalTarget;
+      mCtx = nullptr;
+      mFinalTarget = nullptr;
+      return;
+    }
+
+    mTarget = mFinalTarget->CreateShadowDrawTarget(
+        mTempRect.Size(), SurfaceFormat::B8G8R8A8, mSigma);
+
+    if (mTarget) {
+      // See bug 1524554.
+      mTarget->ClearRect(gfx::Rect());
+    }
+
+    if (!mTarget || !mTarget->IsValid()) {
+      // XXX - Deal with the situation where our temp size is too big to
+      // fit in a texture (bug 1066622).
+      mTarget = mFinalTarget;
+      mCtx = nullptr;
+      mFinalTarget = nullptr;
+    } else {
+      mTarget->SetTransform(
+          mFinalTarget->GetTransform().PostTranslate(-mTempRect.TopLeft()));
+    }
+  }
+
+  ~AdjustedTargetForShadow() {
+    if (!mCtx) {
+      return;
+    }
+
+    RefPtr<SourceSurface> snapshot = mTarget->Snapshot();
+
+    mFinalTarget->DrawSurfaceWithShadow(
+        snapshot, mTempRect.TopLeft(),
+        ShadowOptions(ToDeviceColor(mCtx->CurrentState().shadowColor),
+                      mCtx->CurrentState().shadowOffset, mSigma),
+        mCompositionOp);
+  }
+
+  DrawTarget* DT() { return mTarget; }
+
+  gfx::IntPoint OffsetToFinalDT() { return mTempRect.TopLeft(); }
+
+ private:
+  RefPtr<DrawTarget> mTarget;
+  RefPtr<DrawTarget> mFinalTarget;
+  CanvasRenderingContext2D* mCtx;
+  Float mSigma;
+  gfx::IntRect mTempRect;
+  gfx::CompositionOp mCompositionOp;
+};
+
+/*
+ * This is an RAII based class that can be used as a drawtarget for
+ * operations that need a shadow or a filter drawn. It will automatically
+ * provide a temporary target when needed, and if so blend it back with a
+ * shadow, filter, or both.
+ * If both a shadow and a filter are needed, the filter is applied first,
+ * and the shadow is applied to the filtered results.
+ *
+ * aBounds specifies the bounds of the drawing operation that will be
+ * drawn to the target, it is given in device space! If this is nullptr the
+ * drawing operation will be assumed to cover the whole canvas.
+ */
+class AdjustedTarget {
+ public:
+  using ContextState = CanvasRenderingContext2D::ContextState;
+
+  explicit AdjustedTarget(CanvasRenderingContext2D* aCtx,
+                          const gfx::Rect* aBounds = nullptr,
+                          bool aAllowOptimization = false)
+      : mCtx(aCtx),
+        mOptimizeShadow(false),
+        mUsedOperation(aCtx->CurrentState().op) {
+    // All rects in this function are in the device space of ctx->mTarget.
+
+    // In order to keep our temporary surfaces as small as possible, we first
+    // calculate what their maximum required bounds would need to be if we
+    // were to fill the whole canvas. Everything outside those bounds we don't
+    // need to render.
+    gfx::Rect r(0, 0, aCtx->mWidth, aCtx->mHeight);
+    gfx::Rect maxSourceNeededBoundsForShadow =
+        MaxSourceNeededBoundsForShadow(r, aCtx);
+    gfx::Rect maxSourceNeededBoundsForFilter =
+        MaxSourceNeededBoundsForFilter(maxSourceNeededBoundsForShadow, aCtx);
+    if (!aCtx->IsTargetValid()) {
+      return;
+    }
+
+    gfx::Rect bounds = maxSourceNeededBoundsForFilter;
+    if (aBounds) {
+      bounds = bounds.Intersect(*aBounds);
+    }
+    gfx::Rect boundsAfterFilter = BoundsAfterFilter(bounds, aCtx);
+    if (!aCtx->IsTargetValid() || !boundsAfterFilter.IsFinite()) {
+      return;
+    }
+
+    gfx::IntPoint offsetToFinalDT;
+
+    // First set up the shadow draw target, because the shadow goes outside.
+    // It applies to the post-filter results, if both a filter and a shadow
+    // are used.
+    const bool applyFilter = aCtx->NeedToApplyFilter();
+    if (aCtx->NeedToDrawShadow()) {
+      if (aAllowOptimization && !applyFilter) {
+        // If only drawing a shadow and no filter, then avoid buffering to an
+        // intermediate target while drawing the shadow directly to the final
+        // target. When doing so, we want to use the actual composition op
+        // instead of OP_OVER.
+        mTarget = aCtx->mTarget;
+        if (mTarget && mTarget->IsValid()) {
+          mOptimizeShadow = true;
+          return;
+        }
+      }
+      mShadowTarget = MakeUnique<AdjustedTargetForShadow>(
+          aCtx, aCtx->mTarget, boundsAfterFilter, mUsedOperation);
+      mTarget = mShadowTarget->DT();
+      offsetToFinalDT = mShadowTarget->OffsetToFinalDT();
+
+      // If we also have a filter, the filter needs to be drawn with OP_OVER
+      // because shadow drawing already applies op on the result.
+      mUsedOperation = CompositionOp::OP_OVER;
+    }
+
+    // Now set up the filter draw target.
+    if (!aCtx->IsTargetValid()) {
+      return;
+    }
+    if (applyFilter) {
+      bounds.RoundOut();
+
+      if (!mTarget) {
+        mTarget = aCtx->mTarget;
+      }
+      gfx::IntRect intBounds;
+      if (!bounds.ToIntRect(&intBounds)) {
+        return;
+      }
+      mFilterTarget = MakeUnique<AdjustedTargetForFilter>(
+          aCtx, mTarget, offsetToFinalDT, intBounds,
+          gfx::RoundedToInt(boundsAfterFilter), mUsedOperation);
+      mTarget = mFilterTarget->DT();
+      mUsedOperation = CompositionOp::OP_OVER;
+    }
+    if (!mTarget) {
+      mTarget = aCtx->mTarget;
+    }
+  }
+
+  ~AdjustedTarget() {
+    // The order in which the targets are finalized is important.
+    // Filters are inside, any shadow applies to the post-filter results.
+    mFilterTarget.reset();
+    mShadowTarget.reset();
+  }
+
+  operator DrawTarget*() { return mTarget; }
+
+  DrawTarget* operator->() MOZ_NO_ADDREF_RELEASE_ON_RETURN { return mTarget; }
+
+  CompositionOp UsedOperation() const { return mUsedOperation; }
+
+  ShadowOptions ShadowParams() const {
+    const ContextState& state = mCtx->CurrentState();
+    return ShadowOptions(ToDeviceColor(state.shadowColor), state.shadowOffset,
+                         state.ShadowBlurSigma());
+  }
+
+  void Fill(const Path* aPath, const Pattern& aPattern,
+            const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      mTarget->DrawShadow(aPath, aPattern, ShadowParams(), aOptions);
+    }
+    mTarget->Fill(aPath, aPattern, aOptions);
+  }
+
+  void FillRect(const Rect& aRect, const Pattern& aPattern,
+                const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      RefPtr<Path> path = MakePathForRect(*mTarget, aRect);
+      mTarget->DrawShadow(path, aPattern, ShadowParams(), aOptions);
+    }
+    mTarget->FillRect(aRect, aPattern, aOptions);
+  }
+
+  void Stroke(const Path* aPath, const Pattern& aPattern,
+              const StrokeOptions& aStrokeOptions,
+              const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      mTarget->DrawShadow(aPath, aPattern, ShadowParams(), aOptions,
+                          &aStrokeOptions);
+    }
+    mTarget->Stroke(aPath, aPattern, aStrokeOptions, aOptions);
+  }
+
+  void StrokeRect(const Rect& aRect, const Pattern& aPattern,
+                  const StrokeOptions& aStrokeOptions,
+                  const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      RefPtr<Path> path = MakePathForRect(*mTarget, aRect);
+      mTarget->DrawShadow(path, aPattern, ShadowParams(), aOptions,
+                          &aStrokeOptions);
+    }
+    mTarget->StrokeRect(aRect, aPattern, aStrokeOptions, aOptions);
+  }
+
+  void StrokeLine(const Point& aStart, const Point& aEnd,
+                  const Pattern& aPattern, const StrokeOptions& aStrokeOptions,
+                  const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      RefPtr<PathBuilder> builder = mTarget->CreatePathBuilder();
+      builder->MoveTo(aStart);
+      builder->LineTo(aEnd);
+      RefPtr<Path> path = builder->Finish();
+      mTarget->DrawShadow(path, aPattern, ShadowParams(), aOptions,
+                          &aStrokeOptions);
+    }
+    mTarget->StrokeLine(aStart, aEnd, aPattern, aStrokeOptions, aOptions);
+  }
+
+  void DrawSurface(SourceSurface* aSurface, const Rect& aDest,
+                   const Rect& aSource, const DrawSurfaceOptions& aSurfOptions,
+                   const DrawOptions& aOptions) {
+    if (mOptimizeShadow) {
+      RefPtr<Path> path = MakePathForRect(*mTarget, aSource);
+      ShadowOptions shadowParams(ShadowParams());
+      SurfacePattern pattern(aSurface, ExtendMode::CLAMP, Matrix(),
+                             shadowParams.BlurRadius() > 1
+                                 ? SamplingFilter::POINT
+                                 : aSurfOptions.mSamplingFilter);
+      Matrix matrix = Matrix::Scaling(aDest.width / aSource.width,
+                                      aDest.height / aSource.height);
+      matrix.PreTranslate(-aSource.x, -aSource.y);
+      matrix.PostTranslate(aDest.x, aDest.y);
+      AutoRestoreTransform autoRestoreTransform(mTarget);
+      mTarget->ConcatTransform(matrix);
+      mTarget->DrawShadow(path, pattern, shadowParams, aOptions);
+    }
+    mTarget->DrawSurface(aSurface, aDest, aSource, aSurfOptions, aOptions);
+  }
+
+ private:
+  gfx::Rect MaxSourceNeededBoundsForFilter(const gfx::Rect& aDestBounds,
+                                           CanvasRenderingContext2D* aCtx) {
+    const bool applyFilter = aCtx->NeedToApplyFilter();
+    if (!aCtx->IsTargetValid()) {
+      return aDestBounds;
+    }
+    if (!applyFilter) {
+      return aDestBounds;
+    }
+
+    nsIntRegion sourceGraphicNeededRegion;
+    nsIntRegion fillPaintNeededRegion;
+    nsIntRegion strokePaintNeededRegion;
+
+    FilterSupport::ComputeSourceNeededRegions(
+        aCtx->CurrentState().filter, gfx::RoundedToInt(aDestBounds),
+        sourceGraphicNeededRegion, fillPaintNeededRegion,
+        strokePaintNeededRegion);
+
+    return gfx::Rect(sourceGraphicNeededRegion.GetBounds());
+  }
+
+  gfx::Rect MaxSourceNeededBoundsForShadow(const gfx::Rect& aDestBounds,
+                                           CanvasRenderingContext2D* aCtx) {
+    if (!aCtx->NeedToDrawShadow()) {
+      return aDestBounds;
+    }
+
+    const ContextState& state = aCtx->CurrentState();
+    gfx::Rect sourceBounds = aDestBounds - state.shadowOffset;
+    sourceBounds.Inflate(state.ShadowBlurRadius());
+
+    // Union the shadow source with the original rect because we're going to
+    // draw both.
+    return sourceBounds.Union(aDestBounds);
+  }
+
+  gfx::Rect BoundsAfterFilter(const gfx::Rect& aBounds,
+                              CanvasRenderingContext2D* aCtx) {
+    const bool applyFilter = aCtx->NeedToApplyFilter();
+    if (!aCtx->IsTargetValid()) {
+      return aBounds;
+    }
+    if (!applyFilter) {
+      return aBounds;
+    }
+
+    gfx::Rect bounds(aBounds);
+    bounds.RoundOut();
+
+    gfx::IntRect intBounds;
+    if (!bounds.ToIntRect(&intBounds)) {
+      return gfx::Rect();
+    }
+
+    nsIntRegion extents = gfx::FilterSupport::ComputePostFilterExtents(
+        aCtx->CurrentState().filter, intBounds);
+    return gfx::Rect(extents.GetBounds());
+  }
+
+  CanvasRenderingContext2D* mCtx;
+  bool mOptimizeShadow;
+  CompositionOp mUsedOperation;
+  RefPtr<DrawTarget> mTarget;
+  UniquePtr<AdjustedTargetForShadow> mShadowTarget;
+  UniquePtr<AdjustedTargetForFilter> mFilterTarget;
+};
+
+void CanvasPattern::SetTransform(const DOMMatrix2DInit& aInit,
+                                 ErrorResult& aError) {
+  RefPtr<DOMMatrixReadOnly> matrix =
+      DOMMatrixReadOnly::FromMatrix(GetParentObject(), aInit, aError);
+  if (aError.Failed()) {
+    return;
+  }
+  const auto* matrix2D = matrix->GetInternal2D();
+  if (!matrix2D->IsFinite()) {
+    return;
+  }
+  mTransform = Matrix(*matrix2D);
+}
+
+void CanvasGradient::AddColorStop(float aOffset, const nsACString& aColorstr,
+                                  ErrorResult& aRv) {
+  if (aOffset < 0.0 || aOffset > 1.0) {
+    return aRv.ThrowIndexSizeError("Offset out of 0-1.0 range");
+  }
+
+  if (!mContext) {
+    return aRv.ThrowSyntaxError("No canvas context");
+  }
+
+  auto color = mContext->ParseColor(
+      aColorstr, CanvasRenderingContext2D::ResolveCurrentColor::No);
+  if (!color) {
+    return aRv.ThrowSyntaxError("Invalid color");
+  }
+
+  GradientStop newStop;
+
+  newStop.offset = aOffset;
+  newStop.color = ToDeviceColor(*color);
+
+  mRawStops.AppendElement(newStop);
+}
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(CanvasGradient, mContext)
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(CanvasPattern, mContext)
+
+class CanvasShutdownObserver final : public nsIObserver {
+ public:
+  explicit CanvasShutdownObserver(CanvasRenderingContext2D* aCanvas)
+      : mCanvas(aCanvas) {}
+
+  void OnShutdown() {
+    if (!mCanvas) {
+      return;
+    }
+
+    mCanvas = nullptr;
+    nsContentUtils::UnregisterShutdownObserver(this);
+  }
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+ private:
+  ~CanvasShutdownObserver() = default;
+
+  CanvasRenderingContext2D* mCanvas;
+};
+
+NS_IMPL_ISUPPORTS(CanvasShutdownObserver, nsIObserver)
+
+NS_IMETHODIMP
+CanvasShutdownObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                                const char16_t* aData) {
+  if (mCanvas && strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0) {
+    mCanvas->OnShutdown();
+    OnShutdown();
+  }
+
+  return NS_OK;
+}
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(CanvasRenderingContext2D)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(CanvasRenderingContext2D)
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(CanvasRenderingContext2D)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(CanvasRenderingContext2D)
+  // Make sure we remove ourselves from the list of demotable contexts (raw
+  // pointers), since we're logically destructed at this point.
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mCanvasElement)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mOffscreenCanvas)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDocShell)
+  for (uint32_t i = 0; i < tmp->mStyleStack.Length(); i++) {
+    ImplCycleCollectionUnlink(tmp->mStyleStack[i].patternStyles[Style::STROKE]);
+    ImplCycleCollectionUnlink(tmp->mStyleStack[i].patternStyles[Style::FILL]);
+    ImplCycleCollectionUnlink(
+        tmp->mStyleStack[i].gradientStyles[Style::STROKE]);
+    ImplCycleCollectionUnlink(tmp->mStyleStack[i].gradientStyles[Style::FILL]);
+    auto autoSVGFiltersObserver =
+        tmp->mStyleStack[i].autoSVGFiltersObserver.get();
+    if (autoSVGFiltersObserver) {
+      // XXXjwatt: I don't think this call achieves anything.  See the comment
+      // that documents this function.
+      SVGObserverUtils::DetachFromCanvasContext(autoSVGFiltersObserver);
+    }
+    ImplCycleCollectionUnlink(tmp->mStyleStack[i].autoSVGFiltersObserver);
+  }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(CanvasRenderingContext2D)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mCanvasElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOffscreenCanvas)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocShell)
+  for (uint32_t i = 0; i < tmp->mStyleStack.Length(); i++) {
+    ImplCycleCollectionTraverse(
+        cb, tmp->mStyleStack[i].patternStyles[Style::STROKE],
+        "Stroke CanvasPattern");
+    ImplCycleCollectionTraverse(cb,
+                                tmp->mStyleStack[i].patternStyles[Style::FILL],
+                                "Fill CanvasPattern");
+    ImplCycleCollectionTraverse(
+        cb, tmp->mStyleStack[i].gradientStyles[Style::STROKE],
+        "Stroke CanvasGradient");
+    ImplCycleCollectionTraverse(cb,
+                                tmp->mStyleStack[i].gradientStyles[Style::FILL],
+                                "Fill CanvasGradient");
+    ImplCycleCollectionTraverse(cb, tmp->mStyleStack[i].autoSVGFiltersObserver,
+                                "RAII SVG Filters Observer");
+  }
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(CanvasRenderingContext2D)
+  if (nsCCUncollectableMarker::sGeneration && tmp->HasKnownLiveWrapper()) {
+    dom::Element* canvasElement = tmp->mCanvasElement;
+    if (canvasElement) {
+      if (canvasElement->IsPurple()) {
+        canvasElement->RemovePurple();
+      }
+      dom::Element::MarkNodeChildren(canvasElement);
+    }
+    return true;
+  }
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(CanvasRenderingContext2D)
+  return nsCCUncollectableMarker::sGeneration && tmp->HasKnownLiveWrapper();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(CanvasRenderingContext2D)
+  return nsCCUncollectableMarker::sGeneration && tmp->HasKnownLiveWrapper();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(CanvasRenderingContext2D)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsICanvasRenderingContextInternal)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+CanvasRenderingContext2D::ContextState::ContextState() = default;
+
+CanvasRenderingContext2D::ContextState::ContextState(const ContextState& aOther)
+    : fontGroup(aOther.fontGroup),
+      fontLanguage(aOther.fontLanguage),
+      fontFont(aOther.fontFont),
+      gradientStyles(aOther.gradientStyles),
+      patternStyles(aOther.patternStyles),
+      colorStyles(aOther.colorStyles),
+      font(aOther.font),
+      textAlign(aOther.textAlign),
+      textBaseline(aOther.textBaseline),
+      textDirection(aOther.textDirection),
+      fontKerning(aOther.fontKerning),
+      letterSpacing(aOther.letterSpacing),
+      wordSpacing(aOther.wordSpacing),
+      letterSpacingStr(aOther.letterSpacingStr),
+      wordSpacingStr(aOther.wordSpacingStr),
+      shadowColor(aOther.shadowColor),
+      transform(aOther.transform),
+      shadowOffset(aOther.shadowOffset),
+      lineWidth(aOther.lineWidth),
+      miterLimit(aOther.miterLimit),
+      globalAlpha(aOther.globalAlpha),
+      shadowBlur(aOther.shadowBlur),
+      dash(aOther.dash.Clone()),
+      dashOffset(aOther.dashOffset),
+      op(aOther.op),
+      fillRule(aOther.fillRule),
+      lineCap(aOther.lineCap),
+      lineJoin(aOther.lineJoin),
+      filterString(aOther.filterString),
+      filterChain(aOther.filterChain),
+      autoSVGFiltersObserver(aOther.autoSVGFiltersObserver),
+      filter(aOther.filter),
+      filterAdditionalImages(aOther.filterAdditionalImages.Clone()),
+      filterSourceGraphicTainted(aOther.filterSourceGraphicTainted),
+      imageSmoothingEnabled(aOther.imageSmoothingEnabled),
+      fontExplicitLanguage(aOther.fontExplicitLanguage) {}
+
+CanvasRenderingContext2D::ContextState::~ContextState() = default;
+
+void CanvasRenderingContext2D::ContextState::SetColorStyle(Style aWhichStyle,
+                                                           nscolor aColor) {
+  colorStyles[aWhichStyle] = aColor;
+  gradientStyles[aWhichStyle] = nullptr;
+  patternStyles[aWhichStyle] = nullptr;
+}
+
+void CanvasRenderingContext2D::ContextState::SetPatternStyle(
+    Style aWhichStyle, CanvasPattern* aPat) {
+  gradientStyles[aWhichStyle] = nullptr;
+  patternStyles[aWhichStyle] = aPat;
+}
+
+void CanvasRenderingContext2D::ContextState::SetGradientStyle(
+    Style aWhichStyle, CanvasGradient* aGrad) {
+  gradientStyles[aWhichStyle] = aGrad;
+  patternStyles[aWhichStyle] = nullptr;
+}
+
+/**
+ ** CanvasRenderingContext2D impl
+ **/
+
+// Initialize our static variables.
+MOZ_THREAD_LOCAL(uintptr_t) CanvasRenderingContext2D::sNumLivingContexts;
+MOZ_THREAD_LOCAL(DrawTarget*) CanvasRenderingContext2D::sErrorTarget;
+
+CanvasRenderingContext2D::CanvasRenderingContext2D(
+    layers::LayersBackend aCompositorBackend)
+    :  // these are the default values from the Canvas spec
+      mWidth(0),
+      mHeight(0),
+      mZero(false),
+      mOpaqueAttrValue(false),
+      mContextAttributesHasAlpha(true),
+      mOpaque(false),
+      mResetLayer(true),
+      mIPC(false),
+      mHasPendingStableStateCallback(false),
+      mIsEntireFrameInvalid(false),
+      mPredictManyRedrawCalls(false),
+      mFrameCaptureState(FrameCaptureState::CLEAN,
+                         "CanvasRenderingContext2D::mFrameCaptureState"),
+      mPathTransformWillUpdate(false),
+      mInvalidateCount(0),
+      mWriteOnly(false) {
+  sNumLivingContexts.infallibleInit();
+  sErrorTarget.infallibleInit();
+  sNumLivingContexts.set(sNumLivingContexts.get() + 1);
+}
+
+CanvasRenderingContext2D::~CanvasRenderingContext2D() {
+  RemovePostRefreshObserver();
+  RemoveShutdownObserver();
+  ResetBitmap();
+
+  sNumLivingContexts.set(sNumLivingContexts.get() - 1);
+  if (sNumLivingContexts.get() == 0 && sErrorTarget.get()) {
+    RefPtr<DrawTarget> target = dont_AddRef(sErrorTarget.get());
+    sErrorTarget.set(nullptr);
+  }
+}
+
+void CanvasRenderingContext2D::Initialize() { AddShutdownObserver(); }
+
+JSObject* CanvasRenderingContext2D::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return CanvasRenderingContext2D_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+CanvasRenderingContext2D::ColorStyleCacheEntry
+CanvasRenderingContext2D::ParseColorSlow(const nsACString& aString) {
+  ColorStyleCacheEntry result{nsCString(aString)};
+  Document* document = mCanvasElement ? mCanvasElement->OwnerDoc() : nullptr;
+  css::Loader* loader = document ? document->CSSLoader() : nullptr;
+
+  PresShell* presShell = GetPresShell();
+  ServoStyleSet* set = presShell ? presShell->StyleSet() : nullptr;
+  bool wasCurrentColor = false;
+  nscolor color;
+  if (ServoCSSParser::ComputeColor(set, NS_RGB(0, 0, 0), aString, &color,
+                                   &wasCurrentColor, loader)) {
+    result.mWasCurrentColor = wasCurrentColor;
+    result.mColor.emplace(color);
+  }
+
+  return result;
+}
+
+Maybe<nscolor> CanvasRenderingContext2D::ParseColor(
+    const nsACString& aString, ResolveCurrentColor aResolveCurrentColor) {
+  auto entry = mColorStyleCache.Lookup(aString);
+  if (!entry) {
+    entry.Set(ParseColorSlow(aString));
+  }
+
+  const auto& data = entry.Data();
+  if (data.mWasCurrentColor && mCanvasElement &&
+      aResolveCurrentColor == ResolveCurrentColor::Yes) {
+    // If it was currentColor, get the value of the color property, flushing
+    // style if necessary.
+    RefPtr<const ComputedStyle> canvasStyle =
+        nsComputedDOMStyle::GetComputedStyle(mCanvasElement);
+    if (canvasStyle) {
+      return Some(canvasStyle->StyleText()->mColor.ToColor());
+    }
+  }
+  return data.mColor;
+}
+
+void CanvasRenderingContext2D::ResetBitmap(bool aFreeBuffer) {
+  if (mCanvasElement) {
+    mCanvasElement->InvalidateCanvas();
+  }
+
+  // only do this for non-docshell created contexts,
+  // since those are the ones that we created a surface for
+  if (mTarget && IsTargetValid() && !mDocShell) {
+    gCanvasAzureMemoryUsed -= mWidth * mHeight * 4;
+  }
+
+  bool forceReset = true;
+  ReturnTarget(forceReset);
+  mTarget = nullptr;
+  if (aFreeBuffer) {
+    mBufferProvider = nullptr;
+  } else if (mBufferProvider) {
+    // Try to keep the buffer around. However, we still need to clear the
+    // contents as if it was recreated before next use.
+    mBufferNeedsClear = true;
+  }
+
+  // Since the target changes the backing texture will change, and this will
+  // no longer be valid.
+  mIsEntireFrameInvalid = false;
+  mPredictManyRedrawCalls = false;
+  mFrameCaptureState = FrameCaptureState::CLEAN;
+}
+
+void CanvasRenderingContext2D::OnShutdown() {
+  mShutdownObserver = nullptr;
+
+  RefPtr<PersistentBufferProvider> provider = mBufferProvider;
+
+  ResetBitmap();
+
+  if (provider) {
+    provider->OnShutdown();
+  }
+}
+
+void CanvasRenderingContext2D::AddShutdownObserver() {
+  MOZ_ASSERT(!mShutdownObserver);
+  MOZ_ASSERT(NS_IsMainThread());
+
+  mShutdownObserver = new CanvasShutdownObserver(this);
+  nsContentUtils::RegisterShutdownObserver(mShutdownObserver);
+}
+
+void CanvasRenderingContext2D::RemoveShutdownObserver() {
+  if (mShutdownObserver) {
+    mShutdownObserver->OnShutdown();
+    mShutdownObserver = nullptr;
+  }
+}
+
+void CanvasRenderingContext2D::SetStyleFromString(const nsACString& aStr,
+                                                  Style aWhichStyle) {
+  MOZ_ASSERT(!aStr.IsVoid());
+
+  Maybe<nscolor> color = ParseColor(aStr);
+  if (!color) {
+    return;
+  }
+
+  CurrentState().SetColorStyle(aWhichStyle, *color);
+}
+
+void CanvasRenderingContext2D::GetStyleAsUnion(
+    OwningUTF8StringOrCanvasGradientOrCanvasPattern& aValue,
+    Style aWhichStyle) {
+  const ContextState& state = CurrentState();
+  if (state.patternStyles[aWhichStyle]) {
+    aValue.SetAsCanvasPattern() = state.patternStyles[aWhichStyle];
+  } else if (state.gradientStyles[aWhichStyle]) {
+    aValue.SetAsCanvasGradient() = state.gradientStyles[aWhichStyle];
+  } else {
+    StyleColorToString(state.colorStyles[aWhichStyle],
+                       aValue.SetAsUTF8String());
+  }
+}
+
+// static
+void CanvasRenderingContext2D::StyleColorToString(const nscolor& aColor,
+                                                  nsACString& aStr) {
+  aStr.Truncate();
+  // We can't reuse the normal CSS color stringification code,
+  // because the spec calls for a different algorithm for canvas.
+  if (NS_GET_A(aColor) == 255) {
+    aStr.AppendPrintf("#%02x%02x%02x", NS_GET_R(aColor), NS_GET_G(aColor),
+                      NS_GET_B(aColor));
+  } else {
+    aStr.AppendPrintf("rgba(%d, %d, %d, ", NS_GET_R(aColor), NS_GET_G(aColor),
+                      NS_GET_B(aColor));
+    aStr.AppendFloat(nsStyleUtil::ColorComponentToFloat(NS_GET_A(aColor)));
+    aStr.Append(')');
+  }
+}
+
+nsresult CanvasRenderingContext2D::Redraw() {
+  mFrameCaptureState = FrameCaptureState::DIRTY;
+
+  if (mIsEntireFrameInvalid) {
+    return NS_OK;
+  }
+
+  mIsEntireFrameInvalid = true;
+
+  if (mCanvasElement) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
+    mCanvasElement->InvalidateCanvasContent(nullptr);
+  } else if (mOffscreenCanvas) {
+    mOffscreenCanvas->QueueCommitToCompositor();
+  } else {
+    NS_ASSERTION(mDocShell, "Redraw with no canvas element or docshell!");
+  }
+
+  return NS_OK;
+}
+
+void CanvasRenderingContext2D::Redraw(const gfx::Rect& aR) {
+  mFrameCaptureState = FrameCaptureState::DIRTY;
+
+  ++mInvalidateCount;
+
+  if (mIsEntireFrameInvalid) {
+    return;
+  }
+
+  if (mPredictManyRedrawCalls || mInvalidateCount > kCanvasMaxInvalidateCount) {
+    Redraw();
+    return;
+  }
+
+  if (mCanvasElement) {
+    SVGObserverUtils::InvalidateDirectRenderingObservers(mCanvasElement);
+    mCanvasElement->InvalidateCanvasContent(&aR);
+  } else if (mOffscreenCanvas) {
+    mOffscreenCanvas->QueueCommitToCompositor();
+  } else {
+    NS_ASSERTION(mDocShell, "Redraw with no canvas element or docshell!");
+  }
+}
+
+void CanvasRenderingContext2D::DidRefresh() {}
+
+void CanvasRenderingContext2D::RedrawUser(const gfxRect& aR) {
+  mFrameCaptureState = FrameCaptureState::DIRTY;
+
+  if (mIsEntireFrameInvalid) {
+    ++mInvalidateCount;
+    return;
+  }
+
+  gfx::Rect newr = mTarget->GetTransform().TransformBounds(ToRect(aR));
+  Redraw(newr);
+}
+
+bool CanvasRenderingContext2D::CopyBufferProvider(
+    PersistentBufferProvider& aOld, DrawTarget& aTarget, IntRect aCopyRect) {
+  // Borrowing the snapshot must be done after ReturnTarget.
+  RefPtr<SourceSurface> snapshot = aOld.BorrowSnapshot();
+
+  if (!snapshot) {
+    return false;
+  }
+
+  aTarget.CopySurface(snapshot, aCopyRect, IntPoint());
+  aOld.ReturnSnapshot(snapshot.forget());
+  return true;
+}
+
+void CanvasRenderingContext2D::Demote() {}
+
+void CanvasRenderingContext2D::ScheduleStableStateCallback() {
+  if (mHasPendingStableStateCallback) {
+    return;
+  }
+  mHasPendingStableStateCallback = true;
+
+  nsContentUtils::RunInStableState(
+      NewRunnableMethod("dom::CanvasRenderingContext2D::OnStableState", this,
+                        &CanvasRenderingContext2D::OnStableState));
+}
+
+void CanvasRenderingContext2D::OnStableState() {
+  if (!mHasPendingStableStateCallback) {
+    return;
+  }
+
+  ReturnTarget();
+
+  mHasPendingStableStateCallback = false;
+}
+
+void CanvasRenderingContext2D::RestoreClipsAndTransformToTarget() {
+  // Restore clips and transform.
+  mTarget->SetTransform(Matrix());
+
+  if (mTarget->GetBackendType() == gfx::BackendType::CAIRO) {
+    // Cairo doesn't play well with huge clips. When given a very big clip it
+    // will try to allocate big mask surface without taking the target
+    // size into account which can cause OOM. See bug 1034593.
+    // This limits the clip extents to the size of the canvas.
+    // A fix in Cairo would probably be preferable, but requires somewhat
+    // invasive changes.
+    mTarget->PushClipRect(gfx::Rect(0, 0, mWidth, mHeight));
+  }
+
+  for (auto& style : mStyleStack) {
+    for (auto& clipOrTransform : style.clipsAndTransforms) {
+      if (clipOrTransform.IsClip()) {
+        if (mClipsNeedConverting) {
+          // We have possibly changed backends, so we need to convert the clips
+          // in case they are no longer compatible with mTarget.
+          RefPtr<PathBuilder> pathBuilder = mTarget->CreatePathBuilder();
+          clipOrTransform.clip->StreamToSink(pathBuilder);
+          clipOrTransform.clip = pathBuilder->Finish();
+        }
+        mTarget->PushClip(clipOrTransform.clip);
+      } else {
+        mTarget->SetTransform(clipOrTransform.transform);
+      }
+    }
+  }
+
+  mClipsNeedConverting = false;
+}
+
+bool CanvasRenderingContext2D::BorrowTarget(const IntRect& aPersistedRect,
+                                            bool aNeedsClear) {
+  // We are attempting to request a DrawTarget from the current
+  // PersistentBufferProvider. However, if the provider needs to be refreshed,
+  // or if it is accelerated and the application has requested that we disallow
+  // acceleration, then we skip trying to use this provider so that it will be
+  // recreated by EnsureTarget later.
+  if (!mBufferProvider || mBufferProvider->RequiresRefresh() ||
+      (mBufferProvider->IsAccelerated() && mWillReadFrequently)) {
+    return false;
+  }
+  mTarget = mBufferProvider->BorrowDrawTarget(aPersistedRect);
+  if (!mTarget || !mTarget->IsValid()) {
+    if (mTarget) {
+      mBufferProvider->ReturnDrawTarget(mTarget.forget());
+    }
+    return false;
+  }
+  if (mBufferNeedsClear) {
+    if (mBufferProvider->PreservesDrawingState()) {
+      // If the buffer provider preserves the clip and transform state, then
+      // we must ensure it is cleared before reusing the target.
+      if (!mTarget->RemoveAllClips()) {
+        mBufferProvider->ReturnDrawTarget(mTarget.forget());
+        return false;
+      }
+      mTarget->SetTransform(Matrix());
+    }
+    // If the canvas was reset, then we need to clear the target in case its
+    // contents was somehow preserved. We only need to clear the target if
+    // the operation doesn't fill the entire canvas.
+    if (aNeedsClear) {
+      mTarget->ClearRect(gfx::Rect(mTarget->GetRect()));
+    }
+  }
+  if (!mBufferProvider->PreservesDrawingState() || mBufferNeedsClear) {
+    RestoreClipsAndTransformToTarget();
+  }
+  mBufferNeedsClear = false;
+  return true;
+}
+
+bool CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
+                                            bool aWillClear) {
+  if (AlreadyShutDown()) {
+    gfxCriticalError() << "Attempt to render into a Canvas2d after shutdown.";
+    SetErrorState();
+    return false;
+  }
+
+  if (mTarget) {
+    return mTarget != sErrorTarget.get();
+  }
+
+  // Check that the dimensions are sane
+  if (mWidth > StaticPrefs::gfx_canvas_max_size() ||
+      mHeight > StaticPrefs::gfx_canvas_max_size() || mWidth < 0 ||
+      mHeight < 0) {
+    SetErrorState();
+    return false;
+  }
+
+  // If the next drawing command covers the entire canvas, we can skip copying
+  // from the previous frame and/or clearing the canvas.
+  gfx::Rect canvasRect(0, 0, mWidth, mHeight);
+  bool canDiscardContent =
+      aCoveredRect && CurrentState()
+                          .transform.TransformBounds(*aCoveredRect)
+                          .Contains(canvasRect);
+
+  // If a clip is active we don't know for sure that the next drawing command
+  // will really cover the entire canvas.
+  for (const auto& style : mStyleStack) {
+    if (!canDiscardContent) {
+      break;
+    }
+    for (const auto& clipOrTransform : style.clipsAndTransforms) {
+      if (clipOrTransform.IsClip()) {
+        canDiscardContent = false;
+        break;
+      }
+    }
+  }
+
+  ScheduleStableStateCallback();
+
+  IntRect persistedRect = canDiscardContent || mBufferNeedsClear
+                              ? IntRect()
+                              : IntRect(0, 0, mWidth, mHeight);
+
+  // Attempt to reuse the existing buffer provider.
+  if (BorrowTarget(persistedRect, !canDiscardContent)) {
+    return true;
+  }
+
+  RefPtr<DrawTarget> newTarget;
+  RefPtr<PersistentBufferProvider> newProvider;
+
+  if (!TryAcceleratedTarget(newTarget, newProvider) &&
+      !TrySharedTarget(newTarget, newProvider) &&
+      !TryBasicTarget(newTarget, newProvider)) {
+    gfxCriticalError(
+        CriticalLog::DefaultOptions(Factory::ReasonableSurfaceSize(GetSize())))
+        << "Failed borrow shared and basic targets.";
+
+    SetErrorState();
+    return false;
+  }
+
+  MOZ_ASSERT(newTarget);
+  MOZ_ASSERT(newProvider);
+
+  bool needsClear =
+      !canDiscardContent || (mBufferProvider && mBufferNeedsClear);
+  if (newTarget->GetBackendType() == gfx::BackendType::SKIA &&
+      (needsClear || !aWillClear)) {
+    // Skia expects the unused X channel to contains 0xFF even for opaque
+    // operations so we can't skip clearing in that case, even if we are going
+    // to cover the entire canvas in the next drawing operation.
+    newTarget->ClearRect(canvasRect);
+    needsClear = false;
+  }
+
+  // Try to copy data from the previous buffer provider if there is one.
+  if (!canDiscardContent && mBufferProvider && !mBufferNeedsClear &&
+      CopyBufferProvider(*mBufferProvider, *newTarget, persistedRect)) {
+    needsClear = false;
+  }
+
+  if (needsClear) {
+    newTarget->ClearRect(canvasRect);
+  }
+
+  mTarget = std::move(newTarget);
+  mBufferProvider = std::move(newProvider);
+  mBufferNeedsClear = false;
+
+  RegisterAllocation();
+  AddZoneWaitingForGC();
+
+  RestoreClipsAndTransformToTarget();
+
+  // Force a full layer transaction since we didn't have a layer before
+  // and now we might need one.
+  if (mCanvasElement) {
+    mCanvasElement->InvalidateCanvas();
+  }
+  // EnsureTarget hasn't drawn anything. Preserve mFrameCaptureState.
+  FrameCaptureState captureState = mFrameCaptureState;
+  // Calling Redraw() tells our invalidation machinery that the entire
+  // canvas is already invalid, which can speed up future drawing.
+  Redraw();
+  mFrameCaptureState = captureState;
+
+  return true;
+}
+
+void CanvasRenderingContext2D::SetInitialState() {
+  // Set up the initial canvas defaults
+  mPathBuilder = nullptr;
+  mPath = nullptr;
+  mDSPathBuilder = nullptr;
+  mPathTransformWillUpdate = false;
+
+  mStyleStack.Clear();
+  ContextState* state = mStyleStack.AppendElement();
+  state->globalAlpha = 1.0;
+
+  state->colorStyles[Style::FILL] = NS_RGB(0, 0, 0);
+  state->colorStyles[Style::STROKE] = NS_RGB(0, 0, 0);
+  state->shadowColor = NS_RGBA(0, 0, 0, 0);
+}
+
+void CanvasRenderingContext2D::SetErrorState() {
+  EnsureErrorTarget();
+
+  if (mTarget && mTarget != sErrorTarget.get()) {
+    gCanvasAzureMemoryUsed -= mWidth * mHeight * 4;
+  }
+
+  mTarget = sErrorTarget.get();
+  mBufferProvider = nullptr;
+
+  // clear transforms, clips, etc.
+  SetInitialState();
+}
+
+void CanvasRenderingContext2D::RegisterAllocation() {
+  // XXX - It would make more sense to track the allocation in
+  // PeristentBufferProvider, rather than here.
+  static bool registered = false;
+  // FIXME: Disable the reporter for now, see bug 1241865
+  if (!registered && false) {
+    registered = true;
+    RegisterStrongMemoryReporter(new Canvas2dPixelsReporter());
+  }
+}
+
+void CanvasRenderingContext2D::AddZoneWaitingForGC() {
+  JSObject* wrapper = GetWrapperPreserveColor();
+  if (wrapper) {
+    CycleCollectedJSRuntime::Get()->AddZoneWaitingForGC(
+        JS::GetObjectZone(wrapper));
+  }
+}
+
+static WindowRenderer* WindowRendererFromCanvasElement(
+    nsINode* aCanvasElement) {
+  if (!aCanvasElement) {
+    return nullptr;
+  }
+
+  return nsContentUtils::WindowRendererForDocument(aCanvasElement->OwnerDoc());
+}
+
+bool CanvasRenderingContext2D::TryAcceleratedTarget(
+    RefPtr<gfx::DrawTarget>& aOutDT,
+    RefPtr<layers::PersistentBufferProvider>& aOutProvider) {
+  if (!XRE_IsContentProcess()) {
+    // Only allow accelerated contexts to be created in a content process to
+    // ensure it is remoted appropriately and run on the correct parent or
+    // GPU process threads.
+    return false;
+  }
+  if (mBufferProvider && mBufferProvider->IsAccelerated() &&
+      mBufferProvider->RequiresRefresh()) {
+    // If there is already a provider and we got here, then the provider needs
+    // to be refreshed and we should avoid using acceleration in the future.
+    mAllowAcceleration = false;
+  }
+  // Don't try creating an accelerate DrawTarget if either acceleration failed
+  // previously or if the application expects acceleration to be slow.
+  if (!mAllowAcceleration || mWillReadFrequently) {
+    return false;
+  }
+  aOutDT = DrawTargetWebgl::Create(GetSize(), GetSurfaceFormat());
+  if (!aOutDT) {
+    return false;
+  }
+
+  aOutProvider = new PersistentBufferProviderAccelerated(aOutDT);
+  return true;
+}
+
+bool CanvasRenderingContext2D::TrySharedTarget(
+    RefPtr<gfx::DrawTarget>& aOutDT,
+    RefPtr<layers::PersistentBufferProvider>& aOutProvider) {
+  aOutDT = nullptr;
+  aOutProvider = nullptr;
+
+  if (!mCanvasElement) {
+    return false;
+  }
+
+  if (mBufferProvider && mBufferProvider->IsShared()) {
+    // we are already using a shared buffer provider, we are allocating a new
+    // one because the current one failed so let's just fall back to the basic
+    // provider.
+    mClipsNeedConverting = true;
+    return false;
+  }
+
+  WindowRenderer* renderer = WindowRendererFromCanvasElement(mCanvasElement);
+
+  if (!renderer) {
+    return false;
+  }
+
+  aOutProvider =
+      renderer->CreatePersistentBufferProvider(GetSize(), GetSurfaceFormat());
+
+  if (!aOutProvider) {
+    return false;
+  }
+
+  // We can pass an empty persisted rect since we just created the buffer
+  // provider (nothing to restore).
+  aOutDT = aOutProvider->BorrowDrawTarget(IntRect());
+  MOZ_ASSERT(aOutDT);
+
+  return !!aOutDT;
+}
+
+bool CanvasRenderingContext2D::TryBasicTarget(
+    RefPtr<gfx::DrawTarget>& aOutDT,
+    RefPtr<layers::PersistentBufferProvider>& aOutProvider) {
+  aOutDT = gfxPlatform::GetPlatform()->CreateOffscreenCanvasDrawTarget(
+      GetSize(), GetSurfaceFormat());
+  if (!aOutDT) {
+    return false;
+  }
+
+  // See Bug 1524554 - this forces DT initialization.
+  aOutDT->ClearRect(gfx::Rect());
+
+  if (!aOutDT->IsValid()) {
+    aOutDT = nullptr;
+    return false;
+  }
+
+  aOutProvider = new PersistentBufferProviderBasic(aOutDT);
+  return true;
+}
+
+PersistentBufferProvider* CanvasRenderingContext2D::GetBufferProvider() {
+  if (mBufferProvider && mBufferNeedsClear) {
+    // Force the buffer to clear before it is used.
+    EnsureTarget();
+  }
+  return mBufferProvider;
+}
+
+Maybe<SurfaceDescriptor> CanvasRenderingContext2D::GetFrontBuffer(
+    WebGLFramebufferJS*, const bool webvr) {
+  if (auto* provider = GetBufferProvider()) {
+    return provider->GetFrontBuffer();
+  }
+  return Nothing();
+}
+
+PresShell* CanvasRenderingContext2D::GetPresShell() {
+  if (mCanvasElement) {
+    return mCanvasElement->OwnerDoc()->GetPresShell();
+  }
+  if (mDocShell) {
+    return mDocShell->GetPresShell();
+  }
+  return nullptr;
+}
+
+NS_IMETHODIMP
+CanvasRenderingContext2D::SetDimensions(int32_t aWidth, int32_t aHeight) {
+  // Zero sized surfaces can cause problems.
+  mZero = false;
+  if (aHeight == 0) {
+    aHeight = 1;
+    mZero = true;
+  }
+  if (aWidth == 0) {
+    aWidth = 1;
+    mZero = true;
+  }
+
+  ClearTarget(aWidth, aHeight);
+
+  return NS_OK;
+}
+
+void CanvasRenderingContext2D::AddAssociatedMemory() {
+  JSObject* wrapper = GetWrapperMaybeDead();
+  if (wrapper) {
+    JS::AddAssociatedMemory(wrapper, BindingJSObjectMallocBytes(this),
+                            JS::MemoryUse::DOMBinding);
+  }
+}
+
+void CanvasRenderingContext2D::RemoveAssociatedMemory() {
+  JSObject* wrapper = GetWrapperMaybeDead();
+  if (wrapper) {
+    JS::RemoveAssociatedMemory(wrapper, BindingJSObjectMallocBytes(this),
+                               JS::MemoryUse::DOMBinding);
+  }
+}
+
+void CanvasRenderingContext2D::ClearTarget(int32_t aWidth, int32_t aHeight) {
+  // Only free the buffer provider if the size no longer matches.
+  bool freeBuffer = aWidth != mWidth || aHeight != mHeight;
+  ResetBitmap(freeBuffer);
+
+  mResetLayer = true;
+
+  SetInitialState();
+
+  // Update dimensions only if new (strictly positive) values were passed.
+  if (aWidth > 0 && aHeight > 0) {
+    // Update the memory size associated with the wrapper object when we change
+    // the dimensions. Note that we need to keep updating dying wrappers before
+    // they are finalized so that the memory accounting balances out.
+    RemoveAssociatedMemory();
+    mWidth = aWidth;
+    mHeight = aHeight;
+    AddAssociatedMemory();
+  }
+
+  if (mOffscreenCanvas) {
+    OffscreenCanvasDisplayData data;
+    data.mSize = {mWidth, mHeight};
+    data.mIsOpaque = mOpaque;
+    data.mIsAlphaPremult = true;
+    data.mDoPaintCallbacks = true;
+    mOffscreenCanvas->UpdateDisplayData(data);
+  }
+
+  if (!mCanvasElement || !mCanvasElement->IsInComposedDoc()) {
+    return;
+  }
+
+  // For vertical writing-mode, unless text-orientation is sideways,
+  // we'll modify the initial value of textBaseline to 'middle'.
+  RefPtr<const ComputedStyle> canvasStyle =
+      nsComputedDOMStyle::GetComputedStyle(mCanvasElement);
+  if (canvasStyle) {
+    WritingMode wm(canvasStyle);
+    if (wm.IsVertical() && !wm.IsSideways()) {
+      CurrentState().textBaseline = TextBaseline::MIDDLE;
+    }
+  }
+}
+
+void CanvasRenderingContext2D::ReturnTarget(bool aForceReset) {
+  if (mTarget && mBufferProvider && mTarget != sErrorTarget.get()) {
+    CurrentState().transform = mTarget->GetTransform();
+    if (aForceReset || !mBufferProvider->PreservesDrawingState()) {
+      for (const auto& style : mStyleStack) {
+        for (const auto& clipOrTransform : style.clipsAndTransforms) {
+          if (clipOrTransform.IsClip()) {
+            mTarget->PopClip();
+          }
+        }
+      }
+
+      if (mTarget->GetBackendType() == gfx::BackendType::CAIRO) {
+        // With the cairo backend we pushed an extra clip rect which we have to
+        // balance out here. See the comment in
+        // RestoreClipsAndTransformToTarget.
+        mTarget->PopClip();
+      }
+
+      mTarget->SetTransform(Matrix());
+    }
+
+    mBufferProvider->ReturnDrawTarget(mTarget.forget());
+  }
+}
+
+NS_IMETHODIMP
+CanvasRenderingContext2D::InitializeWithDrawTarget(
+    nsIDocShell* aShell, NotNull<gfx::DrawTarget*> aTarget) {
+  RemovePostRefreshObserver();
+  mDocShell = aShell;
+  AddPostRefreshObserverIfNecessary();
+
+  IntSize size = aTarget->GetSize();
+  SetDimensions(size.width, size.height);
+
+  mTarget = aTarget;
+  mBufferProvider = new PersistentBufferProviderBasic(aTarget);
+
+  RestoreClipsAndTransformToTarget();
+
+  return NS_OK;
+}
+
+void CanvasRenderingContext2D::SetOpaqueValueFromOpaqueAttr(
+    bool aOpaqueAttrValue) {
+  if (aOpaqueAttrValue != mOpaqueAttrValue) {
+    mOpaqueAttrValue = aOpaqueAttrValue;
+    UpdateIsOpaque();
+  }
+}
+
+void CanvasRenderingContext2D::UpdateIsOpaque() {
+  mOpaque = !mContextAttributesHasAlpha || mOpaqueAttrValue;
+  ClearTarget();
+}
+
+NS_IMETHODIMP
+CanvasRenderingContext2D::SetContextOptions(JSContext* aCx,
+                                            JS::Handle<JS::Value> aOptions,
+                                            ErrorResult& aRvForDictionaryInit) {
+  if (aOptions.isNullOrUndefined()) {
+    return NS_OK;
+  }
+
+  // This shouldn't be called before drawing starts, so there should be no
+  // drawtarget yet
+  MOZ_ASSERT(!mTarget);
+
+  ContextAttributes2D attributes;
+  if (!attributes.Init(aCx, aOptions)) {
+    aRvForDictionaryInit.Throw(NS_ERROR_UNEXPECTED);
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  mWillReadFrequently = attributes.mWillReadFrequently;
+
+  mContextAttributesHasAlpha = attributes.mAlpha;
+  UpdateIsOpaque();
+
+  return NS_OK;
+}
+
+UniquePtr<uint8_t[]> CanvasRenderingContext2D::GetImageBuffer(
+    int32_t* out_format, gfx::IntSize* out_imageSize) {
+  UniquePtr<uint8_t[]> ret;
+
+  *out_format = 0;
+  *out_imageSize = {};
+
+  if (!GetBufferProvider() && !EnsureTarget()) {
+    return nullptr;
+  }
+
+  RefPtr<SourceSurface> snapshot = mBufferProvider->BorrowSnapshot();
+  if (snapshot) {
+    RefPtr<DataSourceSurface> data = snapshot->GetDataSurface();
+    if (data && data->GetSize() == GetSize()) {
+      *out_format = imgIEncoder::INPUT_FORMAT_HOSTARGB;
+      *out_imageSize = data->GetSize();
+      ret = SurfaceToPackedBGRA(data);
+    }
+  }
+
+  mBufferProvider->ReturnSnapshot(snapshot.forget());
+
+  if (ret && ShouldResistFingerprinting(RFPTarget::CanvasRandomization)) {
+    nsRFPService::RandomizePixels(
+        GetCookieJarSettings(), ret.get(),
+        out_imageSize->width * out_imageSize->height * 4,
+        SurfaceFormat::A8R8G8B8_UINT32);
+  }
+
+  return ret;
+}
+
+NS_IMETHODIMP
+CanvasRenderingContext2D::GetInputStream(const char* aMimeType,
+                                         const nsAString& aEncoderOptions,
+                                         nsIInputStream** aStream) {
+  nsCString enccid("@mozilla.org/image/encoder;2?type=");
+  enccid += aMimeType;
+  nsCOMPtr<imgIEncoder> encoder = do_CreateInstance(enccid.get());
+  if (!encoder) {
+    return NS_ERROR_FAILURE;
+  }
+
+  int32_t format = 0;
+  gfx::IntSize imageSize = {};
+  UniquePtr<uint8_t[]> imageBuffer = GetImageBuffer(&format, &imageSize);
+  if (!imageBuffer) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return ImageEncoder::GetInputStream(imageSize.width, imageSize.height,
+                                      imageBuffer.get(), format, encoder,
+                                      aEncoderOptions, aStream);
+}
+
+already_AddRefed<mozilla::gfx::SourceSurface>
+CanvasRenderingContext2D::GetOptimizedSnapshot(DrawTarget* aTarget,
+                                               gfxAlphaType* aOutAlphaType) {
+  if (aOutAlphaType) {
+    *aOutAlphaType = (mOpaque ? gfxAlphaType::Opaque : gfxAlphaType::Premult);
+  }
+
+  // For GetSurfaceSnapshot we always call EnsureTarget even if mBufferProvider
+  // already exists, otherwise we get performance issues. See bug 1567054.
+  if (!EnsureTarget()) {
+    MOZ_ASSERT(
+        mTarget == sErrorTarget.get(),
+        "On EnsureTarget failure mTarget should be set to sErrorTarget.");
+    // In rare circumstances we may have failed to create an error target.
+    return mTarget ? mTarget->Snapshot() : nullptr;
+  }
+
+  // The concept of BorrowSnapshot seems a bit broken here, but the original
+  // code in GetSurfaceSnapshot just returned a snapshot from mTarget, which
+  // amounts to breaking the concept implicitly.
+  RefPtr<SourceSurface> snapshot = mBufferProvider->BorrowSnapshot(aTarget);
+  RefPtr<SourceSurface> retSurface = snapshot;
+  mBufferProvider->ReturnSnapshot(snapshot.forget());
+  return retSurface.forget();
+}
+
+SurfaceFormat CanvasRenderingContext2D::GetSurfaceFormat() const {
+  return mOpaque ? SurfaceFormat::B8G8R8X8 : SurfaceFormat::B8G8R8A8;
+}
+
+//
+// state
+//
+
+void CanvasRenderingContext2D::Save() {
+  EnsureTarget();
+  if (MOZ_UNLIKELY(!mTarget || mStyleStack.IsEmpty())) {
+    SetErrorState();
+    return;
+  }
+  mStyleStack[mStyleStack.Length() - 1].transform = mTarget->GetTransform();
+  mStyleStack.SetCapacity(mStyleStack.Length() + 1);
+  mStyleStack.AppendElement(CurrentState());
+
+  if (mStyleStack.Length() > MAX_STYLE_STACK_SIZE) {
+    // This is not fast, but is better than OOMing and shouldn't be hit by
+    // reasonable code.
+    mStyleStack.RemoveElementAt(0);
+  }
+}
+
+void CanvasRenderingContext2D::Restore() {
+  if (MOZ_UNLIKELY(mStyleStack.Length() < 2)) {
+    return;
+  }
+
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  for (const auto& clipOrTransform : CurrentState().clipsAndTransforms) {
+    if (clipOrTransform.IsClip()) {
+      mTarget->PopClip();
+    }
+  }
+
+  mStyleStack.RemoveLastElement();
+
+  mTarget->SetTransform(CurrentState().transform);
+}
+
+//
+// transformations
+//
+
+void CanvasRenderingContext2D::Scale(double aX, double aY,
+                                     ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Matrix newMatrix = mTarget->GetTransform();
+  newMatrix.PreScale(aX, aY);
+
+  SetTransformInternal(newMatrix);
+}
+
+void CanvasRenderingContext2D::Rotate(double aAngle, ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Matrix newMatrix = Matrix::Rotation(aAngle) * mTarget->GetTransform();
+
+  SetTransformInternal(newMatrix);
+}
+
+void CanvasRenderingContext2D::Translate(double aX, double aY,
+                                         ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Matrix newMatrix = mTarget->GetTransform();
+  newMatrix.PreTranslate(aX, aY);
+
+  SetTransformInternal(newMatrix);
+}
+
+void CanvasRenderingContext2D::Transform(double aM11, double aM12, double aM21,
+                                         double aM22, double aDx, double aDy,
+                                         ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Matrix newMatrix(aM11, aM12, aM21, aM22, aDx, aDy);
+  newMatrix *= mTarget->GetTransform();
+
+  SetTransformInternal(newMatrix);
+}
+
+already_AddRefed<DOMMatrix> CanvasRenderingContext2D::GetTransform(
+    ErrorResult& aError) {
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+  RefPtr<DOMMatrix> matrix =
+      new DOMMatrix(GetParentObject(), mTarget->GetTransform());
+  return matrix.forget();
+}
+
+void CanvasRenderingContext2D::SetTransform(double aM11, double aM12,
+                                            double aM21, double aM22,
+                                            double aDx, double aDy,
+                                            ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  SetTransformInternal(Matrix(aM11, aM12, aM21, aM22, aDx, aDy));
+}
+
+void CanvasRenderingContext2D::SetTransform(const DOMMatrix2DInit& aInit,
+                                            ErrorResult& aError) {
+  TransformWillUpdate();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  RefPtr<DOMMatrixReadOnly> matrix =
+      DOMMatrixReadOnly::FromMatrix(GetParentObject(), aInit, aError);
+  if (!aError.Failed()) {
+    SetTransformInternal(Matrix(*(matrix->GetInternal2D())));
+  }
+}
+
+void CanvasRenderingContext2D::SetTransformInternal(const Matrix& aTransform) {
+  if (!aTransform.IsFinite()) {
+    return;
+  }
+
+  // Save the transform in the clip stack to be able to replay clips properly.
+  auto& clipsAndTransforms = CurrentState().clipsAndTransforms;
+  if (clipsAndTransforms.IsEmpty() ||
+      clipsAndTransforms.LastElement().IsClip()) {
+    clipsAndTransforms.AppendElement(ClipState(aTransform));
+  } else {
+    // If the last item is a transform we can replace it instead of appending
+    // a new item.
+    clipsAndTransforms.LastElement().transform = aTransform;
+  }
+  mTarget->SetTransform(aTransform);
+}
+
+void CanvasRenderingContext2D::ResetTransform(ErrorResult& aError) {
+  SetTransform(1.0, 0.0, 0.0, 1.0, 0.0, 0.0, aError);
+}
+
+//
+// colors
+//
+
+void CanvasRenderingContext2D::SetStyleFromUnion(
+    const UTF8StringOrCanvasGradientOrCanvasPattern& aValue,
+    Style aWhichStyle) {
+  if (aValue.IsUTF8String()) {
+    SetStyleFromString(aValue.GetAsUTF8String(), aWhichStyle);
+    return;
+  }
+
+  if (aValue.IsCanvasGradient()) {
+    SetStyleFromGradient(aValue.GetAsCanvasGradient(), aWhichStyle);
+    return;
+  }
+
+  if (aValue.IsCanvasPattern()) {
+    CanvasPattern& pattern = aValue.GetAsCanvasPattern();
+    SetStyleFromPattern(pattern, aWhichStyle);
+    if (pattern.mForceWriteOnly) {
+      SetWriteOnly();
+    }
+    return;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Invalid union value");
+}
+
+void CanvasRenderingContext2D::SetFillRule(const nsAString& aString) {
+  FillRule rule;
+
+  if (aString.EqualsLiteral("evenodd"))
+    rule = FillRule::FILL_EVEN_ODD;
+  else if (aString.EqualsLiteral("nonzero"))
+    rule = FillRule::FILL_WINDING;
+  else
+    return;
+
+  CurrentState().fillRule = rule;
+}
+
+void CanvasRenderingContext2D::GetFillRule(nsAString& aString) {
+  switch (CurrentState().fillRule) {
+    case FillRule::FILL_WINDING:
+      aString.AssignLiteral("nonzero");
+      break;
+    case FillRule::FILL_EVEN_ODD:
+      aString.AssignLiteral("evenodd");
+      break;
+  }
+}
+//
+// gradients and patterns
+//
+already_AddRefed<CanvasGradient> CanvasRenderingContext2D::CreateLinearGradient(
+    double aX0, double aY0, double aX1, double aY1) {
+  RefPtr<CanvasGradient> grad =
+      new CanvasLinearGradient(this, Point(aX0, aY0), Point(aX1, aY1));
+
+  return grad.forget();
+}
+
+already_AddRefed<CanvasGradient> CanvasRenderingContext2D::CreateRadialGradient(
+    double aX0, double aY0, double aR0, double aX1, double aY1, double aR1,
+    ErrorResult& aError) {
+  if (aR0 < 0.0 || aR1 < 0.0) {
+    aError.ThrowIndexSizeError("Negative radius");
+    return nullptr;
+  }
+
+  RefPtr<CanvasGradient> grad = new CanvasRadialGradient(
+      this, Point(aX0, aY0), aR0, Point(aX1, aY1), aR1);
+
+  return grad.forget();
+}
+
+already_AddRefed<CanvasGradient> CanvasRenderingContext2D::CreateConicGradient(
+    double aAngle, double aCx, double aCy) {
+  double adjustedStartAngle = aAngle + M_PI / 2.0;
+  return MakeAndAddRef<CanvasConicGradient>(this, adjustedStartAngle,
+                                            Point(aCx, aCy));
+}
+
+already_AddRefed<CanvasPattern> CanvasRenderingContext2D::CreatePattern(
+    const CanvasImageSource& aSource, const nsAString& aRepeat,
+    ErrorResult& aError) {
+  CanvasPattern::RepeatMode repeatMode = CanvasPattern::RepeatMode::NOREPEAT;
+
+  if (aRepeat.IsEmpty() || aRepeat.EqualsLiteral("repeat")) {
+    repeatMode = CanvasPattern::RepeatMode::REPEAT;
+  } else if (aRepeat.EqualsLiteral("repeat-x")) {
+    repeatMode = CanvasPattern::RepeatMode::REPEATX;
+  } else if (aRepeat.EqualsLiteral("repeat-y")) {
+    repeatMode = CanvasPattern::RepeatMode::REPEATY;
+  } else if (aRepeat.EqualsLiteral("no-repeat")) {
+    repeatMode = CanvasPattern::RepeatMode::NOREPEAT;
+  } else {
+    aError.ThrowSyntaxError("Invalid pattern keyword");
+    return nullptr;
+  }
+
+  Element* element = nullptr;
+  OffscreenCanvas* offscreenCanvas = nullptr;
+
+  if (aSource.IsHTMLCanvasElement()) {
+    HTMLCanvasElement* canvas = &aSource.GetAsHTMLCanvasElement();
+    element = canvas;
+
+    nsIntSize size = canvas->GetSize();
+    if (size.width == 0) {
+      aError.ThrowInvalidStateError("Passed-in canvas has width 0");
+      return nullptr;
+    }
+
+    if (size.height == 0) {
+      aError.ThrowInvalidStateError("Passed-in canvas has height 0");
+      return nullptr;
+    }
+
+    // Special case for Canvas, which could be an Azure canvas!
+    nsICanvasRenderingContextInternal* srcCanvas = canvas->GetCurrentContext();
+    if (srcCanvas) {
+      // This might not be an Azure canvas!
+      RefPtr<SourceSurface> srcSurf = srcCanvas->GetSurfaceSnapshot();
+      if (!srcSurf) {
+        aError.ThrowInvalidStateError(
+            "CanvasRenderingContext2D.createPattern() failed to snapshot source"
+            "canvas.");
+        return nullptr;
+      }
+
+      RefPtr<CanvasPattern> pat =
+          new CanvasPattern(this, srcSurf, repeatMode, element->NodePrincipal(),
+                            canvas->IsWriteOnly(), false);
+
+      return pat.forget();
+    }
+  } else if (aSource.IsHTMLImageElement()) {
+    HTMLImageElement* img = &aSource.GetAsHTMLImageElement();
+    element = img;
+  } else if (aSource.IsSVGImageElement()) {
+    SVGImageElement* img = &aSource.GetAsSVGImageElement();
+    element = img;
+  } else if (aSource.IsHTMLVideoElement()) {
+    auto& video = aSource.GetAsHTMLVideoElement();
+    video.LogVisibility(
+        mozilla::dom::HTMLVideoElement::CallerAPI::CREATE_PATTERN);
+    element = &video;
+  } else if (aSource.IsOffscreenCanvas()) {
+    offscreenCanvas = &aSource.GetAsOffscreenCanvas();
+
+    nsIntSize size = offscreenCanvas->GetWidthHeight();
+    if (size.width == 0) {
+      aError.ThrowInvalidStateError("Passed-in canvas has width 0");
+      return nullptr;
+    }
+
+    if (size.height == 0) {
+      aError.ThrowInvalidStateError("Passed-in canvas has height 0");
+      return nullptr;
+    }
+
+    nsICanvasRenderingContextInternal* srcCanvas =
+        offscreenCanvas->GetContext();
+    if (srcCanvas) {
+      RefPtr<SourceSurface> srcSurf = srcCanvas->GetSurfaceSnapshot();
+      if (!srcSurf) {
+        aError.ThrowInvalidStateError(
+            "Passed-in canvas failed to create snapshot");
+        return nullptr;
+      }
+
+      RefPtr<CanvasPattern> pat = new CanvasPattern(
+          this, srcSurf, repeatMode, srcCanvas->PrincipalOrNull(),
+          offscreenCanvas->IsWriteOnly(), false);
+
+      return pat.forget();
+    }
+  } else {
+    // Special case for ImageBitmap
+    ImageBitmap& imgBitmap = aSource.GetAsImageBitmap();
+    EnsureTarget();
+    if (!IsTargetValid()) {
+      aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return nullptr;
+    }
+    RefPtr<SourceSurface> srcSurf = imgBitmap.PrepareForDrawTarget(mTarget);
+    if (!srcSurf) {
+      aError.ThrowInvalidStateError(
+          "Passed-in ImageBitmap has been transferred");
+      return nullptr;
+    }
+
+    // An ImageBitmap never taints others so we set principalForSecurityCheck to
+    // nullptr and set CORSUsed to true for passing the security check in
+    // CanvasUtils::DoDrawImageSecurityCheck().
+    RefPtr<CanvasPattern> pat = new CanvasPattern(
+        this, srcSurf, repeatMode, nullptr, imgBitmap.IsWriteOnly(), true);
+
+    return pat.forget();
+  }
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return nullptr;
+  }
+
+  // The canvas spec says that createPattern should use the first frame
+  // of animated images
+  auto flags = nsLayoutUtils::SFE_WANT_FIRST_FRAME_IF_IMAGE |
+               nsLayoutUtils::SFE_EXACT_SIZE_SURFACE;
+  SurfaceFromElementResult res =
+      offscreenCanvas
+          ? nsLayoutUtils::SurfaceFromOffscreenCanvas(offscreenCanvas, flags,
+                                                      mTarget)
+          : nsLayoutUtils::SurfaceFromElement(element, flags, mTarget);
+
+  // Per spec, we should throw here for the HTMLImageElement and SVGImageElement
+  // cases if the image request state is "broken".  In terms of the infromation
+  // in "res", the "broken" state corresponds to not having a size and not being
+  // still-loading (so there is no size forthcoming).
+  if (aSource.IsHTMLImageElement() || aSource.IsSVGImageElement()) {
+    if (!res.mIsStillLoading && !res.mHasSize) {
+      aError.ThrowInvalidStateError(
+          "Passed-in image's current request's state is \"broken\"");
+      return nullptr;
+    }
+
+    if (res.mSize.width == 0 || res.mSize.height == 0) {
+      return nullptr;
+    }
+
+    // Is the "fully decodable" check already done in SurfaceFromElement?  It's
+    // not clear how to do it from here, exactly.
+  }
+
+  RefPtr<SourceSurface> surface = res.GetSourceSurface();
+  if (!surface) {
+    return nullptr;
+  }
+
+  RefPtr<CanvasPattern> pat =
+      new CanvasPattern(this, surface, repeatMode, res.mPrincipal,
+                        res.mIsWriteOnly, res.mCORSUsed);
+  return pat.forget();
+}
+
+//
+// shadows
+//
+void CanvasRenderingContext2D::SetShadowColor(const nsACString& aShadowColor) {
+  Maybe<nscolor> color = ParseColor(aShadowColor);
+  if (!color) {
+    return;
+  }
+
+  CurrentState().shadowColor = *color;
+}
+
+//
+// filters
+//
+
+static already_AddRefed<StyleLockedDeclarationBlock> CreateDeclarationForServo(
+    nsCSSPropertyID aProperty, const nsACString& aPropertyValue,
+    Document* aDocument) {
+  ServoCSSParser::ParsingEnvironment env{aDocument->DefaultStyleAttrURLData(),
+                                         aDocument->GetCompatibilityMode(),
+                                         aDocument->CSSLoader()};
+  RefPtr<StyleLockedDeclarationBlock> servoDeclarations =
+      ServoCSSParser::ParseProperty(aProperty, aPropertyValue, env);
+
+  if (!servoDeclarations) {
+    // We got a syntax error.  The spec says this value must be ignored.
+    return nullptr;
+  }
+
+  // From canvas spec, force to set line-height property to 'normal' font
+  // property.
+  if (aProperty == eCSSProperty_font) {
+    const nsCString normalString = "normal"_ns;
+    Servo_DeclarationBlock_SetPropertyById(
+        servoDeclarations, eCSSProperty_line_height, &normalString, false,
+        env.mUrlExtraData, ParsingMode::Default, env.mCompatMode, env.mLoader,
+        env.mRuleType, {});
+  }
+
+  return servoDeclarations.forget();
+}
+
+static already_AddRefed<StyleLockedDeclarationBlock>
+CreateFontDeclarationForServo(const nsACString& aFont, Document* aDocument) {
+  return CreateDeclarationForServo(eCSSProperty_font, aFont, aDocument);
+}
+
+static already_AddRefed<const ComputedStyle> GetFontStyleForServo(
+    Element* aElement, const nsACString& aFont, PresShell* aPresShell,
+    nsACString& aOutUsedFont, ErrorResult& aError) {
+  RefPtr<StyleLockedDeclarationBlock> declarations =
+      CreateFontDeclarationForServo(aFont, aPresShell->GetDocument());
+  if (!declarations) {
+    // We got a syntax error.  The spec says this value must be ignored.
+    return nullptr;
+  }
+
+  // In addition to unparseable values, the spec says we need to reject
+  // 'inherit' and 'initial'. The easiest way to check for this is to look
+  // at font-size-adjust, which the font shorthand resets to 'none'.
+  if (Servo_DeclarationBlock_HasCSSWideKeyword(declarations,
+                                               eCSSProperty_font_size_adjust)) {
+    return nullptr;
+  }
+
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
+
+  // Have to get a parent ComputedStyle for inherit-like relative values (2em,
+  // bolder, etc.)
+  RefPtr<const ComputedStyle> parentStyle;
+  if (aElement) {
+    parentStyle = nsComputedDOMStyle::GetComputedStyle(aElement);
+    if (NS_WARN_IF(aPresShell->IsDestroying())) {
+      // The flush might've killed the shell.
+      aError.Throw(NS_ERROR_FAILURE);
+      return nullptr;
+    }
+  }
+  if (!parentStyle) {
+    RefPtr<StyleLockedDeclarationBlock> declarations =
+        CreateFontDeclarationForServo("10px sans-serif"_ns,
+                                      aPresShell->GetDocument());
+    MOZ_ASSERT(declarations);
+
+    parentStyle =
+        aPresShell->StyleSet()->ResolveForDeclarations(nullptr, declarations);
+  }
+
+  MOZ_RELEASE_ASSERT(parentStyle, "Should have a valid parent style");
+
+  MOZ_ASSERT(!aPresShell->IsDestroying(),
+             "We should have returned an error above if the presshell is "
+             "being destroyed.");
+
+  RefPtr<const ComputedStyle> sc =
+      styleSet->ResolveForDeclarations(parentStyle, declarations);
+
+  // https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-font
+  // The font-size component must be converted to CSS px for reserialization,
+  // so we update the declarations with the value from the computed style.
+  if (!sc->StyleFont()->mFont.family.is_system_font) {
+    nsAutoCString computedFontSize;
+    sc->GetComputedPropertyValue(eCSSProperty_font_size, computedFontSize);
+    Servo_DeclarationBlock_SetPropertyById(
+        declarations, eCSSProperty_font_size, &computedFontSize, false, nullptr,
+        ParsingMode::Default, eCompatibility_FullStandards, nullptr,
+        StyleCssRuleType::Style, {});
+  }
+
+  // The font getter is required to be reserialized based on what we
+  // parsed (including having line-height removed).
+  Servo_SerializeFontValueForCanvas(declarations, &aOutUsedFont);
+  return sc.forget();
+}
+
+static already_AddRefed<StyleLockedDeclarationBlock>
+CreateFilterDeclarationForServo(const nsACString& aFilter,
+                                Document* aDocument) {
+  return CreateDeclarationForServo(eCSSProperty_filter, aFilter, aDocument);
+}
+
+static already_AddRefed<const ComputedStyle> ResolveFilterStyleForServo(
+    const nsACString& aFilterString, const ComputedStyle* aParentStyle,
+    PresShell* aPresShell, ErrorResult& aError) {
+  RefPtr<StyleLockedDeclarationBlock> declarations =
+      CreateFilterDeclarationForServo(aFilterString, aPresShell->GetDocument());
+  if (!declarations) {
+    // Refuse to accept the filter, but do not throw an error.
+    return nullptr;
+  }
+
+  // In addition to unparseable values, the spec says we need to reject
+  // 'inherit' and 'initial'.
+  if (Servo_DeclarationBlock_HasCSSWideKeyword(declarations,
+                                               eCSSProperty_filter)) {
+    return nullptr;
+  }
+
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
+  RefPtr<const ComputedStyle> computedValues =
+      styleSet->ResolveForDeclarations(aParentStyle, declarations);
+
+  return computedValues.forget();
+}
+
+bool CanvasRenderingContext2D::ParseFilter(
+    const nsACString& aString, StyleOwnedSlice<StyleFilter>& aFilterChain,
+    ErrorResult& aError) {
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (NS_WARN_IF(!presShell)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return false;
+  }
+
+  nsAutoCString usedFont;  // unused
+
+  RefPtr<const ComputedStyle> parentStyle = GetFontStyleForServo(
+      mCanvasElement, GetFont(), presShell, usedFont, aError);
+  if (!parentStyle) {
+    return false;
+  }
+
+  RefPtr<const ComputedStyle> style =
+      ResolveFilterStyleForServo(aString, parentStyle, presShell, aError);
+  if (!style) {
+    return false;
+  }
+
+  aFilterChain = style->StyleEffects()->mFilters;
+  return true;
+}
+
+void CanvasRenderingContext2D::SetFilter(const nsACString& aFilter,
+                                         ErrorResult& aError) {
+  StyleOwnedSlice<StyleFilter> filterChain;
+  if (ParseFilter(aFilter, filterChain, aError)) {
+    CurrentState().filterString = aFilter;
+    CurrentState().filterChain = std::move(filterChain);
+    if (mCanvasElement) {
+      CurrentState().autoSVGFiltersObserver =
+          SVGObserverUtils::ObserveFiltersForCanvasContext(
+              this, mCanvasElement, CurrentState().filterChain.AsSpan());
+      UpdateFilter();
+    }
+  }
+}
+
+static already_AddRefed<const ComputedStyle> ResolveStyleForServo(
+    nsCSSPropertyID aProperty, const nsACString& aString,
+    const ComputedStyle* aParentStyle, PresShell* aPresShell,
+    ErrorResult& aError) {
+  RefPtr<StyleLockedDeclarationBlock> declarations =
+      CreateDeclarationForServo(aProperty, aString, aPresShell->GetDocument());
+  if (!declarations) {
+    return nullptr;
+  }
+
+  // In addition to unparseable values, reject 'inherit' and 'initial'.
+  if (Servo_DeclarationBlock_HasCSSWideKeyword(declarations, aProperty)) {
+    return nullptr;
+  }
+
+  ServoStyleSet* styleSet = aPresShell->StyleSet();
+  return styleSet->ResolveForDeclarations(aParentStyle, declarations);
+}
+
+already_AddRefed<const ComputedStyle>
+CanvasRenderingContext2D::ResolveStyleForProperty(nsCSSPropertyID aProperty,
+                                                  const nsACString& aValue) {
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (NS_WARN_IF(!presShell)) {
+    return nullptr;
+  }
+
+  nsAutoCString usedFont;
+  IgnoredErrorResult err;
+  RefPtr<const ComputedStyle> parentStyle =
+      GetFontStyleForServo(mCanvasElement, GetFont(), presShell, usedFont, err);
+  if (!parentStyle) {
+    return nullptr;
+  }
+
+  return ResolveStyleForServo(aProperty, aValue, parentStyle, presShell, err);
+}
+
+void CanvasRenderingContext2D::GetLetterSpacing(nsACString& aLetterSpacing) {
+  if (CurrentState().letterSpacingStr.IsEmpty()) {
+    aLetterSpacing.AssignLiteral("0px");
+  } else {
+    aLetterSpacing = CurrentState().letterSpacingStr;
+  }
+}
+
+void CanvasRenderingContext2D::SetLetterSpacing(
+    const nsACString& aLetterSpacing) {
+  ParseSpacing(aLetterSpacing, &CurrentState().letterSpacing,
+               CurrentState().letterSpacingStr);
+}
+
+void CanvasRenderingContext2D::GetWordSpacing(nsACString& aWordSpacing) {
+  if (CurrentState().wordSpacingStr.IsEmpty()) {
+    aWordSpacing.AssignLiteral("0px");
+  } else {
+    aWordSpacing = CurrentState().wordSpacingStr;
+  }
+}
+
+void CanvasRenderingContext2D::SetWordSpacing(const nsACString& aWordSpacing) {
+  ParseSpacing(aWordSpacing, &CurrentState().wordSpacing,
+               CurrentState().wordSpacingStr);
+}
+
+void CanvasRenderingContext2D::ParseSpacing(const nsACString& aSpacing,
+                                            float* aValue,
+                                            nsACString& aNormalized) {
+  // Normalize whitespace in the string before trying to parse it, as we want
+  // to store it in normalized form, and this allows a simple check against the
+  // 'normal' keyword, which is not accepted.
+  nsAutoCString normalized(aSpacing);
+  normalized.CompressWhitespace(true, true);
+  if (normalized.Equals("normal", nsCaseInsensitiveCStringComparator)) {
+    return;
+  }
+  float value;
+  if (!Servo_ParseAbsoluteLength(&normalized, &value)) {
+    if (!GetPresShell()) {
+      return;
+    }
+    RefPtr<const ComputedStyle> style =
+        ResolveStyleForProperty(eCSSProperty_letter_spacing, aSpacing);
+    if (!style) {
+      return;
+    }
+    value = style->StyleText()->mLetterSpacing.ToCSSPixels();
+  }
+  aNormalized = normalized;
+  *aValue = value;
+}
+
+class CanvasUserSpaceMetrics : public UserSpaceMetricsWithSize {
+ public:
+  CanvasUserSpaceMetrics(const gfx::IntSize& aSize, const nsFont& aFont,
+                         nsAtom* aFontLanguage, bool aExplicitLanguage,
+                         nsPresContext* aPresContext)
+      : mSize(aSize),
+        mFont(aFont),
+        mFontLanguage(aFontLanguage),
+        mExplicitLanguage(aExplicitLanguage),
+        mPresContext(aPresContext) {}
+
+  virtual float GetEmLength() const override {
+    return mFont.size.ToCSSPixels();
+  }
+
+  virtual float GetExLength() const override {
+    nsFontMetrics::Params params;
+    params.language = mFontLanguage;
+    params.explicitLanguage = mExplicitLanguage;
+    params.textPerf = mPresContext->GetTextPerfMetrics();
+    params.featureValueLookup = mPresContext->GetFontFeatureValuesLookup();
+    RefPtr<nsFontMetrics> fontMetrics =
+        mPresContext->GetMetricsFor(mFont, params);
+    return NSAppUnitsToFloatPixels(fontMetrics->XHeight(),
+                                   AppUnitsPerCSSPixel());
+  }
+
+  virtual gfx::Size GetSize() const override { return Size(mSize); }
+
+ private:
+  gfx::IntSize mSize;
+  const nsFont& mFont;
+  nsAtom* mFontLanguage;
+  bool mExplicitLanguage;
+  nsPresContext* mPresContext;
+};
+
+// The filter might reference an SVG filter that is declared inside this
+// document. Flush frames so that we'll have a SVGFilterFrame to work
+// with.
+static bool FiltersNeedFrameFlush(Span<const StyleFilter> aFilters) {
+  for (const auto& filter : aFilters) {
+    if (filter.IsUrl()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void CanvasRenderingContext2D::UpdateFilter() {
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (!presShell || presShell->IsDestroying()) {
+    // Ensure we set an empty filter and update the state to
+    // reflect the current "taint" status of the canvas
+    CurrentState().filter = FilterDescription();
+    CurrentState().filterSourceGraphicTainted =
+        mCanvasElement && mCanvasElement->IsWriteOnly();
+    return;
+  }
+
+  if (FiltersNeedFrameFlush(CurrentState().filterChain.AsSpan())) {
+    presShell->FlushPendingNotifications(FlushType::Frames);
+  }
+
+  MOZ_RELEASE_ASSERT(!mStyleStack.IsEmpty());
+  if (MOZ_UNLIKELY(presShell->IsDestroying())) {
+    return;
+  }
+
+  const bool sourceGraphicIsTainted =
+      mCanvasElement && mCanvasElement->IsWriteOnly();
+
+  CurrentState().filter = FilterInstance::GetFilterDescription(
+      mCanvasElement, CurrentState().filterChain.AsSpan(),
+      sourceGraphicIsTainted,
+      CanvasUserSpaceMetrics(
+          GetSize(), CurrentState().fontFont, CurrentState().fontLanguage,
+          CurrentState().fontExplicitLanguage, presShell->GetPresContext()),
+      gfxRect(0, 0, mWidth, mHeight), CurrentState().filterAdditionalImages);
+  CurrentState().filterSourceGraphicTainted = sourceGraphicIsTainted;
+}
+
+//
+// rects
+//
+
+static bool ValidateRect(double& aX, double& aY, double& aWidth,
+                         double& aHeight, bool aIsZeroSizeValid) {
+  if (!aIsZeroSizeValid && (aWidth == 0.0 || aHeight == 0.0)) {
+    return false;
+  }
+
+  // bug 1018527
+  // The values of canvas API input are in double precision, but Moz2D APIs are
+  // using float precision. Bypass canvas API calls when the input is out of
+  // float precision to avoid precision problem
+  if (!std::isfinite((float)aX) || !std::isfinite((float)aY) ||
+      !std::isfinite((float)aWidth) || !std::isfinite((float)aHeight)) {
+    return false;
+  }
+
+  // bug 1074733
+  // The canvas spec does not forbid rects with negative w or h, so given
+  // corners (x, y), (x+w, y), (x+w, y+h), and (x, y+h) we must generate
+  // the appropriate rect by flipping negative dimensions. This prevents
+  // draw targets from receiving "empty" rects later on.
+  if (aWidth < 0) {
+    aWidth = -aWidth;
+    aX -= aWidth;
+  }
+  if (aHeight < 0) {
+    aHeight = -aHeight;
+    aY -= aHeight;
+  }
+  return true;
+}
+
+void CanvasRenderingContext2D::ClearRect(double aX, double aY, double aW,
+                                         double aH) {
+  // Do not allow zeros - it's a no-op at that point per spec.
+  if (!ValidateRect(aX, aY, aW, aH, false)) {
+    return;
+  }
+
+  gfx::Rect clearRect(aX, aY, aW, aH);
+
+  EnsureTarget(&clearRect, true);
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  mTarget->ClearRect(clearRect);
+
+  RedrawUser(gfxRect(aX, aY, aW, aH));
+}
+
+void CanvasRenderingContext2D::FillRect(double aX, double aY, double aW,
+                                        double aH) {
+  if (!ValidateRect(aX, aY, aW, aH, true)) {
+    return;
+  }
+
+  const ContextState* state = &CurrentState();
+  if (state->patternStyles[Style::FILL]) {
+    auto& style = state->patternStyles[Style::FILL];
+    CanvasPattern::RepeatMode repeat = style->mRepeat;
+    // In the FillRect case repeat modes are easy to deal with.
+    bool limitx = repeat == CanvasPattern::RepeatMode::NOREPEAT ||
+                  repeat == CanvasPattern::RepeatMode::REPEATY;
+    bool limity = repeat == CanvasPattern::RepeatMode::NOREPEAT ||
+                  repeat == CanvasPattern::RepeatMode::REPEATX;
+    if ((limitx || limity) && style->mTransform.IsRectilinear()) {
+      // For rectilinear transforms, we can just get the transformed pattern
+      // bounds and intersect them with the fill rectangle bounds.
+      // TODO: If the transform is not rectilinear, then we would need a fully
+      // general clip path to represent the X and Y clip planes bounding the
+      // pattern. For such cases, it would be more efficient to rely on Skia's
+      // Decal tiling mode rather than trying to generate a path. Until then,
+      // just punt to relying on the default Clamp mode.
+      gfx::Rect patternBounds(style->mSurface->GetRect());
+      patternBounds = style->mTransform.TransformBounds(patternBounds);
+      if (style->mTransform.HasNonAxisAlignedTransform()) {
+        // If there is an rotation (90 or 270 degrees), the X axis of the
+        // pattern projects onto the Y axis of the geometry, and vice versa.
+        std::swap(limitx, limity);
+      }
+      // We always need to execute painting for non-over operators, even if
+      // we end up with w/h = 0. The default Rect::Intersect can cause both
+      // dimensions to become empty if either dimension individually fails
+      // to overlap, which is unsuitable. Instead, we need to independently
+      // limit the supplied rectangle on each dimension as required.
+      if (limitx) {
+        double x2 = aX + aW;
+        aX = std::max(aX, double(patternBounds.x));
+        aW = std::max(std::min(x2, double(patternBounds.XMost())) - aX, 0.0);
+      }
+      if (limity) {
+        double y2 = aY + aH;
+        aY = std::max(aY, double(patternBounds.y));
+        aH = std::max(std::min(y2, double(patternBounds.YMost())) - aY, 0.0);
+      }
+    }
+  }
+  state = nullptr;
+
+  bool isColor;
+  bool discardContent = PatternIsOpaque(Style::FILL, &isColor) &&
+                        (CurrentState().op == CompositionOp::OP_OVER ||
+                         CurrentState().op == CompositionOp::OP_SOURCE);
+  const gfx::Rect fillRect(aX, aY, aW, aH);
+  EnsureTarget(discardContent ? &fillRect : nullptr, discardContent && isColor);
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  gfx::Rect bounds;
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  if (needBounds) {
+    bounds = mTarget->GetTransform().TransformBounds(fillRect);
+  }
+
+  AntialiasMode antialiasMode = CurrentState().imageSmoothingEnabled
+                                    ? AntialiasMode::DEFAULT
+                                    : AntialiasMode::NONE;
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  CompositionOp op = target.UsedOperation();
+  if (!target) {
+    return;
+  }
+  target.FillRect(gfx::Rect(aX, aY, aW, aH),
+                  CanvasGeneralPattern().ForStyle(this, Style::FILL, mTarget),
+                  DrawOptions(CurrentState().globalAlpha, op, antialiasMode));
+
+  RedrawUser(gfxRect(aX, aY, aW, aH));
+}
+
+void CanvasRenderingContext2D::StrokeRect(double aX, double aY, double aW,
+                                          double aH) {
+  if (!aW && !aH) {
+    return;
+  }
+
+  if (!ValidateRect(aX, aY, aW, aH, true)) {
+    return;
+  }
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  gfx::Rect bounds;
+  if (needBounds) {
+    const ContextState& state = CurrentState();
+    bounds = gfx::Rect(aX - state.lineWidth / 2.0f, aY - state.lineWidth / 2.0f,
+                       aW + state.lineWidth, aH + state.lineWidth);
+    bounds = mTarget->GetTransform().TransformBounds(bounds);
+  }
+
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  if (!aH) {
+    CapStyle cap = CapStyle::BUTT;
+    if (CurrentState().lineJoin == JoinStyle::ROUND) {
+      cap = CapStyle::ROUND;
+    }
+    AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+    auto op = target.UsedOperation();
+    if (!target) {
+      return;
+    }
+
+    const ContextState& state = CurrentState();
+    target.StrokeLine(
+        Point(aX, aY), Point(aX + aW, aY),
+        CanvasGeneralPattern().ForStyle(this, Style::STROKE, mTarget),
+        StrokeOptions(state.lineWidth, state.lineJoin, cap, state.miterLimit,
+                      state.dash.Length(), state.dash.Elements(),
+                      state.dashOffset),
+        DrawOptions(state.globalAlpha, op));
+    return;
+  }
+
+  if (!aW) {
+    CapStyle cap = CapStyle::BUTT;
+    if (CurrentState().lineJoin == JoinStyle::ROUND) {
+      cap = CapStyle::ROUND;
+    }
+    AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+    auto op = target.UsedOperation();
+    if (!target) {
+      return;
+    }
+
+    const ContextState& state = CurrentState();
+    target.StrokeLine(
+        Point(aX, aY), Point(aX, aY + aH),
+        CanvasGeneralPattern().ForStyle(this, Style::STROKE, mTarget),
+        StrokeOptions(state.lineWidth, state.lineJoin, cap, state.miterLimit,
+                      state.dash.Length(), state.dash.Elements(),
+                      state.dashOffset),
+        DrawOptions(state.globalAlpha, op));
+    return;
+  }
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  auto op = target.UsedOperation();
+  if (!target) {
+    return;
+  }
+
+  const ContextState& state = CurrentState();
+  target.StrokeRect(
+      gfx::Rect(aX, aY, aW, aH),
+      CanvasGeneralPattern().ForStyle(this, Style::STROKE, mTarget),
+      StrokeOptions(state.lineWidth, state.lineJoin, state.lineCap,
+                    state.miterLimit, state.dash.Length(),
+                    state.dash.Elements(), state.dashOffset),
+      DrawOptions(state.globalAlpha, op));
+
+  Redraw();
+}
+
+//
+// path bits
+//
+
+void CanvasRenderingContext2D::BeginPath() {
+  mPath = nullptr;
+  mPathBuilder = nullptr;
+  mDSPathBuilder = nullptr;
+  mPathTransformWillUpdate = false;
+}
+
+void CanvasRenderingContext2D::Fill(const CanvasWindingRule& aWinding) {
+  EnsureUserSpacePath(aWinding);
+
+  if (!mPath) {
+    return;
+  }
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  gfx::Rect bounds;
+  if (needBounds) {
+    bounds = mPath->GetBounds(mTarget->GetTransform());
+  }
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  if (!target) {
+    return;
+  }
+
+  auto op = target.UsedOperation();
+  if (!IsTargetValid() || !target) {
+    return;
+  }
+  target.Fill(mPath,
+              CanvasGeneralPattern().ForStyle(this, Style::FILL, mTarget),
+              DrawOptions(CurrentState().globalAlpha, op));
+  Redraw();
+}
+
+void CanvasRenderingContext2D::Fill(const CanvasPath& aPath,
+                                    const CanvasWindingRule& aWinding) {
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  RefPtr<gfx::Path> gfxpath = aPath.GetPath(aWinding, mTarget);
+  if (!gfxpath) {
+    return;
+  }
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  gfx::Rect bounds;
+  if (needBounds) {
+    bounds = gfxpath->GetBounds(mTarget->GetTransform());
+  }
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  if (!target) {
+    return;
+  }
+
+  auto op = target.UsedOperation();
+  if (!IsTargetValid() || !target) {
+    return;
+  }
+  target.Fill(gfxpath,
+              CanvasGeneralPattern().ForStyle(this, Style::FILL, mTarget),
+              DrawOptions(CurrentState().globalAlpha, op));
+  Redraw();
+}
+
+void CanvasRenderingContext2D::Stroke() {
+  EnsureUserSpacePath();
+
+  if (!mPath) {
+    return;
+  }
+
+  const ContextState* state = &CurrentState();
+  StrokeOptions strokeOptions(state->lineWidth, state->lineJoin, state->lineCap,
+                              state->miterLimit, state->dash.Length(),
+                              state->dash.Elements(), state->dashOffset);
+  state = nullptr;
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  gfx::Rect bounds;
+  if (needBounds) {
+    bounds = mPath->GetStrokedBounds(strokeOptions, mTarget->GetTransform());
+  }
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  if (!target) {
+    return;
+  }
+
+  auto op = target.UsedOperation();
+  if (!IsTargetValid() || !target) {
+    return;
+  }
+  target.Stroke(mPath,
+                CanvasGeneralPattern().ForStyle(this, Style::STROKE, mTarget),
+                strokeOptions, DrawOptions(CurrentState().globalAlpha, op));
+  Redraw();
+}
+
+void CanvasRenderingContext2D::Stroke(const CanvasPath& aPath) {
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  RefPtr<gfx::Path> gfxpath =
+      aPath.GetPath(CanvasWindingRule::Nonzero, mTarget);
+
+  if (!gfxpath) {
+    return;
+  }
+
+  const ContextState* state = &CurrentState();
+  StrokeOptions strokeOptions(state->lineWidth, state->lineJoin, state->lineCap,
+                              state->miterLimit, state->dash.Length(),
+                              state->dash.Elements(), state->dashOffset);
+  state = nullptr;
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  gfx::Rect bounds;
+  if (needBounds) {
+    bounds = gfxpath->GetStrokedBounds(strokeOptions, mTarget->GetTransform());
+  }
+
+  AdjustedTarget target(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+  if (!target) {
+    return;
+  }
+
+  auto op = target.UsedOperation();
+  if (!IsTargetValid() || !target) {
+    return;
+  }
+  target.Stroke(gfxpath,
+                CanvasGeneralPattern().ForStyle(this, Style::STROKE, mTarget),
+                strokeOptions, DrawOptions(CurrentState().globalAlpha, op));
+  Redraw();
+}
+
+void CanvasRenderingContext2D::DrawFocusIfNeeded(
+    mozilla::dom::Element& aElement, ErrorResult& aRv) {
+  EnsureUserSpacePath();
+  if (!mPath) {
+    return;
+  }
+
+  if (DrawCustomFocusRing(aElement)) {
+    AutoSaveRestore asr(this);
+
+    // set state to conforming focus state
+    ContextState* state = &CurrentState();
+    state->globalAlpha = 1.0;
+    state->shadowBlur = 0;
+    state->shadowOffset.x = 0;
+    state->shadowOffset.y = 0;
+    state->op = mozilla::gfx::CompositionOp::OP_OVER;
+
+    state->lineCap = CapStyle::BUTT;
+    state->lineJoin = mozilla::gfx::JoinStyle::MITER_OR_BEVEL;
+    state->lineWidth = 1;
+    state->dash.Clear();
+
+    // color and style of the rings is the same as for image maps
+    // set the background focus color
+    state->SetColorStyle(Style::STROKE, NS_RGBA(255, 255, 255, 255));
+    state = nullptr;
+
+    // draw the focus ring
+    Stroke();
+    if (!mPath) {
+      return;
+    }
+
+    // set dashing for foreground
+    nsTArray<mozilla::gfx::Float>& dash = CurrentState().dash;
+    for (uint32_t i = 0; i < 2; ++i) {
+      if (!dash.AppendElement(1, fallible)) {
+        aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+        return;
+      }
+    }
+
+    // set the foreground focus color
+    CurrentState().SetColorStyle(Style::STROKE, NS_RGBA(0, 0, 0, 255));
+    // draw the focus ring
+    Stroke();
+    if (!mPath) {
+      return;
+    }
+  }
+}
+
+bool CanvasRenderingContext2D::DrawCustomFocusRing(Element& aElement) {
+  if (!aElement.State().HasState(ElementState::FOCUSRING)) {
+    return false;
+  }
+
+  HTMLCanvasElement* canvas = GetCanvas();
+  if (!canvas || !aElement.IsInclusiveDescendantOf(canvas)) {
+    return false;
+  }
+
+  EnsureUserSpacePath();
+  return true;
+}
+
+void CanvasRenderingContext2D::Clip(const CanvasWindingRule& aWinding) {
+  EnsureUserSpacePath(aWinding);
+
+  if (!mPath) {
+    return;
+  }
+
+  mTarget->PushClip(mPath);
+  CurrentState().clipsAndTransforms.AppendElement(ClipState(mPath));
+}
+
+void CanvasRenderingContext2D::Clip(const CanvasPath& aPath,
+                                    const CanvasWindingRule& aWinding) {
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  RefPtr<gfx::Path> gfxpath = aPath.GetPath(aWinding, mTarget);
+
+  if (!gfxpath) {
+    return;
+  }
+
+  mTarget->PushClip(gfxpath);
+  CurrentState().clipsAndTransforms.AppendElement(ClipState(gfxpath));
+}
+
+void CanvasRenderingContext2D::ArcTo(double aX1, double aY1, double aX2,
+                                     double aY2, double aRadius,
+                                     ErrorResult& aError) {
+  if (aRadius < 0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsureWritablePath();
+
+  // Current point in user space!
+  Point p0;
+  if (mPathBuilder) {
+    p0 = mPathBuilder->CurrentPoint();
+  } else {
+    Matrix invTransform = mTarget->GetTransform();
+    if (!invTransform.Invert()) {
+      return;
+    }
+
+    p0 = invTransform.TransformPoint(mDSPathBuilder->CurrentPoint());
+  }
+
+  Point p1(aX1, aY1);
+  Point p2(aX2, aY2);
+
+  // Execute these calculations in double precision to avoid cumulative
+  // rounding errors.
+  double dir, a2, b2, c2, cosx, sinx, d, anx, any, bnx, bny, x3, y3, x4, y4, cx,
+      cy, angle0, angle1;
+  bool anticlockwise;
+
+  if (p0 == p1 || p1 == p2 || aRadius == 0) {
+    LineTo(p1.x, p1.y);
+    return;
+  }
+
+  // Check for colinearity
+  dir = (p2.x.value - p1.x.value) * (p0.y.value - p1.y.value) +
+        (p2.y.value - p1.y.value) * (p1.x.value - p0.x.value);
+  if (dir == 0) {
+    LineTo(p1.x, p1.y);
+    return;
+  }
+
+  // XXX - Math for this code was already available from the non-azure code
+  // and would be well tested. Perhaps converting to bezier directly might
+  // be more efficient longer run.
+  a2 = (p0.x - aX1) * (p0.x - aX1) + (p0.y - aY1) * (p0.y - aY1);
+  b2 = (aX1 - aX2) * (aX1 - aX2) + (aY1 - aY2) * (aY1 - aY2);
+  c2 = (p0.x - aX2) * (p0.x - aX2) + (p0.y - aY2) * (p0.y - aY2);
+  cosx = (a2 + b2 - c2) / (2 * sqrt(a2 * b2));
+
+  sinx = sqrt(1 - cosx * cosx);
+  d = aRadius / ((1 - cosx) / sinx);
+
+  anx = (aX1 - p0.x) / sqrt(a2);
+  any = (aY1 - p0.y) / sqrt(a2);
+  bnx = (aX1 - aX2) / sqrt(b2);
+  bny = (aY1 - aY2) / sqrt(b2);
+  x3 = aX1 - anx * d;
+  y3 = aY1 - any * d;
+  x4 = aX1 - bnx * d;
+  y4 = aY1 - bny * d;
+  anticlockwise = (dir < 0);
+  cx = x3 + any * aRadius * (anticlockwise ? 1 : -1);
+  cy = y3 - anx * aRadius * (anticlockwise ? 1 : -1);
+  angle0 = atan2((y3 - cy), (x3 - cx));
+  angle1 = atan2((y4 - cy), (x4 - cx));
+
+  LineTo(x3, y3);
+
+  Arc(cx, cy, aRadius, angle0, angle1, anticlockwise, aError);
+}
+
+void CanvasRenderingContext2D::Arc(double aX, double aY, double aR,
+                                   double aStartAngle, double aEndAngle,
+                                   bool aAnticlockwise, ErrorResult& aError) {
+  if (aR < 0.0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsureWritablePath();
+
+  ArcToBezier(this, Point(aX, aY), Size(aR, aR), aStartAngle, aEndAngle,
+              aAnticlockwise);
+}
+
+void CanvasRenderingContext2D::Rect(double aX, double aY, double aW,
+                                    double aH) {
+  EnsureWritablePath();
+
+  if (mPathBuilder) {
+    mPathBuilder->MoveTo(Point(aX, aY));
+    mPathBuilder->LineTo(Point(aX + aW, aY));
+    mPathBuilder->LineTo(Point(aX + aW, aY + aH));
+    mPathBuilder->LineTo(Point(aX, aY + aH));
+    mPathBuilder->Close();
+  } else {
+    mDSPathBuilder->MoveTo(
+        mTarget->GetTransform().TransformPoint(Point(aX, aY)));
+    mDSPathBuilder->LineTo(
+        mTarget->GetTransform().TransformPoint(Point(aX + aW, aY)));
+    mDSPathBuilder->LineTo(
+        mTarget->GetTransform().TransformPoint(Point(aX + aW, aY + aH)));
+    mDSPathBuilder->LineTo(
+        mTarget->GetTransform().TransformPoint(Point(aX, aY + aH)));
+    mDSPathBuilder->Close();
+  }
+}
+
+// https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-roundrect
+static void RoundRectImpl(
+    PathBuilder* aPathBuilder, const Maybe<Matrix>& aTransform, double aX,
+    double aY, double aW, double aH,
+    const UnrestrictedDoubleOrDOMPointInitOrUnrestrictedDoubleOrDOMPointInitSequence&
+        aRadii,
+    ErrorResult& aError) {
+  // Step 1. If any of x, y, w, or h are infinite or NaN, then return.
+  if (!std::isfinite(aX) || !std::isfinite(aY) || !std::isfinite(aW) ||
+      !std::isfinite(aH)) {
+    return;
+  }
+
+  nsTArray<OwningUnrestrictedDoubleOrDOMPointInit> radii;
+  // Step 2. If radii is an unrestricted double or DOMPointInit, then set radii
+  // to « radii ».
+  if (aRadii.IsUnrestrictedDouble()) {
+    radii.AppendElement()->SetAsUnrestrictedDouble() =
+        aRadii.GetAsUnrestrictedDouble();
+  } else if (aRadii.IsDOMPointInit()) {
+    radii.AppendElement()->SetAsDOMPointInit() = aRadii.GetAsDOMPointInit();
+  } else {
+    radii = aRadii.GetAsUnrestrictedDoubleOrDOMPointInitSequence();
+    // Step 3. If radii is not a list of size one, two, three, or
+    // four, then throw a RangeError.
+    if (radii.Length() < 1 || radii.Length() > 4) {
+      aError.ThrowRangeError("Can have between 1 and 4 radii");
+      return;
+    }
+  }
+
+  // Step 4. Let normalizedRadii be an empty list.
+  AutoTArray<Size, 4> normalizedRadii;
+
+  // Step 5. For each radius of radii:
+  for (const auto& radius : radii) {
+    // Step 5.1. If radius is a DOMPointInit:
+    if (radius.IsDOMPointInit()) {
+      const DOMPointInit& point = radius.GetAsDOMPointInit();
+      // Step 5.1.1. If radius["x"] or radius["y"] is infinite or NaN, then
+      // return.
+      if (!std::isfinite(point.mX) || !std::isfinite(point.mY)) {
+        return;
+      }
+
+      // Step 5.1.2. If radius["x"] or radius["y"] is negative, then
+      // throw a RangeError.
+      if (point.mX < 0 || point.mY < 0) {
+        aError.ThrowRangeError("Radius can not be negative");
+        return;
+      }
+
+      // Step 5.1.3. Otherwise, append radius to
+      // normalizedRadii.
+      normalizedRadii.AppendElement(
+          Size(gfx::Float(point.mX), gfx::Float(point.mY)));
+      continue;
+    }
+
+    // Step 5.2. If radius is a unrestricted double:
+    double r = radius.GetAsUnrestrictedDouble();
+    // Step 5.2.1. If radius is infinite or NaN, then return.
+    if (!std::isfinite(r)) {
+      return;
+    }
+
+    // Step 5.2.2. If radius is negative, then throw a RangeError.
+    if (r < 0) {
+      aError.ThrowRangeError("Radius can not be negative");
+      return;
+    }
+
+    // Step 5.2.3. Otherwise append «[ "x" → radius, "y" → radius ]» to
+    // normalizedRadii.
+    normalizedRadii.AppendElement(Size(gfx::Float(r), gfx::Float(r)));
+  }
+
+  // Step 6. Let upperLeft, upperRight, lowerRight, and lowerLeft be null.
+  Size upperLeft, upperRight, lowerRight, lowerLeft;
+
+  if (normalizedRadii.Length() == 4) {
+    // Step 7. If normalizedRadii's size is 4, then set upperLeft to
+    // normalizedRadii[0], set upperRight to normalizedRadii[1], set lowerRight
+    // to normalizedRadii[2], and set lowerLeft to normalizedRadii[3].
+    upperLeft = normalizedRadii[0];
+    upperRight = normalizedRadii[1];
+    lowerRight = normalizedRadii[2];
+    lowerLeft = normalizedRadii[3];
+  } else if (normalizedRadii.Length() == 3) {
+    // Step 8. If normalizedRadii's size is 3, then set upperLeft to
+    // normalizedRadii[0], set upperRight and lowerLeft to normalizedRadii[1],
+    // and set lowerRight to normalizedRadii[2].
+    upperLeft = normalizedRadii[0];
+    upperRight = normalizedRadii[1];
+    lowerRight = normalizedRadii[2];
+    lowerLeft = normalizedRadii[1];
+  } else if (normalizedRadii.Length() == 2) {
+    // Step 9. If normalizedRadii's size is 2, then set upperLeft and lowerRight
+    // to normalizedRadii[0] and set upperRight and lowerLeft to
+    // normalizedRadii[1].
+    upperLeft = normalizedRadii[0];
+    upperRight = normalizedRadii[1];
+    lowerRight = normalizedRadii[0];
+    lowerLeft = normalizedRadii[1];
+  } else {
+    // Step 10. If normalizedRadii's size is 1, then set upperLeft, upperRight,
+    // lowerRight, and lowerLeft to normalizedRadii[0].
+    MOZ_ASSERT(normalizedRadii.Length() == 1);
+    upperLeft = normalizedRadii[0];
+    upperRight = normalizedRadii[0];
+    lowerRight = normalizedRadii[0];
+    lowerLeft = normalizedRadii[0];
+  }
+
+  // This is not as specified but copied from Chrome.
+  // XXX Maybe if we implemented Step 12 (the path algorithm) per
+  // spec this wouldn't be needed?
+  Float x(aX), y(aY), w(aW), h(aH);
+  bool clockwise = true;
+  if (w < 0) {
+    // Horizontal flip
+    clockwise = false;
+    x += w;
+    w = -w;
+    std::swap(upperLeft, upperRight);
+    std::swap(lowerLeft, lowerRight);
+  }
+
+  if (h < 0) {
+    // Vertical flip
+    clockwise = !clockwise;
+    y += h;
+    h = -h;
+    std::swap(upperLeft, lowerLeft);
+    std::swap(upperRight, lowerRight);
+  }
+
+  // Step 11. Corner curves must not overlap. Scale all radii to prevent this:
+  // Step 11.1. Let top be upperLeft["x"] + upperRight["x"].
+  Float top = upperLeft.width + upperRight.width;
+  // Step 11.2. Let right be upperRight["y"] + lowerRight["y"].
+  Float right = upperRight.height + lowerRight.height;
+  // Step 11.3. Let bottom be lowerRight["x"] + lowerLeft["x"].
+  Float bottom = lowerRight.width + lowerLeft.width;
+  // Step 11.4. Let left be upperLeft["y"] + lowerLeft["y"].
+  Float left = upperLeft.height + lowerLeft.height;
+  // Step 11.5. Let scale be the minimum value of the ratios w / top, h / right,
+  // w / bottom, h / left.
+  Float scale = std::min({w / top, h / right, w / bottom, h / left});
+  // Step 11.6. If scale is less than 1, then set the x and y members of
+  // upperLeft, upperRight, lowerLeft, and lowerRight to their current values
+  // multiplied by scale.
+  if (scale < 1.0f) {
+    upperLeft = upperLeft * scale;
+    upperRight = upperRight * scale;
+    lowerLeft = lowerLeft * scale;
+    lowerRight = lowerRight * scale;
+  }
+
+  // Step 12. Create a new subpath:
+  // Step 13. Mark the subpath as closed.
+  // Note: Implemented by AppendRoundedRectToPath, which is shared with CSS
+  // borders etc.
+  gfx::Rect rect{x, y, w, h};
+  RectCornerRadii cornerRadii(upperLeft, upperRight, lowerRight, lowerLeft);
+  AppendRoundedRectToPath(aPathBuilder, rect, cornerRadii, clockwise,
+                          aTransform);
+
+  // Step 14. Create a new subpath with the point (x, y) as the only point in
+  // the subpath.
+  // XXX We don't seem to be doing this for ::Rect either?
+}
+
+void CanvasRenderingContext2D::RoundRect(
+    double aX, double aY, double aW, double aH,
+    const UnrestrictedDoubleOrDOMPointInitOrUnrestrictedDoubleOrDOMPointInitSequence&
+        aRadii,
+    ErrorResult& aError) {
+  EnsureWritablePath();
+
+  PathBuilder* builder = mPathBuilder;
+  Maybe<Matrix> transform = Nothing();
+  if (!builder) {
+    builder = mDSPathBuilder;
+    transform = Some(mTarget->GetTransform());
+  }
+
+  RoundRectImpl(builder, transform, aX, aY, aW, aH, aRadii, aError);
+}
+
+void CanvasRenderingContext2D::Ellipse(double aX, double aY, double aRadiusX,
+                                       double aRadiusY, double aRotation,
+                                       double aStartAngle, double aEndAngle,
+                                       bool aAnticlockwise,
+                                       ErrorResult& aError) {
+  if (aRadiusX < 0.0 || aRadiusY < 0.0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsureWritablePath();
+
+  ArcToBezier(this, Point(aX, aY), Size(aRadiusX, aRadiusY), aStartAngle,
+              aEndAngle, aAnticlockwise, aRotation);
+}
+
+void CanvasRenderingContext2D::EnsureWritablePath() {
+  EnsureTarget();
+  // NOTE: IsTargetValid() may be false here (mTarget == sErrorTarget) but we
+  // go ahead and create a path anyway since callers depend on that.
+
+  if (mDSPathBuilder) {
+    return;
+  }
+
+  FillRule fillRule = CurrentState().fillRule;
+
+  if (mPathBuilder) {
+    if (mPathTransformWillUpdate) {
+      mPath = mPathBuilder->Finish();
+      mDSPathBuilder = mPath->TransformedCopyToBuilder(mPathToDS, fillRule);
+      mPath = nullptr;
+      mPathBuilder = nullptr;
+      mPathTransformWillUpdate = false;
+    }
+    return;
+  }
+
+  if (!mPath) {
+    NS_ASSERTION(
+        !mPathTransformWillUpdate,
+        "mPathTransformWillUpdate should be false, if all paths are null");
+    mPathBuilder = mTarget->CreatePathBuilder(fillRule);
+  } else if (!mPathTransformWillUpdate) {
+    mPathBuilder = mPath->CopyToBuilder(fillRule);
+  } else {
+    mDSPathBuilder = mPath->TransformedCopyToBuilder(mPathToDS, fillRule);
+    mPathTransformWillUpdate = false;
+    mPath = nullptr;
+  }
+}
+
+void CanvasRenderingContext2D::EnsureUserSpacePath(
+    const CanvasWindingRule& aWinding) {
+  FillRule fillRule = CurrentState().fillRule;
+  if (aWinding == CanvasWindingRule::Evenodd)
+    fillRule = FillRule::FILL_EVEN_ODD;
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  if (!mPath && !mPathBuilder && !mDSPathBuilder) {
+    mPathBuilder = mTarget->CreatePathBuilder(fillRule);
+  }
+
+  if (mPathBuilder) {
+    mPath = mPathBuilder->Finish();
+    mPathBuilder = nullptr;
+  }
+
+  if (mPath && mPathTransformWillUpdate) {
+    mDSPathBuilder = mPath->TransformedCopyToBuilder(mPathToDS, fillRule);
+    mPath = nullptr;
+    mPathTransformWillUpdate = false;
+  }
+
+  if (mDSPathBuilder) {
+    RefPtr<Path> dsPath;
+    dsPath = mDSPathBuilder->Finish();
+    mDSPathBuilder = nullptr;
+
+    Matrix inverse = mTarget->GetTransform();
+    if (!inverse.Invert()) {
+      NS_WARNING("Could not invert transform");
+      return;
+    }
+
+    mPathBuilder = dsPath->TransformedCopyToBuilder(inverse, fillRule);
+    mPath = mPathBuilder->Finish();
+    mPathBuilder = nullptr;
+  }
+
+  if (mPath && mPath->GetFillRule() != fillRule) {
+    mPathBuilder = mPath->CopyToBuilder(fillRule);
+    mPath = mPathBuilder->Finish();
+    mPathBuilder = nullptr;
+  }
+
+  NS_ASSERTION(mPath, "mPath should exist");
+}
+
+void CanvasRenderingContext2D::TransformWillUpdate() {
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  // Store the matrix that would transform the current path to device
+  // space.
+  if (mPath || mPathBuilder) {
+    if (!mPathTransformWillUpdate) {
+      // If the transform has already been updated, but a device space builder
+      // has not been created yet mPathToDS contains the right transform to
+      // transform the current mPath into device space.
+      // We should leave it alone.
+      mPathToDS = mTarget->GetTransform();
+    }
+    mPathTransformWillUpdate = true;
+  }
+}
+
+//
+// text
+//
+
+void CanvasRenderingContext2D::SetFont(const nsACString& aFont,
+                                       ErrorResult& aError) {
+  SetFontInternal(aFont, aError);
+  if (aError.Failed()) {
+    return;
+  }
+
+  // If letterSpacing or wordSpacing is present, recompute to account for
+  // changes to font-relative dimensions.
+  UpdateSpacing();
+}
+
+bool CanvasRenderingContext2D::SetFontInternal(const nsACString& aFont,
+                                               ErrorResult& aError) {
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (!presShell) {
+    return SetFontInternalDisconnected(aFont, aError);
+  }
+
+  nsPresContext* c = presShell->GetPresContext();
+  FontStyleCacheKey key{aFont, c->RestyleManager()->GetRestyleGeneration()};
+  auto entry = mFontStyleCache.Lookup(key);
+  if (!entry) {
+    FontStyleData newData;
+    newData.mKey = key;
+    newData.mStyle = GetFontStyleForServo(mCanvasElement, aFont, presShell,
+                                          newData.mUsedFont, aError);
+    entry.Set(newData);
+  }
+
+  const auto& data = entry.Data();
+  if (!data.mStyle) {
+    return false;
+  }
+
+  const nsStyleFont* fontStyle = data.mStyle->StyleFont();
+
+  // Purposely ignore the font size that respects the user's minimum
+  // font preference (fontStyle->mFont.size) in favor of the computed
+  // size (fontStyle->mSize).  See
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=698652.
+  // FIXME: Nobody initializes mAllowZoom for servo?
+  // MOZ_ASSERT(!fontStyle->mAllowZoom,
+  //           "expected text zoom to be disabled on this nsStyleFont");
+  nsFont resizedFont(fontStyle->mFont);
+  // Create a font group working in units of CSS pixels instead of the usual
+  // device pixels, to avoid being affected by page zoom. nsFontMetrics will
+  // convert nsFont size in app units to device pixels for the font group, so
+  // here we first apply to the size the equivalent of a conversion from device
+  // pixels to CSS pixels, to adjust for the difference in expectations from
+  // other nsFontMetrics clients.
+  resizedFont.size =
+      fontStyle->mSize.ScaledBy(1.0f / c->CSSToDevPixelScale().scale);
+
+  // Our FontKerning constants (see the enum definition) are the same as the
+  // NS_FONT_KERNING_* values so we can simply assign here.
+  resizedFont.kerning = uint8_t(CurrentState().fontKerning);
+
+  c->Document()->FlushUserFontSet();
+
+  nsFontMetrics::Params params;
+  params.language = fontStyle->mLanguage;
+  params.explicitLanguage = fontStyle->mExplicitLanguage;
+  params.userFontSet = c->GetUserFontSet();
+  params.textPerf = c->GetTextPerfMetrics();
+  RefPtr<nsFontMetrics> metrics = c->GetMetricsFor(resizedFont, params);
+
+  gfxFontGroup* newFontGroup = metrics->GetThebesFontGroup();
+  CurrentState().fontGroup = newFontGroup;
+  NS_ASSERTION(CurrentState().fontGroup, "Could not get font group");
+  CurrentState().font = data.mUsedFont;
+  CurrentState().fontFont = fontStyle->mFont;
+  CurrentState().fontFont.size = fontStyle->mSize;
+  CurrentState().fontLanguage = fontStyle->mLanguage;
+  CurrentState().fontExplicitLanguage = fontStyle->mExplicitLanguage;
+
+  return true;
+}
+
+static nsAutoCString FamilyListToString(
+    const StyleFontFamilyList& aFamilyList) {
+  return StringJoin(","_ns, aFamilyList.list.AsSpan(),
+                    [](nsACString& dst, const StyleSingleFontFamily& name) {
+                      name.AppendToString(dst);
+                    });
+}
+
+static void SerializeFontForCanvas(const StyleFontFamilyList& aList,
+                                   const gfxFontStyle& aStyle,
+                                   nsACString& aUsedFont) {
+  // Re-serialize the font shorthand as required by the canvas spec.
+  aUsedFont.Truncate();
+
+  if (!aStyle.style.IsNormal()) {
+    aStyle.style.ToString(aUsedFont);
+    aUsedFont.Append(" ");
+  }
+
+  // font-weight is serialized as a number
+  if (!aStyle.weight.IsNormal()) {
+    aUsedFont.AppendFloat(aStyle.weight.ToFloat());
+    aUsedFont.Append(" ");
+  }
+
+  // font-stretch is serialized using CSS Fonts 3 keywords, not percentages.
+  if (!aStyle.stretch.IsNormal() &&
+      Servo_FontStretch_SerializeKeyword(&aStyle.stretch, &aUsedFont)) {
+    aUsedFont.Append(" ");
+  }
+
+  // Serialize the computed (not specified) size, and the family name(s).
+  aUsedFont.AppendFloat(aStyle.size);
+  aUsedFont.Append("px ");
+  aUsedFont.Append(FamilyListToString(aList));
+}
+
+bool CanvasRenderingContext2D::SetFontInternalDisconnected(
+    const nsACString& aFont, ErrorResult& aError) {
+  FontFaceSet* fontFaceSet = nullptr;
+  if (mCanvasElement) {
+    fontFaceSet = mCanvasElement->OwnerDoc()->Fonts();
+  } else {
+    nsIGlobalObject* global = GetParentObject();
+    fontFaceSet = global ? global->GetFonts() : nullptr;
+  }
+
+  FontFaceSetImpl* fontFaceSetImpl =
+      fontFaceSet ? fontFaceSet->GetImpl() : nullptr;
+  RefPtr<URLExtraData> urlExtraData =
+      fontFaceSetImpl ? fontFaceSetImpl->GetURLExtraData() : nullptr;
+
+  if (NS_WARN_IF(!urlExtraData)) {
+    // Provided we have a FontFaceSetImpl object, this should only happen on
+    // worker threads, where we failed to initialize the worker before it was
+    // shutdown.
+    aError.ThrowInvalidStateError("Missing URLExtraData");
+    return false;
+  }
+
+  if (fontFaceSetImpl) {
+    fontFaceSetImpl->FlushUserFontSet();
+  }
+
+  // In the OffscreenCanvas case we don't have the context necessary to call
+  // GetFontStyleForServo(), as we do in the main-thread canvas context, so
+  // instead we borrow ParseFontShorthandForMatching to parse the attribute.
+  StyleComputedFontStyleDescriptor style(
+      StyleComputedFontStyleDescriptor::Normal());
+  StyleFontFamilyList list;
+  gfxFontStyle fontStyle;
+  float size = 0.0f;
+  if (!ServoCSSParser::ParseFontShorthandForMatching(
+          aFont, urlExtraData, list, fontStyle.style, fontStyle.stretch,
+          fontStyle.weight, &size)) {
+    return false;
+  }
+
+  fontStyle.size = size;
+
+  // Set the kerning feature, if required by the fontKerning attribute.
+  gfxFontFeature setting{TRUETYPE_TAG('k', 'e', 'r', 'n'), 0};
+  switch (CurrentState().fontKerning) {
+    case FontKerning::NONE:
+      setting.mValue = 0;
+      fontStyle.featureSettings.AppendElement(setting);
+      break;
+    case FontKerning::NORMAL:
+      setting.mValue = 1;
+      fontStyle.featureSettings.AppendElement(setting);
+      break;
+    default:
+      // auto case implies use user agent default
+      break;
+  }
+
+  // If we have a canvas element, get its lang (if known).
+  RefPtr<nsAtom> language;
+  bool explicitLanguage = false;
+  if (mCanvasElement) {
+    language = mCanvasElement->FragmentOrElement::GetLang();
+    if (language) {
+      explicitLanguage = true;
+    } else {
+      language = mCanvasElement->OwnerDoc()->GetLanguageForStyle();
+    }
+  } else {
+    // Pass the OS default language, to behave similarly to HTML or canvas-
+    // element content with no language tag.
+    language = nsLanguageAtomService::GetService()->GetLocaleLanguage();
+  }
+
+  // TODO: Cache fontGroups in the Worker (use an nsFontCache?)
+  gfxFontGroup* fontGroup =
+      new gfxFontGroup(nullptr,           // aPresContext
+                       list,              // aFontFamilyList
+                       &fontStyle,        // aStyle
+                       language,          // aLanguage
+                       explicitLanguage,  // aExplicitLanguage
+                       nullptr,           // aTextPerf
+                       fontFaceSetImpl,   // aUserFontSet
+                       1.0,               // aDevToCssSize
+                       StyleFontVariantEmoji::Normal);
+  CurrentState().fontGroup = fontGroup;
+  SerializeFontForCanvas(list, fontStyle, CurrentState().font);
+  CurrentState().fontFont = nsFont(StyleFontFamily{list, false, false},
+                                   StyleCSSPixelLength::FromPixels(size));
+  CurrentState().fontLanguage = nullptr;
+  CurrentState().fontExplicitLanguage = false;
+  return true;
+}
+
+void CanvasRenderingContext2D::UpdateSpacing() {
+  auto state = CurrentState();
+  if (!state.letterSpacingStr.IsEmpty()) {
+    SetLetterSpacing(state.letterSpacingStr);
+  }
+  if (!state.wordSpacingStr.IsEmpty()) {
+    SetWordSpacing(state.wordSpacingStr);
+  }
+}
+
+void CanvasRenderingContext2D::SetTextAlign(const nsAString& aTextAlign) {
+  if (aTextAlign.EqualsLiteral("start"))
+    CurrentState().textAlign = TextAlign::START;
+  else if (aTextAlign.EqualsLiteral("end"))
+    CurrentState().textAlign = TextAlign::END;
+  else if (aTextAlign.EqualsLiteral("left"))
+    CurrentState().textAlign = TextAlign::LEFT;
+  else if (aTextAlign.EqualsLiteral("right"))
+    CurrentState().textAlign = TextAlign::RIGHT;
+  else if (aTextAlign.EqualsLiteral("center"))
+    CurrentState().textAlign = TextAlign::CENTER;
+}
+
+void CanvasRenderingContext2D::GetTextAlign(nsAString& aTextAlign) {
+  switch (CurrentState().textAlign) {
+    case TextAlign::START:
+      aTextAlign.AssignLiteral("start");
+      break;
+    case TextAlign::END:
+      aTextAlign.AssignLiteral("end");
+      break;
+    case TextAlign::LEFT:
+      aTextAlign.AssignLiteral("left");
+      break;
+    case TextAlign::RIGHT:
+      aTextAlign.AssignLiteral("right");
+      break;
+    case TextAlign::CENTER:
+      aTextAlign.AssignLiteral("center");
+      break;
+  }
+}
+
+void CanvasRenderingContext2D::SetTextBaseline(const nsAString& aTextBaseline) {
+  if (aTextBaseline.EqualsLiteral("top"))
+    CurrentState().textBaseline = TextBaseline::TOP;
+  else if (aTextBaseline.EqualsLiteral("hanging"))
+    CurrentState().textBaseline = TextBaseline::HANGING;
+  else if (aTextBaseline.EqualsLiteral("middle"))
+    CurrentState().textBaseline = TextBaseline::MIDDLE;
+  else if (aTextBaseline.EqualsLiteral("alphabetic"))
+    CurrentState().textBaseline = TextBaseline::ALPHABETIC;
+  else if (aTextBaseline.EqualsLiteral("ideographic"))
+    CurrentState().textBaseline = TextBaseline::IDEOGRAPHIC;
+  else if (aTextBaseline.EqualsLiteral("bottom"))
+    CurrentState().textBaseline = TextBaseline::BOTTOM;
+}
+
+void CanvasRenderingContext2D::GetTextBaseline(nsAString& aTextBaseline) {
+  switch (CurrentState().textBaseline) {
+    case TextBaseline::TOP:
+      aTextBaseline.AssignLiteral("top");
+      break;
+    case TextBaseline::HANGING:
+      aTextBaseline.AssignLiteral("hanging");
+      break;
+    case TextBaseline::MIDDLE:
+      aTextBaseline.AssignLiteral("middle");
+      break;
+    case TextBaseline::ALPHABETIC:
+      aTextBaseline.AssignLiteral("alphabetic");
+      break;
+    case TextBaseline::IDEOGRAPHIC:
+      aTextBaseline.AssignLiteral("ideographic");
+      break;
+    case TextBaseline::BOTTOM:
+      aTextBaseline.AssignLiteral("bottom");
+      break;
+  }
+}
+
+void CanvasRenderingContext2D::SetDirection(const nsAString& aDirection) {
+  if (aDirection.EqualsLiteral("ltr")) {
+    CurrentState().textDirection = TextDirection::LTR;
+  } else if (aDirection.EqualsLiteral("rtl")) {
+    CurrentState().textDirection = TextDirection::RTL;
+  } else if (aDirection.EqualsLiteral("inherit")) {
+    CurrentState().textDirection = TextDirection::INHERIT;
+  }
+}
+
+void CanvasRenderingContext2D::GetDirection(nsAString& aDirection) {
+  switch (CurrentState().textDirection) {
+    case TextDirection::LTR:
+      aDirection.AssignLiteral("ltr");
+      break;
+    case TextDirection::RTL:
+      aDirection.AssignLiteral("rtl");
+      break;
+    case TextDirection::INHERIT:
+      aDirection.AssignLiteral("inherit");
+      break;
+  }
+}
+
+void CanvasRenderingContext2D::SetFontKerning(const nsAString& aFontKerning) {
+  auto oldValue = CurrentState().fontKerning;
+  if (aFontKerning.EqualsLiteral("auto")) {
+    CurrentState().fontKerning = FontKerning::AUTO;
+  } else if (aFontKerning.EqualsLiteral("normal")) {
+    CurrentState().fontKerning = FontKerning::NORMAL;
+  } else if (aFontKerning.EqualsLiteral("none")) {
+    CurrentState().fontKerning = FontKerning::NONE;
+  }
+  if (CurrentState().fontKerning != oldValue) {
+    CurrentState().fontGroup = nullptr;
+  }
+}
+
+void CanvasRenderingContext2D::GetFontKerning(nsAString& aFontKerning) {
+  switch (CurrentState().fontKerning) {
+    case FontKerning::AUTO:
+      aFontKerning.AssignLiteral("auto");
+      break;
+    case FontKerning::NORMAL:
+      aFontKerning.AssignLiteral("normal");
+      break;
+    case FontKerning::NONE:
+      aFontKerning.AssignLiteral("none");
+      break;
+  }
+}
+
+/*
+ * Helper function that replaces the whitespace characters in a string
+ * with U+0020 SPACE. The whitespace characters are defined as U+0020 SPACE,
+ * U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000B LINE
+ * TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).
+ * We also replace characters with Bidi type Segment Separator or Block
+ * Separator.
+ * @param str The string whose whitespace characters to replace.
+ */
+static inline void TextReplaceWhitespaceCharacters(nsAutoString& aStr) {
+  aStr.ReplaceChar(u"\x09\x0A\x0B\x0C\x0D\x1C\x1D\x1E\x1F\x85\x2029",
+                   char16_t(' '));
+}
+
+void CanvasRenderingContext2D::FillText(const nsAString& aText, double aX,
+                                        double aY,
+                                        const Optional<double>& aMaxWidth,
+                                        ErrorResult& aError) {
+  DebugOnly<TextMetrics*> metrics = DrawOrMeasureText(
+      aText, aX, aY, aMaxWidth, TextDrawOperation::FILL, aError);
+  MOZ_ASSERT(!metrics);  // drawing operation never returns TextMetrics
+}
+
+void CanvasRenderingContext2D::StrokeText(const nsAString& aText, double aX,
+                                          double aY,
+                                          const Optional<double>& aMaxWidth,
+                                          ErrorResult& aError) {
+  DebugOnly<TextMetrics*> metrics = DrawOrMeasureText(
+      aText, aX, aY, aMaxWidth, TextDrawOperation::STROKE, aError);
+  MOZ_ASSERT(!metrics);  // drawing operation never returns TextMetrics
+}
+
+TextMetrics* CanvasRenderingContext2D::MeasureText(const nsAString& aRawText,
+                                                   ErrorResult& aError) {
+  Optional<double> maxWidth;
+  return DrawOrMeasureText(aRawText, 0, 0, maxWidth, TextDrawOperation::MEASURE,
+                           aError);
+}
+
+/**
+ * Used for nsBidiPresUtils::ProcessText
+ */
+struct MOZ_STACK_CLASS CanvasBidiProcessor final
+    : public nsBidiPresUtils::BidiProcessor {
+  using Style = CanvasRenderingContext2D::Style;
+
+  CanvasBidiProcessor() : nsBidiPresUtils::BidiProcessor() {
+    if (StaticPrefs::gfx_missing_fonts_notify()) {
+      mMissingFonts = MakeUnique<gfxMissingFontRecorder>();
+    }
+  }
+
+  ~CanvasBidiProcessor() {
+    // notify front-end code if we encountered missing glyphs in any script
+    if (mMissingFonts) {
+      mMissingFonts->Flush();
+    }
+  }
+
+  class PropertyProvider : public gfxTextRun::PropertyProvider {
+   public:
+    explicit PropertyProvider(const CanvasBidiProcessor& aProcessor)
+        : mProcessor(aProcessor) {}
+
+    void GetSpacing(gfxTextRun::Range aRange,
+                    gfxFont::Spacing* aSpacing) const {
+      for (auto i = aRange.start; i < aRange.end; ++i) {
+        auto* charGlyphs = mProcessor.mTextRun->GetCharacterGlyphs();
+        if (i == mProcessor.mTextRun->GetLength() - 1 ||
+            (charGlyphs[i + 1].IsClusterStart() &&
+             charGlyphs[i + 1].IsLigatureGroupStart())) {
+          // Currently we add all the letterspacing to the right of the glyph,
+          // which is similar to Chrome's behavior, though the LTR vs RTL
+          // asymmetry seems unfortunate.
+          if (mProcessor.mTextRun->IsRightToLeft()) {
+            aSpacing->mAfter = 0;
+            aSpacing->mBefore = mProcessor.mLetterSpacing;
+          } else {
+            aSpacing->mBefore = 0;
+            aSpacing->mAfter = mProcessor.mLetterSpacing;
+          }
+        } else {
+          aSpacing->mBefore = 0;
+          aSpacing->mAfter = 0;
+        }
+        if (charGlyphs[i].CharIsSpace()) {
+          if (mProcessor.mTextRun->IsRightToLeft()) {
+            aSpacing->mBefore += mProcessor.mWordSpacing;
+          } else {
+            aSpacing->mAfter += mProcessor.mWordSpacing;
+          }
+        }
+        aSpacing++;
+      }
+    }
+
+    mozilla::StyleHyphens GetHyphensOption() const {
+      return mozilla::StyleHyphens::None;
+    }
+
+    // Methods only used when hyphenation is active, not relevant to canvas2d:
+    void GetHyphenationBreaks(gfxTextRun::Range aRange,
+                              gfxTextRun::HyphenType* aBreakBefore) const {
+      MOZ_ASSERT_UNREACHABLE("no hyphenation in canvas2d text!");
+    }
+    gfxFloat GetHyphenWidth() const {
+      MOZ_ASSERT_UNREACHABLE("no hyphenation in canvas2d text!");
+      return 0.0;
+    }
+    already_AddRefed<DrawTarget> GetDrawTarget() const {
+      MOZ_ASSERT_UNREACHABLE("no hyphenation in canvas2d text!");
+      return nullptr;
+    }
+    uint32_t GetAppUnitsPerDevUnit() const {
+      MOZ_ASSERT_UNREACHABLE("no hyphenation in canvas2d text!");
+      return 60;
+    }
+    gfx::ShapedTextFlags GetShapedTextFlags() const {
+      MOZ_ASSERT_UNREACHABLE("no hyphenation in canvas2d text!");
+      return gfx::ShapedTextFlags();
+    }
+
+   private:
+    const CanvasBidiProcessor& mProcessor;
+  };
+
+  using ContextState = CanvasRenderingContext2D::ContextState;
+
+  void SetText(const char16_t* aText, int32_t aLength,
+               intl::BidiDirection aDirection) override {
+    if (mIgnoreSetText) {
+      // We've been told to ignore SetText because the processor is only ever
+      // handling a single, fixed string.
+      MOZ_ASSERT(mTextRun && mTextRun->GetLength() == uint32_t(aLength));
+      return;
+    }
+    mSetTextCount++;
+    auto* pfl = gfxPlatformFontList::PlatformFontList();
+    pfl->Lock();
+    mFontgrp->CheckForUpdatedPlatformList();
+    mFontgrp->UpdateUserFonts();  // ensure user font generation is current
+    // adjust flags for current direction run
+    gfx::ShapedTextFlags flags = mTextRunFlags;
+    if (aDirection == intl::BidiDirection::RTL) {
+      flags |= gfx::ShapedTextFlags::TEXT_IS_RTL;
+    } else {
+      flags &= ~gfx::ShapedTextFlags::TEXT_IS_RTL;
+    }
+    mTextRun = mFontgrp->MakeTextRun(
+        aText, aLength, mDrawTarget, mAppUnitsPerDevPixel, flags,
+        nsTextFrameUtils::Flags::DontSkipDrawingForPendingUserFonts,
+        mMissingFonts.get());
+    pfl->Unlock();
+  }
+
+  nscoord GetWidth() override {
+    PropertyProvider provider(*this);
+    gfxTextRun::Metrics textRunMetrics = mTextRun->MeasureText(
+        mDoMeasureBoundingBox ? gfxFont::TIGHT_INK_EXTENTS
+                              : gfxFont::LOOSE_INK_EXTENTS,
+        mDrawTarget, &provider);
+
+    // this only measures the height; the total width is gotten from the
+    // the return value of ProcessText.
+    if (mDoMeasureBoundingBox) {
+      textRunMetrics.mBoundingBox.Scale(1.0 / mAppUnitsPerDevPixel);
+      mBoundingBox = mBoundingBox.Union(textRunMetrics.mBoundingBox);
+    }
+
+    return NSToCoordRound(textRunMetrics.mAdvanceWidth);
+  }
+
+  already_AddRefed<gfxPattern> GetGradientFor(Style aStyle) {
+    RefPtr<gfxPattern> pattern;
+    CanvasGradient* gradient = mCtx->CurrentState().gradientStyles[aStyle];
+    CanvasGradient::Type type = gradient->GetType();
+
+    switch (type) {
+      case CanvasGradient::Type::CONIC: {
+        auto conic = static_cast<CanvasConicGradient*>(gradient);
+        pattern = new gfxPattern(conic->mCenter.x, conic->mCenter.y,
+                                 conic->mAngle, 0, 1);
+        break;
+      }
+      case CanvasGradient::Type::RADIAL: {
+        auto radial = static_cast<CanvasRadialGradient*>(gradient);
+        pattern = new gfxPattern(radial->mCenter1.x, radial->mCenter1.y,
+                                 radial->mRadius1, radial->mCenter2.x,
+                                 radial->mCenter2.y, radial->mRadius2);
+        break;
+      }
+      case CanvasGradient::Type::LINEAR: {
+        auto linear = static_cast<CanvasLinearGradient*>(gradient);
+        pattern = new gfxPattern(linear->mBegin.x, linear->mBegin.y,
+                                 linear->mEnd.x, linear->mEnd.y);
+        break;
+      }
+      default:
+        MOZ_ASSERT(false, "Should be linear, radial or conic gradient.");
+        return nullptr;
+    }
+
+    for (auto stop : gradient->mRawStops) {
+      pattern->AddColorStop(stop.offset, stop.color);
+    }
+
+    return pattern.forget();
+  }
+
+  gfx::ExtendMode CvtCanvasRepeatToGfxRepeat(
+      CanvasPattern::RepeatMode aRepeatMode) {
+    switch (aRepeatMode) {
+      case CanvasPattern::RepeatMode::REPEAT:
+        return gfx::ExtendMode::REPEAT;
+      case CanvasPattern::RepeatMode::REPEATX:
+        return gfx::ExtendMode::REPEAT_X;
+      case CanvasPattern::RepeatMode::REPEATY:
+        return gfx::ExtendMode::REPEAT_Y;
+      case CanvasPattern::RepeatMode::NOREPEAT:
+        return gfx::ExtendMode::CLAMP;
+      default:
+        return gfx::ExtendMode::CLAMP;
+    }
+  }
+
+  already_AddRefed<gfxPattern> GetPatternFor(Style aStyle) {
+    const CanvasPattern* pat = mCtx->CurrentState().patternStyles[aStyle];
+    RefPtr<gfxPattern> pattern = new gfxPattern(pat->mSurface, pat->mTransform);
+    pattern->SetExtend(CvtCanvasRepeatToGfxRepeat(pat->mRepeat));
+    return pattern.forget();
+  }
+
+  void DrawText(nscoord aXOffset) override {
+    gfx::Point point = mPt;
+    bool rtl = mTextRun->IsRightToLeft();
+    bool verticalRun = mTextRun->IsVertical();
+    RefPtr<gfxPattern> pattern;
+
+    float& inlineCoord = verticalRun ? point.y.value : point.x.value;
+    inlineCoord += aXOffset;
+
+    PropertyProvider provider(*this);
+
+    // offset is given in terms of left side of string
+    if (rtl) {
+      // Bug 581092 - don't use rounded pixel width to advance to
+      // right-hand end of run, because this will cause different
+      // glyph positioning for LTR vs RTL drawing of the same
+      // glyph string on OS X and DWrite where textrun widths may
+      // involve fractional pixels.
+      gfxTextRun::Metrics textRunMetrics = mTextRun->MeasureText(
+          mDoMeasureBoundingBox ? gfxFont::TIGHT_INK_EXTENTS
+                                : gfxFont::LOOSE_INK_EXTENTS,
+          mDrawTarget, &provider);
+      inlineCoord += textRunMetrics.mAdvanceWidth;
+      // old code was:
+      //   point.x += width * mAppUnitsPerDevPixel;
+      // TODO: restore this if/when we move to fractional coords
+      // throughout the text layout process
+    }
+
+    mCtx->EnsureTarget();
+    if (!mCtx->IsTargetValid()) {
+      return;
+    }
+
+    // Defer the tasks to gfxTextRun which will handle color/svg-in-ot fonts
+    // appropriately.
+    StrokeOptions strokeOpts;
+    DrawOptions drawOpts;
+    Style style = (mOp == CanvasRenderingContext2D::TextDrawOperation::FILL)
+                      ? Style::FILL
+                      : Style::STROKE;
+    const ContextState& state = mCtx->CurrentState();
+
+    gfx::Rect bounds;
+    if (mCtx->NeedToCalculateBounds()) {
+      bounds = ToRect(mBoundingBox);
+      bounds.MoveBy(mPt / mAppUnitsPerDevPixel);
+      if (style == Style::STROKE) {
+        bounds.Inflate(state.lineWidth / 2.0);
+      }
+      bounds = mDrawTarget->GetTransform().TransformBounds(bounds);
+    }
+
+    AdjustedTarget target(mCtx, bounds.IsEmpty() ? nullptr : &bounds, false);
+    if (!target) {
+      return;
+    }
+
+    gfxContext thebes(target, /* aPreserveTransform */ true);
+    gfxTextRun::DrawParams params(&thebes);
+
+    params.allowGDI = false;
+
+    if (state.StyleIsColor(style)) {  // Color
+      nscolor fontColor = state.colorStyles[style];
+      if (style == Style::FILL) {
+        params.context->SetColor(sRGBColor::FromABGR(fontColor));
+      } else {
+        params.textStrokeColor = fontColor;
+      }
+    } else {
+      if (state.gradientStyles[style]) {  // Gradient
+        pattern = GetGradientFor(style);
+      } else if (state.patternStyles[style]) {  // Pattern
+        pattern = GetPatternFor(style);
+      } else {
+        MOZ_ASSERT(false, "Should never reach here.");
+        return;
+      }
+      MOZ_ASSERT(pattern, "No valid pattern.");
+
+      if (style == Style::FILL) {
+        params.context->SetPattern(pattern);
+      } else {
+        params.textStrokePattern = pattern;
+      }
+    }
+
+    drawOpts.mAlpha = state.globalAlpha;
+    drawOpts.mCompositionOp = target.UsedOperation();
+    if (!mCtx->IsTargetValid()) {
+      return;
+    }
+
+    params.drawOpts = &drawOpts;
+    params.provider = &provider;
+
+    if (style == Style::STROKE) {
+      strokeOpts.mLineWidth = state.lineWidth;
+      strokeOpts.mLineJoin = state.lineJoin;
+      strokeOpts.mLineCap = state.lineCap;
+      strokeOpts.mMiterLimit = state.miterLimit;
+      strokeOpts.mDashLength = state.dash.Length();
+      strokeOpts.mDashPattern =
+          (strokeOpts.mDashLength > 0) ? state.dash.Elements() : 0;
+      strokeOpts.mDashOffset = state.dashOffset;
+
+      params.drawMode = DrawMode::GLYPH_STROKE;
+      params.strokeOpts = &strokeOpts;
+    }
+
+    mTextRun->Draw(gfxTextRun::Range(mTextRun.get()), point, params);
+  }
+
+  // current text run
+  RefPtr<gfxTextRun> mTextRun;
+
+  // pointer to a screen reference context used to measure text and such
+  RefPtr<DrawTarget> mDrawTarget;
+
+  // Pointer to the draw target we should fill our text to
+  CanvasRenderingContext2D* mCtx = nullptr;
+
+  // position of the left side of the string, alphabetic baseline
+  gfx::Point mPt;
+
+  // current font
+  gfxFontGroup* mFontgrp = nullptr;
+
+  // spacing adjustments to be applied
+  gfx::Float mLetterSpacing = 0.0f;
+  gfx::Float mWordSpacing = 0.0f;
+
+  // to record any unsupported characters found in the text,
+  // and notify front-end if it is interested
+  UniquePtr<gfxMissingFontRecorder> mMissingFonts;
+
+  // dev pixel conversion factor
+  int32_t mAppUnitsPerDevPixel = 0;
+
+  // operation (fill or stroke)
+  CanvasRenderingContext2D::TextDrawOperation mOp =
+      CanvasRenderingContext2D::TextDrawOperation::FILL;
+
+  // union of bounding boxes of all runs, needed for shadows
+  gfxRect mBoundingBox;
+
+  // flags to use when creating textrun, based on CSS style
+  gfx::ShapedTextFlags mTextRunFlags = gfx::ShapedTextFlags();
+
+  // Count of how many times SetText has been called on this processor.
+  uint32_t mSetTextCount = 0;
+
+  // true iff the bounding box should be measured
+  bool mDoMeasureBoundingBox = false;
+
+  // true if future SetText calls should be ignored
+  bool mIgnoreSetText = false;
+};
+
+TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
+    const nsAString& aRawText, float aX, float aY,
+    const Optional<double>& aMaxWidth, TextDrawOperation aOp,
+    ErrorResult& aError) {
+  // Approximated baselines. In an ideal world, we'd read the baseline info
+  // directly from the font (where available). Alas we currently lack
+  // that functionality. These numbers are best guesses and should
+  // suffice for now. Both are fractions of the em ascent/descent from the
+  // alphabetic baseline.
+  const double kHangingBaselineDefault = 0.8;      // fraction of ascent
+  const double kIdeographicBaselineDefault = 0.5;  // fraction of descent
+
+  RefPtr<gfxFontGroup> currentFontStyle = GetCurrentFontStyle();
+  if (NS_WARN_IF(!currentFontStyle)) {
+    aError = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+
+  RefPtr<PresShell> presShell = GetPresShell();
+  RefPtr<Document> document = presShell ? presShell->GetDocument() : nullptr;
+
+  // replace all the whitespace characters with U+0020 SPACE
+  nsAutoString textToDraw(aRawText);
+  TextReplaceWhitespaceCharacters(textToDraw);
+
+  // According to spec, the API should return an empty array if maxWidth was
+  // provided but is less than or equal to zero or equal to NaN.
+  if (aMaxWidth.WasPassed() &&
+      (aMaxWidth.Value() <= 0 || std::isnan(aMaxWidth.Value()))) {
+    textToDraw.Truncate();
+  }
+
+  RefPtr<const ComputedStyle> canvasStyle;
+  if (mCanvasElement) {
+    canvasStyle = nsComputedDOMStyle::GetComputedStyle(mCanvasElement);
+  }
+
+  // Get text direction, either from the property or inherited from context.
+  const ContextState& state = CurrentState();
+  bool isRTL;
+  switch (state.textDirection) {
+    case TextDirection::LTR:
+      isRTL = false;
+      break;
+    case TextDirection::RTL:
+      isRTL = true;
+      break;
+    case TextDirection::INHERIT:
+      if (canvasStyle) {
+        isRTL =
+            canvasStyle->StyleVisibility()->mDirection == StyleDirection::Rtl;
+      } else if (document) {
+        isRTL = GET_BIDI_OPTION_DIRECTION(document->GetBidiOptions()) ==
+                IBMBIDI_TEXTDIRECTION_RTL;
+      } else {
+        isRTL = false;
+      }
+      break;
+  }
+
+  // This is only needed to know if we can know the drawing bounding box easily.
+  const bool doCalculateBounds = NeedToCalculateBounds();
+  if (presShell && presShell->IsDestroying()) {
+    aError = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+
+  nsPresContext* presContext =
+      presShell ? presShell->GetPresContext() : nullptr;
+
+  if (presContext) {
+    // ensure user font set is up to date
+    presContext->Document()->FlushUserFontSet();
+    currentFontStyle->SetUserFontSet(presContext->GetUserFontSet());
+  }
+
+  if (currentFontStyle->GetStyle()->size == 0.0F) {
+    aError = NS_OK;
+    if (aOp == TextDrawOperation::MEASURE) {
+      return new TextMetrics(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
+                             0.0, 0.0);
+    }
+    return nullptr;
+  }
+
+  if (!std::isfinite(aX) || !std::isfinite(aY)) {
+    aError = NS_OK;
+    // This may not be correct - what should TextMetrics contain in the case of
+    // infinite width or height?
+    if (aOp == TextDrawOperation::MEASURE) {
+      return new TextMetrics(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
+                             0.0, 0.0);
+    }
+    return nullptr;
+  }
+
+  CanvasBidiProcessor processor;
+
+  // If we don't have a ComputedStyle, we can't set up vertical-text flags
+  // (for now, at least; perhaps we need new Canvas API to control this).
+  processor.mTextRunFlags =
+      canvasStyle ? nsLayoutUtils::GetTextRunFlagsForStyle(
+                        canvasStyle, presContext, canvasStyle->StyleFont(),
+                        canvasStyle->StyleText(), 0)
+                  : gfx::ShapedTextFlags();
+
+  GetAppUnitsValues(&processor.mAppUnitsPerDevPixel, nullptr);
+  processor.mPt = gfx::Point(aX, aY);
+  processor.mDrawTarget = gfxPlatform::ThreadLocalScreenReferenceDrawTarget();
+
+  // If we don't have a target then we don't have a transform. A target won't
+  // be needed in the case where we're measuring the text size. This allows
+  // to avoid creating a target if it's only being used to measure text sizes.
+  if (mTarget) {
+    processor.mDrawTarget->SetTransform(mTarget->GetTransform());
+  }
+  processor.mCtx = this;
+  processor.mOp = aOp;
+  processor.mBoundingBox = gfxRect(0, 0, 0, 0);
+  processor.mDoMeasureBoundingBox = doCalculateBounds ||
+                                    !mIsEntireFrameInvalid ||
+                                    aOp == TextDrawOperation::MEASURE;
+  processor.mFontgrp = currentFontStyle;
+
+  if (state.letterSpacing != 0.0 || state.wordSpacing != 0.0) {
+    processor.mLetterSpacing =
+        state.letterSpacing * processor.mAppUnitsPerDevPixel;
+    processor.mWordSpacing = state.wordSpacing * processor.mAppUnitsPerDevPixel;
+    processor.mTextRunFlags |= gfx::ShapedTextFlags::TEXT_ENABLE_SPACING;
+    if (state.letterSpacing != 0.0) {
+      processor.mTextRunFlags |=
+          gfx::ShapedTextFlags::TEXT_DISABLE_OPTIONAL_LIGATURES;
+    }
+  }
+
+  nscoord totalWidthCoord;
+
+  processor.mFontgrp
+      ->UpdateUserFonts();  // ensure user font generation is current
+  RefPtr<gfxFont> font = processor.mFontgrp->GetFirstValidFont();
+  const gfxFont::Metrics& fontMetrics =
+      font->GetMetrics(nsFontMetrics::eHorizontal);
+
+  // calls bidi algo twice since it needs the full text width and the
+  // bounding boxes before rendering anything
+  aError = nsBidiPresUtils::ProcessText(
+      textToDraw.get(), textToDraw.Length(),
+      isRTL ? intl::BidiEmbeddingLevel::RTL() : intl::BidiEmbeddingLevel::LTR(),
+      presContext, processor, nsBidiPresUtils::MODE_MEASURE, nullptr, 0,
+      &totalWidthCoord, mBidiEngine);
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  // If ProcessText only called SetText once, we're dealing with a single run,
+  // and so we don't need to repeat SetText and textRun construction at drawing
+  // time below; we can just re-use the existing textRun.
+  if (processor.mSetTextCount == 1) {
+    processor.mIgnoreSetText = true;
+  }
+
+  float totalWidth = float(totalWidthCoord) / processor.mAppUnitsPerDevPixel;
+
+  // offset pt.x based on text align
+  gfxFloat anchorX;
+
+  if (state.textAlign == TextAlign::CENTER) {
+    anchorX = .5;
+  } else if (state.textAlign == TextAlign::LEFT ||
+             (!isRTL && state.textAlign == TextAlign::START) ||
+             (isRTL && state.textAlign == TextAlign::END)) {
+    anchorX = 0;
+  } else {
+    anchorX = 1;
+  }
+
+  float offsetX = anchorX * totalWidth;
+  processor.mPt.x -= offsetX;
+
+  // offset pt.y (or pt.x, for vertical text) based on text baseline
+  gfxFloat baselineAnchor;
+
+  switch (state.textBaseline) {
+    case TextBaseline::HANGING:
+      baselineAnchor = fontMetrics.emAscent * kHangingBaselineDefault;
+      break;
+    case TextBaseline::TOP:
+      baselineAnchor = fontMetrics.emAscent;
+      break;
+    case TextBaseline::MIDDLE:
+      baselineAnchor = (fontMetrics.emAscent - fontMetrics.emDescent) * .5f;
+      break;
+    case TextBaseline::ALPHABETIC:
+      baselineAnchor = 0;
+      break;
+    case TextBaseline::IDEOGRAPHIC:
+      baselineAnchor = -fontMetrics.emDescent * kIdeographicBaselineDefault;
+      break;
+    case TextBaseline::BOTTOM:
+      baselineAnchor = -fontMetrics.emDescent;
+      break;
+    default:
+      MOZ_CRASH("GFX: unexpected TextBaseline");
+  }
+
+  // We can't query the textRun directly, as it may not have been created yet;
+  // so instead we check the flags that will be used to initialize it.
+  gfx::ShapedTextFlags runOrientation =
+      (processor.mTextRunFlags & gfx::ShapedTextFlags::TEXT_ORIENT_MASK);
+  if (runOrientation != gfx::ShapedTextFlags::TEXT_ORIENT_HORIZONTAL) {
+    if (runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_MIXED ||
+        runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_UPRIGHT) {
+      // Adjust to account for mTextRun being shaped using center baseline
+      // rather than alphabetic.
+      baselineAnchor -= (fontMetrics.emAscent - fontMetrics.emDescent) * .5f;
+    }
+    processor.mPt.x -= baselineAnchor;
+  } else {
+    processor.mPt.y += baselineAnchor;
+  }
+
+  // if only measuring, don't need to do any more work
+  if (aOp == TextDrawOperation::MEASURE) {
+    aError = NS_OK;
+    // Note that actualBoundingBoxLeft measures the distance in the leftward
+    // direction, so its sign is reversed from our usual physical coordinates.
+    double actualBoundingBoxLeft = offsetX - processor.mBoundingBox.X();
+    double actualBoundingBoxRight = processor.mBoundingBox.XMost() - offsetX;
+    double actualBoundingBoxAscent =
+        -processor.mBoundingBox.Y() - baselineAnchor;
+    double actualBoundingBoxDescent =
+        processor.mBoundingBox.YMost() + baselineAnchor;
+    double hangingBaseline =
+        fontMetrics.emAscent * kHangingBaselineDefault - baselineAnchor;
+    double ideographicBaseline =
+        -fontMetrics.emDescent * kIdeographicBaselineDefault - baselineAnchor;
+    return new TextMetrics(
+        totalWidth, actualBoundingBoxLeft, actualBoundingBoxRight,
+        fontMetrics.maxAscent - baselineAnchor,   // fontBBAscent
+        fontMetrics.maxDescent + baselineAnchor,  // fontBBDescent
+        actualBoundingBoxAscent, actualBoundingBoxDescent,
+        fontMetrics.emAscent - baselineAnchor,    // emHeightAscent
+        -fontMetrics.emDescent - baselineAnchor,  // emHeightDescent
+        hangingBaseline,
+        -baselineAnchor,  // alphabeticBaseline
+        ideographicBaseline);
+  }
+
+  // If we did not actually calculate bounds, set up a simple bounding box
+  // based on the text position and advance.
+  if (!doCalculateBounds) {
+    processor.mBoundingBox.width = totalWidth;
+    processor.mBoundingBox.MoveBy(gfxPoint(processor.mPt.x, processor.mPt.y));
+  }
+
+  processor.mPt.x *= processor.mAppUnitsPerDevPixel;
+  processor.mPt.y *= processor.mAppUnitsPerDevPixel;
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    aError = NS_ERROR_FAILURE;
+    return nullptr;
+  }
+
+  Matrix oldTransform = mTarget->GetTransform();
+  // if text is over aMaxWidth, then scale the text horizontally such that its
+  // width is precisely aMaxWidth
+  if (aMaxWidth.WasPassed() && aMaxWidth.Value() > 0 &&
+      totalWidth > aMaxWidth.Value()) {
+    Matrix newTransform = oldTransform;
+
+    // Translate so that the anchor point is at 0,0, then scale and then
+    // translate back.
+    newTransform.PreTranslate(aX, 0);
+    newTransform.PreScale(aMaxWidth.Value() / totalWidth, 1);
+    newTransform.PreTranslate(-aX, 0);
+    /* we do this to avoid an ICE in the android compiler */
+    Matrix androidCompilerBug = newTransform;
+    mTarget->SetTransform(androidCompilerBug);
+  }
+
+  // save the previous bounding box
+  gfxRect boundingBox = processor.mBoundingBox;
+
+  // don't ever need to measure the bounding box twice
+  processor.mDoMeasureBoundingBox = false;
+
+  aError = nsBidiPresUtils::ProcessText(
+      textToDraw.get(), textToDraw.Length(),
+      isRTL ? intl::BidiEmbeddingLevel::RTL() : intl::BidiEmbeddingLevel::LTR(),
+      presContext, processor, nsBidiPresUtils::MODE_DRAW, nullptr, 0, nullptr,
+      mBidiEngine);
+
+  if (aError.Failed()) {
+    return nullptr;
+  }
+
+  mTarget->SetTransform(oldTransform);
+
+  if (aOp == CanvasRenderingContext2D::TextDrawOperation::FILL &&
+      !doCalculateBounds) {
+    RedrawUser(boundingBox);
+  } else {
+    Redraw();
+  }
+
+  aError = NS_OK;
+  return nullptr;
+}
+
+gfxFontGroup* CanvasRenderingContext2D::GetCurrentFontStyle() {
+  // Use lazy (re)initialization for the fontGroup since it's rather expensive.
+
+  RefPtr<PresShell> presShell = GetPresShell();
+  nsPresContext* presContext =
+      presShell ? presShell->GetPresContext() : nullptr;
+
+  // If we have a cached fontGroup, check that it is valid for the current
+  // prescontext; if not, we need to discard and re-create it.
+  RefPtr<gfxFontGroup>& fontGroup = CurrentState().fontGroup;
+  if (fontGroup) {
+    if (fontGroup->GetPresContext() != presContext) {
+      fontGroup = nullptr;
+    }
+  }
+
+  if (!fontGroup) {
+    ErrorResult err;
+    constexpr auto kDefaultFontStyle = "10px sans-serif"_ns;
+    const float kDefaultFontSize = 10.0;
+    // If the font has already been set, we're re-creating the fontGroup
+    // and should re-use the existing font attribute; if not, we initialize
+    // it to the canvas default.
+    const nsCString& currentFont = CurrentState().font;
+    bool fontUpdated = SetFontInternal(
+        currentFont.IsEmpty() ? kDefaultFontStyle : currentFont, err);
+    if (err.Failed() || !fontUpdated) {
+      err.SuppressException();
+      // XXX Should we get a default lang from the prescontext or something?
+      nsAtom* language = nsGkAtoms::x_western;
+      bool explicitLanguage = false;
+      gfxFontStyle style;
+      style.size = kDefaultFontSize;
+      int32_t perDevPixel, perCSSPixel;
+      GetAppUnitsValues(&perDevPixel, &perCSSPixel);
+      gfxFloat devToCssSize = gfxFloat(perDevPixel) / gfxFloat(perCSSPixel);
+      const auto* sans =
+          Servo_FontFamily_Generic(StyleGenericFontFamily::SansSerif);
+      fontGroup = new gfxFontGroup(
+          presContext, sans->families, &style, language, explicitLanguage,
+          presContext ? presContext->GetTextPerfMetrics() : nullptr, nullptr,
+          devToCssSize, StyleFontVariantEmoji::Normal);
+      if (fontGroup) {
+        CurrentState().font = kDefaultFontStyle;
+      } else {
+        NS_ERROR("Default canvas font is invalid");
+      }
+    }
+  } else {
+    // The fontgroup needs to check if its cached families/faces are valid.
+    fontGroup->CheckForUpdatedPlatformList();
+  }
+
+  return fontGroup;
+}
+
+//
+// line caps/joins
+//
+
+void CanvasRenderingContext2D::SetLineCap(const nsAString& aLinecapStyle) {
+  CapStyle cap;
+
+  if (aLinecapStyle.EqualsLiteral("butt")) {
+    cap = CapStyle::BUTT;
+  } else if (aLinecapStyle.EqualsLiteral("round")) {
+    cap = CapStyle::ROUND;
+  } else if (aLinecapStyle.EqualsLiteral("square")) {
+    cap = CapStyle::SQUARE;
+  } else {
+    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
+    return;
+  }
+
+  CurrentState().lineCap = cap;
+}
+
+void CanvasRenderingContext2D::GetLineCap(nsAString& aLinecapStyle) {
+  switch (CurrentState().lineCap) {
+    case CapStyle::BUTT:
+      aLinecapStyle.AssignLiteral("butt");
+      break;
+    case CapStyle::ROUND:
+      aLinecapStyle.AssignLiteral("round");
+      break;
+    case CapStyle::SQUARE:
+      aLinecapStyle.AssignLiteral("square");
+      break;
+  }
+}
+
+void CanvasRenderingContext2D::SetLineJoin(const nsAString& aLinejoinStyle) {
+  JoinStyle j;
+
+  if (aLinejoinStyle.EqualsLiteral("round")) {
+    j = JoinStyle::ROUND;
+  } else if (aLinejoinStyle.EqualsLiteral("bevel")) {
+    j = JoinStyle::BEVEL;
+  } else if (aLinejoinStyle.EqualsLiteral("miter")) {
+    j = JoinStyle::MITER_OR_BEVEL;
+  } else {
+    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
+    return;
+  }
+
+  CurrentState().lineJoin = j;
+}
+
+void CanvasRenderingContext2D::GetLineJoin(nsAString& aLinejoinStyle,
+                                           ErrorResult& aError) {
+  switch (CurrentState().lineJoin) {
+    case JoinStyle::ROUND:
+      aLinejoinStyle.AssignLiteral("round");
+      break;
+    case JoinStyle::BEVEL:
+      aLinejoinStyle.AssignLiteral("bevel");
+      break;
+    case JoinStyle::MITER_OR_BEVEL:
+      aLinejoinStyle.AssignLiteral("miter");
+      break;
+    default:
+      aError.Throw(NS_ERROR_FAILURE);
+  }
+}
+
+void CanvasRenderingContext2D::SetLineDash(const Sequence<double>& aSegments,
+                                           ErrorResult& aRv) {
+  nsTArray<mozilla::gfx::Float> dash;
+
+  for (uint32_t x = 0; x < aSegments.Length(); x++) {
+    if (aSegments[x] < 0.0) {
+      // Pattern elements must be finite "numbers" >= 0, with "finite"
+      // taken care of by WebIDL
+      return;
+    }
+
+    if (!dash.AppendElement(aSegments[x], fallible)) {
+      aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+      return;
+    }
+  }
+  if (aSegments.Length() %
+      2) {  // If the number of elements is odd, concatenate again
+    for (uint32_t x = 0; x < aSegments.Length(); x++) {
+      if (!dash.AppendElement(aSegments[x], fallible)) {
+        aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+        return;
+      }
+    }
+  }
+
+  CurrentState().dash = std::move(dash);
+}
+
+void CanvasRenderingContext2D::GetLineDash(nsTArray<double>& aSegments) const {
+  const nsTArray<mozilla::gfx::Float>& dash = CurrentState().dash;
+  aSegments.Clear();
+
+  for (uint32_t x = 0; x < dash.Length(); x++) {
+    aSegments.AppendElement(dash[x]);
+  }
+}
+
+void CanvasRenderingContext2D::SetLineDashOffset(double aOffset) {
+  CurrentState().dashOffset = aOffset;
+}
+
+double CanvasRenderingContext2D::LineDashOffset() const {
+  return CurrentState().dashOffset;
+}
+
+bool CanvasRenderingContext2D::IsPointInPath(JSContext* aCx, double aX,
+                                             double aY,
+                                             const CanvasWindingRule& aWinding,
+                                             nsIPrincipal& aSubjectPrincipal) {
+  return IsPointInPath(aCx, aX, aY, aWinding, Some(&aSubjectPrincipal));
+}
+
+bool CanvasRenderingContext2D::IsPointInPath(
+    JSContext* aCx, double aX, double aY, const CanvasWindingRule& aWinding,
+    Maybe<nsIPrincipal*> aSubjectPrincipal) {
+  if (!FloatValidate(aX, aY)) {
+    return false;
+  }
+
+  // Check for site-specific permission and return false if no permission.
+  if (mCanvasElement) {
+    nsCOMPtr<Document> ownerDoc = mCanvasElement->OwnerDoc();
+    if (!CanvasUtils::IsImageExtractionAllowed(ownerDoc, aCx,
+                                               aSubjectPrincipal)) {
+      return false;
+    }
+  } else if (mOffscreenCanvas && mOffscreenCanvas->ShouldResistFingerprinting(
+                                     RFPTarget::CanvasImageExtractionPrompt)) {
+    return false;
+  }
+
+  EnsureUserSpacePath(aWinding);
+  if (!mPath) {
+    return false;
+  }
+
+  if (mPathTransformWillUpdate) {
+    return mPath->ContainsPoint(Point(aX, aY), mPathToDS);
+  }
+
+  return mPath->ContainsPoint(Point(aX, aY), mTarget->GetTransform());
+}
+
+bool CanvasRenderingContext2D::IsPointInPath(JSContext* aCx,
+                                             const CanvasPath& aPath, double aX,
+                                             double aY,
+                                             const CanvasWindingRule& aWinding,
+                                             nsIPrincipal& aSubjectPrincipal) {
+  return IsPointInPath(aCx, aPath, aX, aY, aWinding, Some(&aSubjectPrincipal));
+}
+
+bool CanvasRenderingContext2D::IsPointInPath(JSContext* aCx,
+                                             const CanvasPath& aPath, double aX,
+                                             double aY,
+                                             const CanvasWindingRule& aWinding,
+                                             Maybe<nsIPrincipal*>) {
+  if (!FloatValidate(aX, aY)) {
+    return false;
+  }
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return false;
+  }
+
+  RefPtr<gfx::Path> tempPath = aPath.GetPath(aWinding, mTarget);
+
+  return tempPath->ContainsPoint(Point(aX, aY), mTarget->GetTransform());
+}
+
+bool CanvasRenderingContext2D::IsPointInStroke(
+    JSContext* aCx, double aX, double aY, nsIPrincipal& aSubjectPrincipal) {
+  return IsPointInStroke(aCx, aX, aY, Some(&aSubjectPrincipal));
+}
+
+bool CanvasRenderingContext2D::IsPointInStroke(
+    JSContext* aCx, double aX, double aY,
+    Maybe<nsIPrincipal*> aSubjectPrincipal) {
+  if (!FloatValidate(aX, aY)) {
+    return false;
+  }
+
+  // Check for site-specific permission and return false if no permission.
+  if (mCanvasElement) {
+    nsCOMPtr<Document> ownerDoc = mCanvasElement->OwnerDoc();
+    if (!CanvasUtils::IsImageExtractionAllowed(ownerDoc, aCx,
+                                               aSubjectPrincipal)) {
+      return false;
+    }
+  } else if (mOffscreenCanvas && mOffscreenCanvas->ShouldResistFingerprinting(
+                                     RFPTarget::CanvasImageExtractionPrompt)) {
+    return false;
+  }
+
+  EnsureUserSpacePath();
+  if (!mPath) {
+    return false;
+  }
+
+  const ContextState& state = CurrentState();
+
+  StrokeOptions strokeOptions(state.lineWidth, state.lineJoin, state.lineCap,
+                              state.miterLimit, state.dash.Length(),
+                              state.dash.Elements(), state.dashOffset);
+
+  if (mPathTransformWillUpdate) {
+    return mPath->StrokeContainsPoint(strokeOptions, Point(aX, aY), mPathToDS);
+  }
+
+  return mPath->StrokeContainsPoint(strokeOptions, Point(aX, aY),
+                                    mTarget->GetTransform());
+}
+
+bool CanvasRenderingContext2D::IsPointInStroke(
+    JSContext* aCx, const CanvasPath& aPath, double aX, double aY,
+    nsIPrincipal& aSubjectPrincipal) {
+  return IsPointInStroke(aCx, aPath, aX, aY, Some(&aSubjectPrincipal));
+}
+
+bool CanvasRenderingContext2D::IsPointInStroke(JSContext* aCx,
+                                               const CanvasPath& aPath,
+                                               double aX, double aY,
+                                               Maybe<nsIPrincipal*>) {
+  if (!FloatValidate(aX, aY)) {
+    return false;
+  }
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return false;
+  }
+
+  RefPtr<gfx::Path> tempPath =
+      aPath.GetPath(CanvasWindingRule::Nonzero, mTarget);
+
+  const ContextState& state = CurrentState();
+
+  StrokeOptions strokeOptions(state.lineWidth, state.lineJoin, state.lineCap,
+                              state.miterLimit, state.dash.Length(),
+                              state.dash.Elements(), state.dashOffset);
+
+  return tempPath->StrokeContainsPoint(strokeOptions, Point(aX, aY),
+                                       mTarget->GetTransform());
+}
+
+// Returns a surface that contains only the part needed to draw aSourceRect.
+// On entry, aSourceRect is relative to aSurface, and on return aSourceRect is
+// relative to the returned surface.
+static already_AddRefed<SourceSurface> ExtractSubrect(SourceSurface* aSurface,
+                                                      gfx::Rect* aSourceRect,
+                                                      DrawTarget* aTargetDT) {
+  gfx::Rect roundedOutSourceRect = *aSourceRect;
+  roundedOutSourceRect.RoundOut();
+  gfx::IntRect roundedOutSourceRectInt;
+  if (!roundedOutSourceRect.ToIntRect(&roundedOutSourceRectInt)) {
+    RefPtr<SourceSurface> surface(aSurface);
+    return surface.forget();
+  }
+
+  // Try to extract an optimized sub-surface.
+  if (RefPtr<SourceSurface> surface =
+          aSurface->ExtractSubrect(roundedOutSourceRectInt)) {
+    *aSourceRect -= roundedOutSourceRect.TopLeft();
+    return surface.forget();
+  }
+
+  RefPtr<DrawTarget> subrectDT = aTargetDT->CreateSimilarDrawTarget(
+      roundedOutSourceRectInt.Size(), SurfaceFormat::B8G8R8A8);
+
+  if (subrectDT) {
+    // See bug 1524554.
+    subrectDT->ClearRect(gfx::Rect());
+  }
+
+  if (!subrectDT || !subrectDT->IsValid()) {
+    RefPtr<SourceSurface> surface(aSurface);
+    return surface.forget();
+  }
+
+  *aSourceRect -= roundedOutSourceRect.TopLeft();
+
+  subrectDT->CopySurface(aSurface, roundedOutSourceRectInt, IntPoint());
+  return subrectDT->Snapshot();
+}
+
+//
+// image
+//
+
+static void ClipImageDimension(double& aSourceCoord, double& aSourceSize,
+                               int32_t aImageSize, double& aDestCoord,
+                               double& aDestSize) {
+  double scale = aDestSize / aSourceSize;
+  if (aSourceCoord < 0.0) {
+    double destEnd = aDestCoord + aDestSize;
+    aDestCoord -= aSourceCoord * scale;
+    aDestSize = destEnd - aDestCoord;
+    aSourceSize += aSourceCoord;
+    aSourceCoord = 0.0;
+  }
+  double delta = aImageSize - (aSourceCoord + aSourceSize);
+  if (delta < 0.0) {
+    aDestSize += delta * scale;
+    aSourceSize = aImageSize - aSourceCoord;
+  }
+}
+
+// Acts like nsLayoutUtils::SurfaceFromElement, but it'll attempt
+// to pull a SourceSurface from our cache. This allows us to avoid
+// reoptimizing surfaces if content and canvas backends are different.
+SurfaceFromElementResult CanvasRenderingContext2D::CachedSurfaceFromElement(
+    Element* aElement) {
+  SurfaceFromElementResult res;
+  nsCOMPtr<nsIImageLoadingContent> imageLoader = do_QueryInterface(aElement);
+  if (!imageLoader) {
+    return res;
+  }
+
+  nsCOMPtr<imgIRequest> imgRequest;
+  imageLoader->GetRequest(nsIImageLoadingContent::CURRENT_REQUEST,
+                          getter_AddRefs(imgRequest));
+  if (!imgRequest) {
+    return res;
+  }
+
+  uint32_t status = 0;
+  if (NS_FAILED(imgRequest->GetImageStatus(&status)) ||
+      !(status & imgIRequest::STATUS_LOAD_COMPLETE)) {
+    return res;
+  }
+
+  nsCOMPtr<nsIPrincipal> principal;
+  if (NS_FAILED(imgRequest->GetImagePrincipal(getter_AddRefs(principal))) ||
+      !principal) {
+    return res;
+  }
+
+  if (NS_FAILED(imgRequest->GetHadCrossOriginRedirects(
+          &res.mHadCrossOriginRedirects))) {
+    return res;
+  }
+
+  res.mSourceSurface = CanvasImageCache::LookupAllCanvas(aElement, mTarget);
+  if (!res.mSourceSurface) {
+    return res;
+  }
+
+  res.mCORSUsed = nsLayoutUtils::ImageRequestUsesCORS(imgRequest);
+  res.mSize = res.mIntrinsicSize = res.mSourceSurface->GetSize();
+  res.mPrincipal = std::move(principal);
+  res.mImageRequest = std::move(imgRequest);
+  res.mIsWriteOnly = CheckWriteOnlySecurity(res.mCORSUsed, res.mPrincipal,
+                                            res.mHadCrossOriginRedirects);
+
+  return res;
+}
+
+static void SwapScaleWidthHeightForRotation(gfx::Rect& aRect,
+                                            VideoInfo::Rotation aDegrees) {
+  if (aDegrees == VideoInfo::Rotation::kDegree_90 ||
+      aDegrees == VideoInfo::Rotation::kDegree_270) {
+    std::swap(aRect.width, aRect.height);
+  }
+}
+
+static Matrix ComputeRotationMatrix(gfxFloat aRotatedWidth,
+                                    gfxFloat aRotatedHeight,
+                                    VideoInfo::Rotation aDegrees) {
+  Matrix shiftVideoCenterToOrigin;
+  if (aDegrees == VideoInfo::Rotation::kDegree_90 ||
+      aDegrees == VideoInfo::Rotation::kDegree_270) {
+    shiftVideoCenterToOrigin =
+        Matrix::Translation(-aRotatedHeight / 2.0, -aRotatedWidth / 2.0);
+  } else {
+    shiftVideoCenterToOrigin =
+        Matrix::Translation(-aRotatedWidth / 2.0, -aRotatedHeight / 2.0);
+  }
+
+  auto angle = static_cast<double>(aDegrees) / 180.0 * M_PI;
+  Matrix rotation = Matrix::Rotation(static_cast<gfx::Float>(angle));
+  Matrix shiftLeftTopToOrigin =
+      Matrix::Translation(aRotatedWidth / 2.0, aRotatedHeight / 2.0);
+  return shiftVideoCenterToOrigin * rotation * shiftLeftTopToOrigin;
+}
+
+// drawImage(in HTMLImageElement image, in float dx, in float dy);
+//   -- render image from 0,0 at dx,dy top-left coords
+// drawImage(in HTMLImageElement image, in float dx, in float dy, in float dw,
+//           in float dh);
+//   -- render image from 0,0 at dx,dy top-left coords clipping it to dw,dh
+// drawImage(in HTMLImageElement image, in float sx, in float sy, in float sw,
+//           in float sh, in float dx, in float dy, in float dw, in float dh);
+//   -- render the region defined by (sx,sy,sw,wh) in image-local space into the
+//      region (dx,dy,dw,dh) on the canvas
+
+// If only dx and dy are passed in then optional_argc should be 0. If only
+// dx, dy, dw and dh are passed in then optional_argc should be 2. The only
+// other valid value for optional_argc is 6 if sx, sy, sw, sh, dx, dy, dw and dh
+// are all passed in.
+
+void CanvasRenderingContext2D::DrawImage(const CanvasImageSource& aImage,
+                                         double aSx, double aSy, double aSw,
+                                         double aSh, double aDx, double aDy,
+                                         double aDw, double aDh,
+                                         uint8_t aOptional_argc,
+                                         ErrorResult& aError) {
+  MOZ_ASSERT(aOptional_argc == 0 || aOptional_argc == 2 || aOptional_argc == 6);
+
+  if (!ValidateRect(aDx, aDy, aDw, aDh, true)) {
+    return;
+  }
+  if (aOptional_argc == 6) {
+    if (!ValidateRect(aSx, aSy, aSw, aSh, true)) {
+      return;
+    }
+  }
+
+  RefPtr<SourceSurface> srcSurf;
+  gfx::IntSize imgSize;
+  gfx::IntSize intrinsicImgSize;
+  Element* element = nullptr;
+  OffscreenCanvas* offscreenCanvas = nullptr;
+
+  EnsureTarget();
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  if (aImage.IsHTMLCanvasElement()) {
+    HTMLCanvasElement* canvas = &aImage.GetAsHTMLCanvasElement();
+    element = canvas;
+    nsIntSize size = canvas->GetSize();
+    if (size.width == 0 || size.height == 0) {
+      return aError.ThrowInvalidStateError("Passed-in canvas is empty");
+    }
+
+    if (canvas->IsWriteOnly()) {
+      SetWriteOnly();
+    }
+  } else if (aImage.IsOffscreenCanvas()) {
+    offscreenCanvas = &aImage.GetAsOffscreenCanvas();
+    nsIntSize size = offscreenCanvas->GetWidthHeight();
+    if (size.IsEmpty()) {
+      return aError.ThrowInvalidStateError("Passed-in canvas is empty");
+    }
+
+    srcSurf = offscreenCanvas->GetSurfaceSnapshot();
+    if (srcSurf) {
+      imgSize = intrinsicImgSize = srcSurf->GetSize();
+    }
+
+    if (offscreenCanvas->IsWriteOnly()) {
+      SetWriteOnly();
+    }
+  } else if (aImage.IsImageBitmap()) {
+    ImageBitmap& imageBitmap = aImage.GetAsImageBitmap();
+    srcSurf = imageBitmap.PrepareForDrawTarget(mTarget);
+
+    if (!srcSurf) {
+      if (imageBitmap.IsClosed()) {
+        aError.ThrowInvalidStateError("Passed-in ImageBitmap is closed");
+      }
+      return;
+    }
+
+    if (imageBitmap.IsWriteOnly()) {
+      SetWriteOnly();
+    }
+
+    imgSize = intrinsicImgSize =
+        gfx::IntSize(imageBitmap.Width(), imageBitmap.Height());
+  } else {
+    if (aImage.IsHTMLImageElement()) {
+      HTMLImageElement* img = &aImage.GetAsHTMLImageElement();
+      element = img;
+    } else if (aImage.IsSVGImageElement()) {
+      SVGImageElement* img = &aImage.GetAsSVGImageElement();
+      element = img;
+    } else {
+      HTMLVideoElement* video = &aImage.GetAsHTMLVideoElement();
+      video->LogVisibility(
+          mozilla::dom::HTMLVideoElement::CallerAPI::DRAW_IMAGE);
+      element = video;
+    }
+
+    srcSurf = CanvasImageCache::LookupCanvas(element, mCanvasElement, mTarget,
+                                             &imgSize, &intrinsicImgSize);
+  }
+
+  DirectDrawInfo drawInfo;
+
+  if (!srcSurf) {
+    // The canvas spec says that drawImage should draw the first frame
+    // of animated images. We also don't want to rasterize vector images.
+    uint32_t sfeFlags = nsLayoutUtils::SFE_WANT_FIRST_FRAME_IF_IMAGE |
+                        nsLayoutUtils::SFE_NO_RASTERIZING_VECTORS |
+                        nsLayoutUtils::SFE_EXACT_SIZE_SURFACE;
+
+    SurfaceFromElementResult res;
+    if (offscreenCanvas) {
+      res = nsLayoutUtils::SurfaceFromOffscreenCanvas(offscreenCanvas, sfeFlags,
+                                                      mTarget);
+    } else {
+      res = CanvasRenderingContext2D::CachedSurfaceFromElement(element);
+      if (!res.mSourceSurface) {
+        res = nsLayoutUtils::SurfaceFromElement(element, sfeFlags, mTarget);
+      }
+    }
+
+    if (!res.mSourceSurface && !res.mDrawInfo.mImgContainer) {
+      // https://html.spec.whatwg.org/#check-the-usability-of-the-image-argument:
+      //
+      // Only throw if the request is broken and the element is an
+      // HTMLImageElement / SVGImageElement. Note that even for those the spec
+      // says to silently do nothing in the following cases:
+      //   - The element is still loading.
+      //   - The image is bad, but it's not in the broken state (i.e., we could
+      //     decode the headers and get the size).
+      if (!res.mIsStillLoading && !res.mHasSize &&
+          (aImage.IsHTMLImageElement() || aImage.IsSVGImageElement())) {
+        aError.ThrowInvalidStateError("Passed-in image is \"broken\"");
+      }
+      return;
+    }
+
+    imgSize = res.mSize;
+    intrinsicImgSize = res.mIntrinsicSize;
+    DoSecurityCheck(res.mPrincipal, res.mIsWriteOnly, res.mCORSUsed);
+
+    if (res.mSourceSurface) {
+      if (res.mImageRequest) {
+        CanvasImageCache::NotifyDrawImage(element, mCanvasElement, mTarget,
+                                          res.mSourceSurface, imgSize,
+                                          intrinsicImgSize);
+      }
+      srcSurf = res.mSourceSurface;
+    } else {
+      drawInfo = res.mDrawInfo;
+    }
+  }
+
+  if (aOptional_argc == 0) {
+    aSx = aSy = 0.0;
+    aSw = (double)imgSize.width;
+    aSh = (double)imgSize.height;
+    aDw = (double)intrinsicImgSize.width;
+    aDh = (double)intrinsicImgSize.height;
+  } else if (aOptional_argc == 2) {
+    aSx = aSy = 0.0;
+    aSw = (double)imgSize.width;
+    aSh = (double)imgSize.height;
+  }
+
+  if (aSw == 0.0 || aSh == 0.0) {
+    return;
+  }
+
+  ClipImageDimension(aSx, aSw, imgSize.width, aDx, aDw);
+  ClipImageDimension(aSy, aSh, imgSize.height, aDy, aDh);
+
+  if (aSw <= 0.0 || aSh <= 0.0 || aDw <= 0.0 || aDh <= 0.0) {
+    // source and/or destination are fully clipped, so nothing is painted
+    return;
+  }
+
+  // Per spec, the smoothing setting applies only to scaling up a bitmap image.
+  // When down-scaling the user agent is free to choose whether or not to smooth
+  // the image. Nearest sampling when down-scaling is rarely desirable and
+  // smoothing when down-scaling matches chromium's behavior.
+  // If any dimension is up-scaled, we consider the image as being up-scaled.
+  auto scale = mTarget->GetTransform().ScaleFactors();
+  bool isDownScale =
+      aDw * Abs(scale.xScale) < aSw && aDh * Abs(scale.yScale) < aSh;
+
+  SamplingFilter samplingFilter;
+  AntialiasMode antialiasMode;
+
+  if (CurrentState().imageSmoothingEnabled || isDownScale) {
+    samplingFilter = gfx::SamplingFilter::LINEAR;
+    antialiasMode = AntialiasMode::DEFAULT;
+  } else {
+    samplingFilter = gfx::SamplingFilter::POINT;
+    antialiasMode = AntialiasMode::NONE;
+  }
+
+  const bool needBounds = NeedToCalculateBounds();
+  if (!IsTargetValid()) {
+    return;
+  }
+  gfx::Rect bounds;
+  if (needBounds) {
+    bounds = gfx::Rect(aDx, aDy, aDw, aDh);
+    bounds = mTarget->GetTransform().TransformBounds(bounds);
+  }
+
+  if (!IsTargetValid()) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  if (srcSurf) {
+    gfx::Rect sourceRect(aSx, aSy, aSw, aSh);
+    if (element == mCanvasElement) {
+      // srcSurf is a snapshot of mTarget. If we draw to mTarget now, we'll
+      // trigger a COW copy of the whole canvas into srcSurf. That's a huge
+      // waste if sourceRect doesn't cover the whole canvas.
+      // We avoid copying the whole canvas by manually copying just the part
+      // that we need.
+      srcSurf = ExtractSubrect(srcSurf, &sourceRect, mTarget);
+    }
+
+    AdjustedTarget tempTarget(this, bounds.IsEmpty() ? nullptr : &bounds, true);
+    if (!tempTarget) {
+      gfxWarning() << "Invalid adjusted target in Canvas2D "
+                   << gfx::hexa((DrawTarget*)mTarget) << ", "
+                   << NeedToDrawShadow() << NeedToApplyFilter();
+      return;
+    }
+
+    auto op = tempTarget.UsedOperation();
+    if (!IsTargetValid() || !tempTarget) {
+      return;
+    }
+
+    VideoInfo::Rotation rotationDeg = VideoInfo::Rotation::kDegree_0;
+    if (HTMLVideoElement* video = HTMLVideoElement::FromNodeOrNull(element)) {
+      rotationDeg = video->RotationDegrees();
+    }
+
+    gfx::Rect destRect(aDx, aDy, aDw, aDh);
+
+    Matrix transform;
+    if (rotationDeg != VideoInfo::Rotation::kDegree_0) {
+      Matrix preTransform = ComputeRotationMatrix(aDw, aDh, rotationDeg);
+      transform = preTransform * Matrix::Translation(aDx, aDy);
+
+      SwapScaleWidthHeightForRotation(destRect, rotationDeg);
+      // When rotation exists, aDx, aDy is handled by transform, Since aDest.x
+      // aDest.y handling of DrawSurface() does not care about the rotation.
+      destRect.x = 0;
+      destRect.y = 0;
+    }
+    Matrix currentTransform = tempTarget->GetTransform();
+    transform *= currentTransform;
+
+    tempTarget->SetTransform(transform);
+
+    tempTarget.DrawSurface(
+        srcSurf, destRect, sourceRect,
+        DrawSurfaceOptions(samplingFilter, SamplingBounds::UNBOUNDED),
+        DrawOptions(CurrentState().globalAlpha, op, antialiasMode));
+
+    tempTarget->SetTransform(currentTransform);
+
+  } else {
+    DrawDirectlyToCanvas(drawInfo, &bounds, gfx::Rect(aDx, aDy, aDw, aDh),
+                         gfx::Rect(aSx, aSy, aSw, aSh), imgSize);
+  }
+
+  RedrawUser(gfxRect(aDx, aDy, aDw, aDh));
+}
+
+void CanvasRenderingContext2D::DrawDirectlyToCanvas(
+    const DirectDrawInfo& aImage, gfx::Rect* aBounds, gfx::Rect aDest,
+    gfx::Rect aSrc, gfx::IntSize aImgSize) {
+  MOZ_ASSERT(aSrc.width > 0 && aSrc.height > 0,
+             "Need positive source width and height");
+
+  AdjustedTarget tempTarget(this, aBounds->IsEmpty() ? nullptr : aBounds);
+  if (!tempTarget || !tempTarget->IsValid()) {
+    return;
+  }
+
+  // Get any existing transforms on the context, including transformations used
+  // for context shadow.
+  Matrix matrix = tempTarget->GetTransform();
+  gfxMatrix contextMatrix = ThebesMatrix(matrix);
+  MatrixScalesDouble contextScale = contextMatrix.ScaleFactors();
+
+  // Scale the dest rect to include the context scale.
+  aDest.Scale((float)contextScale.xScale, (float)contextScale.yScale);
+
+  // Scale the image size to the dest rect, and adjust the source rect to match.
+  MatrixScalesDouble scale(aDest.width / aSrc.width,
+                           aDest.height / aSrc.height);
+  IntSize scaledImageSize =
+      IntSize::Ceil(static_cast<float>(scale.xScale * aImgSize.width),
+                    static_cast<float>(scale.yScale * aImgSize.height));
+  aSrc.Scale(static_cast<float>(scale.xScale),
+             static_cast<float>(scale.yScale));
+
+  // We're wrapping tempTarget's (our) DrawTarget here, so we need to restore
+  // the matrix even though this is a temp gfxContext.
+  AutoRestoreTransform autoRestoreTransform(mTarget);
+
+  gfxContext context(tempTarget);
+  context.SetMatrixDouble(
+      contextMatrix
+          .PreScale(1.0 / contextScale.xScale, 1.0 / contextScale.yScale)
+          .PreTranslate(aDest.x - aSrc.x, aDest.y - aSrc.y));
+
+  context.SetOp(tempTarget.UsedOperation());
+
+  // FLAG_CLAMP is added for increased performance, since we never tile here.
+  uint32_t modifiedFlags = aImage.mDrawingFlags | imgIContainer::FLAG_CLAMP;
+
+  // XXX hmm is scaledImageSize really in CSS pixels?
+  CSSIntSize sz(scaledImageSize.width, scaledImageSize.height);
+  SVGImageContext svgContext(Some(sz));
+
+  auto result = aImage.mImgContainer->Draw(
+      &context, scaledImageSize,
+      ImageRegion::Create(gfxRect(aSrc.x, aSrc.y, aSrc.width, aSrc.height)),
+      aImage.mWhichFrame, SamplingFilter::GOOD, svgContext, modifiedFlags,
+      CurrentState().globalAlpha);
+
+  if (result != ImgDrawResult::SUCCESS) {
+    NS_WARNING("imgIContainer::Draw failed");
+  }
+}
+
+void CanvasRenderingContext2D::SetGlobalCompositeOperation(
+    const nsAString& aOp, ErrorResult& aError) {
+  CompositionOp comp_op;
+
+#define CANVAS_OP_TO_GFX_OP(cvsop, op2d) \
+  if (aOp.EqualsLiteral(cvsop)) comp_op = CompositionOp::OP_##op2d;
+
+  CANVAS_OP_TO_GFX_OP("clear", CLEAR)
+  else CANVAS_OP_TO_GFX_OP("copy", SOURCE)
+  else CANVAS_OP_TO_GFX_OP("source-atop", ATOP)
+  else CANVAS_OP_TO_GFX_OP("source-in", IN)
+  else CANVAS_OP_TO_GFX_OP("source-out", OUT)
+  else CANVAS_OP_TO_GFX_OP("source-over", OVER)
+  else CANVAS_OP_TO_GFX_OP("destination-in", DEST_IN)
+  else CANVAS_OP_TO_GFX_OP("destination-out", DEST_OUT)
+  else CANVAS_OP_TO_GFX_OP("destination-over", DEST_OVER)
+  else CANVAS_OP_TO_GFX_OP("destination-atop", DEST_ATOP)
+  else CANVAS_OP_TO_GFX_OP("lighter", ADD)
+  else CANVAS_OP_TO_GFX_OP("xor", XOR)
+  else CANVAS_OP_TO_GFX_OP("multiply", MULTIPLY)
+  else CANVAS_OP_TO_GFX_OP("screen", SCREEN)
+  else CANVAS_OP_TO_GFX_OP("overlay", OVERLAY)
+  else CANVAS_OP_TO_GFX_OP("darken", DARKEN)
+  else CANVAS_OP_TO_GFX_OP("lighten", LIGHTEN)
+  else CANVAS_OP_TO_GFX_OP("color-dodge", COLOR_DODGE)
+  else CANVAS_OP_TO_GFX_OP("color-burn", COLOR_BURN)
+  else CANVAS_OP_TO_GFX_OP("hard-light", HARD_LIGHT)
+  else CANVAS_OP_TO_GFX_OP("soft-light", SOFT_LIGHT)
+  else CANVAS_OP_TO_GFX_OP("difference", DIFFERENCE)
+  else CANVAS_OP_TO_GFX_OP("exclusion", EXCLUSION)
+  else CANVAS_OP_TO_GFX_OP("hue", HUE)
+  else CANVAS_OP_TO_GFX_OP("saturation", SATURATION)
+  else CANVAS_OP_TO_GFX_OP("color", COLOR)
+  else CANVAS_OP_TO_GFX_OP("luminosity", LUMINOSITY)
+  // XXX ERRMSG we need to report an error to developers here! (bug 329026)
+  else return;
+
+#undef CANVAS_OP_TO_GFX_OP
+  CurrentState().op = comp_op;
+}
+
+void CanvasRenderingContext2D::GetGlobalCompositeOperation(
+    nsAString& aOp, ErrorResult& aError) {
+  CompositionOp comp_op = CurrentState().op;
+
+#define CANVAS_OP_TO_GFX_OP(cvsop, op2d) \
+  if (comp_op == CompositionOp::OP_##op2d) aOp.AssignLiteral(cvsop);
+
+  CANVAS_OP_TO_GFX_OP("clear", CLEAR)
+  else CANVAS_OP_TO_GFX_OP("copy", SOURCE)
+  else CANVAS_OP_TO_GFX_OP("destination-atop", DEST_ATOP)
+  else CANVAS_OP_TO_GFX_OP("destination-in", DEST_IN)
+  else CANVAS_OP_TO_GFX_OP("destination-out", DEST_OUT)
+  else CANVAS_OP_TO_GFX_OP("destination-over", DEST_OVER)
+  else CANVAS_OP_TO_GFX_OP("lighter", ADD)
+  else CANVAS_OP_TO_GFX_OP("source-atop", ATOP)
+  else CANVAS_OP_TO_GFX_OP("source-in", IN)
+  else CANVAS_OP_TO_GFX_OP("source-out", OUT)
+  else CANVAS_OP_TO_GFX_OP("source-over", OVER)
+  else CANVAS_OP_TO_GFX_OP("xor", XOR)
+  else CANVAS_OP_TO_GFX_OP("multiply", MULTIPLY)
+  else CANVAS_OP_TO_GFX_OP("screen", SCREEN)
+  else CANVAS_OP_TO_GFX_OP("overlay", OVERLAY)
+  else CANVAS_OP_TO_GFX_OP("darken", DARKEN)
+  else CANVAS_OP_TO_GFX_OP("lighten", LIGHTEN)
+  else CANVAS_OP_TO_GFX_OP("color-dodge", COLOR_DODGE)
+  else CANVAS_OP_TO_GFX_OP("color-burn", COLOR_BURN)
+  else CANVAS_OP_TO_GFX_OP("hard-light", HARD_LIGHT)
+  else CANVAS_OP_TO_GFX_OP("soft-light", SOFT_LIGHT)
+  else CANVAS_OP_TO_GFX_OP("difference", DIFFERENCE)
+  else CANVAS_OP_TO_GFX_OP("exclusion", EXCLUSION)
+  else CANVAS_OP_TO_GFX_OP("hue", HUE)
+  else CANVAS_OP_TO_GFX_OP("saturation", SATURATION)
+  else CANVAS_OP_TO_GFX_OP("color", COLOR)
+  else CANVAS_OP_TO_GFX_OP("luminosity", LUMINOSITY)
+  else {
+    aError.Throw(NS_ERROR_FAILURE);
+  }
+
+#undef CANVAS_OP_TO_GFX_OP
+}
+
+void CanvasRenderingContext2D::DrawWindow(nsGlobalWindowInner& aWindow,
+                                          double aX, double aY, double aW,
+                                          double aH, const nsACString& aBgColor,
+                                          uint32_t aFlags,
+                                          nsIPrincipal& aSubjectPrincipal,
+                                          ErrorResult& aError) {
+  if (int32_t(aW) == 0 || int32_t(aH) == 0) {
+    return;
+  }
+
+  // protect against too-large surfaces that will cause allocation
+  // or overflow issues
+  if (!Factory::CheckSurfaceSize(IntSize(int32_t(aW), int32_t(aH)), 0xffff)) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Document* doc = aWindow.GetExtantDoc();
+  if (doc && aSubjectPrincipal.GetIsAddonOrExpandedAddonPrincipal()) {
+    doc->WarnOnceAbout(
+        DeprecatedOperations::eDrawWindowCanvasRenderingContext2D);
+  }
+
+  // Flush layout updates
+  if (!(aFlags & CanvasRenderingContext2D_Binding::DRAWWINDOW_DO_NOT_FLUSH)) {
+    nsContentUtils::FlushLayoutForTree(aWindow.GetOuterWindow());
+  }
+
+  CompositionOp op = CurrentState().op;
+  bool discardContent =
+      GlobalAlpha() == 1.0f &&
+      (op == CompositionOp::OP_OVER || op == CompositionOp::OP_SOURCE);
+  const gfx::Rect drawRect(aX, aY, aW, aH);
+  EnsureTarget(discardContent ? &drawRect : nullptr);
+  if (!IsTargetValid()) {
+    return;
+  }
+
+  RefPtr<nsPresContext> presContext;
+  nsIDocShell* docshell = aWindow.GetDocShell();
+  if (docshell) {
+    presContext = docshell->GetPresContext();
+  }
+  if (!presContext) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  Maybe<nscolor> backgroundColor = ParseColor(aBgColor);
+  if (!backgroundColor) {
+    aError.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  nsRect r(nsPresContext::CSSPixelsToAppUnits((float)aX),
+           nsPresContext::CSSPixelsToAppUnits((float)aY),
+           nsPresContext::CSSPixelsToAppUnits((float)aW),
+           nsPresContext::CSSPixelsToAppUnits((float)aH));
+  RenderDocumentFlags renderDocFlags =
+      (RenderDocumentFlags::IgnoreViewportScrolling |
+       RenderDocumentFlags::DocumentRelative);
+  if (aFlags & CanvasRenderingContext2D_Binding::DRAWWINDOW_DRAW_CARET) {
+    renderDocFlags |= RenderDocumentFlags::DrawCaret;
+  }
+  if (aFlags & CanvasRenderingContext2D_Binding::DRAWWINDOW_DRAW_VIEW) {
+    renderDocFlags &= ~(RenderDocumentFlags::IgnoreViewportScrolling |
+                        RenderDocumentFlags::DocumentRelative);
+  }
+  if (aFlags & CanvasRenderingContext2D_Binding::DRAWWINDOW_USE_WIDGET_LAYERS) {
+    renderDocFlags |= RenderDocumentFlags::UseWidgetLayers;
+  }
+  if (aFlags &
+      CanvasRenderingContext2D_Binding::DRAWWINDOW_ASYNC_DECODE_IMAGES) {
+    renderDocFlags |= RenderDocumentFlags::AsyncDecodeImages;
+  }
+  if (aFlags & CanvasRenderingContext2D_Binding::DRAWWINDOW_DO_NOT_FLUSH) {
+    renderDocFlags |= RenderDocumentFlags::DrawWindowNotFlushing;
+  }
+
+  // gfxContext-over-Azure may modify the DrawTarget's transform, so
+  // save and restore it
+  Matrix matrix = mTarget->GetTransform();
+  double sw = matrix._11 * aW;
+  double sh = matrix._22 * aH;
+  if (!sw || !sh) {
+    return;
+  }
+
+  Maybe<gfxContext> thebes;
+  RefPtr<DrawTarget> drawDT;
+  // Rendering directly is faster and can be done if mTarget supports Azure
+  // and does not need alpha blending.
+  // Since the pre-transaction callback calls ReturnTarget, we can't have a
+  // gfxContext wrapped around it when using a shared buffer provider because
+  // the DrawTarget's shared buffer may be unmapped in ReturnTarget.
+  op = CompositionOp::OP_ADD;
+  if (gfxPlatform::GetPlatform()->SupportsAzureContentForDrawTarget(mTarget) &&
+      GlobalAlpha() == 1.0f) {
+    op = CurrentState().op;
+    if (!IsTargetValid()) {
+      aError.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+  }
+  if (op == CompositionOp::OP_OVER &&
+      (!mBufferProvider || !mBufferProvider->IsShared())) {
+    thebes.emplace(mTarget);
+    thebes.ref().SetMatrix(matrix);
+  } else {
+    IntSize dtSize = IntSize::Ceil(sw, sh);
+    if (!Factory::AllowedSurfaceSize(dtSize)) {
+      // attempt to limit the DT to what will actually cover the target
+      Size limitSize(mTarget->GetSize());
+      limitSize.Scale(matrix._11, matrix._22);
+      dtSize = Min(dtSize, IntSize::Ceil(limitSize));
+      // if the DT is still too big, then error
+      if (!Factory::AllowedSurfaceSize(dtSize)) {
+        aError.Throw(NS_ERROR_FAILURE);
+        return;
+      }
+    }
+    drawDT = gfxPlatform::GetPlatform()->CreateOffscreenContentDrawTarget(
+        dtSize, SurfaceFormat::B8G8R8A8);
+    if (!drawDT || !drawDT->IsValid()) {
+      aError.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+
+    thebes.emplace(drawDT);
+    thebes.ref().SetMatrix(Matrix::Scaling(matrix._11, matrix._22));
+  }
+  MOZ_ASSERT(thebes.isSome());
+
+  RefPtr<PresShell> presShell = presContext->PresShell();
+
+  Unused << presShell->RenderDocument(r, renderDocFlags, *backgroundColor,
+                                      &thebes.ref());
+  // If this canvas was contained in the drawn window, the pre-transaction
+  // callback may have returned its DT. If so, we must reacquire it here.
+  EnsureTarget(discardContent ? &drawRect : nullptr);
+
+  if (drawDT) {
+    RefPtr<SourceSurface> snapshot = drawDT->Snapshot();
+    if (NS_WARN_IF(!snapshot)) {
+      aError.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+
+    op = CurrentState().op;
+    if (!IsTargetValid()) {
+      aError.Throw(NS_ERROR_FAILURE);
+      return;
+    }
+    gfx::Rect destRect(0, 0, aW, aH);
+    gfx::Rect sourceRect(0, 0, sw, sh);
+    mTarget->DrawSurface(snapshot, destRect, sourceRect,
+                         DrawSurfaceOptions(gfx::SamplingFilter::POINT),
+                         DrawOptions(GlobalAlpha(), op, AntialiasMode::NONE));
+  } else {
+    mTarget->SetTransform(matrix);
+  }
+
+  // note that x and y are coordinates in the document that
+  // we're drawing; x and y are drawn to 0,0 in current user
+  // space.
+  RedrawUser(gfxRect(0, 0, aW, aH));
+}
+
+//
+// device pixel getting/setting
+//
+
+already_AddRefed<ImageData> CanvasRenderingContext2D::GetImageData(
+    JSContext* aCx, int32_t aSx, int32_t aSy, int32_t aSw, int32_t aSh,
+    nsIPrincipal& aSubjectPrincipal, ErrorResult& aError) {
+  return GetImageData(aCx, aSx, aSy, aSw, aSh, Some(&aSubjectPrincipal),
+                      aError);
+}
+
+already_AddRefed<ImageData> CanvasRenderingContext2D::GetImageData(
+    JSContext* aCx, int32_t aSx, int32_t aSy, int32_t aSw, int32_t aSh,
+    Maybe<nsIPrincipal*> aSubjectPrincipal, ErrorResult& aError) {
+  if (!mCanvasElement && !mDocShell && !mOffscreenCanvas) {
+    NS_ERROR("No canvas element and no docshell in GetImageData!!!");
+    aError.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return nullptr;
+  }
+
+  // Check only if we have a canvas element; if we were created with a docshell,
+  // then it's special internal use.
+  nsIPrincipal* subjectPrincipal =
+      aSubjectPrincipal ? *aSubjectPrincipal : nullptr;
+  if (IsWriteOnly() ||
+      (mCanvasElement && !mCanvasElement->CallerCanRead(subjectPrincipal)) ||
+      (mOffscreenCanvas &&
+       !mOffscreenCanvas->CallerCanRead(subjectPrincipal))) {
+    // XXX ERRMSG we need to report an error to developers here! (bug 329026)
+    aError.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return nullptr;
+  }
+
+  if (!aSw || !aSh) {
+    aError.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return nullptr;
+  }
+
+  // Handle negative width and height by flipping the rectangle over in the
+  // relevant direction.
+  uint32_t w, h;
+  if (aSw < 0) {
+    w = -aSw;
+    aSx -= w;
+  } else {
+    w = aSw;
+  }
+  if (aSh < 0) {
+    h = -aSh;
+    aSy -= h;
+  } else {
+    h = aSh;
+  }
+
+  if (w == 0) {
+    w = 1;
+  }
+  if (h == 0) {
+    h = 1;
+  }
+
+  JS::Rooted<JSObject*> array(aCx);
+  aError = GetImageDataArray(aCx, aSx, aSy, w, h, aSubjectPrincipal,
+                             array.address());
+  if (aError.Failed()) {
+    return nullptr;
+  }
+  MOZ_ASSERT(array);
+  return MakeAndAddRef<ImageData>(w, h, *array);
+}
+
+static IntRect ClipImageDataTransfer(IntRect& aSrc, const IntPoint& aDestOffset,
+                                     const IntSize& aDestBounds) {
+  IntRect dest = aSrc;
+  dest.SafeMoveBy(aDestOffset);
+  dest = IntRect(IntPoint(0, 0), aDestBounds).SafeIntersect(dest);
+
+  aSrc = aSrc.SafeIntersect(dest - aDestOffset);
+  return aSrc + aDestOffset;
+}
+
+nsresult CanvasRenderingContext2D::GetImageDataArray(
+    JSContext* aCx, int32_t aX, int32_t aY, uint32_t aWidth, uint32_t aHeight,
+    Maybe<nsIPrincipal*> aSubjectPrincipal, JSObject** aRetval) {
+  MOZ_ASSERT(aWidth && aHeight);
+
+  // Restrict the typed array length to INT32_MAX because that's all we support
+  // in dom::TypedArray::ComputeState.
+  CheckedInt<uint32_t> len = CheckedInt<uint32_t>(aWidth) * aHeight * 4;
+  if (!len.isValid() || len.value() > INT32_MAX) {
+    return NS_ERROR_DOM_INDEX_SIZE_ERR;
+  }
+
+  CheckedInt<int32_t> rightMost = CheckedInt<int32_t>(aX) + aWidth;
+  CheckedInt<int32_t> bottomMost = CheckedInt<int32_t>(aY) + aHeight;
+
+  if (!rightMost.isValid() || !bottomMost.isValid()) {
+    return NS_ERROR_DOM_SYNTAX_ERR;
+  }
+
+  JS::Rooted<JSObject*> darray(aCx, JS_NewUint8ClampedArray(aCx, len.value()));
+  if (!darray) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  if (mZero) {
+    *aRetval = darray;
+    return NS_OK;
+  }
+
+  IntRect dstWriteRect(0, 0, aWidth, aHeight);
+  IntRect srcReadRect = ClipImageDataTransfer(dstWriteRect, IntPoint(aX, aY),
+                                              IntSize(mWidth, mHeight));
+  if (srcReadRect.IsEmpty()) {
+    *aRetval = darray;
+    return NS_OK;
+  }
+
+  if (!GetBufferProvider() && !EnsureTarget()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<SourceSurface> snapshot = mBufferProvider->BorrowSnapshot();
+  if (!snapshot) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  RefPtr<DataSourceSurface> readback = snapshot->GetDataSurface();
+  mBufferProvider->ReturnSnapshot(snapshot.forget());
+
+  // Check for site-specific permission.  This check is not needed if the
+  // canvas was created with a docshell (that is only done for special
+  // internal uses).
+  bool usePlaceholder = false;
+  if (mCanvasElement) {
+    nsCOMPtr<Document> ownerDoc = mCanvasElement->OwnerDoc();
+    usePlaceholder = !CanvasUtils::IsImageExtractionAllowed(ownerDoc, aCx,
+                                                            aSubjectPrincipal);
+  } else if (mOffscreenCanvas) {
+    usePlaceholder = mOffscreenCanvas->ShouldResistFingerprinting(
+        RFPTarget::CanvasImageExtractionPrompt);
+  }
+
+  // Clone the data source surface if canvas randomization is enabled. We need
+  // to do this because we don't want to alter the actual image buffer.
+  // Otherwise, we will provide inconsistent image data with multiple calls.
+  //
+  // Note that we don't need to clone if we will use the place holder because
+  // the place holder doesn't use actual image data.
+  bool needRandomizePixels = false;
+  if (!usePlaceholder &&
+      ShouldResistFingerprinting(RFPTarget::CanvasRandomization)) {
+    needRandomizePixels = true;
+    readback = CreateDataSourceSurfaceByCloning(readback);
+  }
+
+  DataSourceSurface::MappedSurface rawData;
+  if (!readback || !readback->Map(DataSourceSurface::READ, &rawData)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  do {
+    uint8_t* randomData;
+    if (usePlaceholder) {
+      // Since we cannot call any GC-able functions (like requesting the RNG
+      // service) after we call JS_GetUint8ClampedArrayData, we will
+      // pre-generate the randomness required for GeneratePlaceholderCanvasData.
+      randomData = TryToGenerateRandomDataForPlaceholderCanvasData();
+    } else if (needRandomizePixels) {
+      // Apply the random noises if canvan randomization is enabled. We don't
+      // need to calculate random noises if we are going to use the place
+      // holder.
+
+      const IntSize size = readback->GetSize();
+      nsRFPService::RandomizePixels(GetCookieJarSettings(), rawData.mData,
+                                    size.height * size.width * 4,
+                                    SurfaceFormat::A8R8G8B8_UINT32);
+    }
+
+    JS::AutoCheckCannotGC nogc;
+    bool isShared;
+    uint8_t* data = JS_GetUint8ClampedArrayData(darray, &isShared, nogc);
+    MOZ_ASSERT(!isShared);  // Should not happen, data was created above
+
+    if (usePlaceholder) {
+      FillPlaceholderCanvas(randomData, len.value(), data);
+      break;
+    }
+
+    uint32_t srcStride = rawData.mStride;
+    uint8_t* src =
+        rawData.mData + srcReadRect.y * srcStride + srcReadRect.x * 4;
+
+    uint8_t* dst = data + dstWriteRect.y * (aWidth * 4) + dstWriteRect.x * 4;
+
+    if (mOpaque) {
+      SwizzleData(src, srcStride, SurfaceFormat::X8R8G8B8_UINT32, dst,
+                  aWidth * 4, SurfaceFormat::R8G8B8A8, dstWriteRect.Size());
+    } else {
+      UnpremultiplyData(src, srcStride, SurfaceFormat::A8R8G8B8_UINT32, dst,
+                        aWidth * 4, SurfaceFormat::R8G8B8A8,
+                        dstWriteRect.Size());
+    }
+  } while (false);
+
+  readback->Unmap();
+  *aRetval = darray;
+  return NS_OK;
+}
+
+void CanvasRenderingContext2D::EnsureErrorTarget() {
+  if (sErrorTarget.get()) {
+    return;
+  }
+
+  RefPtr<DrawTarget> errorTarget =
+      gfxPlatform::GetPlatform()->CreateOffscreenCanvasDrawTarget(
+          IntSize(1, 1), SurfaceFormat::B8G8R8A8);
+  MOZ_ASSERT(errorTarget, "Failed to allocate the error target!");
+
+  sErrorTarget.set(errorTarget.forget().take());
+}
+
+void CanvasRenderingContext2D::FillRuleChanged() {
+  if (mPath) {
+    mPathBuilder = mPath->CopyToBuilder(CurrentState().fillRule);
+    mPath = nullptr;
+  }
+}
+
+void CanvasRenderingContext2D::PutImageData(ImageData& aImageData, int32_t aDx,
+                                            int32_t aDy, ErrorResult& aRv) {
+  RootedSpiderMonkeyInterface<Uint8ClampedArray> arr(RootingCx());
+  PutImageData_explicit(aDx, aDy, aImageData, false, 0, 0, 0, 0, aRv);
+}
+
+void CanvasRenderingContext2D::PutImageData(ImageData& aImageData, int32_t aDx,
+                                            int32_t aDy, int32_t aDirtyX,
+                                            int32_t aDirtyY,
+                                            int32_t aDirtyWidth,
+                                            int32_t aDirtyHeight,
+                                            ErrorResult& aRv) {
+  PutImageData_explicit(aDx, aDy, aImageData, true, aDirtyX, aDirtyY,
+                        aDirtyWidth, aDirtyHeight, aRv);
+}
+
+void CanvasRenderingContext2D::PutImageData_explicit(
+    int32_t aX, int32_t aY, ImageData& aImageData, bool aHasDirtyRect,
+    int32_t aDirtyX, int32_t aDirtyY, int32_t aDirtyWidth, int32_t aDirtyHeight,
+    ErrorResult& aRv) {
+  RootedSpiderMonkeyInterface<Uint8ClampedArray> arr(RootingCx());
+  if (!arr.Init(aImageData.GetDataObject())) {
+    return aRv.ThrowInvalidStateError(
+        "Failed to extract Uint8ClampedArray from ImageData (security check "
+        "failed?)");
+  }
+
+  const uint32_t width = aImageData.Width();
+  const uint32_t height = aImageData.Height();
+  if (width == 0 || height == 0) {
+    return aRv.ThrowInvalidStateError("Passed-in image is empty");
+  }
+
+  IntRect dirtyRect;
+  IntRect imageDataRect(0, 0, width, height);
+
+  if (aHasDirtyRect) {
+    // fix up negative dimensions
+    if (aDirtyWidth < 0) {
+      if (aDirtyWidth == INT_MIN) {
+        return aRv.ThrowInvalidStateError("Dirty width is invalid");
+      }
+
+      CheckedInt32 checkedDirtyX = CheckedInt32(aDirtyX) + aDirtyWidth;
+
+      if (!checkedDirtyX.isValid()) {
+        return aRv.ThrowInvalidStateError("Dirty width is invalid");
+      }
+
+      aDirtyX = checkedDirtyX.value();
+      aDirtyWidth = -aDirtyWidth;
+    }
+
+    if (aDirtyHeight < 0) {
+      if (aDirtyHeight == INT_MIN) {
+        return aRv.ThrowInvalidStateError("Dirty height is invalid");
+      }
+
+      CheckedInt32 checkedDirtyY = CheckedInt32(aDirtyY) + aDirtyHeight;
+
+      if (!checkedDirtyY.isValid()) {
+        return aRv.ThrowInvalidStateError("Dirty height is invalid");
+      }
+
+      aDirtyY = checkedDirtyY.value();
+      aDirtyHeight = -aDirtyHeight;
+    }
+
+    // bound the dirty rect within the imageData rectangle
+    dirtyRect = imageDataRect.Intersect(
+        IntRect(aDirtyX, aDirtyY, aDirtyWidth, aDirtyHeight));
+
+    if (dirtyRect.Width() <= 0 || dirtyRect.Height() <= 0) {
+      return;
+    }
+  } else {
+    dirtyRect = imageDataRect;
+  }
+
+  IntRect srcRect = dirtyRect;
+  dirtyRect = ClipImageDataTransfer(srcRect, IntPoint(aX, aY),
+                                    IntSize(mWidth, mHeight));
+  if (dirtyRect.IsEmpty()) {
+    return;
+  }
+
+  arr.ComputeState();
+
+  uint32_t dataLen = arr.Length();
+
+  uint32_t len = width * height * 4;
+  if (dataLen != len) {
+    return aRv.ThrowInvalidStateError("Invalid width or height");
+  }
+
+  // The canvas spec says that the current path, transformation matrix, shadow
+  // attributes, global alpha, the clipping region, and global composition
+  // operator must not affect the getImageData() and putImageData() methods.
+  const gfx::Rect putRect(dirtyRect);
+  EnsureTarget(&putRect);
+
+  if (!IsTargetValid()) {
+    return aRv.Throw(NS_ERROR_FAILURE);
+  }
+
+  DataSourceSurface::MappedSurface map;
+  RefPtr<DataSourceSurface> sourceSurface;
+  uint8_t* lockedBits = nullptr;
+  uint8_t* dstData;
+  IntSize dstSize;
+  int32_t dstStride;
+  SurfaceFormat dstFormat;
+  if (mTarget->LockBits(&lockedBits, &dstSize, &dstStride, &dstFormat)) {
+    dstData = lockedBits + dirtyRect.y * dstStride + dirtyRect.x * 4;
+  } else {
+    sourceSurface = Factory::CreateDataSourceSurface(
+        dirtyRect.Size(), SurfaceFormat::B8G8R8A8, false);
+
+    // In certain scenarios, requesting larger than 8k image fails.  Bug 803568
+    // covers the details of how to run into it, but the full detailed
+    // investigation hasn't been done to determine the underlying cause.  We
+    // will just handle the failure to allocate the surface to avoid a crash.
+    if (!sourceSurface) {
+      return aRv.Throw(NS_ERROR_FAILURE);
+    }
+    if (!sourceSurface->Map(DataSourceSurface::READ_WRITE, &map)) {
+      return aRv.Throw(NS_ERROR_FAILURE);
+    }
+
+    dstData = map.mData;
+    if (!dstData) {
+      return aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    }
+    dstStride = map.mStride;
+    dstFormat = sourceSurface->GetFormat();
+  }
+
+  uint8_t* srcData = arr.Data() + srcRect.y * (width * 4) + srcRect.x * 4;
+
+  PremultiplyData(
+      srcData, width * 4, SurfaceFormat::R8G8B8A8, dstData, dstStride,
+      mOpaque ? SurfaceFormat::X8R8G8B8_UINT32 : SurfaceFormat::A8R8G8B8_UINT32,
+      dirtyRect.Size());
+
+  if (lockedBits) {
+    mTarget->ReleaseBits(lockedBits);
+  } else if (sourceSurface) {
+    sourceSurface->Unmap();
+    mTarget->CopySurface(sourceSurface, dirtyRect - dirtyRect.TopLeft(),
+                         dirtyRect.TopLeft());
+  }
+
+  Redraw(
+      gfx::Rect(dirtyRect.x, dirtyRect.y, dirtyRect.width, dirtyRect.height));
+}
+
+static already_AddRefed<ImageData> CreateImageData(
+    JSContext* aCx, CanvasRenderingContext2D* aContext, uint32_t aW,
+    uint32_t aH, ErrorResult& aError) {
+  if (aW == 0) aW = 1;
+  if (aH == 0) aH = 1;
+
+  // Restrict the typed array length to INT32_MAX because that's all we support
+  // in dom::TypedArray::ComputeState.
+  CheckedInt<uint32_t> len = CheckedInt<uint32_t>(aW) * aH * 4;
+  if (!len.isValid() || len.value() > INT32_MAX) {
+    aError.ThrowIndexSizeError("Invalid width or height");
+    return nullptr;
+  }
+
+  // Create the fast typed array; it's initialized to 0 by default.
+  JSObject* darray = Uint8ClampedArray::Create(aCx, aContext, len.value());
+  if (!darray) {
+    // TODO: Should use OOMReporter.
+    aError.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+
+  return do_AddRef(new ImageData(aW, aH, *darray));
+}
+
+already_AddRefed<ImageData> CanvasRenderingContext2D::CreateImageData(
+    JSContext* aCx, int32_t aSw, int32_t aSh, ErrorResult& aError) {
+  if (!aSw || !aSh) {
+    aError.ThrowIndexSizeError("Invalid width or height");
+    return nullptr;
+  }
+
+  uint32_t w = Abs(aSw);
+  uint32_t h = Abs(aSh);
+  return dom::CreateImageData(aCx, this, w, h, aError);
+}
+
+already_AddRefed<ImageData> CanvasRenderingContext2D::CreateImageData(
+    JSContext* aCx, ImageData& aImagedata, ErrorResult& aError) {
+  return dom::CreateImageData(aCx, this, aImagedata.Width(),
+                              aImagedata.Height(), aError);
+}
+
+void CanvasRenderingContext2D::OnMemoryPressure() {
+  if (mBufferProvider) {
+    mBufferProvider->OnMemoryPressure();
+  }
+}
+
+void CanvasRenderingContext2D::OnBeforePaintTransaction() {
+  if (!mTarget) return;
+  OnStableState();
+}
+
+void CanvasRenderingContext2D::OnDidPaintTransaction() { MarkContextClean(); }
+
+bool CanvasRenderingContext2D::UpdateWebRenderCanvasData(
+    nsDisplayListBuilder* aBuilder, WebRenderCanvasData* aCanvasData) {
+  if (mOpaque) {
+    // If we're opaque then make sure we have a surface so we paint black
+    // instead of transparent.
+    EnsureTarget();
+  }
+
+  // Don't call EnsureTarget() ... if there isn't already a surface, then
+  // we have nothing to paint and there is no need to create a surface just
+  // to paint nothing. Also, EnsureTarget() can cause creation of a persistent
+  // layer manager which must NOT happen during a paint.
+  if (!mBufferProvider && !IsTargetValid()) {
+    // No DidTransactionCallback will be received, so mark the context clean
+    // now so future invalidations will be dispatched.
+    MarkContextClean();
+    // Clear CanvasRenderer of WebRenderCanvasData
+    aCanvasData->ClearCanvasRenderer();
+    return false;
+  }
+
+  auto renderer = aCanvasData->GetCanvasRenderer();
+
+  if (!mResetLayer && renderer) {
+    CanvasRendererData data;
+    data.mContext = this;
+    data.mSize = GetSize();
+
+    if (renderer->IsDataValid(data)) {
+      return true;
+    }
+  }
+
+  renderer = aCanvasData->CreateCanvasRenderer();
+  if (!InitializeCanvasRenderer(aBuilder, renderer)) {
+    // Clear CanvasRenderer of WebRenderCanvasData
+    aCanvasData->ClearCanvasRenderer();
+    return false;
+  }
+
+  MOZ_ASSERT(renderer);
+  mResetLayer = false;
+  return true;
+}
+
+bool CanvasRenderingContext2D::InitializeCanvasRenderer(
+    nsDisplayListBuilder* aBuilder, CanvasRenderer* aRenderer) {
+  CanvasRendererData data;
+  data.mContext = this;
+  data.mSize = GetSize();
+  data.mIsOpaque = mOpaque;
+  data.mDoPaintCallbacks = true;
+
+  if (!mBufferProvider) {
+    // Force the creation of a buffer provider.
+    EnsureTarget();
+    ReturnTarget();
+    if (!mBufferProvider) {
+      MarkContextClean();
+      return false;
+    }
+  }
+
+  aRenderer->Initialize(data);
+  aRenderer->SetDirty();
+  return true;
+}
+
+void CanvasRenderingContext2D::MarkContextClean() {
+  if (mInvalidateCount > 0) {
+    mPredictManyRedrawCalls = mInvalidateCount > kCanvasMaxInvalidateCount;
+  }
+  mIsEntireFrameInvalid = false;
+  mInvalidateCount = 0;
+}
+
+void CanvasRenderingContext2D::GetAppUnitsValues(int32_t* aPerDevPixel,
+                                                 int32_t* aPerCSSPixel) {
+  // If we don't have a canvas element, we just return something generic.
+  if (aPerDevPixel) {
+    *aPerDevPixel = 60;
+  }
+  if (aPerCSSPixel) {
+    *aPerCSSPixel = 60;
+  }
+  PresShell* presShell = GetPresShell();
+  if (!presShell) {
+    return;
+  }
+  nsPresContext* presContext = presShell->GetPresContext();
+  if (!presContext) {
+    return;
+  }
+  if (aPerDevPixel) {
+    *aPerDevPixel = presContext->AppUnitsPerDevPixel();
+  }
+  if (aPerCSSPixel) {
+    *aPerCSSPixel = AppUnitsPerCSSPixel();
+  }
+}
+
+void CanvasRenderingContext2D::SetWriteOnly() {
+  mWriteOnly = true;
+  if (mCanvasElement) {
+    mCanvasElement->SetWriteOnly();
+  } else if (mOffscreenCanvas) {
+    mOffscreenCanvas->SetWriteOnly();
+  }
+}
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(CanvasPath, mParent)
+
+CanvasPath::CanvasPath(nsISupports* aParent) : mParent(aParent) {
+  mPathBuilder =
+      gfxPlatform::ThreadLocalScreenReferenceDrawTarget()->CreatePathBuilder();
+}
+
+CanvasPath::CanvasPath(nsISupports* aParent,
+                       already_AddRefed<PathBuilder> aPathBuilder)
+    : mParent(aParent), mPathBuilder(aPathBuilder) {
+  if (!mPathBuilder) {
+    mPathBuilder = gfxPlatform::ThreadLocalScreenReferenceDrawTarget()
+                       ->CreatePathBuilder();
+  }
+}
+
+JSObject* CanvasPath::WrapObject(JSContext* aCx,
+                                 JS::Handle<JSObject*> aGivenProto) {
+  return Path2D_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+already_AddRefed<CanvasPath> CanvasPath::Constructor(
+    const GlobalObject& aGlobal) {
+  RefPtr<CanvasPath> path = new CanvasPath(aGlobal.GetAsSupports());
+  return path.forget();
+}
+
+already_AddRefed<CanvasPath> CanvasPath::Constructor(
+    const GlobalObject& aGlobal, CanvasPath& aCanvasPath) {
+  RefPtr<gfx::DrawTarget> drawTarget =
+      gfxPlatform::ThreadLocalScreenReferenceDrawTarget();
+  RefPtr<gfx::Path> tempPath =
+      aCanvasPath.GetPath(CanvasWindingRule::Nonzero, drawTarget.get());
+
+  RefPtr<CanvasPath> path =
+      new CanvasPath(aGlobal.GetAsSupports(), tempPath->CopyToBuilder());
+  return path.forget();
+}
+
+already_AddRefed<CanvasPath> CanvasPath::Constructor(
+    const GlobalObject& aGlobal, const nsAString& aPathString) {
+  RefPtr<gfx::Path> tempPath = SVGContentUtils::GetPath(aPathString);
+  if (!tempPath) {
+    return Constructor(aGlobal);
+  }
+
+  RefPtr<CanvasPath> path =
+      new CanvasPath(aGlobal.GetAsSupports(), tempPath->CopyToBuilder());
+  return path.forget();
+}
+
+void CanvasPath::ClosePath() {
+  EnsurePathBuilder();
+
+  mPathBuilder->Close();
+}
+
+void CanvasPath::MoveTo(double aX, double aY) {
+  EnsurePathBuilder();
+
+  mPathBuilder->MoveTo(Point(ToFloat(aX), ToFloat(aY)));
+}
+
+void CanvasPath::LineTo(double aX, double aY) {
+  EnsurePathBuilder();
+
+  mPathBuilder->LineTo(Point(ToFloat(aX), ToFloat(aY)));
+}
+
+void CanvasPath::QuadraticCurveTo(double aCpx, double aCpy, double aX,
+                                  double aY) {
+  EnsurePathBuilder();
+
+  mPathBuilder->QuadraticBezierTo(gfx::Point(ToFloat(aCpx), ToFloat(aCpy)),
+                                  gfx::Point(ToFloat(aX), ToFloat(aY)));
+}
+
+void CanvasPath::BezierCurveTo(double aCp1x, double aCp1y, double aCp2x,
+                               double aCp2y, double aX, double aY) {
+  BezierTo(gfx::Point(ToFloat(aCp1x), ToFloat(aCp1y)),
+           gfx::Point(ToFloat(aCp2x), ToFloat(aCp2y)),
+           gfx::Point(ToFloat(aX), ToFloat(aY)));
+}
+
+void CanvasPath::ArcTo(double aX1, double aY1, double aX2, double aY2,
+                       double aRadius, ErrorResult& aError) {
+  if (aRadius < 0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsurePathBuilder();
+
+  // Current point in user space!
+  Point p0 = mPathBuilder->CurrentPoint();
+  Point p1(aX1, aY1);
+  Point p2(aX2, aY2);
+
+  // Execute these calculations in double precision to avoid cumulative
+  // rounding errors.
+  double dir, a2, b2, c2, cosx, sinx, d, anx, any, bnx, bny, x3, y3, x4, y4, cx,
+      cy, angle0, angle1;
+  bool anticlockwise;
+
+  if (p0 == p1 || p1 == p2 || aRadius == 0) {
+    LineTo(p1.x, p1.y);
+    return;
+  }
+
+  // Check for colinearity
+  dir = (p2.x.value - p1.x.value) * (p0.y.value - p1.y.value) +
+        (p2.y.value - p1.y.value) * (p1.x.value - p0.x.value);
+  if (dir == 0) {
+    LineTo(p1.x, p1.y);
+    return;
+  }
+
+  // XXX - Math for this code was already available from the non-azure code
+  // and would be well tested. Perhaps converting to bezier directly might
+  // be more efficient longer run.
+  a2 = (p0.x - aX1) * (p0.x - aX1) + (p0.y - aY1) * (p0.y - aY1);
+  b2 = (aX1 - aX2) * (aX1 - aX2) + (aY1 - aY2) * (aY1 - aY2);
+  c2 = (p0.x - aX2) * (p0.x - aX2) + (p0.y - aY2) * (p0.y - aY2);
+  cosx = (a2 + b2 - c2) / (2 * sqrt(a2 * b2));
+
+  sinx = sqrt(1 - cosx * cosx);
+  d = aRadius / ((1 - cosx) / sinx);
+
+  anx = (aX1 - p0.x) / sqrt(a2);
+  any = (aY1 - p0.y) / sqrt(a2);
+  bnx = (aX1 - aX2) / sqrt(b2);
+  bny = (aY1 - aY2) / sqrt(b2);
+  x3 = aX1 - anx * d;
+  y3 = aY1 - any * d;
+  x4 = aX1 - bnx * d;
+  y4 = aY1 - bny * d;
+  anticlockwise = (dir < 0);
+  cx = x3 + any * aRadius * (anticlockwise ? 1 : -1);
+  cy = y3 - anx * aRadius * (anticlockwise ? 1 : -1);
+  angle0 = atan2((y3 - cy), (x3 - cx));
+  angle1 = atan2((y4 - cy), (x4 - cx));
+
+  LineTo(x3, y3);
+
+  Arc(cx, cy, aRadius, angle0, angle1, anticlockwise, aError);
+}
+
+void CanvasPath::Rect(double aX, double aY, double aW, double aH) {
+  MoveTo(aX, aY);
+  LineTo(aX + aW, aY);
+  LineTo(aX + aW, aY + aH);
+  LineTo(aX, aY + aH);
+  ClosePath();
+}
+
+void CanvasPath::RoundRect(
+    double aX, double aY, double aW, double aH,
+    const UnrestrictedDoubleOrDOMPointInitOrUnrestrictedDoubleOrDOMPointInitSequence&
+        aRadii,
+    ErrorResult& aError) {
+  EnsurePathBuilder();
+
+  RoundRectImpl(mPathBuilder, Nothing(), aX, aY, aW, aH, aRadii, aError);
+}
+
+void CanvasPath::Arc(double aX, double aY, double aRadius, double aStartAngle,
+                     double aEndAngle, bool aAnticlockwise,
+                     ErrorResult& aError) {
+  if (aRadius < 0.0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsurePathBuilder();
+
+  ArcToBezier(this, Point(aX, aY), Size(aRadius, aRadius), aStartAngle,
+              aEndAngle, aAnticlockwise);
+}
+
+void CanvasPath::Ellipse(double x, double y, double radiusX, double radiusY,
+                         double rotation, double startAngle, double endAngle,
+                         bool anticlockwise, ErrorResult& aError) {
+  if (radiusX < 0.0 || radiusY < 0.0) {
+    return aError.ThrowIndexSizeError("Negative radius");
+  }
+
+  EnsurePathBuilder();
+
+  ArcToBezier(this, Point(x, y), Size(radiusX, radiusY), startAngle, endAngle,
+              anticlockwise, rotation);
+}
+
+void CanvasPath::LineTo(const gfx::Point& aPoint) {
+  EnsurePathBuilder();
+
+  mPathBuilder->LineTo(aPoint);
+}
+
+void CanvasPath::BezierTo(const gfx::Point& aCP1, const gfx::Point& aCP2,
+                          const gfx::Point& aCP3) {
+  EnsurePathBuilder();
+
+  mPathBuilder->BezierTo(aCP1, aCP2, aCP3);
+}
+
+void CanvasPath::AddPath(CanvasPath& aCanvasPath, const DOMMatrix2DInit& aInit,
+                         ErrorResult& aError) {
+  RefPtr<gfx::DrawTarget> drawTarget =
+      gfxPlatform::ThreadLocalScreenReferenceDrawTarget();
+  RefPtr<gfx::Path> tempPath =
+      aCanvasPath.GetPath(CanvasWindingRule::Nonzero, drawTarget.get());
+
+  RefPtr<DOMMatrixReadOnly> matrix =
+      DOMMatrixReadOnly::FromMatrix(GetParentObject(), aInit, aError);
+  if (aError.Failed()) {
+    return;
+  }
+
+  Matrix transform(*(matrix->GetInternal2D()));
+
+  if (!transform.IsFinite()) {
+    return;
+  }
+
+  if (!transform.IsIdentity()) {
+    RefPtr<PathBuilder> tempBuilder =
+        tempPath->TransformedCopyToBuilder(transform, FillRule::FILL_WINDING);
+    tempPath = tempBuilder->Finish();
+  }
+
+  EnsurePathBuilder();  // in case a path is added to itself
+  tempPath->StreamToSink(mPathBuilder);
+}
+
+already_AddRefed<gfx::Path> CanvasPath::GetPath(
+    const CanvasWindingRule& aWinding, const DrawTarget* aTarget) const {
+  FillRule fillRule = FillRule::FILL_WINDING;
+  if (aWinding == CanvasWindingRule::Evenodd) {
+    fillRule = FillRule::FILL_EVEN_ODD;
+  }
+
+  if (mPath && (mPath->GetBackendType() == aTarget->GetBackendType()) &&
+      (mPath->GetFillRule() == fillRule)) {
+    RefPtr<gfx::Path> path(mPath);
+    return path.forget();
+  }
+
+  if (!mPath) {
+    // if there is no path, there must be a pathbuilder
+    MOZ_ASSERT(mPathBuilder);
+    mPath = mPathBuilder->Finish();
+    if (!mPath) {
+      RefPtr<gfx::Path> path(mPath);
+      return path.forget();
+    }
+
+    mPathBuilder = nullptr;
+  }
+
+  // retarget our backend if we're used with a different backend
+  if (mPath->GetBackendType() != aTarget->GetBackendType()) {
+    RefPtr<PathBuilder> tmpPathBuilder = aTarget->CreatePathBuilder(fillRule);
+    mPath->StreamToSink(tmpPathBuilder);
+    mPath = tmpPathBuilder->Finish();
+  } else if (mPath->GetFillRule() != fillRule) {
+    RefPtr<PathBuilder> tmpPathBuilder = mPath->CopyToBuilder(fillRule);
+    mPath = tmpPathBuilder->Finish();
+  }
+
+  RefPtr<gfx::Path> path(mPath);
+  return path.forget();
+}
+
+void CanvasPath::EnsurePathBuilder() const {
+  if (mPathBuilder) {
+    return;
+  }
+
+  // if there is not pathbuilder, there must be a path
+  MOZ_ASSERT(mPath);
+  mPathBuilder = mPath->CopyToBuilder();
+  mPath = nullptr;
+}
+
+size_t BindingJSObjectMallocBytes(CanvasRenderingContext2D* aContext) {
+  IntSize size = aContext->GetSize();
+
+  // TODO: Bug 1552137: No memory will be allocated if either dimension is
+  // greater than gfxPrefs::gfx_canvas_max_size(). We should check this here
+  // too.
+
+  CheckedInt<uint32_t> bytes =
+      CheckedInt<uint32_t>(size.width) * size.height * 4;
+  if (!bytes.isValid()) {
+    return 0;
+  }
+
+  return bytes.value();
+}
+
+}  // namespace mozilla::dom