1 files changed, 296 insertions, 0 deletions
diff --git a/layout/base/ViewportUtils.cpp b/layout/base/ViewportUtils.cpp
new file mode 100644
index 0000000000..f0d18510bf
--- /dev/null
+++ b/layout/base/ViewportUtils.cpp
@@ -0,0 +1,296 @@
+/* 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 "Units.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/ViewportFrame.h"
+#include "mozilla/ViewportUtils.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/InputAPZContext.h"
+#include "mozilla/layers/ScrollableLayerGuid.h"
+#include "nsIContent.h"
+#include "nsIFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsQueryFrame.h"
+#include "nsStyleStruct.h"
+
+namespace mozilla {
+
+using layers::APZCCallbackHelper;
+using layers::InputAPZContext;
+using layers::ScrollableLayerGuid;
+
+template <typename Units>
+gfx::Matrix4x4Typed<Units, Units> ViewportUtils::GetVisualToLayoutTransform(
+    ScrollableLayerGuid::ViewID aScrollId) {
+  static_assert(
+      std::is_same_v<Units, CSSPixel> ||
+          std::is_same_v<Units, LayoutDevicePixel>,
+      "GetCallbackTransform() may only be used with CSS or LayoutDevice units");
+
+  if (aScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    return {};
+  }
+  nsCOMPtr<nsIContent> content = nsLayoutUtils::FindContentFor(aScrollId);
+  if (!content || !content->GetPrimaryFrame()) {
+    return {};
+  }
+
+  // First, scale inversely by the root content document's pres shell
+  // resolution to cancel the scale-to-resolution transform that the
+  // compositor adds to the layer with the pres shell resolution. The points
+  // sent to Gecko by APZ don't have this transform unapplied (unlike other
+  // compositor-side transforms) because Gecko needs it applied when hit
+  // testing against content that's conceptually outside the resolution,
+  // such as scrollbars.
+  float resolution = 1.0f;
+  if (PresShell* presShell =
+          APZCCallbackHelper::GetRootContentDocumentPresShellForContent(
+              content)) {
+    resolution = presShell->GetResolution();
+  }
+
+  // Now apply the callback-transform. This is only approximately correct,
+  // see the comment on GetCumulativeApzCallbackTransform for details.
+  gfx::PointTyped<Units> transform;
+  CSSPoint transformCSS = nsLayoutUtils::GetCumulativeApzCallbackTransform(
+      content->GetPrimaryFrame());
+  if constexpr (std::is_same_v<Units, CSSPixel>) {
+    transform = transformCSS;
+  } else {  // Units == LayoutDevicePixel
+    transform = transformCSS *
+                content->GetPrimaryFrame()->PresContext()->CSSToDevPixelScale();
+  }
+
+  return gfx::Matrix4x4Typed<Units, Units>::Scaling(1 / resolution,
+                                                    1 / resolution, 1)
+      .PostTranslate(transform.x, transform.y, 0);
+}
+
+CSSToCSSMatrix4x4 GetVisualToLayoutTransform(PresShell* aContext) {
+  ScrollableLayerGuid::ViewID targetScrollId =
+      InputAPZContext::GetTargetLayerGuid().mScrollId;
+  if (targetScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    if (nsIFrame* rootScrollFrame = aContext->GetRootScrollFrame()) {
+      targetScrollId =
+          nsLayoutUtils::FindOrCreateIDFor(rootScrollFrame->GetContent());
+    }
+  }
+  return ViewportUtils::GetVisualToLayoutTransform(targetScrollId);
+}
+
+nsPoint ViewportUtils::VisualToLayout(const nsPoint& aPt, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
+  cssPt = visualToLayout.TransformPoint(cssPt);
+  return CSSPoint::ToAppUnits(cssPt);
+}
+
+nsRect ViewportUtils::VisualToLayout(const nsRect& aRect, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSRect cssRect = CSSRect::FromAppUnits(aRect);
+  cssRect = visualToLayout.TransformBounds(cssRect);
+  nsRect result = CSSRect::ToAppUnits(cssRect);
+
+  // In hit testing codepaths, the input rect often has dimensions of one app
+  // units. If we are zoomed in enough, the rounded size of the output rect
+  // can be zero app units, which will fail to Intersect() with anything, and
+  // therefore cause hit testing to fail. To avoid this, we expand the output
+  // rect to one app units.
+  if (!aRect.IsEmpty() && result.IsEmpty()) {
+    result.width = 1;
+    result.height = 1;
+  }
+
+  return result;
+}
+
+nsPoint ViewportUtils::LayoutToVisual(const nsPoint& aPt, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
+  auto transformed = visualToLayout.Inverse().TransformPoint(cssPt);
+  return CSSPoint::ToAppUnits(transformed);
+}
+
+LayoutDevicePoint ViewportUtils::DocumentRelativeLayoutToVisual(
+    const LayoutDevicePoint& aPoint, PresShell* aShell) {
+  ScrollableLayerGuid::ViewID targetScrollId =
+      nsLayoutUtils::ScrollIdForRootScrollFrame(aShell->GetPresContext());
+  auto visualToLayout =
+      ViewportUtils::GetVisualToLayoutTransform<LayoutDevicePixel>(
+          targetScrollId);
+  return visualToLayout.Inverse().TransformPoint(aPoint);
+}
+
+LayoutDeviceRect ViewportUtils::DocumentRelativeLayoutToVisual(
+    const LayoutDeviceRect& aRect, PresShell* aShell) {
+  ScrollableLayerGuid::ViewID targetScrollId =
+      nsLayoutUtils::ScrollIdForRootScrollFrame(aShell->GetPresContext());
+  auto visualToLayout =
+      ViewportUtils::GetVisualToLayoutTransform<LayoutDevicePixel>(
+          targetScrollId);
+  return visualToLayout.Inverse().TransformBounds(aRect);
+}
+
+LayoutDeviceRect ViewportUtils::DocumentRelativeLayoutToVisual(
+    const LayoutDeviceIntRect& aRect, PresShell* aShell) {
+  return DocumentRelativeLayoutToVisual(IntRectToRect(aRect), aShell);
+}
+
+CSSRect ViewportUtils::DocumentRelativeLayoutToVisual(const CSSRect& aRect,
+                                                      PresShell* aShell) {
+  ScrollableLayerGuid::ViewID targetScrollId =
+      nsLayoutUtils::ScrollIdForRootScrollFrame(aShell->GetPresContext());
+  auto visualToLayout =
+      ViewportUtils::GetVisualToLayoutTransform(targetScrollId);
+  return visualToLayout.Inverse().TransformBounds(aRect);
+}
+
+template <class SourceUnits, class DestUnits>
+gfx::PointTyped<DestUnits> TransformPointOrRect(
+    const gfx::Matrix4x4Typed<SourceUnits, DestUnits>& aMatrix,
+    const gfx::PointTyped<SourceUnits>& aPoint) {
+  return aMatrix.TransformPoint(aPoint);
+}
+
+template <class SourceUnits, class DestUnits>
+gfx::RectTyped<DestUnits> TransformPointOrRect(
+    const gfx::Matrix4x4Typed<SourceUnits, DestUnits>& aMatrix,
+    const gfx::RectTyped<SourceUnits>& aRect) {
+  return aMatrix.TransformBounds(aRect);
+}
+
+template <class LDPointOrRect>
+LDPointOrRect ConvertToScreenRelativeVisual(const LDPointOrRect& aInput,
+                                            nsPresContext* aCtx) {
+  MOZ_ASSERT(aCtx);
+
+  LDPointOrRect layoutToVisual(aInput);
+  nsIFrame* prevRootFrame = nullptr;
+  nsPresContext* prevCtx = nullptr;
+
+  // Walk up to the rootmost prescontext, transforming as we go.
+  for (nsPresContext* ctx = aCtx; ctx; ctx = ctx->GetParentPresContext()) {
+    PresShell* shell = ctx->PresShell();
+    nsIFrame* rootFrame = shell->GetRootFrame();
+    if (prevRootFrame) {
+      // Convert layoutToVisual from being relative to `prevRootFrame`
+      // to being relative to `rootFrame` (layout space).
+      nscoord apd = prevCtx->AppUnitsPerDevPixel();
+      nsPoint offset = prevRootFrame->GetOffsetToCrossDoc(rootFrame, apd);
+      layoutToVisual += LayoutDevicePoint::FromAppUnits(offset, apd);
+    }
+    if (shell->GetResolution() != 1.0) {
+      // Found the APZ zoom root, so do the layout -> visual conversion.
+      layoutToVisual =
+          ViewportUtils::DocumentRelativeLayoutToVisual(layoutToVisual, shell);
+    }
+
+    prevRootFrame = rootFrame;
+    prevCtx = ctx;
+  }
+
+  // If we're in a nested content process, the above traversal will not have
+  // encountered the APZ zoom root. The translation part of the layout-to-visual
+  // transform will be included in |rootScreenRect.TopLeft()|, added below
+  // (that ultimately comes from nsIWidget::WidgetToScreenOffset(), which for an
+  // OOP iframe's widget includes this translation), but the scale part needs to
+  // be computed and added separately.
+  Scale2D enclosingResolution =
+      ViewportUtils::TryInferEnclosingResolution(prevCtx->GetPresShell());
+  if (enclosingResolution != Scale2D{1.0f, 1.0f}) {
+    layoutToVisual = TransformPointOrRect(
+        LayoutDeviceToLayoutDeviceMatrix4x4::Scaling(
+            enclosingResolution.xScale, enclosingResolution.yScale, 1.0f),
+        layoutToVisual);
+  }
+
+  // Then we do the conversion from the rootmost presContext's root frame (in
+  // visual space) to screen space.
+  LayoutDeviceIntRect rootScreenRect =
+      LayoutDeviceIntRect::FromAppUnitsToNearest(
+          prevRootFrame->GetScreenRectInAppUnits(),
+          prevCtx->AppUnitsPerDevPixel());
+
+  return layoutToVisual + rootScreenRect.TopLeft();
+}
+
+LayoutDevicePoint ViewportUtils::ToScreenRelativeVisual(
+    const LayoutDevicePoint& aPt, nsPresContext* aCtx) {
+  return ConvertToScreenRelativeVisual(aPt, aCtx);
+}
+
+LayoutDeviceRect ViewportUtils::ToScreenRelativeVisual(
+    const LayoutDeviceRect& aRect, nsPresContext* aCtx) {
+  return ConvertToScreenRelativeVisual(aRect, aCtx);
+}
+
+// Definitions of the two explicit instantiations forward declared in the header
+// file. This causes code for these instantiations to be emitted into the object
+// file for ViewportUtils.cpp.
+template CSSToCSSMatrix4x4 ViewportUtils::GetVisualToLayoutTransform<CSSPixel>(
+    ScrollableLayerGuid::ViewID);
+template LayoutDeviceToLayoutDeviceMatrix4x4
+    ViewportUtils::GetVisualToLayoutTransform<LayoutDevicePixel>(
+        ScrollableLayerGuid::ViewID);
+
+const nsIFrame* ViewportUtils::IsZoomedContentRoot(const nsIFrame* aFrame) {
+  if (!aFrame) {
+    return nullptr;
+  }
+  if (aFrame->Type() == LayoutFrameType::Canvas ||
+      aFrame->Type() == LayoutFrameType::PageSequence) {
+    nsIScrollableFrame* sf = do_QueryFrame(aFrame->GetParent());
+    if (sf && sf->IsRootScrollFrameOfDocument() &&
+        aFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
+      return aFrame->GetParent();
+    }
+  } else if (aFrame->StyleDisplay()->mPosition ==
+             StylePositionProperty::Fixed) {
+    if (ViewportFrame* viewportFrame = do_QueryFrame(aFrame->GetParent())) {
+      if (viewportFrame->PresContext()->IsRootContentDocumentCrossProcess()) {
+        return viewportFrame->PresShell()->GetRootScrollFrame();
+      }
+    }
+  }
+  return nullptr;
+}
+
+Scale2D ViewportUtils::TryInferEnclosingResolution(PresShell* aShell) {
+  MOZ_ASSERT(aShell && aShell->GetPresContext());
+  MOZ_ASSERT(!aShell->GetPresContext()->GetParentPresContext(),
+             "TryInferEnclosingResolution can only be called for a root pres "
+             "shell within a process");
+  if (dom::BrowserChild* bc = dom::BrowserChild::GetFrom(aShell)) {
+    if (!bc->IsTopLevel()) {
+      // The enclosing resolution is not directly available in the BrowserChild.
+      // The closest thing available is GetChildToParentConversionMatrix(),
+      // which also includes any enclosing CSS transforms.
+      // The behaviour implemented here will not provide an accurate answer
+      // in the presence of CSS transforms, but it tries to do something
+      // reasonable:
+      //  - If there are no enclosing CSS transforms, it will return the
+      //    resolution.
+      //  - If the enclosing transforms contain scales and translations only,
+      //    it will return the resolution times the CSS transform scale
+      //    (choosing the x-scale if they are different).
+      //  - Otherwise, it will return the resolution times a scale component
+      //    of the transform as returned by Matrix4x4Typed::Decompose().
+      //  - If the enclosing transform is sufficiently complex that
+      //    Decompose() returns false, give up and return 1.0.
+      gfx::Point3DTyped<gfx::UnknownUnits> translation;
+      gfx::Quaternion rotation;
+      gfx::Point3DTyped<gfx::UnknownUnits> scale;
+      if (bc->GetChildToParentConversionMatrix().Decompose(translation,
+                                                           rotation, scale)) {
+        return {scale.x, scale.y};
+      }
+    }
+  }
+  return {1.0f, 1.0f};
+}
+
+}  // namespace mozilla