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diff --git a/layout/svg/SVGContextPaint.h b/layout/svg/SVGContextPaint.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef LAYOUT_SVG_SVGCONTEXTPAINT_H_
+#define LAYOUT_SVG_SVGCONTEXTPAINT_H_
+
+#include "DrawMode.h"
+#include "gfxMatrix.h"
+#include "gfxPattern.h"
+#include "gfxTypes.h"
+#include "gfxUtils.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/gfx/2D.h"
+#include "nsColor.h"
+#include "nsStyleStruct.h"
+#include "nsTArray.h"
+#include "ImgDrawResult.h"
+#include "nsRefPtrHashtable.h"
+
+class gfxContext;
+
+namespace mozilla {
+class SVGPaintServerFrame;
+
+namespace dom {
+class Document;
+}
+
+/**
+ * This class is used to pass information about a context element through to
+ * SVG painting code in order to resolve the 'context-fill' and related
+ * keywords. See:
+ *
+ *   https://www.w3.org/TR/SVG2/painting.html#context-paint
+ *
+ * This feature allows the color in an SVG-in-OpenType glyph to come from the
+ * computed style for the text that is being drawn, for example, or for color
+ * in an SVG embedded by an <img> element to come from the embedding <img>
+ * element.
+ *
+ * This class is reference counted so that it can be shared among many similar
+ * SVGImageContext objects. (SVGImageContext objects are frequently
+ * copy-constructed with small modifications, and we'd like for those copies to
+ * be able to share their context-paint data cheaply.)  However, in most cases,
+ * SVGContextPaint instances are stored in a local RefPtr and only last for the
+ * duration of a function call.
+ * XXX Note: SVGImageContext doesn't actually have a SVGContextPaint member yet,
+ * but it will in a later patch in the patch series that added this comment.
+ */
+class SVGContextPaint : public RefCounted<SVGContextPaint> {
+ protected:
+  using DrawTarget = mozilla::gfx::DrawTarget;
+  using Float = mozilla::gfx::Float;
+  using imgDrawingParams = mozilla::image::imgDrawingParams;
+
+  SVGContextPaint() : mDashOffset(0.0f), mStrokeWidth(0.0f) {}
+
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(SVGContextPaint)
+
+  virtual ~SVGContextPaint() = default;
+
+  virtual already_AddRefed<gfxPattern> GetFillPattern(
+      const DrawTarget* aDrawTarget, float aOpacity, const gfxMatrix& aCTM,
+      imgDrawingParams& aImgParams) = 0;
+  virtual already_AddRefed<gfxPattern> GetStrokePattern(
+      const DrawTarget* aDrawTarget, float aOpacity, const gfxMatrix& aCTM,
+      imgDrawingParams& aImgParams) = 0;
+  virtual float GetFillOpacity() const = 0;
+  virtual float GetStrokeOpacity() const = 0;
+
+  already_AddRefed<gfxPattern> GetFillPattern(const DrawTarget* aDrawTarget,
+                                              const gfxMatrix& aCTM,
+                                              imgDrawingParams& aImgParams) {
+    return GetFillPattern(aDrawTarget, GetFillOpacity(), aCTM, aImgParams);
+  }
+
+  already_AddRefed<gfxPattern> GetStrokePattern(const DrawTarget* aDrawTarget,
+                                                const gfxMatrix& aCTM,
+                                                imgDrawingParams& aImgParams) {
+    return GetStrokePattern(aDrawTarget, GetStrokeOpacity(), aCTM, aImgParams);
+  }
+
+  static SVGContextPaint* GetContextPaint(nsIContent* aContent);
+
+  // XXX This gets the geometry params from the gfxContext.  We should get that
+  // information from the actual paint context!
+  void InitStrokeGeometry(gfxContext* aContext, float devUnitsPerSVGUnit);
+
+  const FallibleTArray<Float>& GetStrokeDashArray() const { return mDashes; }
+
+  Float GetStrokeDashOffset() const { return mDashOffset; }
+
+  Float GetStrokeWidth() const { return mStrokeWidth; }
+
+  virtual uint32_t Hash() const {
+    MOZ_ASSERT_UNREACHABLE(
+        "Only VectorImage needs to hash, and that should "
+        "only be operating on our SVGEmbeddingContextPaint "
+        "subclass");
+    return 0;
+  }
+
+  /**
+   * Returns true if image context paint is allowed to be used in an image that
+   * has the given URI, else returns false.
+   */
+  static bool IsAllowedForImageFromURI(nsIURI* aURI);
+
+ private:
+  // Member-vars are initialized in InitStrokeGeometry.
+  FallibleTArray<Float> mDashes;
+  MOZ_INIT_OUTSIDE_CTOR Float mDashOffset;
+  MOZ_INIT_OUTSIDE_CTOR Float mStrokeWidth;
+};
+
+/**
+ * RAII class used to temporarily set and remove an SVGContextPaint while a
+ * piece of SVG is being painted.  The context paint is set on the SVG's owner
+ * document, as expected by SVGContextPaint::GetContextPaint.  Any pre-existing
+ * context paint is restored after this class removes the context paint that it
+ * set.
+ */
+class MOZ_RAII AutoSetRestoreSVGContextPaint {
+ public:
+  AutoSetRestoreSVGContextPaint(const SVGContextPaint* aContextPaint,
+                                dom::Document* aDocument);
+  ~AutoSetRestoreSVGContextPaint();
+
+ private:
+  dom::Document* mDocument;
+  // The context paint that needs to be restored by our dtor after it removes
+  // aContextPaint:
+  const SVGContextPaint* mOuterContextPaint;
+};
+
+/**
+ * This class should be flattened into SVGContextPaint once we get rid of the
+ * other sub-class (SimpleTextContextPaint).
+ */
+struct SVGContextPaintImpl : public SVGContextPaint {
+ protected:
+  using DrawTarget = mozilla::gfx::DrawTarget;
+
+ public:
+  DrawMode Init(const DrawTarget* aDrawTarget, const gfxMatrix& aContextMatrix,
+                nsIFrame* aFrame, SVGContextPaint* aOuterContextPaint,
+                imgDrawingParams& aImgParams);
+
+  already_AddRefed<gfxPattern> GetFillPattern(
+      const DrawTarget* aDrawTarget, float aOpacity, const gfxMatrix& aCTM,
+      imgDrawingParams& aImgParams) override;
+  already_AddRefed<gfxPattern> GetStrokePattern(
+      const DrawTarget* aDrawTarget, float aOpacity, const gfxMatrix& aCTM,
+      imgDrawingParams& aImgParams) override;
+
+  void SetFillOpacity(float aOpacity) { mFillOpacity = aOpacity; }
+  float GetFillOpacity() const override { return mFillOpacity; }
+
+  void SetStrokeOpacity(float aOpacity) { mStrokeOpacity = aOpacity; }
+  float GetStrokeOpacity() const override { return mStrokeOpacity; }
+
+  struct Paint {
+    enum class Tag : uint8_t {
+      None,
+      Color,
+      PaintServer,
+      ContextFill,
+      ContextStroke,
+    };
+
+    Paint() : mPaintDefinition{}, mPaintType(Tag::None) {}
+
+    void SetPaintServer(nsIFrame* aFrame, const gfxMatrix& aContextMatrix,
+                        SVGPaintServerFrame* aPaintServerFrame) {
+      mPaintType = Tag::PaintServer;
+      mPaintDefinition.mPaintServerFrame = aPaintServerFrame;
+      mFrame = aFrame;
+      mContextMatrix = aContextMatrix;
+    }
+
+    void SetColor(const nscolor& aColor) {
+      mPaintType = Tag::Color;
+      mPaintDefinition.mColor = aColor;
+    }
+
+    void SetContextPaint(SVGContextPaint* aContextPaint, Tag aTag) {
+      MOZ_ASSERT(aTag == Tag::ContextFill || aTag == Tag::ContextStroke);
+      mPaintType = aTag;
+      mPaintDefinition.mContextPaint = aContextPaint;
+    }
+
+    union {
+      SVGPaintServerFrame* mPaintServerFrame;
+      SVGContextPaint* mContextPaint;
+      nscolor mColor;
+    } mPaintDefinition;
+
+    // Initialized (if needed) in SetPaintServer():
+    MOZ_INIT_OUTSIDE_CTOR nsIFrame* mFrame;
+    // CTM defining the user space for the pattern we will use.
+    gfxMatrix mContextMatrix;
+    Tag mPaintType;
+
+    // Device-space-to-pattern-space
+    gfxMatrix mPatternMatrix;
+    nsRefPtrHashtable<nsFloatHashKey, gfxPattern> mPatternCache;
+
+    already_AddRefed<gfxPattern> GetPattern(
+        const DrawTarget* aDrawTarget, float aOpacity,
+        StyleSVGPaint nsStyleSVG::*aFillOrStroke, const gfxMatrix& aCTM,
+        imgDrawingParams& aImgParams);
+  };
+
+  Paint mFillPaint;
+  Paint mStrokePaint;
+
+  float mFillOpacity;
+  float mStrokeOpacity;
+};
+
+/**
+ * This class is used to pass context paint to an SVG image when an element
+ * references that image (e.g. via HTML <img> or SVG <image>, or by referencing
+ * it from a CSS property such as 'background-image').  In this case we only
+ * support context colors and not paint servers.
+ */
+class SVGEmbeddingContextPaint : public SVGContextPaint {
+  using DeviceColor = gfx::DeviceColor;
+
+ public:
+  SVGEmbeddingContextPaint() : mFillOpacity(1.0f), mStrokeOpacity(1.0f) {}
+
+  bool operator==(const SVGEmbeddingContextPaint& aOther) const {
+    MOZ_ASSERT(GetStrokeWidth() == aOther.GetStrokeWidth() &&
+                   GetStrokeDashOffset() == aOther.GetStrokeDashOffset() &&
+                   GetStrokeDashArray() == aOther.GetStrokeDashArray(),
+               "We don't currently include these in the context information "
+               "from an embedding element");
+    return mFill == aOther.mFill && mStroke == aOther.mStroke &&
+           mFillOpacity == aOther.mFillOpacity &&
+           mStrokeOpacity == aOther.mStrokeOpacity;
+  }
+
+  void SetFill(nscolor aFill) { mFill.emplace(gfx::ToDeviceColor(aFill)); }
+  const Maybe<DeviceColor>& GetFill() const { return mFill; }
+  void SetStroke(nscolor aStroke) {
+    mStroke.emplace(gfx::ToDeviceColor(aStroke));
+  }
+  const Maybe<DeviceColor>& GetStroke() const { return mStroke; }
+
+  /**
+   * Returns a pattern of type PatternType::COLOR, or else nullptr.
+   */
+  already_AddRefed<gfxPattern> GetFillPattern(
+      const DrawTarget* aDrawTarget, float aFillOpacity, const gfxMatrix& aCTM,
+      imgDrawingParams& aImgParams) override;
+
+  /**
+   * Returns a pattern of type PatternType::COLOR, or else nullptr.
+   */
+  already_AddRefed<gfxPattern> GetStrokePattern(
+      const DrawTarget* aDrawTarget, float aStrokeOpacity,
+      const gfxMatrix& aCTM, imgDrawingParams& aImgParams) override;
+
+  void SetFillOpacity(float aOpacity) { mFillOpacity = aOpacity; }
+  float GetFillOpacity() const override { return mFillOpacity; };
+
+  void SetStrokeOpacity(float aOpacity) { mStrokeOpacity = aOpacity; }
+  float GetStrokeOpacity() const override { return mStrokeOpacity; };
+
+  uint32_t Hash() const override;
+
+ private:
+  Maybe<DeviceColor> mFill;
+  Maybe<DeviceColor> mStroke;
+  float mFillOpacity;
+  float mStrokeOpacity;
+};
+
+}  // namespace mozilla
+
+#endif  // LAYOUT_SVG_SVGCONTEXTPAINT_H_