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, 1299 insertions, 0 deletions

diff --git a/layout/painting/nsCSSRenderingGradients.cpp b/layout/painting/nsCSSRenderingGradients.cpp
new file mode 100644
index 0000000000..f4a859cf34
--- /dev/null
+++ b/layout/painting/nsCSSRenderingGradients.cpp
@@ -0,0 +1,1299 @@
+/* -*- 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/. */
+
+/* utility functions for drawing borders and backgrounds */
+
+#include "nsCSSRenderingGradients.h"
+
+#include <tuple>
+
+#include "gfx2DGlue.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/ComputedStyle.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Helpers.h"
+#include "mozilla/MathAlgorithms.h"
+#include "mozilla/ProfilerLabels.h"
+
+#include "nsLayoutUtils.h"
+#include "nsStyleConsts.h"
+#include "nsPresContext.h"
+#include "nsPoint.h"
+#include "nsRect.h"
+#include "nsCSSColorUtils.h"
+#include "gfxContext.h"
+#include "nsStyleStructInlines.h"
+#include "nsCSSProps.h"
+#include "gfxUtils.h"
+#include "gfxGradientCache.h"
+
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/webrender/WebRenderTypes.h"
+#include "mozilla/webrender/WebRenderAPI.h"
+#include "Units.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+
+static CSSPoint ResolvePosition(const Position& aPos, const CSSSize& aSize) {
+  CSSCoord h = aPos.horizontal.ResolveToCSSPixels(aSize.width);
+  CSSCoord v = aPos.vertical.ResolveToCSSPixels(aSize.height);
+  return CSSPoint(h, v);
+}
+
+// Given a box with size aBoxSize and origin (0,0), and an angle aAngle,
+// and a starting point for the gradient line aStart, find the endpoint of
+// the gradient line --- the intersection of the gradient line with a line
+// perpendicular to aAngle that passes through the farthest corner in the
+// direction aAngle.
+static CSSPoint ComputeGradientLineEndFromAngle(const CSSPoint& aStart,
+                                                double aAngle,
+                                                const CSSSize& aBoxSize) {
+  double dx = cos(-aAngle);
+  double dy = sin(-aAngle);
+  CSSPoint farthestCorner(dx > 0 ? aBoxSize.width : 0,
+                          dy > 0 ? aBoxSize.height : 0);
+  CSSPoint delta = farthestCorner - aStart;
+  double u = delta.x * dy - delta.y * dx;
+  return farthestCorner + CSSPoint(-u * dy, u * dx);
+}
+
+// Compute the start and end points of the gradient line for a linear gradient.
+static std::tuple<CSSPoint, CSSPoint> ComputeLinearGradientLine(
+    nsPresContext* aPresContext, const StyleGradient& aGradient,
+    const CSSSize& aBoxSize) {
+  using X = StyleHorizontalPositionKeyword;
+  using Y = StyleVerticalPositionKeyword;
+
+  const StyleLineDirection& direction = aGradient.AsLinear().direction;
+  const bool isModern =
+      aGradient.AsLinear().compat_mode == StyleGradientCompatMode::Modern;
+
+  CSSPoint center(aBoxSize.width / 2, aBoxSize.height / 2);
+  switch (direction.tag) {
+    case StyleLineDirection::Tag::Angle: {
+      double angle = direction.AsAngle().ToRadians();
+      if (isModern) {
+        angle = M_PI_2 - angle;
+      }
+      CSSPoint end = ComputeGradientLineEndFromAngle(center, angle, aBoxSize);
+      CSSPoint start = CSSPoint(aBoxSize.width, aBoxSize.height) - end;
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Vertical: {
+      CSSPoint start(center.x, 0);
+      CSSPoint end(center.x, aBoxSize.height);
+      if (isModern == (direction.AsVertical() == Y::Top)) {
+        std::swap(start.y, end.y);
+      }
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Horizontal: {
+      CSSPoint start(0, center.y);
+      CSSPoint end(aBoxSize.width, center.y);
+      if (isModern == (direction.AsHorizontal() == X::Left)) {
+        std::swap(start.x, end.x);
+      }
+      return {start, end};
+    }
+    case StyleLineDirection::Tag::Corner: {
+      const auto& corner = direction.AsCorner();
+      const X& h = corner._0;
+      const Y& v = corner._1;
+
+      if (isModern) {
+        float xSign = h == X::Right ? 1.0 : -1.0;
+        float ySign = v == Y::Top ? 1.0 : -1.0;
+        double angle = atan2(ySign * aBoxSize.width, xSign * aBoxSize.height);
+        CSSPoint end = ComputeGradientLineEndFromAngle(center, angle, aBoxSize);
+        CSSPoint start = CSSPoint(aBoxSize.width, aBoxSize.height) - end;
+        return {start, end};
+      }
+
+      CSSCoord startX = h == X::Left ? 0.0 : aBoxSize.width;
+      CSSCoord startY = v == Y::Top ? 0.0 : aBoxSize.height;
+
+      CSSPoint start(startX, startY);
+      CSSPoint end = CSSPoint(aBoxSize.width, aBoxSize.height) - start;
+      return {start, end};
+    }
+    default:
+      break;
+  }
+  MOZ_ASSERT_UNREACHABLE("Unknown line direction");
+  return {CSSPoint(), CSSPoint()};
+}
+
+using EndingShape = StyleGenericEndingShape<Length, LengthPercentage>;
+using RadialGradientRadii =
+    Variant<StyleShapeExtent, std::pair<CSSCoord, CSSCoord>>;
+
+static RadialGradientRadii ComputeRadialGradientRadii(const EndingShape& aShape,
+                                                      const CSSSize& aSize) {
+  if (aShape.IsCircle()) {
+    auto& circle = aShape.AsCircle();
+    if (circle.IsExtent()) {
+      return RadialGradientRadii(circle.AsExtent());
+    }
+    CSSCoord radius = circle.AsRadius().ToCSSPixels();
+    return RadialGradientRadii(std::make_pair(radius, radius));
+  }
+  auto& ellipse = aShape.AsEllipse();
+  if (ellipse.IsExtent()) {
+    return RadialGradientRadii(ellipse.AsExtent());
+  }
+
+  auto& radii = ellipse.AsRadii();
+  return RadialGradientRadii(
+      std::make_pair(radii._0.ResolveToCSSPixels(aSize.width),
+                     radii._1.ResolveToCSSPixels(aSize.height)));
+}
+
+// Compute the start and end points of the gradient line for a radial gradient.
+// Also returns the horizontal and vertical radii defining the circle or
+// ellipse to use.
+static std::tuple<CSSPoint, CSSPoint, CSSCoord, CSSCoord>
+ComputeRadialGradientLine(const StyleGradient& aGradient,
+                          const CSSSize& aBoxSize) {
+  const auto& radial = aGradient.AsRadial();
+  const EndingShape& endingShape = radial.shape;
+  const Position& position = radial.position;
+  CSSPoint start = ResolvePosition(position, aBoxSize);
+
+  // Compute gradient shape: the x and y radii of an ellipse.
+  CSSCoord radiusX, radiusY;
+  CSSCoord leftDistance = Abs(start.x);
+  CSSCoord rightDistance = Abs(aBoxSize.width - start.x);
+  CSSCoord topDistance = Abs(start.y);
+  CSSCoord bottomDistance = Abs(aBoxSize.height - start.y);
+
+  auto radii = ComputeRadialGradientRadii(endingShape, aBoxSize);
+  if (radii.is<StyleShapeExtent>()) {
+    switch (radii.as<StyleShapeExtent>()) {
+      case StyleShapeExtent::ClosestSide:
+        radiusX = std::min(leftDistance, rightDistance);
+        radiusY = std::min(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = std::min(radiusX, radiusY);
+        }
+        break;
+      case StyleShapeExtent::ClosestCorner: {
+        // Compute x and y distances to nearest corner
+        CSSCoord offsetX = std::min(leftDistance, rightDistance);
+        CSSCoord offsetY = std::min(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = NS_hypot(offsetX, offsetY);
+        } else {
+          // maintain aspect ratio
+          radiusX = offsetX * M_SQRT2;
+          radiusY = offsetY * M_SQRT2;
+        }
+        break;
+      }
+      case StyleShapeExtent::FarthestSide:
+        radiusX = std::max(leftDistance, rightDistance);
+        radiusY = std::max(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = std::max(radiusX, radiusY);
+        }
+        break;
+      case StyleShapeExtent::FarthestCorner: {
+        // Compute x and y distances to nearest corner
+        CSSCoord offsetX = std::max(leftDistance, rightDistance);
+        CSSCoord offsetY = std::max(topDistance, bottomDistance);
+        if (endingShape.IsCircle()) {
+          radiusX = radiusY = NS_hypot(offsetX, offsetY);
+        } else {
+          // maintain aspect ratio
+          radiusX = offsetX * M_SQRT2;
+          radiusY = offsetY * M_SQRT2;
+        }
+        break;
+      }
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unknown shape extent keyword?");
+        radiusX = radiusY = 0;
+    }
+  } else {
+    auto pair = radii.as<std::pair<CSSCoord, CSSCoord>>();
+    radiusX = pair.first;
+    radiusY = pair.second;
+  }
+
+  // The gradient line end point is where the gradient line intersects
+  // the ellipse.
+  CSSPoint end = start + CSSPoint(radiusX, 0);
+  return {start, end, radiusX, radiusY};
+}
+
+// Compute the center and the start angle of the conic gradient.
+static std::tuple<CSSPoint, float> ComputeConicGradientProperties(
+    const StyleGradient& aGradient, const CSSSize& aBoxSize) {
+  const auto& conic = aGradient.AsConic();
+  const Position& position = conic.position;
+  float angle = static_cast<float>(conic.angle.ToRadians());
+  CSSPoint center = ResolvePosition(position, aBoxSize);
+
+  return {center, angle};
+}
+
+static float Interpolate(float aF1, float aF2, float aFrac) {
+  return aF1 + aFrac * (aF2 - aF1);
+}
+
+static StyleAbsoluteColor Interpolate(const StyleAbsoluteColor& aLeft,
+                                      const StyleAbsoluteColor& aRight,
+                                      float aFrac) {
+  // NOTE: This has to match the interpolation method that WebRender uses which
+  // right now is sRGB. In the future we should implement interpolation in more
+  // gradient color-spaces.
+  static constexpr auto kMethod = StyleColorInterpolationMethod{
+      StyleColorSpace::Srgb,
+      StyleHueInterpolationMethod::Shorter,
+  };
+  return Servo_InterpolateColor(kMethod, &aRight, &aLeft, aFrac);
+}
+
+static nscoord FindTileStart(nscoord aDirtyCoord, nscoord aTilePos,
+                             nscoord aTileDim) {
+  NS_ASSERTION(aTileDim > 0, "Non-positive tile dimension");
+  double multiples = floor(double(aDirtyCoord - aTilePos) / aTileDim);
+  return NSToCoordRound(multiples * aTileDim + aTilePos);
+}
+
+static gfxFloat LinearGradientStopPositionForPoint(
+    const gfxPoint& aGradientStart, const gfxPoint& aGradientEnd,
+    const gfxPoint& aPoint) {
+  gfxPoint d = aGradientEnd - aGradientStart;
+  gfxPoint p = aPoint - aGradientStart;
+  /**
+   * Compute a parameter t such that a line perpendicular to the
+   * d vector, passing through aGradientStart + d*t, also
+   * passes through aPoint.
+   *
+   * t is given by
+   *   (p.x - d.x*t)*d.x + (p.y - d.y*t)*d.y = 0
+   *
+   * Solving for t we get
+   *   numerator = d.x*p.x + d.y*p.y
+   *   denominator = d.x^2 + d.y^2
+   *   t = numerator/denominator
+   *
+   * In nsCSSRendering::PaintGradient we know the length of d
+   * is not zero.
+   */
+  double numerator = d.x.value * p.x.value + d.y.value * p.y.value;
+  double denominator = d.x.value * d.x.value + d.y.value * d.y.value;
+  return numerator / denominator;
+}
+
+static bool RectIsBeyondLinearGradientEdge(const gfxRect& aRect,
+                                           const gfxMatrix& aPatternMatrix,
+                                           const nsTArray<ColorStop>& aStops,
+                                           const gfxPoint& aGradientStart,
+                                           const gfxPoint& aGradientEnd,
+                                           StyleAbsoluteColor* aOutEdgeColor) {
+  gfxFloat topLeft = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.TopLeft()));
+  gfxFloat topRight = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.TopRight()));
+  gfxFloat bottomLeft = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.BottomLeft()));
+  gfxFloat bottomRight = LinearGradientStopPositionForPoint(
+      aGradientStart, aGradientEnd,
+      aPatternMatrix.TransformPoint(aRect.BottomRight()));
+
+  const ColorStop& firstStop = aStops[0];
+  if (topLeft < firstStop.mPosition && topRight < firstStop.mPosition &&
+      bottomLeft < firstStop.mPosition && bottomRight < firstStop.mPosition) {
+    *aOutEdgeColor = firstStop.mColor;
+    return true;
+  }
+
+  const ColorStop& lastStop = aStops.LastElement();
+  if (topLeft >= lastStop.mPosition && topRight >= lastStop.mPosition &&
+      bottomLeft >= lastStop.mPosition && bottomRight >= lastStop.mPosition) {
+    *aOutEdgeColor = lastStop.mColor;
+    return true;
+  }
+
+  return false;
+}
+
+static void ResolveMidpoints(nsTArray<ColorStop>& stops) {
+  for (size_t x = 1; x < stops.Length() - 1;) {
+    if (!stops[x].mIsMidpoint) {
+      x++;
+      continue;
+    }
+
+    const auto& color1 = stops[x - 1].mColor;
+    const auto& color2 = stops[x + 1].mColor;
+    float offset1 = stops[x - 1].mPosition;
+    float offset2 = stops[x + 1].mPosition;
+    float offset = stops[x].mPosition;
+    // check if everything coincides. If so, ignore the midpoint.
+    if (offset - offset1 == offset2 - offset) {
+      stops.RemoveElementAt(x);
+      continue;
+    }
+
+    // Check if we coincide with the left colorstop.
+    if (offset1 == offset) {
+      // Morph the midpoint to a regular stop with the color of the next
+      // color stop.
+      stops[x].mColor = color2;
+      stops[x].mIsMidpoint = false;
+      continue;
+    }
+
+    // Check if we coincide with the right colorstop.
+    if (offset2 == offset) {
+      // Morph the midpoint to a regular stop with the color of the previous
+      // color stop.
+      stops[x].mColor = color1;
+      stops[x].mIsMidpoint = false;
+      continue;
+    }
+
+    float midpoint = (offset - offset1) / (offset2 - offset1);
+    ColorStop newStops[9];
+    if (midpoint > .5f) {
+      for (size_t y = 0; y < 7; y++) {
+        newStops[y].mPosition = offset1 + (offset - offset1) * (7 + y) / 13;
+      }
+
+      newStops[7].mPosition = offset + (offset2 - offset) / 3;
+      newStops[8].mPosition = offset + (offset2 - offset) * 2 / 3;
+    } else {
+      newStops[0].mPosition = offset1 + (offset - offset1) / 3;
+      newStops[1].mPosition = offset1 + (offset - offset1) * 2 / 3;
+
+      for (size_t y = 0; y < 7; y++) {
+        newStops[y + 2].mPosition = offset + (offset2 - offset) * y / 13;
+      }
+    }
+    // calculate colors
+
+    for (auto& newStop : newStops) {
+      // Calculate the intermediate color stops per the formula of the CSS
+      // images spec. http://dev.w3.org/csswg/css-images/#color-stop-syntax 9
+      // points were chosen since it is the minimum number of stops that always
+      // give the smoothest appearace regardless of midpoint position and
+      // difference in luminance of the end points.
+      const float relativeOffset =
+          (newStop.mPosition - offset1) / (offset2 - offset1);
+      const float multiplier = powf(relativeOffset, logf(.5f) / logf(midpoint));
+
+      auto srgb1 = color1.ToColorSpace(StyleColorSpace::Srgb);
+      auto srgb2 = color2.ToColorSpace(StyleColorSpace::Srgb);
+
+      const float red =
+          srgb1.components._0 +
+          multiplier * (srgb2.components._0 - srgb1.components._0);
+      const float green =
+          srgb1.components._1 +
+          multiplier * (srgb2.components._1 - srgb1.components._1);
+      const float blue =
+          srgb1.components._2 +
+          multiplier * (srgb2.components._2 - srgb1.components._2);
+      const float alpha =
+          srgb1.alpha + multiplier * (srgb2.alpha - srgb1.alpha);
+
+      newStop.mColor = StyleAbsoluteColor::Srgb(red, green, blue, alpha);
+    }
+
+    stops.ReplaceElementsAt(x, 1, newStops, 9);
+    x += 9;
+  }
+}
+
+static StyleAbsoluteColor TransparentColor(const StyleAbsoluteColor& aColor) {
+  auto color = aColor;
+  color.alpha = 0.0f;
+  return color;
+}
+
+// Adjusts and adds color stops in such a way that drawing the gradient with
+// unpremultiplied interpolation looks nearly the same as if it were drawn with
+// premultiplied interpolation.
+static const float kAlphaIncrementPerGradientStep = 0.1f;
+static void ResolvePremultipliedAlpha(nsTArray<ColorStop>& aStops) {
+  for (size_t x = 1; x < aStops.Length(); x++) {
+    const ColorStop leftStop = aStops[x - 1];
+    const ColorStop rightStop = aStops[x];
+
+    // if the left and right stop have the same alpha value, we don't need
+    // to do anything. Hardstops should be instant, and also should never
+    // require dealing with interpolation.
+    if (leftStop.mColor.alpha == rightStop.mColor.alpha ||
+        leftStop.mPosition == rightStop.mPosition) {
+      continue;
+    }
+
+    // Is the stop on the left 100% transparent? If so, have it adopt the color
+    // of the right stop
+    if (leftStop.mColor.alpha == 0) {
+      aStops[x - 1].mColor = TransparentColor(rightStop.mColor);
+      continue;
+    }
+
+    // Is the stop on the right completely transparent?
+    // If so, duplicate it and assign it the color on the left.
+    if (rightStop.mColor.alpha == 0) {
+      ColorStop newStop = rightStop;
+      newStop.mColor = TransparentColor(leftStop.mColor);
+      aStops.InsertElementAt(x, newStop);
+      x++;
+      continue;
+    }
+
+    // Now handle cases where one or both of the stops are partially
+    // transparent.
+    if (leftStop.mColor.alpha != 1.0f || rightStop.mColor.alpha != 1.0f) {
+      // Calculate how many extra steps. We do a step per 10% transparency.
+      size_t stepCount =
+          NSToIntFloor(fabsf(leftStop.mColor.alpha - rightStop.mColor.alpha) /
+                       kAlphaIncrementPerGradientStep);
+      for (size_t y = 1; y < stepCount; y++) {
+        float frac = static_cast<float>(y) / stepCount;
+        ColorStop newStop(
+            Interpolate(leftStop.mPosition, rightStop.mPosition, frac), false,
+            Interpolate(leftStop.mColor, rightStop.mColor, frac));
+        aStops.InsertElementAt(x, newStop);
+        x++;
+      }
+    }
+  }
+}
+
+static ColorStop InterpolateColorStop(const ColorStop& aFirst,
+                                      const ColorStop& aSecond,
+                                      double aPosition,
+                                      const StyleAbsoluteColor& aDefault) {
+  MOZ_ASSERT(aFirst.mPosition <= aPosition);
+  MOZ_ASSERT(aPosition <= aSecond.mPosition);
+
+  double delta = aSecond.mPosition - aFirst.mPosition;
+  if (delta < 1e-6) {
+    return ColorStop(aPosition, false, aDefault);
+  }
+
+  return ColorStop(aPosition, false,
+                   Interpolate(aFirst.mColor, aSecond.mColor,
+                               (aPosition - aFirst.mPosition) / delta));
+}
+
+// Clamp and extend the given ColorStop array in-place to fit exactly into the
+// range [0, 1].
+static void ClampColorStops(nsTArray<ColorStop>& aStops) {
+  MOZ_ASSERT(aStops.Length() > 0);
+
+  // If all stops are outside the range, then get rid of everything and replace
+  // with a single colour.
+  if (aStops.Length() < 2 || aStops[0].mPosition > 1 ||
+      aStops.LastElement().mPosition < 0) {
+    const auto c = aStops[0].mPosition > 1 ? aStops[0].mColor
+                                           : aStops.LastElement().mColor;
+    aStops.Clear();
+    aStops.AppendElement(ColorStop(0, false, c));
+    return;
+  }
+
+  // Create the 0 and 1 points if they fall in the range of |aStops|, and
+  // discard all stops outside the range [0, 1].
+  // XXX: If we have stops positioned at 0 or 1, we only keep the innermost of
+  // those stops. This should be fine for the current user(s) of this function.
+  for (size_t i = aStops.Length() - 1; i > 0; i--) {
+    if (aStops[i - 1].mPosition < 1 && aStops[i].mPosition >= 1) {
+      // Add a point to position 1.
+      aStops[i] =
+          InterpolateColorStop(aStops[i - 1], aStops[i],
+                               /* aPosition = */ 1, aStops[i - 1].mColor);
+      // Remove all the elements whose position is greater than 1.
+      aStops.RemoveLastElements(aStops.Length() - (i + 1));
+    }
+    if (aStops[i - 1].mPosition <= 0 && aStops[i].mPosition > 0) {
+      // Add a point to position 0.
+      aStops[i - 1] =
+          InterpolateColorStop(aStops[i - 1], aStops[i],
+                               /* aPosition = */ 0, aStops[i].mColor);
+      // Remove all of the preceding stops -- they are all negative.
+      aStops.RemoveElementsAt(0, i - 1);
+      break;
+    }
+  }
+
+  MOZ_ASSERT(aStops[0].mPosition >= -1e6);
+  MOZ_ASSERT(aStops.LastElement().mPosition - 1 <= 1e6);
+
+  // The end points won't exist yet if they don't fall in the original range of
+  // |aStops|. Create them if needed.
+  if (aStops[0].mPosition > 0) {
+    aStops.InsertElementAt(0, ColorStop(0, false, aStops[0].mColor));
+  }
+  if (aStops.LastElement().mPosition < 1) {
+    aStops.AppendElement(ColorStop(1, false, aStops.LastElement().mColor));
+  }
+}
+
+namespace mozilla {
+
+template <typename T>
+static StyleAbsoluteColor GetSpecifiedColor(
+    const StyleGenericGradientItem<StyleColor, T>& aItem,
+    const ComputedStyle& aStyle) {
+  if (aItem.IsInterpolationHint()) {
+    return StyleAbsoluteColor::Transparent();
+  }
+  const StyleColor& c = aItem.IsSimpleColorStop()
+                            ? aItem.AsSimpleColorStop()
+                            : aItem.AsComplexColorStop().color;
+
+  return c.ResolveColor(aStyle.StyleText()->mColor);
+}
+
+static Maybe<double> GetSpecifiedGradientPosition(
+    const StyleGenericGradientItem<StyleColor, StyleLengthPercentage>& aItem,
+    CSSCoord aLineLength) {
+  if (aItem.IsSimpleColorStop()) {
+    return Nothing();
+  }
+
+  const LengthPercentage& pos = aItem.IsComplexColorStop()
+                                    ? aItem.AsComplexColorStop().position
+                                    : aItem.AsInterpolationHint();
+
+  if (pos.ConvertsToPercentage()) {
+    return Some(pos.ToPercentage());
+  }
+
+  if (aLineLength < 1e-6) {
+    return Some(0.0);
+  }
+  return Some(pos.ResolveToCSSPixels(aLineLength) / aLineLength);
+}
+
+// aLineLength argument is unused for conic-gradients.
+static Maybe<double> GetSpecifiedGradientPosition(
+    const StyleGenericGradientItem<StyleColor, StyleAngleOrPercentage>& aItem,
+    CSSCoord aLineLength) {
+  if (aItem.IsSimpleColorStop()) {
+    return Nothing();
+  }
+
+  const StyleAngleOrPercentage& pos = aItem.IsComplexColorStop()
+                                          ? aItem.AsComplexColorStop().position
+                                          : aItem.AsInterpolationHint();
+
+  if (pos.IsPercentage()) {
+    return Some(pos.AsPercentage()._0);
+  }
+
+  return Some(pos.AsAngle().ToRadians() / (2 * M_PI));
+}
+
+template <typename T>
+static nsTArray<ColorStop> ComputeColorStopsForItems(
+    ComputedStyle* aComputedStyle,
+    Span<const StyleGenericGradientItem<StyleColor, T>> aItems,
+    CSSCoord aLineLength) {
+  MOZ_ASSERT(aItems.Length() >= 2,
+             "The parser should reject gradients with less than two stops");
+
+  nsTArray<ColorStop> stops(aItems.Length());
+
+  // If there is a run of stops before stop i that did not have specified
+  // positions, then this is the index of the first stop in that run.
+  Maybe<size_t> firstUnsetPosition;
+  for (size_t i = 0; i < aItems.Length(); ++i) {
+    const auto& stop = aItems[i];
+    double position;
+
+    Maybe<double> specifiedPosition =
+        GetSpecifiedGradientPosition(stop, aLineLength);
+
+    if (specifiedPosition) {
+      position = *specifiedPosition;
+    } else if (i == 0) {
+      // First stop defaults to position 0.0
+      position = 0.0;
+    } else if (i == aItems.Length() - 1) {
+      // Last stop defaults to position 1.0
+      position = 1.0;
+    } else {
+      // Other stops with no specified position get their position assigned
+      // later by interpolation, see below.
+      // Remember where the run of stops with no specified position starts,
+      // if it starts here.
+      if (firstUnsetPosition.isNothing()) {
+        firstUnsetPosition.emplace(i);
+      }
+      MOZ_ASSERT(!stop.IsInterpolationHint(),
+                 "Interpolation hints always specify position");
+      auto color = GetSpecifiedColor(stop, *aComputedStyle);
+      stops.AppendElement(ColorStop(0, false, color));
+      continue;
+    }
+
+    if (i > 0) {
+      // Prevent decreasing stop positions by advancing this position
+      // to the previous stop position, if necessary
+      double previousPosition = firstUnsetPosition
+                                    ? stops[*firstUnsetPosition - 1].mPosition
+                                    : stops[i - 1].mPosition;
+      position = std::max(position, previousPosition);
+    }
+    auto stopColor = GetSpecifiedColor(stop, *aComputedStyle);
+    stops.AppendElement(
+        ColorStop(position, stop.IsInterpolationHint(), stopColor));
+    if (firstUnsetPosition) {
+      // Interpolate positions for all stops that didn't have a specified
+      // position
+      double p = stops[*firstUnsetPosition - 1].mPosition;
+      double d = (stops[i].mPosition - p) / (i - *firstUnsetPosition + 1);
+      for (size_t j = *firstUnsetPosition; j < i; ++j) {
+        p += d;
+        stops[j].mPosition = p;
+      }
+      firstUnsetPosition.reset();
+    }
+  }
+
+  return stops;
+}
+
+static nsTArray<ColorStop> ComputeColorStops(ComputedStyle* aComputedStyle,
+                                             const StyleGradient& aGradient,
+                                             CSSCoord aLineLength) {
+  if (aGradient.IsLinear()) {
+    return ComputeColorStopsForItems(
+        aComputedStyle, aGradient.AsLinear().items.AsSpan(), aLineLength);
+  }
+  if (aGradient.IsRadial()) {
+    return ComputeColorStopsForItems(
+        aComputedStyle, aGradient.AsRadial().items.AsSpan(), aLineLength);
+  }
+  return ComputeColorStopsForItems(
+      aComputedStyle, aGradient.AsConic().items.AsSpan(), aLineLength);
+}
+
+nsCSSGradientRenderer nsCSSGradientRenderer::Create(
+    nsPresContext* aPresContext, ComputedStyle* aComputedStyle,
+    const StyleGradient& aGradient, const nsSize& aIntrinsicSize) {
+  auto srcSize = CSSSize::FromAppUnits(aIntrinsicSize);
+
+  // Compute "gradient line" start and end relative to the intrinsic size of
+  // the gradient.
+  CSSPoint lineStart, lineEnd, center;  // center is for conic gradients only
+  CSSCoord radiusX = 0, radiusY = 0;    // for radial gradients only
+  float angle = 0.0;                    // for conic gradients only
+  if (aGradient.IsLinear()) {
+    std::tie(lineStart, lineEnd) =
+        ComputeLinearGradientLine(aPresContext, aGradient, srcSize);
+  } else if (aGradient.IsRadial()) {
+    std::tie(lineStart, lineEnd, radiusX, radiusY) =
+        ComputeRadialGradientLine(aGradient, srcSize);
+  } else {
+    MOZ_ASSERT(aGradient.IsConic());
+    std::tie(center, angle) =
+        ComputeConicGradientProperties(aGradient, srcSize);
+  }
+  // Avoid sending Infs or Nans to downwind draw targets.
+  if (!lineStart.IsFinite() || !lineEnd.IsFinite()) {
+    lineStart = lineEnd = CSSPoint(0, 0);
+  }
+  if (!center.IsFinite()) {
+    center = CSSPoint(0, 0);
+  }
+  CSSCoord lineLength =
+      NS_hypot(lineEnd.x - lineStart.x, lineEnd.y - lineStart.y);
+
+  // Build color stop array and compute stop positions
+  nsTArray<ColorStop> stops =
+      ComputeColorStops(aComputedStyle, aGradient, lineLength);
+
+  ResolveMidpoints(stops);
+
+  nsCSSGradientRenderer renderer;
+  renderer.mPresContext = aPresContext;
+  renderer.mGradient = &aGradient;
+  renderer.mStops = std::move(stops);
+  renderer.mLineStart = {
+      aPresContext->CSSPixelsToDevPixels(lineStart.x),
+      aPresContext->CSSPixelsToDevPixels(lineStart.y),
+  };
+  renderer.mLineEnd = {
+      aPresContext->CSSPixelsToDevPixels(lineEnd.x),
+      aPresContext->CSSPixelsToDevPixels(lineEnd.y),
+  };
+  renderer.mRadiusX = aPresContext->CSSPixelsToDevPixels(radiusX);
+  renderer.mRadiusY = aPresContext->CSSPixelsToDevPixels(radiusY);
+  renderer.mCenter = {
+      aPresContext->CSSPixelsToDevPixels(center.x),
+      aPresContext->CSSPixelsToDevPixels(center.y),
+  };
+  renderer.mAngle = angle;
+  return renderer;
+}
+
+void nsCSSGradientRenderer::Paint(gfxContext& aContext, const nsRect& aDest,
+                                  const nsRect& aFillArea,
+                                  const nsSize& aRepeatSize,
+                                  const CSSIntRect& aSrc,
+                                  const nsRect& aDirtyRect, float aOpacity) {
+  AUTO_PROFILER_LABEL("nsCSSGradientRenderer::Paint", GRAPHICS);
+
+  if (aDest.IsEmpty() || aFillArea.IsEmpty()) {
+    return;
+  }
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  gfxFloat lineLength =
+      NS_hypot(mLineEnd.x - mLineStart.x, mLineEnd.y - mLineStart.y);
+  bool cellContainsFill = aDest.Contains(aFillArea);
+
+  // If a non-repeating linear gradient is axis-aligned and there are no gaps
+  // between tiles, we can optimise away most of the work by converting to a
+  // repeating linear gradient and filling the whole destination rect at once.
+  bool forceRepeatToCoverTiles =
+      mGradient->IsLinear() &&
+      (mLineStart.x == mLineEnd.x) != (mLineStart.y == mLineEnd.y) &&
+      aRepeatSize.width == aDest.width && aRepeatSize.height == aDest.height &&
+      !mGradient->AsLinear().repeating && !aSrc.IsEmpty() && !cellContainsFill;
+
+  gfxMatrix matrix;
+  if (forceRepeatToCoverTiles) {
+    // Length of the source rectangle along the gradient axis.
+    double rectLen;
+    // The position of the start of the rectangle along the gradient.
+    double offset;
+
+    // The gradient line is "backwards". Flip the line upside down to make
+    // things easier, and then rotate the matrix to turn everything back the
+    // right way up.
+    if (mLineStart.x > mLineEnd.x || mLineStart.y > mLineEnd.y) {
+      std::swap(mLineStart, mLineEnd);
+      matrix.PreScale(-1, -1);
+    }
+
+    // Fit the gradient line exactly into the source rect.
+    // aSrc is relative to aIntrinsincSize.
+    // srcRectDev will be relative to srcSize, so in the same coordinate space
+    // as lineStart / lineEnd.
+    gfxRect srcRectDev = nsLayoutUtils::RectToGfxRect(
+        CSSPixel::ToAppUnits(aSrc), appUnitsPerDevPixel);
+    if (mLineStart.x != mLineEnd.x) {
+      rectLen = srcRectDev.width;
+      offset = (srcRectDev.x - mLineStart.x) / lineLength;
+      mLineStart.x = srcRectDev.x;
+      mLineEnd.x = srcRectDev.XMost();
+    } else {
+      rectLen = srcRectDev.height;
+      offset = (srcRectDev.y - mLineStart.y) / lineLength;
+      mLineStart.y = srcRectDev.y;
+      mLineEnd.y = srcRectDev.YMost();
+    }
+
+    // Adjust gradient stop positions for the new gradient line.
+    double scale = lineLength / rectLen;
+    for (size_t i = 0; i < mStops.Length(); i++) {
+      mStops[i].mPosition = (mStops[i].mPosition - offset) * fabs(scale);
+    }
+
+    // Clamp or extrapolate gradient stops to exactly [0, 1].
+    ClampColorStops(mStops);
+
+    lineLength = rectLen;
+  }
+
+  // Eliminate negative-position stops if the gradient is radial.
+  double firstStop = mStops[0].mPosition;
+  if (mGradient->IsRadial() && firstStop < 0.0) {
+    if (mGradient->AsRadial().repeating) {
+      // Choose an instance of the repeated pattern that gives us all positive
+      // stop-offsets.
+      double lastStop = mStops[mStops.Length() - 1].mPosition;
+      double stopDelta = lastStop - firstStop;
+      // If all the stops are in approximately the same place then logic below
+      // will kick in that makes us draw just the last stop color, so don't
+      // try to do anything in that case. We certainly need to avoid
+      // dividing by zero.
+      if (stopDelta >= 1e-6) {
+        double instanceCount = ceil(-firstStop / stopDelta);
+        // Advance stops by instanceCount multiples of the period of the
+        // repeating gradient.
+        double offset = instanceCount * stopDelta;
+        for (uint32_t i = 0; i < mStops.Length(); i++) {
+          mStops[i].mPosition += offset;
+        }
+      }
+    } else {
+      // Move negative-position stops to position 0.0. We may also need
+      // to set the color of the stop to the color the gradient should have
+      // at the center of the ellipse.
+      for (uint32_t i = 0; i < mStops.Length(); i++) {
+        double pos = mStops[i].mPosition;
+        if (pos < 0.0) {
+          mStops[i].mPosition = 0.0;
+          // If this is the last stop, we don't need to adjust the color,
+          // it will fill the entire area.
+          if (i < mStops.Length() - 1) {
+            double nextPos = mStops[i + 1].mPosition;
+            // If nextPos is approximately equal to pos, then we don't
+            // need to adjust the color of this stop because it's
+            // not going to be displayed.
+            // If nextPos is negative, we don't need to adjust the color of
+            // this stop since it's not going to be displayed because
+            // nextPos will also be moved to 0.0.
+            if (nextPos >= 0.0 && nextPos - pos >= 1e-6) {
+              // Compute how far the new position 0.0 is along the interval
+              // between pos and nextPos.
+              // XXX Color interpolation (in cairo, too) should use the
+              // CSS 'color-interpolation' property!
+              float frac = float((0.0 - pos) / (nextPos - pos));
+              mStops[i].mColor =
+                  Interpolate(mStops[i].mColor, mStops[i + 1].mColor, frac);
+            }
+          }
+        }
+      }
+    }
+    firstStop = mStops[0].mPosition;
+    MOZ_ASSERT(firstStop >= 0.0, "Failed to fix stop offsets");
+  }
+
+  if (mGradient->IsRadial() && !mGradient->AsRadial().repeating) {
+    // Direct2D can only handle a particular class of radial gradients because
+    // of the way the it specifies gradients. Setting firstStop to 0, when we
+    // can, will help us stay on the fast path. Currently we don't do this
+    // for repeating gradients but we could by adjusting the stop collection
+    // to start at 0
+    firstStop = 0;
+  }
+
+  double lastStop = mStops[mStops.Length() - 1].mPosition;
+  // Cairo gradients must have stop positions in the range [0, 1]. So,
+  // stop positions will be normalized below by subtracting firstStop and then
+  // multiplying by stopScale.
+  double stopScale;
+  double stopOrigin = firstStop;
+  double stopEnd = lastStop;
+  double stopDelta = lastStop - firstStop;
+  bool zeroRadius =
+      mGradient->IsRadial() && (mRadiusX < 1e-6 || mRadiusY < 1e-6);
+  if (stopDelta < 1e-6 || (!mGradient->IsConic() && lineLength < 1e-6) ||
+      zeroRadius) {
+    // Stops are all at the same place. Map all stops to 0.0.
+    // For repeating radial gradients, or for any radial gradients with
+    // a zero radius, we need to fill with the last stop color, so just set
+    // both radii to 0.
+    if (mGradient->Repeating() || zeroRadius) {
+      mRadiusX = mRadiusY = 0.0;
+    }
+    stopDelta = 0.0;
+  }
+
+  // Don't normalize non-repeating or degenerate gradients below 0..1
+  // This keeps the gradient line as large as the box and doesn't
+  // lets us avoiding having to get padding correct for stops
+  // at 0 and 1
+  if (!mGradient->Repeating() || stopDelta == 0.0) {
+    stopOrigin = std::min(stopOrigin, 0.0);
+    stopEnd = std::max(stopEnd, 1.0);
+  }
+  stopScale = 1.0 / (stopEnd - stopOrigin);
+
+  // Create the gradient pattern.
+  RefPtr<gfxPattern> gradientPattern;
+  gfxPoint gradientStart;
+  gfxPoint gradientEnd;
+  if (mGradient->IsLinear()) {
+    // Compute the actual gradient line ends we need to pass to cairo after
+    // stops have been normalized.
+    gradientStart = mLineStart + (mLineEnd - mLineStart) * stopOrigin;
+    gradientEnd = mLineStart + (mLineEnd - mLineStart) * stopEnd;
+
+    if (stopDelta == 0.0) {
+      // Stops are all at the same place. For repeating gradients, this will
+      // just paint the last stop color. We don't need to do anything.
+      // For non-repeating gradients, this should render as two colors, one
+      // on each "side" of the gradient line segment, which is a point. All
+      // our stops will be at 0.0; we just need to set the direction vector
+      // correctly.
+      gradientEnd = gradientStart + (mLineEnd - mLineStart);
+    }
+
+    gradientPattern = new gfxPattern(gradientStart.x, gradientStart.y,
+                                     gradientEnd.x, gradientEnd.y);
+  } else if (mGradient->IsRadial()) {
+    NS_ASSERTION(firstStop >= 0.0,
+                 "Negative stops not allowed for radial gradients");
+
+    // To form an ellipse, we'll stretch a circle vertically, if necessary.
+    // So our radii are based on radiusX.
+    double innerRadius = mRadiusX * stopOrigin;
+    double outerRadius = mRadiusX * stopEnd;
+    if (stopDelta == 0.0) {
+      // Stops are all at the same place.  See above (except we now have
+      // the inside vs. outside of an ellipse).
+      outerRadius = innerRadius + 1;
+    }
+    gradientPattern = new gfxPattern(mLineStart.x, mLineStart.y, innerRadius,
+                                     mLineStart.x, mLineStart.y, outerRadius);
+    if (mRadiusX != mRadiusY) {
+      // Stretch the circles into ellipses vertically by setting a transform
+      // in the pattern.
+      // Recall that this is the transform from user space to pattern space.
+      // So to stretch the ellipse by factor of P vertically, we scale
+      // user coordinates by 1/P.
+      matrix.PreTranslate(mLineStart);
+      matrix.PreScale(1.0, mRadiusX / mRadiusY);
+      matrix.PreTranslate(-mLineStart);
+    }
+  } else {
+    gradientPattern =
+        new gfxPattern(mCenter.x, mCenter.y, mAngle, stopOrigin, stopEnd);
+  }
+  // Use a pattern transform to take account of source and dest rects
+  matrix.PreTranslate(gfxPoint(mPresContext->CSSPixelsToDevPixels(aSrc.x),
+                               mPresContext->CSSPixelsToDevPixels(aSrc.y)));
+  matrix.PreScale(
+      gfxFloat(nsPresContext::CSSPixelsToAppUnits(aSrc.width)) / aDest.width,
+      gfxFloat(nsPresContext::CSSPixelsToAppUnits(aSrc.height)) / aDest.height);
+  gradientPattern->SetMatrix(matrix);
+
+  if (stopDelta == 0.0) {
+    // Non-repeating gradient with all stops in same place -> just add
+    // first stop and last stop, both at position 0.
+    // Repeating gradient with all stops in the same place, or radial
+    // gradient with radius of 0 -> just paint the last stop color.
+    // We use firstStop offset to keep |stops| with same units (will later
+    // normalize to 0).
+    auto firstColor(mStops[0].mColor);
+    auto lastColor(mStops.LastElement().mColor);
+    mStops.Clear();
+
+    if (!mGradient->Repeating() && !zeroRadius) {
+      mStops.AppendElement(ColorStop(firstStop, false, firstColor));
+    }
+    mStops.AppendElement(ColorStop(firstStop, false, lastColor));
+  }
+
+  ResolvePremultipliedAlpha(mStops);
+
+  bool isRepeat = mGradient->Repeating() || forceRepeatToCoverTiles;
+
+  // Now set normalized color stops in pattern.
+  // Offscreen gradient surface cache (not a tile):
+  // On some backends (e.g. D2D), the GradientStops object holds an offscreen
+  // surface which is a lookup table used to evaluate the gradient. This surface
+  // can use much memory (ram and/or GPU ram) and can be expensive to create. So
+  // we cache it. The cache key correlates 1:1 with the arguments for
+  // CreateGradientStops (also the implied backend type) Note that GradientStop
+  // is a simple struct with a stop value (while GradientStops has the surface).
+  nsTArray<gfx::GradientStop> rawStops(mStops.Length());
+  rawStops.SetLength(mStops.Length());
+  for (uint32_t i = 0; i < mStops.Length(); i++) {
+    rawStops[i].color = ToDeviceColor(mStops[i].mColor);
+    rawStops[i].color.a *= aOpacity;
+    rawStops[i].offset = stopScale * (mStops[i].mPosition - stopOrigin);
+  }
+  RefPtr<mozilla::gfx::GradientStops> gs =
+      gfxGradientCache::GetOrCreateGradientStops(
+          aContext.GetDrawTarget(), rawStops,
+          isRepeat ? gfx::ExtendMode::REPEAT : gfx::ExtendMode::CLAMP);
+  gradientPattern->SetColorStops(gs);
+
+  // Paint gradient tiles. This isn't terribly efficient, but doing it this
+  // way is simple and sure to get pixel-snapping right. We could speed things
+  // up by drawing tiles into temporary surfaces and copying those to the
+  // destination, but after pixel-snapping tiles may not all be the same size.
+  nsRect dirty;
+  if (!dirty.IntersectRect(aDirtyRect, aFillArea)) return;
+
+  gfxRect areaToFill =
+      nsLayoutUtils::RectToGfxRect(aFillArea, appUnitsPerDevPixel);
+  gfxRect dirtyAreaToFill =
+      nsLayoutUtils::RectToGfxRect(dirty, appUnitsPerDevPixel);
+  dirtyAreaToFill.RoundOut();
+
+  Matrix ctm = aContext.CurrentMatrix();
+  bool isCTMPreservingAxisAlignedRectangles =
+      ctm.PreservesAxisAlignedRectangles();
+
+  // xStart/yStart are the top-left corner of the top-left tile.
+  nscoord xStart = FindTileStart(dirty.x, aDest.x, aRepeatSize.width);
+  nscoord yStart = FindTileStart(dirty.y, aDest.y, aRepeatSize.height);
+  nscoord xEnd = forceRepeatToCoverTiles ? xStart + aDest.width : dirty.XMost();
+  nscoord yEnd =
+      forceRepeatToCoverTiles ? yStart + aDest.height : dirty.YMost();
+
+  if (TryPaintTilesWithExtendMode(aContext, gradientPattern, xStart, yStart,
+                                  dirtyAreaToFill, aDest, aRepeatSize,
+                                  forceRepeatToCoverTiles)) {
+    return;
+  }
+
+  // x and y are the top-left corner of the tile to draw
+  for (nscoord y = yStart; y < yEnd; y += aRepeatSize.height) {
+    for (nscoord x = xStart; x < xEnd; x += aRepeatSize.width) {
+      // The coordinates of the tile
+      gfxRect tileRect = nsLayoutUtils::RectToGfxRect(
+          nsRect(x, y, aDest.width, aDest.height), appUnitsPerDevPixel);
+      // The actual area to fill with this tile is the intersection of this
+      // tile with the overall area we're supposed to be filling
+      gfxRect fillRect =
+          forceRepeatToCoverTiles ? areaToFill : tileRect.Intersect(areaToFill);
+      // Try snapping the fill rect. Snap its top-left and bottom-right
+      // independently to preserve the orientation.
+      gfxPoint snappedFillRectTopLeft = fillRect.TopLeft();
+      gfxPoint snappedFillRectTopRight = fillRect.TopRight();
+      gfxPoint snappedFillRectBottomRight = fillRect.BottomRight();
+      // Snap three points instead of just two to ensure we choose the
+      // correct orientation if there's a reflection.
+      if (isCTMPreservingAxisAlignedRectangles &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectTopLeft, true) &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectBottomRight, true) &&
+          aContext.UserToDevicePixelSnapped(snappedFillRectTopRight, true)) {
+        if (snappedFillRectTopLeft.x == snappedFillRectBottomRight.x ||
+            snappedFillRectTopLeft.y == snappedFillRectBottomRight.y) {
+          // Nothing to draw; avoid scaling by zero and other weirdness that
+          // could put the context in an error state.
+          continue;
+        }
+        // Set the context's transform to the transform that maps fillRect to
+        // snappedFillRect. The part of the gradient that was going to
+        // exactly fill fillRect will fill snappedFillRect instead.
+        gfxMatrix transform = gfxUtils::TransformRectToRect(
+            fillRect, snappedFillRectTopLeft, snappedFillRectTopRight,
+            snappedFillRectBottomRight);
+        aContext.SetMatrixDouble(transform);
+      }
+      aContext.NewPath();
+      aContext.Rectangle(fillRect);
+
+      gfxRect dirtyFillRect = fillRect.Intersect(dirtyAreaToFill);
+      gfxRect fillRectRelativeToTile = dirtyFillRect - tileRect.TopLeft();
+      auto edgeColor = StyleAbsoluteColor::Transparent();
+      if (mGradient->IsLinear() && !isRepeat &&
+          RectIsBeyondLinearGradientEdge(fillRectRelativeToTile, matrix, mStops,
+                                         gradientStart, gradientEnd,
+                                         &edgeColor)) {
+        edgeColor.alpha *= aOpacity;
+        aContext.SetColor(ToSRGBColor(edgeColor));
+      } else {
+        aContext.SetMatrixDouble(
+            aContext.CurrentMatrixDouble().Copy().PreTranslate(
+                tileRect.TopLeft()));
+        aContext.SetPattern(gradientPattern);
+      }
+      aContext.Fill();
+      aContext.SetMatrix(ctm);
+    }
+  }
+}
+
+bool nsCSSGradientRenderer::TryPaintTilesWithExtendMode(
+    gfxContext& aContext, gfxPattern* aGradientPattern, nscoord aXStart,
+    nscoord aYStart, const gfxRect& aDirtyAreaToFill, const nsRect& aDest,
+    const nsSize& aRepeatSize, bool aForceRepeatToCoverTiles) {
+  // If we have forced a non-repeating gradient to repeat to cover tiles,
+  // then it will be faster to just paint it once using that optimization
+  if (aForceRepeatToCoverTiles) {
+    return false;
+  }
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  // We can only use this fast path if we don't have to worry about pixel
+  // snapping, and there is no spacing between tiles. We could handle spacing
+  // by increasing the size of tileSurface and leaving it transparent, but I'm
+  // not sure it's worth it
+  bool canUseExtendModeForTiling = (aXStart % appUnitsPerDevPixel == 0) &&
+                                   (aYStart % appUnitsPerDevPixel == 0) &&
+                                   (aDest.width % appUnitsPerDevPixel == 0) &&
+                                   (aDest.height % appUnitsPerDevPixel == 0) &&
+                                   (aRepeatSize.width == aDest.width) &&
+                                   (aRepeatSize.height == aDest.height);
+
+  if (!canUseExtendModeForTiling) {
+    return false;
+  }
+
+  IntSize tileSize{
+      NSAppUnitsToIntPixels(aDest.width, appUnitsPerDevPixel),
+      NSAppUnitsToIntPixels(aDest.height, appUnitsPerDevPixel),
+  };
+
+  // Check whether this is a reasonable surface size and doesn't overflow
+  // before doing calculations with the tile size
+  if (!Factory::ReasonableSurfaceSize(tileSize)) {
+    return false;
+  }
+
+  // We only want to do this when there are enough tiles to justify the
+  // overhead of painting to an offscreen surface. The heuristic here
+  // is when we will be painting at least 16 tiles or more, this is kind
+  // of arbitrary
+  bool shouldUseExtendModeForTiling =
+      aDirtyAreaToFill.Area() > (tileSize.width * tileSize.height) * 16.0;
+
+  if (!shouldUseExtendModeForTiling) {
+    return false;
+  }
+
+  // Draw the gradient pattern into a surface for our single tile
+  RefPtr<gfx::SourceSurface> tileSurface;
+  {
+    RefPtr<gfx::DrawTarget> tileTarget =
+        aContext.GetDrawTarget()->CreateSimilarDrawTarget(
+            tileSize, gfx::SurfaceFormat::B8G8R8A8);
+    if (!tileTarget || !tileTarget->IsValid()) {
+      return false;
+    }
+
+    {
+      gfxContext tileContext(tileTarget);
+
+      tileContext.SetPattern(aGradientPattern);
+      tileContext.Paint();
+    }
+
+    tileSurface = tileTarget->Snapshot();
+    tileTarget = nullptr;
+  }
+
+  // Draw the gradient using tileSurface as a repeating pattern masked by
+  // the dirtyRect
+  Matrix tileTransform = Matrix::Translation(
+      NSAppUnitsToFloatPixels(aXStart, appUnitsPerDevPixel),
+      NSAppUnitsToFloatPixels(aYStart, appUnitsPerDevPixel));
+
+  aContext.NewPath();
+  aContext.Rectangle(aDirtyAreaToFill);
+  aContext.Fill(SurfacePattern(tileSurface, ExtendMode::REPEAT, tileTransform));
+
+  return true;
+}
+
+void nsCSSGradientRenderer::BuildWebRenderParameters(
+    float aOpacity, wr::ExtendMode& aMode, nsTArray<wr::GradientStop>& aStops,
+    LayoutDevicePoint& aLineStart, LayoutDevicePoint& aLineEnd,
+    LayoutDeviceSize& aGradientRadius, LayoutDevicePoint& aGradientCenter,
+    float& aGradientAngle) {
+  aMode =
+      mGradient->Repeating() ? wr::ExtendMode::Repeat : wr::ExtendMode::Clamp;
+
+  aStops.SetLength(mStops.Length());
+  for (uint32_t i = 0; i < mStops.Length(); i++) {
+    aStops[i].color = wr::ToColorF(ToDeviceColor(mStops[i].mColor));
+    aStops[i].color.a *= aOpacity;
+    aStops[i].offset = mStops[i].mPosition;
+  }
+
+  aLineStart = LayoutDevicePoint(mLineStart.x, mLineStart.y);
+  aLineEnd = LayoutDevicePoint(mLineEnd.x, mLineEnd.y);
+  aGradientRadius = LayoutDeviceSize(mRadiusX, mRadiusY);
+  aGradientCenter = LayoutDevicePoint(mCenter.x, mCenter.y);
+  aGradientAngle = mAngle;
+}
+
+void nsCSSGradientRenderer::BuildWebRenderDisplayItems(
+    wr::DisplayListBuilder& aBuilder, const layers::StackingContextHelper& aSc,
+    const nsRect& aDest, const nsRect& aFillArea, const nsSize& aRepeatSize,
+    const CSSIntRect& aSrc, bool aIsBackfaceVisible, float aOpacity) {
+  if (aDest.IsEmpty() || aFillArea.IsEmpty()) {
+    return;
+  }
+
+  wr::ExtendMode extendMode;
+  nsTArray<wr::GradientStop> stops;
+  LayoutDevicePoint lineStart;
+  LayoutDevicePoint lineEnd;
+  LayoutDeviceSize gradientRadius;
+  LayoutDevicePoint gradientCenter;
+  float gradientAngle;
+  BuildWebRenderParameters(aOpacity, extendMode, stops, lineStart, lineEnd,
+                           gradientRadius, gradientCenter, gradientAngle);
+
+  nscoord appUnitsPerDevPixel = mPresContext->AppUnitsPerDevPixel();
+
+  nsPoint firstTile =
+      nsPoint(FindTileStart(aFillArea.x, aDest.x, aRepeatSize.width),
+              FindTileStart(aFillArea.y, aDest.y, aRepeatSize.height));
+
+  // Translate the parameters into device coordinates
+  LayoutDeviceRect clipBounds =
+      LayoutDevicePixel::FromAppUnits(aFillArea, appUnitsPerDevPixel);
+  LayoutDeviceRect firstTileBounds = LayoutDevicePixel::FromAppUnits(
+      nsRect(firstTile, aDest.Size()), appUnitsPerDevPixel);
+  LayoutDeviceSize tileRepeat =
+      LayoutDevicePixel::FromAppUnits(aRepeatSize, appUnitsPerDevPixel);
+
+  // Calculate the bounds of the gradient display item, which starts at the
+  // first tile and extends to the end of clip bounds
+  LayoutDevicePoint tileToClip =
+      clipBounds.BottomRight() - firstTileBounds.TopLeft();
+  LayoutDeviceRect gradientBounds = LayoutDeviceRect(
+      firstTileBounds.TopLeft(), LayoutDeviceSize(tileToClip.x, tileToClip.y));
+
+  // Calculate the tile spacing, which is the repeat size minus the tile size
+  LayoutDeviceSize tileSpacing = tileRepeat - firstTileBounds.Size();
+
+  // srcTransform is used for scaling the gradient to match aSrc
+  LayoutDeviceRect srcTransform = LayoutDeviceRect(
+      nsPresContext::CSSPixelsToAppUnits(aSrc.x),
+      nsPresContext::CSSPixelsToAppUnits(aSrc.y),
+      aDest.width / ((float)nsPresContext::CSSPixelsToAppUnits(aSrc.width)),
+      aDest.height / ((float)nsPresContext::CSSPixelsToAppUnits(aSrc.height)));
+
+  lineStart.x = (lineStart.x - srcTransform.x) * srcTransform.width;
+  lineStart.y = (lineStart.y - srcTransform.y) * srcTransform.height;
+
+  gradientCenter.x = (gradientCenter.x - srcTransform.x) * srcTransform.width;
+  gradientCenter.y = (gradientCenter.y - srcTransform.y) * srcTransform.height;
+
+  if (mGradient->IsLinear()) {
+    lineEnd.x = (lineEnd.x - srcTransform.x) * srcTransform.width;
+    lineEnd.y = (lineEnd.y - srcTransform.y) * srcTransform.height;
+
+    aBuilder.PushLinearGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(lineStart),
+        mozilla::wr::ToLayoutPoint(lineEnd), stops, extendMode,
+        mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  } else if (mGradient->IsRadial()) {
+    gradientRadius.width *= srcTransform.width;
+    gradientRadius.height *= srcTransform.height;
+
+    aBuilder.PushRadialGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(lineStart),
+        mozilla::wr::ToLayoutSize(gradientRadius), stops, extendMode,
+        mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  } else {
+    MOZ_ASSERT(mGradient->IsConic());
+    aBuilder.PushConicGradient(
+        mozilla::wr::ToLayoutRect(gradientBounds),
+        mozilla::wr::ToLayoutRect(clipBounds), aIsBackfaceVisible,
+        mozilla::wr::ToLayoutPoint(gradientCenter), gradientAngle, stops,
+        extendMode, mozilla::wr::ToLayoutSize(firstTileBounds.Size()),
+        mozilla::wr::ToLayoutSize(tileSpacing));
+  }
+}
+
+}  // namespace mozilla