Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 762 insertions, 0 deletions

diff --git a/layout/base/MotionPathUtils.cpp b/layout/base/MotionPathUtils.cpp
new file mode 100644
index 0000000000..c81020645d
--- /dev/null
+++ b/layout/base/MotionPathUtils.cpp
@@ -0,0 +1,762 @@
+/* -*- 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/. */
+
+#include "mozilla/MotionPathUtils.h"
+
+#include "gfxPlatform.h"
+#include "mozilla/dom/SVGGeometryElement.h"
+#include "mozilla/dom/SVGPathData.h"
+#include "mozilla/dom/SVGViewportElement.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Matrix.h"
+#include "mozilla/layers/LayersMessages.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/SVGObserverUtils.h"
+#include "mozilla/ShapeUtils.h"
+#include "nsIFrame.h"
+#include "nsLayoutUtils.h"
+#include "nsStyleTransformMatrix.h"
+
+#include <math.h>
+
+namespace mozilla {
+
+using nsStyleTransformMatrix::TransformReferenceBox;
+
+/* static */
+CSSPoint MotionPathUtils::ComputeAnchorPointAdjustment(const nsIFrame& aFrame) {
+  if (!aFrame.HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    return {};
+  }
+
+  auto transformBox = aFrame.StyleDisplay()->mTransformBox;
+  if (transformBox == StyleTransformBox::ViewBox ||
+      transformBox == StyleTransformBox::BorderBox) {
+    return {};
+  }
+
+  if (aFrame.IsSVGContainerFrame()) {
+    nsRect boxRect = nsLayoutUtils::ComputeSVGReferenceRect(
+        const_cast<nsIFrame*>(&aFrame), StyleGeometryBox::FillBox);
+    return CSSPoint::FromAppUnits(boxRect.TopLeft());
+  }
+  return CSSPoint::FromAppUnits(aFrame.GetPosition());
+}
+
+// Convert the StyleCoordBox into the StyleGeometryBox in CSS layout.
+// https://drafts.csswg.org/css-box-4/#keywords
+static StyleGeometryBox CoordBoxToGeometryBoxInCSSLayout(
+    StyleCoordBox aCoordBox) {
+  switch (aCoordBox) {
+    case StyleCoordBox::ContentBox:
+      return StyleGeometryBox::ContentBox;
+    case StyleCoordBox::PaddingBox:
+      return StyleGeometryBox::PaddingBox;
+    case StyleCoordBox::BorderBox:
+      return StyleGeometryBox::BorderBox;
+    case StyleCoordBox::FillBox:
+      return StyleGeometryBox::ContentBox;
+    case StyleCoordBox::StrokeBox:
+    case StyleCoordBox::ViewBox:
+      return StyleGeometryBox::BorderBox;
+  }
+  MOZ_ASSERT_UNREACHABLE("Unknown coord-box type");
+  return StyleGeometryBox::BorderBox;
+}
+
+/* static */
+const nsIFrame* MotionPathUtils::GetOffsetPathReferenceBox(
+    const nsIFrame* aFrame, nsRect& aOutputRect) {
+  const StyleOffsetPath& offsetPath = aFrame->StyleDisplay()->mOffsetPath;
+  if (offsetPath.IsNone()) {
+    return nullptr;
+  }
+
+  if (aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)) {
+    MOZ_ASSERT(aFrame->GetContent()->IsSVGElement());
+    auto* viewportElement =
+        dom::SVGElement::FromNode(aFrame->GetContent())->GetCtx();
+    aOutputRect = nsLayoutUtils::ComputeSVGOriginBox(viewportElement);
+    return viewportElement ? viewportElement->GetPrimaryFrame() : nullptr;
+  }
+
+  const nsIFrame* containingBlock = aFrame->GetContainingBlock();
+  const StyleCoordBox coordBox = offsetPath.IsCoordBox()
+                                     ? offsetPath.AsCoordBox()
+                                     : offsetPath.AsOffsetPath().coord_box;
+  aOutputRect = nsLayoutUtils::ComputeHTMLReferenceRect(
+      containingBlock, CoordBoxToGeometryBoxInCSSLayout(coordBox));
+  return containingBlock;
+}
+
+/* static */
+CSSCoord MotionPathUtils::GetRayContainReferenceSize(nsIFrame* aFrame) {
+  // We use the border-box size to calculate the reduced path length when using
+  // "contain" keyword.
+  // https://drafts.fxtf.org/motion-1/#valdef-ray-contain
+  //
+  // Note: Per the spec, border-box is treated as stroke-box in the SVG context,
+  // https://drafts.csswg.org/css-box-4/#valdef-box-border-box
+
+  // To calculate stroke bounds for an element with `non-scaling-stroke` we
+  // need to resolve its transform to its outer-svg, but to resolve that
+  // transform when it has `transform-box:stroke-box` (or `border-box`)
+  // may require its stroke bounds. There's no ideal way to break this
+  // cyclical dependency, but we break it by using the FillBox.
+  // https://github.com/w3c/csswg-drafts/issues/9640
+
+  const auto size = CSSSize::FromAppUnits(
+      (aFrame->HasAnyStateBits(NS_FRAME_SVG_LAYOUT)
+           ? nsLayoutUtils::ComputeSVGReferenceRect(
+                 aFrame, aFrame->StyleSVGReset()->HasNonScalingStroke()
+                             ? StyleGeometryBox::FillBox
+                             : StyleGeometryBox::StrokeBox)
+           : nsLayoutUtils::ComputeHTMLReferenceRect(
+                 aFrame, StyleGeometryBox::BorderBox))
+          .Size());
+  return std::max(size.width, size.height);
+}
+
+/* static */
+nsTArray<nscoord> MotionPathUtils::ComputeBorderRadii(
+    const StyleBorderRadius& aBorderRadius, const nsRect& aCoordBox) {
+  const nsRect insetRect = ShapeUtils::ComputeInsetRect(
+      StyleRect<LengthPercentage>::WithAllSides(LengthPercentage::Zero()),
+      aCoordBox);
+  nsTArray<nscoord> result(8);
+  result.SetLength(8);
+  if (!ShapeUtils::ComputeRectRadii(aBorderRadius, aCoordBox, insetRect,
+                                    result.Elements())) {
+    result.Clear();
+  }
+  return result;
+}
+
+// The distance is measured between the origin and the intersection of the ray
+// with the reference box of the containing block.
+// Note: |aOrigin| and |aContaingBlock| should be in the same coordinate system
+// (i.e. the nsIFrame::mRect of the containing block).
+// https://drafts.fxtf.org/motion-1/#size-sides
+static CSSCoord ComputeSides(const CSSPoint& aOrigin,
+                             const CSSRect& aContainingBlock,
+                             const StyleAngle& aAngle) {
+  const CSSPoint& topLeft = aContainingBlock.TopLeft();
+  // Given an acute angle |theta| (i.e. |t|) of a right-angled triangle, the
+  // hypotenuse |h| is the side that connects the two acute angles. The side
+  // |b| adjacent to |theta| is the side of the triangle that connects |theta|
+  // to the right angle.
+  //
+  // e.g. if the angle |t| is 0 ~ 90 degrees, and b * tan(theta) <= b',
+  //      h = b / cos(t):
+  //                       b*tan(t)
+  //    (topLeft) #--------*-----*--# (aContainingBlock.XMost(), topLeft.y)
+  //              |        |    /   |
+  //              |        |   /    |
+  //              |        b  h     |
+  //              |        |t/      |
+  //              |        |/       |
+  //             (aOrigin) *---b'---* (aContainingBlock.XMost(), aOrigin.y)
+  //              |        |        |
+  //              |        |        |
+  //              |        |        |
+  //              |        |        |
+  //              |        |        |
+  //              #-----------------# (aContainingBlock.XMost(),
+  //        (topLeft.x,                aContainingBlock.YMost())
+  //         aContainingBlock.YMost())
+  const double theta = aAngle.ToRadians();
+  double sint = std::sin(theta);
+  double cost = std::cos(theta);
+
+  const double b = cost >= 0 ? aOrigin.y.value - topLeft.y
+                             : aContainingBlock.YMost() - aOrigin.y.value;
+  const double bPrime = sint >= 0 ? aContainingBlock.XMost() - aOrigin.x.value
+                                  : aOrigin.x.value - topLeft.x;
+  sint = std::fabs(sint);
+  cost = std::fabs(cost);
+
+  // The trigonometric formula here doesn't work well if |theta| is 0deg or
+  // 90deg, so we handle these edge cases first.
+  if (sint < std::numeric_limits<double>::epsilon()) {
+    // For 0deg (or 180deg), we use |b| directly.
+    return static_cast<float>(b);
+  }
+
+  if (cost < std::numeric_limits<double>::epsilon()) {
+    // For 90deg (or 270deg), we use |bPrime| directly. This can also avoid 0/0
+    // if both |b| and |cost| are 0.0. (i.e. b / cost).
+    return static_cast<float>(bPrime);
+  }
+
+  // Note: The following formula works well only when 0 < theta < 90deg. So we
+  // handle 0deg and 90deg above first.
+  //
+  // If |b * tan(theta)| is larger than |bPrime|, the intersection is
+  // on the other side, and |b'| is the opposite side of angle |theta| in this
+  // case.
+  //
+  // e.g. If b * tan(theta) > b', h = b' / sin(theta):
+  //   *----*
+  //   |    |
+  //   |   /|
+  //   b  /t|
+  //   |t/  |
+  //   |/   |
+  //   *-b'-*
+  if (b * sint > bPrime * cost) {
+    return bPrime / sint;
+  }
+  return b / cost;
+}
+
+// Compute the position of "at <position>" together with offset starting
+// position (i.e. offset-position).
+static nsPoint ComputePosition(const StylePositionOrAuto& aAtPosition,
+                               const StyleOffsetPosition& aOffsetPosition,
+                               const nsRect& aCoordBox,
+                               const nsPoint& aCurrentCoord) {
+  if (aAtPosition.IsPosition()) {
+    // Resolve this by using the <position> to position a 0x0 object area within
+    // the box’s containing block.
+    return ShapeUtils::ComputePosition(aAtPosition.AsPosition(), aCoordBox);
+  }
+
+  MOZ_ASSERT(aAtPosition.IsAuto(), "\"at <position>\" should be omitted");
+
+  // Use the offset starting position of the element, given by offset-position.
+  // https://drafts.fxtf.org/motion-1/#valdef-ray-at-position
+  if (aOffsetPosition.IsPosition()) {
+    return ShapeUtils::ComputePosition(aOffsetPosition.AsPosition(), aCoordBox);
+  }
+
+  if (aOffsetPosition.IsNormal()) {
+    // If the element doesn’t have an offset starting position either, it
+    // behaves as at center.
+    const StylePosition& center = StylePosition::FromPercentage(0.5);
+    return ShapeUtils::ComputePosition(center, aCoordBox);
+  }
+
+  MOZ_ASSERT(aOffsetPosition.IsAuto());
+  return aCurrentCoord;
+}
+
+static CSSCoord ComputeRayPathLength(const StyleRaySize aRaySizeType,
+                                     const StyleAngle& aAngle,
+                                     const CSSPoint& aOrigin,
+                                     const CSSRect& aContainingBlock) {
+  if (aRaySizeType == StyleRaySize::Sides) {
+    // If the initial position is not within the box, the distance is 0.
+    //
+    // Note: If the origin is at XMost() (and/or YMost()), we should consider it
+    // to be inside containing block (because we expect 100% x (or y) coordinate
+    // is still to be considered inside the containing block.
+    if (!aContainingBlock.ContainsInclusively(aOrigin)) {
+      return 0.0;
+    }
+
+    return ComputeSides(aOrigin, aContainingBlock, aAngle);
+  }
+
+  // left: the length between the origin and the left side.
+  // right: the length between the origin and the right side.
+  // top: the length between the origin and the top side.
+  // bottom: the lenght between the origin and the bottom side.
+  const CSSPoint& topLeft = aContainingBlock.TopLeft();
+  const CSSCoord left = std::abs(aOrigin.x - topLeft.x);
+  const CSSCoord right = std::abs(aContainingBlock.XMost() - aOrigin.x);
+  const CSSCoord top = std::abs(aOrigin.y - topLeft.y);
+  const CSSCoord bottom = std::abs(aContainingBlock.YMost() - aOrigin.y);
+
+  switch (aRaySizeType) {
+    case StyleRaySize::ClosestSide:
+      return std::min({left, right, top, bottom});
+
+    case StyleRaySize::FarthestSide:
+      return std::max({left, right, top, bottom});
+
+    case StyleRaySize::ClosestCorner:
+    case StyleRaySize::FarthestCorner: {
+      CSSCoord h = 0;
+      CSSCoord v = 0;
+      if (aRaySizeType == StyleRaySize::ClosestCorner) {
+        h = std::min(left, right);
+        v = std::min(top, bottom);
+      } else {
+        h = std::max(left, right);
+        v = std::max(top, bottom);
+      }
+      return sqrt(h.value * h.value + v.value * v.value);
+    }
+    case StyleRaySize::Sides:
+      MOZ_ASSERT_UNREACHABLE("Unsupported ray size");
+  }
+
+  return 0.0;
+}
+
+static CSSCoord ComputeRayUsedDistance(
+    const StyleRayFunction& aRay, const LengthPercentage& aDistance,
+    const CSSCoord& aPathLength, const CSSCoord& aRayContainReferenceLength) {
+  CSSCoord usedDistance = aDistance.ResolveToCSSPixels(aPathLength);
+  if (!aRay.contain) {
+    return usedDistance;
+  }
+
+  // The length of the offset path is reduced so that the element stays within
+  // the containing block even at offset-distance: 100%. Specifically, the
+  // path’s length is reduced by half the width or half the height of the
+  // element’s border box, whichever is larger, and floored at zero.
+  // https://drafts.fxtf.org/motion-1/#valdef-ray-contain
+  return std::max((usedDistance - aRayContainReferenceLength / 2.0f).value,
+                  0.0f);
+}
+
+/* static */
+Maybe<ResolvedMotionPathData> MotionPathUtils::ResolveMotionPath(
+    const OffsetPathData& aPath, const LengthPercentage& aDistance,
+    const StyleOffsetRotate& aRotate, const StylePositionOrAuto& aAnchor,
+    const StyleOffsetPosition& aPosition, const CSSPoint& aTransformOrigin,
+    TransformReferenceBox& aRefBox, const CSSPoint& aAnchorPointAdjustment) {
+  if (aPath.IsNone()) {
+    return Nothing();
+  }
+
+  // Compute the point and angle for creating the equivalent translate and
+  // rotate.
+  double directionAngle = 0.0;
+  gfx::Point point;
+  if (aPath.IsShape()) {
+    const auto& data = aPath.AsShape();
+    RefPtr<gfx::Path> path = data.mGfxPath;
+    MOZ_ASSERT(path, "The empty path is not allowed");
+
+    // Per the spec, we have to convert offset distance to pixels, with 100%
+    // being converted to total length. So here |gfxPath| is built with CSS
+    // pixel, and we calculate |pathLength| and |computedDistance| with CSS
+    // pixel as well.
+    gfx::Float pathLength = path->ComputeLength();
+    gfx::Float usedDistance =
+        aDistance.ResolveToCSSPixels(CSSCoord(pathLength));
+    if (data.mIsClosedLoop) {
+      // Per the spec, let used offset distance be equal to offset distance
+      // modulus the total length of the path. If the total length of the path
+      // is 0, used offset distance is also 0.
+      usedDistance = pathLength > 0.0 ? fmod(usedDistance, pathLength) : 0.0;
+      // We make sure |usedDistance| is 0.0 or a positive value.
+      if (usedDistance < 0.0) {
+        usedDistance += pathLength;
+      }
+    } else {
+      // Per the spec, for unclosed interval, let used offset distance be equal
+      // to offset distance clamped by 0 and the total length of the path.
+      usedDistance = clamped(usedDistance, 0.0f, pathLength);
+    }
+    gfx::Point tangent;
+    point = path->ComputePointAtLength(usedDistance, &tangent);
+    // Basically, |point| should be a relative distance between the current
+    // position and the target position. The built |path| is in the coordinate
+    // system of its containing block. Therefore, we have to take the current
+    // position of this box into account to offset the translation so it's final
+    // position is not affected by other boxes in the same containing block.
+    point -= NSPointToPoint(data.mCurrentPosition, AppUnitsPerCSSPixel());
+    directionAngle = atan2((double)tangent.y, (double)tangent.x);  // in Radian.
+  } else if (aPath.IsRay()) {
+    const auto& ray = aPath.AsRay();
+    MOZ_ASSERT(ray.mRay);
+
+    // Compute the origin, where the ray’s line begins (the 0% position).
+    // https://drafts.fxtf.org/motion-1/#ray-origin
+    const CSSPoint origin = CSSPoint::FromAppUnits(ComputePosition(
+        ray.mRay->position, aPosition, ray.mCoordBox, ray.mCurrentPosition));
+    const CSSCoord pathLength =
+        ComputeRayPathLength(ray.mRay->size, ray.mRay->angle, origin,
+                             CSSRect::FromAppUnits(ray.mCoordBox));
+    const CSSCoord usedDistance = ComputeRayUsedDistance(
+        *ray.mRay, aDistance, pathLength, ray.mContainReferenceLength);
+
+    // 0deg pointing up and positive angles representing clockwise rotation.
+    directionAngle =
+        StyleAngle{ray.mRay->angle.ToDegrees() - 90.0f}.ToRadians();
+
+    // The vector from the current position of this box to the origin of this
+    // polar coordinate system.
+    const gfx::Point vectorToOrigin =
+        (origin - CSSPoint::FromAppUnits(ray.mCurrentPosition))
+            .ToUnknownPoint();
+    // |vectorToOrigin| + The vector from the origin to this polar coordinate,
+    // (|usedDistance|, |directionAngle|), i.e. the vector from the current
+    // position to this polar coordinate.
+    point =
+        vectorToOrigin +
+        gfx::Point(usedDistance * static_cast<gfx::Float>(cos(directionAngle)),
+                   usedDistance * static_cast<gfx::Float>(sin(directionAngle)));
+  } else {
+    MOZ_ASSERT_UNREACHABLE("Unsupported offset-path value");
+    return Nothing();
+  }
+
+  // If |rotate.auto_| is true, the element should be rotated by the angle of
+  // the direction (i.e. directional tangent vector) of the offset-path, and the
+  // computed value of <angle> is added to this.
+  // Otherwise, the element has a constant clockwise rotation transformation
+  // applied to it by the specified rotation angle. (i.e. Don't need to
+  // consider the direction of the path.)
+  gfx::Float angle = static_cast<gfx::Float>(
+      (aRotate.auto_ ? directionAngle : 0.0) + aRotate.angle.ToRadians());
+
+  // Compute the offset for motion path translate.
+  // Bug 1559232: the translate parameters will be adjusted more after we
+  // support offset-position.
+  // Per the spec, the default offset-anchor is `auto`, so initialize the anchor
+  // point to transform-origin.
+  CSSPoint anchorPoint(aTransformOrigin);
+  gfx::Point shift;
+  if (!aAnchor.IsAuto()) {
+    const auto& pos = aAnchor.AsPosition();
+    anchorPoint = nsStyleTransformMatrix::Convert2DPosition(
+        pos.horizontal, pos.vertical, aRefBox);
+    // We need this value to shift the origin from transform-origin to
+    // offset-anchor (and vice versa).
+    // See nsStyleTransformMatrix::ReadTransform for more details.
+    shift = (anchorPoint - aTransformOrigin).ToUnknownPoint();
+  }
+
+  anchorPoint += aAnchorPointAdjustment;
+
+  return Some(ResolvedMotionPathData{point - anchorPoint.ToUnknownPoint(),
+                                     angle, shift});
+}
+
+static inline bool IsClosedLoop(const StyleSVGPathData& aPathData) {
+  return !aPathData._0.AsSpan().empty() &&
+         aPathData._0.AsSpan().rbegin()->IsClosePath();
+}
+
+// Create a path for "inset(0 round X)", where X is the value of border-radius
+// on the element that establishes the containing block for this element.
+static already_AddRefed<gfx::Path> BuildSimpleInsetPath(
+    const StyleBorderRadius& aBorderRadius, const nsRect& aCoordBox,
+    gfx::PathBuilder* aPathBuilder) {
+  if (!aPathBuilder) {
+    return nullptr;
+  }
+
+  const nsRect insetRect = ShapeUtils::ComputeInsetRect(
+      StyleRect<LengthPercentage>::WithAllSides(LengthPercentage::Zero()),
+      aCoordBox);
+  nscoord radii[8];
+  const bool hasRadii =
+      ShapeUtils::ComputeRectRadii(aBorderRadius, aCoordBox, insetRect, radii);
+  return ShapeUtils::BuildRectPath(insetRect, hasRadii ? radii : nullptr,
+                                   aCoordBox, AppUnitsPerCSSPixel(),
+                                   aPathBuilder);
+}
+
+// Create a path for `path("m 0 0")`, which is the default URL path if we cannot
+// resolve a SVG shape element.
+// https://drafts.fxtf.org/motion-1/#valdef-offset-path-url
+static already_AddRefed<gfx::Path> BuildDefaultPathForURL(
+    gfx::PathBuilder* aBuilder) {
+  if (!aBuilder) {
+    return nullptr;
+  }
+
+  Array<const StylePathCommand, 1> array(StylePathCommand::MoveTo(
+      StyleCoordPair(gfx::Point{0.0, 0.0}), StyleIsAbsolute::No));
+  return SVGPathData::BuildPath(array, aBuilder, StyleStrokeLinecap::Butt, 0.0);
+}
+
+// Generate data for motion path on the main thread.
+static OffsetPathData GenerateOffsetPathData(const nsIFrame* aFrame) {
+  const StyleOffsetPath& offsetPath = aFrame->StyleDisplay()->mOffsetPath;
+  if (offsetPath.IsNone()) {
+    return OffsetPathData::None();
+  }
+
+  // Handle ray().
+  if (offsetPath.IsRay()) {
+    nsRect coordBox;
+    const nsIFrame* containingBlockFrame =
+        MotionPathUtils::GetOffsetPathReferenceBox(aFrame, coordBox);
+    return !containingBlockFrame
+               ? OffsetPathData::None()
+               : OffsetPathData::Ray(
+                     offsetPath.AsRay(), std::move(coordBox),
+                     aFrame->GetOffsetTo(containingBlockFrame),
+                     MotionPathUtils::GetRayContainReferenceSize(
+                         const_cast<nsIFrame*>(aFrame)));
+  }
+
+  // Handle path(). We cache it so we handle it separately.
+  // FIXME: Bug 1837042, cache gfx::Path for shapes other than path(). Once we
+  // cache all basic shapes, we can merge this branch into other basic shapes.
+  if (offsetPath.IsPath()) {
+    const StyleSVGPathData& pathData = offsetPath.AsSVGPathData();
+    RefPtr<gfx::Path> gfxPath =
+        aFrame->GetProperty(nsIFrame::OffsetPathCache());
+    MOZ_ASSERT(gfxPath || pathData._0.IsEmpty(),
+               "Should have a valid cached gfx::Path or an empty path string");
+    // FIXME: Bug 1836847. Once we support "at <position>" for path(), we have
+    // to give it the current box position.
+    return OffsetPathData::Shape(gfxPath.forget(), {}, IsClosedLoop(pathData));
+  }
+
+  nsRect coordBox;
+  const nsIFrame* containingFrame =
+      MotionPathUtils::GetOffsetPathReferenceBox(aFrame, coordBox);
+  if (!containingFrame || coordBox.IsEmpty()) {
+    return OffsetPathData::None();
+  }
+  nsPoint currentPosition = aFrame->GetOffsetTo(containingFrame);
+  RefPtr<gfx::PathBuilder> builder = MotionPathUtils::GetPathBuilder();
+
+  if (offsetPath.IsUrl()) {
+    dom::SVGGeometryElement* element =
+        SVGObserverUtils::GetAndObserveGeometry(const_cast<nsIFrame*>(aFrame));
+    if (!element) {
+      // Note: This behaves as path("m 0 0") (a <basic-shape>).
+      RefPtr<gfx::Path> path = BuildDefaultPathForURL(builder);
+      // FIXME: Bug 1836847. Once we support "at <position>" for path(), we have
+      // to give it the current box position.
+      return path ? OffsetPathData::Shape(path.forget(), {}, false)
+                  : OffsetPathData::None();
+    }
+
+    // We just need this path to calculate the specific point and direction
+    // angle, so use measuring function and get the benefit of caching the path
+    // in the SVG shape element.
+    RefPtr<gfx::Path> path = element->GetOrBuildPathForMeasuring();
+
+    // The built |path| from SVG shape element doesn't take |coordBox| into
+    // account. It uses the SVG viewport as its coordinate system. So after
+    // mapping it into the CSS layout, we should use |coordBox| as its viewport
+    // and user coordinate system. |currentPosition| is based on the border-box
+    // of the containing block. Therefore, we have to apply an extra translation
+    // to put it at the correct position based on |coordBox|.
+    //
+    // Note: we reuse |OffsetPathData::ShapeData::mCurrentPosition| to include
+    // this extra translation, so we don't have to add an extra field.
+    nsPoint positionInCoordBox = currentPosition - coordBox.TopLeft();
+    return path ? OffsetPathData::Shape(path.forget(),
+                                        std::move(positionInCoordBox),
+                                        element->IsClosedLoop())
+                : OffsetPathData::None();
+  }
+
+  // The rest part is to handle "<basic-shape> || <coord-box>".
+  MOZ_ASSERT(offsetPath.IsBasicShapeOrCoordBox());
+
+  const nsStyleDisplay* disp = aFrame->StyleDisplay();
+  RefPtr<gfx::Path> path =
+      disp->mOffsetPath.IsCoordBox()
+          ? BuildSimpleInsetPath(containingFrame->StyleBorder()->mBorderRadius,
+                                 coordBox, builder)
+          : MotionPathUtils::BuildPath(
+                disp->mOffsetPath.AsOffsetPath().path->AsShape(),
+                disp->mOffsetPosition, coordBox, currentPosition, builder);
+  return path ? OffsetPathData::Shape(path.forget(), std::move(currentPosition),
+                                      true)
+              : OffsetPathData::None();
+}
+
+/* static*/
+Maybe<ResolvedMotionPathData> MotionPathUtils::ResolveMotionPath(
+    const nsIFrame* aFrame, TransformReferenceBox& aRefBox) {
+  MOZ_ASSERT(aFrame);
+
+  const nsStyleDisplay* display = aFrame->StyleDisplay();
+
+  // FIXME: It's possible to refactor the calculation of transform-origin, so we
+  // could calculate from the caller, and reuse the value in nsDisplayList.cpp.
+  CSSPoint transformOrigin = nsStyleTransformMatrix::Convert2DPosition(
+      display->mTransformOrigin.horizontal, display->mTransformOrigin.vertical,
+      aRefBox);
+
+  return ResolveMotionPath(
+      GenerateOffsetPathData(aFrame), display->mOffsetDistance,
+      display->mOffsetRotate, display->mOffsetAnchor, display->mOffsetPosition,
+      transformOrigin, aRefBox, ComputeAnchorPointAdjustment(*aFrame));
+}
+
+// Generate data for motion path on the compositor thread.
+static OffsetPathData GenerateOffsetPathData(
+    const StyleOffsetPath& aOffsetPath,
+    const StyleOffsetPosition& aOffsetPosition,
+    const layers::MotionPathData& aMotionPathData,
+    gfx::Path* aCachedMotionPath) {
+  if (aOffsetPath.IsNone()) {
+    return OffsetPathData::None();
+  }
+
+  // Handle ray().
+  if (aOffsetPath.IsRay()) {
+    return aMotionPathData.coordBox().IsEmpty()
+               ? OffsetPathData::None()
+               : OffsetPathData::Ray(
+                     aOffsetPath.AsRay(), aMotionPathData.coordBox(),
+                     aMotionPathData.currentPosition(),
+                     aMotionPathData.rayContainReferenceLength());
+  }
+
+  // Handle path().
+  // FIXME: Bug 1837042, cache gfx::Path for shapes other than path().
+  if (aOffsetPath.IsPath()) {
+    const StyleSVGPathData& pathData = aOffsetPath.AsSVGPathData();
+    // If aCachedMotionPath is valid, we have a fixed path.
+    // This means we have pre-built it already and no need to update.
+    RefPtr<gfx::Path> path = aCachedMotionPath;
+    if (!path) {
+      RefPtr<gfx::PathBuilder> builder =
+          MotionPathUtils::GetCompositorPathBuilder();
+      path = MotionPathUtils::BuildSVGPath(pathData, builder);
+    }
+    // FIXME: Bug 1836847. Once we support "at <position>" for path(), we have
+    // to give it the current box position.
+    return OffsetPathData::Shape(path.forget(), {}, IsClosedLoop(pathData));
+  }
+
+  // The rest part is to handle "<basic-shape> || <coord-box>".
+  MOZ_ASSERT(aOffsetPath.IsBasicShapeOrCoordBox());
+
+  const nsRect& coordBox = aMotionPathData.coordBox();
+  if (coordBox.IsEmpty()) {
+    return OffsetPathData::None();
+  }
+
+  RefPtr<gfx::PathBuilder> builder =
+      MotionPathUtils::GetCompositorPathBuilder();
+  if (!builder) {
+    return OffsetPathData::None();
+  }
+
+  RefPtr<gfx::Path> path;
+  if (aOffsetPath.IsCoordBox()) {
+    const nsRect insetRect = ShapeUtils::ComputeInsetRect(
+        StyleRect<LengthPercentage>::WithAllSides(LengthPercentage::Zero()),
+        coordBox);
+    const nsTArray<nscoord>& radii = aMotionPathData.coordBoxInsetRadii();
+    path = ShapeUtils::BuildRectPath(
+        insetRect, radii.IsEmpty() ? nullptr : radii.Elements(), coordBox,
+        AppUnitsPerCSSPixel(), builder);
+  } else {
+    path = MotionPathUtils::BuildPath(
+        aOffsetPath.AsOffsetPath().path->AsShape(), aOffsetPosition, coordBox,
+        aMotionPathData.currentPosition(), builder);
+  }
+
+  return path ? OffsetPathData::Shape(
+                    path.forget(), nsPoint(aMotionPathData.currentPosition()),
+                    true)
+              : OffsetPathData::None();
+}
+
+/* static */
+Maybe<ResolvedMotionPathData> MotionPathUtils::ResolveMotionPath(
+    const StyleOffsetPath* aPath, const StyleLengthPercentage* aDistance,
+    const StyleOffsetRotate* aRotate, const StylePositionOrAuto* aAnchor,
+    const StyleOffsetPosition* aPosition,
+    const Maybe<layers::MotionPathData>& aMotionPathData,
+    TransformReferenceBox& aRefBox, gfx::Path* aCachedMotionPath) {
+  if (!aPath) {
+    return Nothing();
+  }
+
+  MOZ_ASSERT(aMotionPathData);
+
+  auto zeroOffsetDistance = LengthPercentage::Zero();
+  auto autoOffsetRotate = StyleOffsetRotate{true, StyleAngle::Zero()};
+  auto autoOffsetAnchor = StylePositionOrAuto::Auto();
+  auto autoOffsetPosition = StyleOffsetPosition::Auto();
+  return ResolveMotionPath(
+      GenerateOffsetPathData(*aPath,
+                             aPosition ? *aPosition : autoOffsetPosition,
+                             *aMotionPathData, aCachedMotionPath),
+      aDistance ? *aDistance : zeroOffsetDistance,
+      aRotate ? *aRotate : autoOffsetRotate,
+      aAnchor ? *aAnchor : autoOffsetAnchor,
+      aPosition ? *aPosition : autoOffsetPosition, aMotionPathData->origin(),
+      aRefBox, aMotionPathData->anchorAdjustment());
+}
+
+/* static */
+already_AddRefed<gfx::Path> MotionPathUtils::BuildSVGPath(
+    const StyleSVGPathData& aPath, gfx::PathBuilder* aPathBuilder) {
+  if (!aPathBuilder) {
+    return nullptr;
+  }
+
+  const Span<const StylePathCommand>& path = aPath._0.AsSpan();
+  return SVGPathData::BuildPath(path, aPathBuilder, StyleStrokeLinecap::Butt,
+                                0.0);
+}
+
+/* static */
+already_AddRefed<gfx::Path> MotionPathUtils::BuildPath(
+    const StyleBasicShape& aBasicShape,
+    const StyleOffsetPosition& aOffsetPosition, const nsRect& aCoordBox,
+    const nsPoint& aCurrentPosition, gfx::PathBuilder* aPathBuilder) {
+  if (!aPathBuilder) {
+    return nullptr;
+  }
+
+  switch (aBasicShape.tag) {
+    case StyleBasicShape::Tag::Circle: {
+      const nsPoint center =
+          ComputePosition(aBasicShape.AsCircle().position, aOffsetPosition,
+                          aCoordBox, aCurrentPosition);
+      return ShapeUtils::BuildCirclePath(aBasicShape, aCoordBox, center,
+                                         AppUnitsPerCSSPixel(), aPathBuilder);
+    }
+    case StyleBasicShape::Tag::Ellipse: {
+      const nsPoint center =
+          ComputePosition(aBasicShape.AsEllipse().position, aOffsetPosition,
+                          aCoordBox, aCurrentPosition);
+      return ShapeUtils::BuildEllipsePath(aBasicShape, aCoordBox, center,
+                                          AppUnitsPerCSSPixel(), aPathBuilder);
+    }
+    case StyleBasicShape::Tag::Rect:
+      return ShapeUtils::BuildInsetPath(aBasicShape, aCoordBox,
+                                        AppUnitsPerCSSPixel(), aPathBuilder);
+    case StyleBasicShape::Tag::Polygon:
+      return ShapeUtils::BuildPolygonPath(aBasicShape, aCoordBox,
+                                          AppUnitsPerCSSPixel(), aPathBuilder);
+    case StyleBasicShape::Tag::Path:
+      // FIXME: Bug 1836847. Once we support "at <position>" for path(), we have
+      // to also check its containing block as well. For now, we are still
+      // building its gfx::Path directly by its SVGPathData without other
+      // reference. https://github.com/w3c/fxtf-drafts/issues/504
+      return BuildSVGPath(aBasicShape.AsPath().path, aPathBuilder);
+  }
+
+  return nullptr;
+}
+
+/* static */
+already_AddRefed<gfx::PathBuilder> MotionPathUtils::GetPathBuilder() {
+  // Here we only need to build a valid path for motion path, so
+  // using the default values of stroke-width, stoke-linecap, and fill-rule
+  // is fine for now because what we want is to get the point and its normal
+  // vector along the path, instead of rendering it.
+  RefPtr<gfx::PathBuilder> builder =
+      gfxPlatform::GetPlatform()
+          ->ScreenReferenceDrawTarget()
+          ->CreatePathBuilder(gfx::FillRule::FILL_WINDING);
+  return builder.forget();
+}
+
+/* static */
+already_AddRefed<gfx::PathBuilder> MotionPathUtils::GetCompositorPathBuilder() {
+  // FIXME: Perhaps we need a PathBuilder which is independent on the backend.
+  RefPtr<gfx::PathBuilder> builder =
+      gfxPlatform::Initialized()
+          ? gfxPlatform::GetPlatform()
+                ->ScreenReferenceDrawTarget()
+                ->CreatePathBuilder(gfx::FillRule::FILL_WINDING)
+          : gfx::Factory::CreateSimplePathBuilder();
+  return builder.forget();
+}
+
+}  // namespace mozilla