author Markus Stange <>
Wed, 30 Mar 2016 15:34:03 -0400
changeset 347733 ff6c2806545ebe2f2fa9ea9fd5b0d65cba478d59
parent 347252 110538d89648260440c66045dcde9e0f1eb6dde1
child 347734 4f1bcad3f4d6edb149785e1bbeb876ef74869bb0
permissions -rw-r--r--
Bug 1260335 - Add a comment that explains why the perspective child can't have more than one frame metrics. r=mattwoodrow MozReview-Commit-ID: BsB8XRtUd4b

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=2 et 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 */

#include "mozilla/layers/AsyncCompositionManager.h"
#include <stdint.h>                     // for uint32_t
#include "apz/src/AsyncPanZoomController.h"
#include "FrameMetrics.h"               // for FrameMetrics
#include "LayerManagerComposite.h"      // for LayerManagerComposite, etc
#include "Layers.h"                     // for Layer, ContainerLayer, etc
#include "gfxPoint.h"                   // for gfxPoint, gfxSize
#include "gfxPrefs.h"                   // for gfxPrefs
#include "mozilla/StyleAnimationValue.h" // for StyleAnimationValue, etc
#include "mozilla/WidgetUtils.h"        // for ComputeTransformForRotation
#include "mozilla/dom/KeyframeEffect.h" // for KeyframeEffectReadOnly
#include "mozilla/dom/AnimationEffectReadOnlyBinding.h" // for dom::FillMode
#include "mozilla/gfx/BaseRect.h"       // for BaseRect
#include "mozilla/gfx/Point.h"          // for RoundedToInt, PointTyped
#include "mozilla/gfx/Rect.h"           // for RoundedToInt, RectTyped
#include "mozilla/gfx/ScaleFactor.h"    // for ScaleFactor
#include "mozilla/layers/APZUtils.h"    // for CompleteAsyncTransform
#include "mozilla/layers/Compositor.h"  // for Compositor
#include "mozilla/layers/CompositorBridgeParent.h" // for CompositorBridgeParent, etc
#include "mozilla/layers/LayerAnimationUtils.h" // for TimingFunctionToComputedTimingFunction
#include "mozilla/layers/LayerMetricsWrapper.h" // for LayerMetricsWrapper
#include "nsCoord.h"                    // for NSAppUnitsToFloatPixels, etc
#include "nsDebug.h"                    // for NS_ASSERTION, etc
#include "nsDeviceContext.h"            // for nsDeviceContext
#include "nsDisplayList.h"              // for nsDisplayTransform, etc
#include "nsMathUtils.h"                // for NS_round
#include "nsPoint.h"                    // for nsPoint
#include "nsRect.h"                     // for mozilla::gfx::IntRect
#include "nsRegion.h"                   // for nsIntRegion
#include "nsTArray.h"                   // for nsTArray, nsTArray_Impl, etc
#include "nsTArrayForwardDeclare.h"     // for InfallibleTArray
#include "UnitTransforms.h"             // for TransformTo
#include "gfxPrefs.h"
# include <android/log.h>
# include "AndroidBridge.h"
#include "GeckoProfiler.h"
#include "FrameUniformityData.h"
#include "TreeTraversal.h"
#include "VsyncSource.h"

struct nsCSSValueSharedList;

namespace mozilla {
namespace layers {

using namespace mozilla::gfx;

enum Op { Resolve, Detach };

static bool
IsSameDimension(dom::ScreenOrientationInternal o1, dom::ScreenOrientationInternal o2)
  bool isO1portrait = (o1 == dom::eScreenOrientation_PortraitPrimary || o1 == dom::eScreenOrientation_PortraitSecondary);
  bool isO2portrait = (o2 == dom::eScreenOrientation_PortraitPrimary || o2 == dom::eScreenOrientation_PortraitSecondary);
  return !(isO1portrait ^ isO2portrait);

static bool
ContentMightReflowOnOrientationChange(const IntRect& rect)
  return rect.width != rect.height;

template<Op OP>
static void
WalkTheTree(Layer* aLayer,
            bool& aReady,
            const TargetConfig& aTargetConfig,
            CompositorBridgeParent* aCompositor,
            bool& aHasRemote,
            bool aWillResolvePlugins,
            bool& aDidResolvePlugins)
  if (RefLayer* ref = aLayer->AsRefLayer()) {
    aHasRemote = true;
    if (const CompositorBridgeParent::LayerTreeState* state = CompositorBridgeParent::GetIndirectShadowTree(ref->GetReferentId())) {
      if (Layer* referent = state->mRoot) {
        if (!ref->GetLocalVisibleRegion().IsEmpty()) {
          dom::ScreenOrientationInternal chromeOrientation = aTargetConfig.orientation();
          dom::ScreenOrientationInternal contentOrientation = state->mTargetConfig.orientation();
          if (!IsSameDimension(chromeOrientation, contentOrientation) &&
              ContentMightReflowOnOrientationChange(aTargetConfig.naturalBounds())) {
            aReady = false;

        if (OP == Resolve) {
#if defined(XP_WIN) || defined(MOZ_WIDGET_GTK)
          if (aCompositor && aWillResolvePlugins) {
            aDidResolvePlugins |=
        } else {
          WalkTheTree<OP>(referent, aReady, aTargetConfig,
                          aCompositor, aHasRemote, aWillResolvePlugins,
  for (Layer* child = aLayer->GetFirstChild();
       child; child = child->GetNextSibling()) {
    WalkTheTree<OP>(child, aReady, aTargetConfig,
                    aCompositor, aHasRemote, aWillResolvePlugins,

AsyncCompositionManager::AsyncCompositionManager(LayerManagerComposite* aManager)
  : mLayerManager(aManager)
  , mIsFirstPaint(true)
  , mLayersUpdated(false)
  , mPaintSyncId(0)
  , mReadyForCompose(true)


AsyncCompositionManager::ResolveRefLayers(CompositorBridgeParent* aCompositor,
                                          bool* aHasRemoteContent,
                                          bool* aResolvePlugins)
  if (aHasRemoteContent) {
    *aHasRemoteContent = false;

  // If valid *aResolvePlugins indicates if we need to update plugin geometry
  // when we walk the tree.
  bool willResolvePlugins = (aResolvePlugins && *aResolvePlugins);
  if (!mLayerManager->GetRoot()) {
    // Updated the return value since this result controls completing composition.
    if (aResolvePlugins) {
      *aResolvePlugins = false;

  mReadyForCompose = true;
  bool hasRemoteContent = false;
  bool didResolvePlugins = false;
  if (aHasRemoteContent) {
    *aHasRemoteContent = hasRemoteContent;
  if (aResolvePlugins) {
    *aResolvePlugins = didResolvePlugins;

  if (!mLayerManager->GetRoot()) {
  CompositorBridgeParent* dummy = nullptr;
  bool ignored = false;
                      ignored, ignored, ignored);

  if (!mTargetConfig.naturalBounds().IsEmpty()) {
    mWorldTransform =

static void
GetBaseTransform(Layer* aLayer, Matrix4x4* aTransform)
  // Start with the animated transform if there is one
  *aTransform =
        ? aLayer->GetLocalTransform()
        : aLayer->GetTransform());

static void
TransformClipRect(Layer* aLayer,
                  const ParentLayerToParentLayerMatrix4x4& aTransform)
  const Maybe<ParentLayerIntRect>& clipRect = aLayer->AsLayerComposite()->GetShadowClipRect();
  if (clipRect) {
    ParentLayerIntRect transformed = TransformBy(aTransform, *clipRect);

 * Set the given transform as the shadow transform on the layer, assuming
 * that the given transform already has the pre- and post-scales applied.
 * That is, this function cancels out the pre- and post-scales from aTransform
 * before setting it as the shadow transform on the layer, so that when
 * the layer's effective transform is computed, the pre- and post-scales will
 * only be applied once.
static void
SetShadowTransform(Layer* aLayer, LayerToParentLayerMatrix4x4 aTransform)
  if (ContainerLayer* c = aLayer->AsContainerLayer()) {
    aTransform.PreScale(1.0f / c->GetPreXScale(),
                        1.0f / c->GetPreYScale(),
  aTransform.PostScale(1.0f / aLayer->GetPostXScale(),
                       1.0f / aLayer->GetPostYScale(),

static void
TranslateShadowLayer(Layer* aLayer,
                     const gfxPoint& aTranslation,
                     bool aAdjustClipRect)
  // This layer might also be a scrollable layer and have an async transform.
  // To make sure we don't clobber that, we start with the shadow transform.
  // (i.e. GetLocalTransform() instead of GetTransform()).
  // Note that the shadow transform is reset on every frame of composition so
  // we don't have to worry about the adjustments compounding over successive
  // frames.
  LayerToParentLayerMatrix4x4 layerTransform = aLayer->GetLocalTransformTyped();

  // Apply the translation to the layer transform.
  layerTransform.PostTranslate(aTranslation.x, aTranslation.y, 0);

  SetShadowTransform(aLayer, layerTransform);

  if (aAdjustClipRect) {
        ParentLayerToParentLayerMatrix4x4::Translation(aTranslation.x, aTranslation.y, 0));

    // If a fixed- or sticky-position layer has a mask layer, that mask should
    // move along with the layer, so apply the translation to the mask layer too.
    if (Layer* maskLayer = aLayer->GetMaskLayer()) {
      TranslateShadowLayer(maskLayer, aTranslation, false);

static void
AccumulateLayerTransforms(Layer* aLayer,
                          Layer* aAncestor,
                          Matrix4x4& aMatrix)
  // Accumulate the transforms between this layer and the subtree root layer.
  for (Layer* l = aLayer; l && l != aAncestor; l = l->GetParent()) {
    Matrix4x4 transform;
    GetBaseTransform(l, &transform);
    aMatrix *= transform;

static LayerPoint
GetLayerFixedMarginsOffset(Layer* aLayer,
                           const ScreenMargin& aFixedLayerMargins)
  // Work out the necessary translation, in root scrollable layer space.
  // Because fixed layer margins are stored relative to the root scrollable
  // layer, we can just take the difference between these values.
  LayerPoint translation;
  int32_t sides = aLayer->GetFixedPositionSides();

  if ((sides & eSideBitsLeftRight) == eSideBitsLeftRight) {
    translation.x += (aFixedLayerMargins.left - aFixedLayerMargins.right) / 2;
  } else if (sides & eSideBitsRight) {
    translation.x -= aFixedLayerMargins.right;
  } else if (sides & eSideBitsLeft) {
    translation.x += aFixedLayerMargins.left;

  if ((sides & eSideBitsTopBottom) == eSideBitsTopBottom) {
    translation.y += ( - aFixedLayerMargins.bottom) / 2;
  } else if (sides & eSideBitsBottom) {
    translation.y -= aFixedLayerMargins.bottom;
  } else if (sides & eSideBitsTop) {
    translation.y +=;

  return translation;

static gfxFloat
IntervalOverlap(gfxFloat aTranslation, gfxFloat aMin, gfxFloat aMax)
  // Determine the amount of overlap between the 1D vector |aTranslation|
  // and the interval [aMin, aMax].
  if (aTranslation > 0) {
    return std::max(0.0, std::min(aMax, aTranslation) - std::max(aMin, 0.0));
  } else {
    return std::min(0.0, std::max(aMin, aTranslation) - std::min(aMax, 0.0));

 * Finds the metrics on |aLayer| with scroll id |aScrollId|, and returns a
 * LayerMetricsWrapper representing the (layer, metrics) pair, or the null
 * LayerMetricsWrapper if no matching metrics could be found.
static LayerMetricsWrapper
FindMetricsWithScrollId(Layer* aLayer, FrameMetrics::ViewID aScrollId)
  for (uint64_t i = 0; i < aLayer->GetScrollMetadataCount(); ++i) {
    if (aLayer->GetFrameMetrics(i).GetScrollId() == aScrollId) {
      return LayerMetricsWrapper(aLayer, i);
  return LayerMetricsWrapper();

 * Checks whether the (layer, metrics) pair (aTransformedLayer, aTransformedMetrics)
 * is on the path from |aFixedLayer| to the metrics with scroll id
 * |aFixedWithRespectTo|, inclusive.
static bool
AsyncTransformShouldBeUnapplied(Layer* aFixedLayer,
                                FrameMetrics::ViewID aFixedWithRespectTo,
                                Layer* aTransformedLayer,
                                FrameMetrics::ViewID aTransformedMetrics)
  LayerMetricsWrapper transformed = FindMetricsWithScrollId(aTransformedLayer, aTransformedMetrics);
  if (!transformed.IsValid()) {
    return false;
  // It's important to start at the bottom, because the fixed layer itself
  // could have the transformed metrics, and they can be at the bottom.
  LayerMetricsWrapper current(aFixedLayer, LayerMetricsWrapper::StartAt::BOTTOM);
  bool encounteredTransformedLayer = false;
  // The transformed layer is on the path from |aFixedLayer| to the fixed-to
  // layer if as we walk up the (layer, metrics) tree starting from
  // |aFixedLayer|, we *first* encounter the transformed layer, and *then* (or
  // at the same time) the fixed-to layer.
  while (current) {
    if (!encounteredTransformedLayer && current == transformed) {
      encounteredTransformedLayer = true;
    if (current.Metrics().GetScrollId() == aFixedWithRespectTo) {
      return encounteredTransformedLayer;
    current = current.GetParent();
    // It's possible that we reach a layers id boundary before we reach an
    // ancestor with the scroll id |aFixedWithRespectTo| (this could happen
    // e.g. if the scroll frame with that scroll id uses containerless
    // scrolling). In such a case, stop the walk, as a new layers id could
    // have a different layer with scroll id |aFixedWithRespectTo| which we
    // don't intend to match.
    if (current && current.AsRefLayer() != nullptr) {
  return false;

AsyncCompositionManager::AlignFixedAndStickyLayers(Layer* aLayer,
                                                   Layer* aTransformedSubtreeRoot,
                                                   FrameMetrics::ViewID aTransformScrollId,
                                                   const LayerToParentLayerMatrix4x4& aPreviousTransformForRoot,
                                                   const LayerToParentLayerMatrix4x4& aCurrentTransformForRoot,
                                                   const ScreenMargin& aFixedLayerMargins,
                                                   bool aTransformAffectsLayerClip)
  FrameMetrics::ViewID fixedTo;  // the scroll id of the scroll frame we are fixed/sticky to
  bool isRootOfFixedSubtree = aLayer->GetIsFixedPosition() &&
  if (isRootOfFixedSubtree) {
    fixedTo = aLayer->GetFixedPositionScrollContainerId();
  bool isSticky = aLayer->GetIsStickyPosition();
  if (isSticky) {
    fixedTo = aLayer->GetStickyScrollContainerId();
  bool needsAsyncTransformUnapplied = false;
  if (isRootOfFixedSubtree || isSticky) {
    needsAsyncTransformUnapplied = AsyncTransformShouldBeUnapplied(aLayer,
        fixedTo, aTransformedSubtreeRoot, aTransformScrollId);

  // We want to process all the fixed and sticky descendants of
  // aTransformedSubtreeRoot. Once we do encounter such a descendant, we don't
  // need to recurse any deeper because the adjustment to the fixed or sticky
  // layer will apply to its subtree.
  if (!needsAsyncTransformUnapplied) {
    for (Layer* child = aLayer->GetFirstChild(); child; child = child->GetNextSibling()) {
      AlignFixedAndStickyLayers(child, aTransformedSubtreeRoot, aTransformScrollId,
                                aCurrentTransformForRoot, aFixedLayerMargins,
                                true /* descendants' clip rects are always affected */);

  // Insert a translation so that the position of the anchor point is the same
  // before and after the change to the transform of aTransformedSubtreeRoot.

  // Accumulate the transforms between this layer and the subtree root layer.
  Matrix4x4 ancestorTransform;
  AccumulateLayerTransforms(aLayer->GetParent(), aTransformedSubtreeRoot,

  // Calculate the cumulative transforms between the subtree root with the
  // old transform and the current transform.
  Matrix4x4 oldCumulativeTransform = ancestorTransform * aPreviousTransformForRoot.ToUnknownMatrix();
  Matrix4x4 newCumulativeTransform = ancestorTransform * aCurrentTransformForRoot.ToUnknownMatrix();
  if (newCumulativeTransform.IsSingular()) {

  // Add in the layer's local transform, if it isn't already included in
  // |aPreviousTransformForRoot| and |aCurrentTransformForRoot| (this happens
  // when the fixed/sticky layer is itself the transformed subtree root).
  Matrix4x4 localTransform;
  GetBaseTransform(aLayer, &localTransform);
  if (aLayer != aTransformedSubtreeRoot) {
    oldCumulativeTransform = localTransform * oldCumulativeTransform;
    newCumulativeTransform = localTransform * newCumulativeTransform;

  // Now work out the translation necessary to make sure the layer doesn't
  // move given the new sub-tree root transform.

  // Get the layer's fixed anchor point, in the layer's local coordinate space
  // (before any cumulative transform is applied).
  LayerPoint anchor = aLayer->GetFixedPositionAnchor();

  // Offset the layer's anchor point to make sure fixed position content
  // respects content document fixed position margins.
  LayerPoint offsetAnchor = anchor + GetLayerFixedMarginsOffset(aLayer, aFixedLayerMargins);

  // Additionally transform the anchor to compensate for the change
  // from the old cumulative transform to the new cumulative transform. We do
  // this by using the old transform to take the offset anchor back into
  // subtree root space, and then the inverse of the new cumulative transform
  // to bring it back to layer space.
  LayerPoint transformedAnchor = ViewAs<LayerPixel>(
      newCumulativeTransform.Inverse() *
      (oldCumulativeTransform * offsetAnchor.ToUnknownPoint()));

  // We want to translate the layer by the difference between |transformedAnchor|
  // and |anchor|. To achieve this, we will add a translation to the layer's
  // transform. This translation will apply on top of the layer's local
  // transform, but |anchor| and |transformedAnchor| are in a coordinate space
  // where the local transform isn't applied yet, so apply it and then subtract
  // to get the desired translation.
  auto localTransformTyped = ViewAs<LayerToParentLayerMatrix4x4>(localTransform);
  ParentLayerPoint translation = TransformBy(localTransformTyped, transformedAnchor)
                               - TransformBy(localTransformTyped, anchor);

  if (aLayer->GetIsStickyPosition()) {
    // For sticky positioned layers, the difference between the two rectangles
    // defines a pair of translation intervals in each dimension through which
    // the layer should not move relative to the scroll container. To
    // accomplish this, we limit each dimension of the |translation| to that
    // part of it which overlaps those intervals.
    const LayerRect& stickyOuter = aLayer->GetStickyScrollRangeOuter();
    const LayerRect& stickyInner = aLayer->GetStickyScrollRangeInner();

    // TODO: There's a unit mismatch here, as |translation| is in ParentLayer
    //       space while |stickyOuter| and |stickyInner| are in Layer space.
    translation.y = IntervalOverlap(translation.y, stickyOuter.y, stickyOuter.YMost()) -
                    IntervalOverlap(translation.y, stickyInner.y, stickyInner.YMost());
    translation.x = IntervalOverlap(translation.x, stickyOuter.x, stickyOuter.XMost()) -
                    IntervalOverlap(translation.x, stickyInner.x, stickyInner.XMost());

  // Finally, apply the translation to the layer transform. Note that in cases
  // where the async transform on |aTransformedSubtreeRoot| affects this layer's
  // clip rect, we need to apply the same translation to said clip rect, so
  // that the effective transform on the clip rect takes it back to where it was
  // originally, had there been no async scroll.
  // Also, some layers want async scrolling to move their clip rect
  // (IsClipFixed() = false), so we don't make a compensating adjustment for
  // those.
  bool adjustClipRect = aTransformAffectsLayerClip && aLayer->IsClipFixed();
  TranslateShadowLayer(aLayer, ThebesPoint(translation.ToUnknownPoint()), adjustClipRect);

static void
SampleValue(float aPortion, Animation& aAnimation, StyleAnimationValue& aStart,
            StyleAnimationValue& aEnd, Animatable* aValue, Layer* aLayer)
  StyleAnimationValue interpolatedValue;
  NS_ASSERTION(aStart.GetUnit() == aEnd.GetUnit() ||
               aStart.GetUnit() == StyleAnimationValue::eUnit_None ||
               aEnd.GetUnit() == StyleAnimationValue::eUnit_None,
               "Must have same unit");
  StyleAnimationValue::Interpolate(, aStart, aEnd,
                                aPortion, interpolatedValue);
  if ( == eCSSProperty_opacity) {
    *aValue = interpolatedValue.GetFloatValue();

  nsCSSValueSharedList* interpolatedList =

  TransformData& data =;
  nsPoint origin = data.origin();
  // we expect all our transform data to arrive in device pixels
  Point3D transformOrigin = data.transformOrigin();
  nsDisplayTransform::FrameTransformProperties props(interpolatedList,

  // If our parent layer is a perspective layer, then the offset into reference
  // frame coordinates is already on that layer. If not, then we need to ask
  // for it to be added here.
  uint32_t flags = 0;
  if (!aLayer->GetParent() || !aLayer->GetParent()->GetTransformIsPerspective()) {
    flags = nsDisplayTransform::OFFSET_BY_ORIGIN;

  Matrix4x4 transform =
    nsDisplayTransform::GetResultingTransformMatrix(props, origin,
                                                    flags, &data.bounds());

  InfallibleTArray<TransformFunction> functions;
  *aValue = functions;

static bool
SampleAnimations(Layer* aLayer, TimeStamp aPoint)
  AnimationArray& animations = aLayer->GetAnimations();
  InfallibleTArray<AnimData>& animationData = aLayer->GetAnimationData();

  bool activeAnimations = false;

  // Process in order, since later animations override earlier ones.
  for (size_t i = 0, iEnd = animations.Length(); i < iEnd; ++i) {
    Animation& animation = animations[i];
    AnimData& animData = animationData[i];

    activeAnimations = true;

               "Failed to resolve start time of pending animations");
    TimeDuration elapsedDuration =
      (aPoint - animation.startTime()).MultDouble(animation.playbackRate());
    // Skip animations that are yet to start.
    // Currently, this should only happen when the refresh driver is under test
    // control and is made to produce a time in the past or is restored from
    // test control causing it to jump backwards in time.
    // Since activeAnimations is true, this could mean we keep compositing
    // unnecessarily during the delay, but so long as this only happens while
    // the refresh driver is under test control that should be ok.
    if (elapsedDuration.ToSeconds() < 0) {

    TimingParams timing;
    // Currently animations run on the compositor have their delay factored
    // into their start time, hence the delay is effectively zero.
    timing.mDelay = TimeDuration(0);
    timing.mIterations = animation.iterations();
    timing.mIterationStart = animation.iterationStart();
    timing.mDirection =
    // Animations typically only run on the compositor during their active
    // interval but if we end up sampling them outside that range (for
    // example, while they are waiting to be removed) we currently just
    // assume that we should fill.
    timing.mFill = dom::FillMode::Both;
    timing.mFunction =

    ComputedTiming computedTiming =
        Nullable<TimeDuration>(elapsedDuration), timing);

               "iteration progress should not be null");

    uint32_t segmentIndex = 0;
    size_t segmentSize = animation.segments().Length();
    AnimationSegment* segment = animation.segments().Elements();
    while (segment->endPortion() < computedTiming.mProgress.Value() &&
           segmentIndex < segmentSize - 1) {

    double positionInSegment =
      (computedTiming.mProgress.Value() - segment->startPortion()) /
      (segment->endPortion() - segment->startPortion());

    double portion =

    // interpolate the property
    Animatable interpolatedValue;
    SampleValue(portion, animation, animData.mStartValues[segmentIndex],
                animData.mEndValues[segmentIndex], &interpolatedValue, aLayer);
    LayerComposite* layerComposite = aLayer->AsLayerComposite();
    switch ( {
    case eCSSProperty_opacity:
    case eCSSProperty_transform:
      Matrix4x4 matrix = interpolatedValue.get_ArrayOfTransformFunction()[0].get_TransformMatrix().value();
      if (ContainerLayer* c = aLayer->AsContainerLayer()) {
        matrix.PostScale(c->GetInheritedXScale(), c->GetInheritedYScale(), 1);
      NS_WARNING("Unhandled animated property");

  for (Layer* child = aLayer->GetFirstChild(); child;
       child = child->GetNextSibling()) {
    activeAnimations |= SampleAnimations(child, aPoint);

  return activeAnimations;

static bool
SampleAPZAnimations(const LayerMetricsWrapper& aLayer, TimeStamp aSampleTime)
  bool activeAnimations = false;
  for (LayerMetricsWrapper child = aLayer.GetFirstChild(); child;
        child = child.GetNextSibling()) {
    activeAnimations |= SampleAPZAnimations(child, aSampleTime);

  if (AsyncPanZoomController* apzc = aLayer.GetApzc()) {
    activeAnimations |= apzc->AdvanceAnimations(aSampleTime);

  return activeAnimations;

AsyncCompositionManager::RecordShadowTransforms(Layer* aLayer)

  for (Layer* child = aLayer->GetFirstChild();
      child; child = child->GetNextSibling()) {

  for (uint32_t i = 0; i < aLayer->GetScrollMetadataCount(); i++) {
    AsyncPanZoomController* apzc = aLayer->GetAsyncPanZoomController(i);
    if (!apzc) {
    gfx::Matrix4x4 shadowTransform = aLayer->AsLayerComposite()->GetShadowBaseTransform();
    if (!shadowTransform.Is2D()) {

    Matrix transform = shadowTransform.As2D();
    if (transform.IsTranslation() && !shadowTransform.IsIdentity()) {
      Point translation = transform.GetTranslation();
      mLayerTransformRecorder.RecordTransform(aLayer, translation);

static AsyncTransformComponentMatrix
AdjustForClip(const AsyncTransformComponentMatrix& asyncTransform, Layer* aLayer)
  AsyncTransformComponentMatrix result = asyncTransform;

  // Container layers start at the origin, but they are clipped to where they
  // actually have content on the screen. The tree transform is meant to apply
  // to the clipped area. If the tree transform includes a scale component,
  // then applying it to container as-is will produce incorrect results. To
  // avoid this, translate the layer so that the clip rect starts at the origin,
  // apply the tree transform, and translate back.
  if (const Maybe<ParentLayerIntRect>& shadowClipRect = aLayer->AsLayerComposite()->GetShadowClipRect()) {
    if (shadowClipRect->TopLeft() != ParentLayerIntPoint()) {  // avoid a gratuitous change of basis
      result.ChangeBasis(shadowClipRect->x, shadowClipRect->y, 0);
  return result;

static void
ExpandRootClipRect(Layer* aLayer, const ScreenMargin& aFixedLayerMargins)
  // For Fennec we want to expand the root scrollable layer clip rect based on
  // the fixed position margins. In particular, we want this while the dynamic
  // toolbar is in the process of sliding offscreen and the area of the
  // LayerView visible to the user is larger than the viewport size that Gecko
  // knows about (and therefore larger than the clip rect). We could also just
  // clear the clip rect on aLayer entirely but this seems more precise.
  Maybe<ParentLayerIntRect> rootClipRect = aLayer->AsLayerComposite()->GetShadowClipRect();
  if (rootClipRect && aFixedLayerMargins != ScreenMargin()) {
    // We should never enter here on anything other than Fennec, since
    // aFixedLayerMargins should be empty everywhere else.
    ParentLayerRect rect(rootClipRect.value());

static void
MoveScrollbarForLayerMargin(Layer* aRoot, FrameMetrics::ViewID aRootScrollId,
                            const ScreenMargin& aFixedLayerMargins)
  // See bug 1223928 comment 9 - once we can detect the RCD with just the
  // isRootContent flag on the metrics, we can probably move this code into
  // ApplyAsyncTransformToScrollbar rather than having it as a separate
  // adjustment on the layer tree.
  Layer* scrollbar = BreadthFirstSearch(aRoot,
    [aRootScrollId](Layer* aNode) {
      return (aNode->GetScrollbarDirection() == Layer::HORIZONTAL &&
              aNode->GetScrollbarTargetContainerId() == aRootScrollId);
  if (scrollbar) {
    // Shift the horizontal scrollbar down into the new space exposed by the
    // dynamic toolbar hiding. Technically we should also scale the vertical
    // scrollbar a bit to expand into the new space but it's not as noticeable
    // and it would add a lot more complexity, so we're going with the "it's not
    // worth it" justification.
    TranslateShadowLayer(scrollbar, gfxPoint(0, -aFixedLayerMargins.bottom), true);
    if (scrollbar->GetParent()) {
      // The layer that has the HORIZONTAL direction sits inside another
      // ContainerLayer. This ContainerLayer also has a clip rect that causes
      // the scrollbar to get clipped. We need to expand that clip rect to
      // prevent that from happening. This is kind of ugly in that we're
      // assuming a particular layer tree structure but short of adding more
      // flags to the layer there doesn't appear to be a good way to do this.
      ExpandRootClipRect(scrollbar->GetParent(), aFixedLayerMargins);

template <typename Units>
IntersectMaybeRects(const Maybe<IntRectTyped<Units>>& a,
                    const Maybe<IntRectTyped<Units>>& b)
  if (!a) {
    return b;
  } else if (!b) {
    return a;
  } else {
    return Some(a->Intersect(*b));

AsyncCompositionManager::ApplyAsyncContentTransformToTree(Layer *aLayer,
                                                          bool* aOutFoundRoot,
                                                          Maybe<ParentLayerIntRect>& aClipDeferredToParent)
  Maybe<ParentLayerIntRect> clipDeferredFromChildren;
  bool appliedTransform = false;
  for (Layer* child = aLayer->GetFirstChild();
      child; child = child->GetNextSibling()) {
    appliedTransform |=
      ApplyAsyncContentTransformToTree(child, aOutFoundRoot,

  LayerToParentLayerMatrix4x4 oldTransform = aLayer->GetTransformTyped() *

  AsyncTransformComponentMatrix combinedAsyncTransform;
  bool hasAsyncTransform = false;
  ScreenMargin fixedLayerMargins;

  // Each layer has multiple clips. Its local clip, which must move with async
  // transforms, and its scrollframe clips, which are the clips between each
  // scrollframe and its ancestor scrollframe. Scrollframe clips include the
  // composition bounds and any other clips induced by layout.
  // The final clip for the layer is the intersection of these clips.
  Maybe<ParentLayerIntRect> asyncClip = aLayer->GetClipRect();

  // The transform of a mask layer is relative to the masked layer's parent
  // layer. So whenever we apply an async transform to a layer, we need to
  // apply that same transform to the layer's own mask layer.
  // A layer can also have "ancestor" mask layers for any rounded clips from
  // its ancestor scroll frames. A scroll frame mask layer only needs to be
  // async transformed for async scrolls of this scroll frame's ancestor
  // scroll frames, not for async scrolls of this scroll frame itself.
  // In the loop below, we iterate over scroll frames from inside to outside.
  // At each iteration, this array contains the layer's ancestor mask layers
  // of all scroll frames inside the current one.
  nsTArray<Layer*> ancestorMaskLayers;

  for (uint32_t i = 0; i < aLayer->GetScrollMetadataCount(); i++) {
    AsyncPanZoomController* controller = aLayer->GetAsyncPanZoomController(i);
    if (!controller) {

    hasAsyncTransform = true;

    AsyncTransform asyncTransformWithoutOverscroll =
    AsyncTransformComponentMatrix overscrollTransform =
    AsyncTransformComponentMatrix asyncTransform =
      * overscrollTransform;

    if (!aLayer->IsScrollInfoLayer()) {

    const ScrollMetadata& scrollMetadata = aLayer->GetScrollMetadata(i);
    const FrameMetrics& metrics = scrollMetadata.GetMetrics();

#if defined(MOZ_ANDROID_APZ)
    // If we find a metrics which is the root content doc, use that. If not, use
    // the root layer. Since this function recurses on children first we should
    // only end up using the root layer if the entire tree was devoid of a
    // root content metrics. This is a temporary solution; in the long term we
    // should not need the root content metrics at all. See bug 1201529 comment
    // 6 for details.
    if (!(*aOutFoundRoot)) {
      *aOutFoundRoot = metrics.IsRootContent() ||       /* RCD */
            (aLayer->GetParent() == nullptr &&          /* rootmost metrics */
             i + 1 >= aLayer->GetScrollMetadataCount());
      if (*aOutFoundRoot) {
        mRootScrollableId = metrics.GetScrollId();
        CSSToLayerScale geckoZoom = metrics.LayersPixelsPerCSSPixel().ToScaleFactor();
        if (mIsFirstPaint) {
          LayerIntPoint scrollOffsetLayerPixels = RoundedToInt(metrics.GetScrollOffset() * geckoZoom);
          mContentRect = metrics.GetScrollableRect();
        } else {
          ParentLayerPoint scrollOffset = controller->GetCurrentAsyncScrollOffset(
          // Compute the painted displayport in document-relative CSS pixels.
          CSSRect displayPort(metrics.GetCriticalDisplayPort().IsEmpty() ?
              metrics.GetDisplayPort() :
          displayPort += metrics.GetScrollOffset();
              geckoZoom * asyncTransformWithoutOverscroll.mScale,
              metrics.GetScrollableRect(), displayPort, geckoZoom, mLayersUpdated,
              mPaintSyncId, fixedLayerMargins);
          mFixedLayerMargins = fixedLayerMargins;
          mLayersUpdated = false;
        mIsFirstPaint = false;
        mPaintSyncId = 0;
    // Non-Android platforms still care about this flag being cleared after
    // the first call to TransformShadowTree().
    mIsFirstPaint = false;

    // Transform the current local clip by this APZC's async transform. If we're
    // using containerful scrolling, then the clip is not part of the scrolled
    // frame and should not be transformed.
    if (asyncClip && !metrics.UsesContainerScrolling()) {
      asyncClip = Some(TransformBy(asyncTransform, *asyncClip));

    combinedAsyncTransform *= asyncTransform;

    // For the purpose of aligning fixed and sticky layers, we disregard
    // the overscroll transform as well as any OMTA transform when computing the
    // 'aCurrentTransformForRoot' parameter. This ensures that the overscroll
    // and OMTA transforms are not unapplied, and therefore that the visual
    // effects apply to fixed and sticky layers. We do this by using
    // GetTransform() as the base transform rather than GetLocalTransform(),
    // which would include those factors.
    LayerToParentLayerMatrix4x4 transformWithoutOverscrollOrOmta =
      * CompleteAsyncTransform(
          AdjustForClip(asyncTransformWithoutOverscroll, aLayer));

    // Since fixed/sticky layers are relative to their nearest scrolling ancestor,
    // we use the ViewID from the bottommost scrollable metrics here.
    AlignFixedAndStickyLayers(aLayer, aLayer, metrics.GetScrollId(), oldTransform,
                              transformWithoutOverscrollOrOmta, fixedLayerMargins,

    // AlignFixedAndStickyLayers may have changed the clip rect, so we have to
    // read it from the layer again.
    asyncClip = aLayer->AsLayerComposite()->GetShadowClipRect();

    // Combine the local clip with the ancestor scrollframe clip. This is not
    // included in the async transform above, since the ancestor clip should not
    // move with this APZC.
    if (scrollMetadata.HasClipRect()) {
      ParentLayerIntRect clip = scrollMetadata.ClipRect();
      if (aLayer->GetParent() && aLayer->GetParent()->GetTransformIsPerspective()) {
        // If our parent layer has a perspective transform, we want to apply
        // our scroll clip to it instead of to this layer (see bug 1168263).
        // A layer with a perspective transform shouldn't have multiple
        // children with FrameMetrics, nor a child with multiple FrameMetrics.
        // (A child with multiple FrameMetrics would mean that there's *another*
        // scrollable element between the one with the CSS perspective and the
        // transformed element. But you'd have to use preserve-3d on the inner
        // scrollable element in order to have the perspective apply to the
        // transformed child, and preserve-3d is not supported on scrollable
        // elements, so this case can't occur.)
        aClipDeferredToParent = Some(clip);
      } else {
        asyncClip = IntersectMaybeRects(Some(clip), asyncClip);

    // Do the same for the ancestor mask layers: ancestorMaskLayers contains
    // the ancestor mask layers for scroll frames *inside* the current scroll
    // frame, so these are the ones we need to shift by our async transform.
    for (Layer* ancestorMaskLayer : ancestorMaskLayers) {
          ancestorMaskLayer->GetLocalTransformTyped() * asyncTransform);

    // Append the ancestor mask layer for this scroll frame to ancestorMaskLayers.
    if (scrollMetadata.GetMaskLayerIndex()) {
      size_t maskLayerIndex = scrollMetadata.GetMaskLayerIndex().value();
      Layer* ancestorMaskLayer = aLayer->GetAncestorMaskLayerAt(maskLayerIndex);

  if (hasAsyncTransform || clipDeferredFromChildren) {
        IntersectMaybeRects(asyncClip, clipDeferredFromChildren));

  if (hasAsyncTransform) {
    // Apply the APZ transform on top of GetLocalTransform() here (rather than
    // GetTransform()) in case the OMTA code in SampleAnimations already set a
    // shadow transform; in that case we want to apply ours on top of that one
    // rather than clobber it.
      * AdjustForClip(combinedAsyncTransform, aLayer));

    // Do the same for the layer's own mask layer, if it has one.
    if (Layer* maskLayer = aLayer->GetMaskLayer()) {
          maskLayer->GetLocalTransformTyped() * combinedAsyncTransform);

    appliedTransform = true;

  ExpandRootClipRect(aLayer, fixedLayerMargins);

  if (aLayer->GetScrollbarDirection() != Layer::NONE) {
  return appliedTransform;

static bool
LayerIsScrollbarTarget(const LayerMetricsWrapper& aTarget, Layer* aScrollbar)
  AsyncPanZoomController* apzc = aTarget.GetApzc();
  if (!apzc) {
    return false;
  const FrameMetrics& metrics = aTarget.Metrics();
  if (metrics.GetScrollId() != aScrollbar->GetScrollbarTargetContainerId()) {
    return false;
  return !aTarget.IsScrollInfoLayer();

static void
ApplyAsyncTransformToScrollbarForContent(Layer* aScrollbar,
                                         const LayerMetricsWrapper& aContent,
                                         bool aScrollbarIsDescendant)
  // We only apply the transform if the scroll-target layer has non-container
  // children (i.e. when it has some possibly-visible content). This is to
  // avoid moving scroll-bars in the situation that only a scroll information
  // layer has been built for a scroll frame, as this would result in a
  // disparity between scrollbars and visible content.
  if (aContent.IsScrollInfoLayer()) {

  const FrameMetrics& metrics = aContent.Metrics();
  AsyncPanZoomController* apzc = aContent.GetApzc();

  AsyncTransformComponentMatrix asyncTransform =

  // |asyncTransform| represents the amount by which we have scrolled and
  // zoomed since the last paint. Because the scrollbar was sized and positioned based
  // on the painted content, we need to adjust it based on asyncTransform so that
  // it reflects what the user is actually seeing now.
  AsyncTransformComponentMatrix scrollbarTransform;
  if (aScrollbar->GetScrollbarDirection() == Layer::VERTICAL) {
    const ParentLayerCoord asyncScrollY = asyncTransform._42;
    const float asyncZoomY = asyncTransform._22;

    // The scroll thumb needs to be scaled in the direction of scrolling by the
    // inverse of the async zoom. This is because zooming in decreases the
    // fraction of the whole srollable rect that is in view.
    const float yScale = 1.f / asyncZoomY;

    // Note: |metrics.GetZoom()| doesn't yet include the async zoom.
    const CSSToParentLayerScale effectiveZoom(metrics.GetZoom().yScale * asyncZoomY);

    // Here we convert the scrollbar thumb ratio into a true unitless ratio by
    // dividing out the conversion factor from the scrollframe's parent's space
    // to the scrollframe's space.
    const float ratio = aScrollbar->GetScrollbarThumbRatio() /
        (metrics.GetPresShellResolution() * asyncZoomY);
    // The scroll thumb needs to be translated in opposite direction of the
    // async scroll. This is because scrolling down, which translates the layer
    // content up, should result in moving the scroll thumb down.
    ParentLayerCoord yTranslation = -asyncScrollY * ratio;

    // The scroll thumb additionally needs to be translated to compensate for
    // the scale applied above. The origin with respect to which the scale is
    // applied is the origin of the entire scrollbar, rather than the origin of
    // the scroll thumb (meaning, for a vertical scrollbar it's at the top of
    // the composition bounds). This means that empty space above the thumb
    // is scaled too, effectively translating the thumb. We undo that
    // translation here.
    // (One can think of the adjustment being done to the translation here as
    // a change of basis. We have a method to help with that,
    // Matrix4x4::ChangeBasis(), but it wouldn't necessarily make the code
    // cleaner in this case).
    const CSSCoord thumbOrigin = (metrics.GetScrollOffset().y * ratio);
    const CSSCoord thumbOriginScaled = thumbOrigin * yScale;
    const CSSCoord thumbOriginDelta = thumbOriginScaled - thumbOrigin;
    const ParentLayerCoord thumbOriginDeltaPL = thumbOriginDelta * effectiveZoom;
    yTranslation -= thumbOriginDeltaPL;

    if (metrics.IsRootContent()) {
      // Scrollbar for the root are painted at the same resolution as the
      // content. Since the coordinate space we apply this transform in includes
      // the resolution, we need to adjust for it as well here. Note that in
      // another metrics.IsRootContent() hunk below we apply a
      // resolution-cancelling transform which ensures the scroll thumb isn't
      // actually rendered at a larger scale.
      yTranslation *= metrics.GetPresShellResolution();

    scrollbarTransform.PostScale(1.f, yScale, 1.f);
    scrollbarTransform.PostTranslate(0, yTranslation, 0);
  if (aScrollbar->GetScrollbarDirection() == Layer::HORIZONTAL) {
    // See detailed comments under the VERTICAL case.

    const ParentLayerCoord asyncScrollX = asyncTransform._41;
    const float asyncZoomX = asyncTransform._11;

    const float xScale = 1.f / asyncZoomX;

    const CSSToParentLayerScale effectiveZoom(metrics.GetZoom().xScale * asyncZoomX);

    const float ratio = aScrollbar->GetScrollbarThumbRatio() /
        (metrics.GetPresShellResolution() * asyncZoomX);
    ParentLayerCoord xTranslation = -asyncScrollX * ratio;

    const CSSCoord thumbOrigin = (metrics.GetScrollOffset().x * ratio);
    const CSSCoord thumbOriginScaled = thumbOrigin * xScale;
    const CSSCoord thumbOriginDelta = thumbOriginScaled - thumbOrigin;
    const ParentLayerCoord thumbOriginDeltaPL = thumbOriginDelta * effectiveZoom;
    xTranslation -= thumbOriginDeltaPL;

    if (metrics.IsRootContent()) {
      xTranslation *= metrics.GetPresShellResolution();

    scrollbarTransform.PostScale(xScale, 1.f, 1.f);
    scrollbarTransform.PostTranslate(xTranslation, 0, 0);

  LayerToParentLayerMatrix4x4 transform =
      aScrollbar->GetLocalTransformTyped() * scrollbarTransform;

  AsyncTransformComponentMatrix compensation;
  // If the scrollbar layer is for the root then the content's resolution
  // applies to the scrollbar as well. Since we don't actually want the scroll
  // thumb's size to vary with the zoom (other than its length reflecting the
  // fraction of the scrollable length that's in view, which is taken care of
  // above), we apply a transform to cancel out this resolution.
  if (metrics.IsRootContent()) {
    compensation =
  // If the scrollbar layer is a child of the content it is a scrollbar for,
  // then we need to adjust for any async transform (including an overscroll
  // transform) on the content. This needs to be cancelled out because layout
  // positions and sizes the scrollbar on the assumption that there is no async
  // transform, and without this adjustment the scrollbar will end up in the
  // wrong place.
  // Note that since the async transform is applied on top of the content's
  // regular transform, we need to make sure to unapply the async transform in
  // the same coordinate space. This requires applying the content transform
  // and then unapplying it after unapplying the async transform.
  if (aScrollbarIsDescendant) {
    AsyncTransformComponentMatrix overscroll =
    Matrix4x4 asyncUntransform = (asyncTransform * overscroll).Inverse().ToUnknownMatrix();
    Matrix4x4 contentTransform = aContent.GetTransform();
    Matrix4x4 contentUntransform = contentTransform.Inverse();

    AsyncTransformComponentMatrix asyncCompensation =
          * asyncUntransform
          * contentUntransform);

    compensation = compensation * asyncCompensation;

    // We also need to make a corresponding change on the clip rect of all the
    // layers on the ancestor chain from the scrollbar layer up to but not
    // including the layer with the async transform. Otherwise the scrollbar
    // shifts but gets clipped and so appears to flicker.
    for (Layer* ancestor = aScrollbar; ancestor != aContent.GetLayer(); ancestor = ancestor->GetParent()) {
      TransformClipRect(ancestor, asyncCompensation);
  transform = transform * compensation;

  SetShadowTransform(aScrollbar, transform);

static LayerMetricsWrapper
FindScrolledLayerRecursive(Layer* aScrollbar, const LayerMetricsWrapper& aSubtreeRoot)
  if (LayerIsScrollbarTarget(aSubtreeRoot, aScrollbar)) {
    return aSubtreeRoot;

  for (LayerMetricsWrapper child = aSubtreeRoot.GetFirstChild();
       child = child.GetNextSibling())
    // Do not recurse into RefLayers, since our initial aSubtreeRoot is the
    // root (or RefLayer root) of a single layer space to search.
    if (child.AsRefLayer()) {

    LayerMetricsWrapper target = FindScrolledLayerRecursive(aScrollbar, child);
    if (target) {
      return target;
  return LayerMetricsWrapper();

static LayerMetricsWrapper
FindScrolledLayerForScrollbar(Layer* aScrollbar, bool* aOutIsAncestor)
  // First check if the scrolled layer is an ancestor of the scrollbar layer.
  LayerMetricsWrapper root(aScrollbar->Manager()->GetRoot());
  LayerMetricsWrapper prevAncestor(aScrollbar);
  for (LayerMetricsWrapper ancestor(aScrollbar); ancestor; ancestor = ancestor.GetParent()) {
    // Don't walk into remote layer trees; the scrollbar will always be in
    // the same layer space.
    if (ancestor.AsRefLayer()) {
      root = prevAncestor;
    prevAncestor = ancestor;

    if (LayerIsScrollbarTarget(ancestor, aScrollbar)) {
      *aOutIsAncestor = true;
      return ancestor;

  // Search the entire layer space of the scrollbar.
  return FindScrolledLayerRecursive(aScrollbar, root);

AsyncCompositionManager::ApplyAsyncTransformToScrollbar(Layer* aLayer)
  // If this layer corresponds to a scrollbar, then there should be a layer that
  // is a previous sibling or a parent that has a matching ViewID on its FrameMetrics.
  // That is the content that this scrollbar is for. We pick up the transient
  // async transform from that layer and use it to update the scrollbar position.
  // Note that it is possible that the content layer is no longer there; in
  // this case we don't need to do anything because there can't be an async
  // transform on the content.
  bool isAncestor = false;
  const LayerMetricsWrapper& scrollTarget = FindScrolledLayerForScrollbar(aLayer, &isAncestor);
  if (scrollTarget) {
    ApplyAsyncTransformToScrollbarForContent(aLayer, scrollTarget, isAncestor);

AsyncCompositionManager::TransformScrollableLayer(Layer* aLayer)
  FrameMetrics metrics = LayerMetricsWrapper::TopmostScrollableMetrics(aLayer);
  if (!metrics.IsScrollable()) {
    // On Fennec it's possible that the there is no scrollable layer in the
    // tree, and this function just gets called with the root layer. In that
    // case TopmostScrollableMetrics will return an empty FrameMetrics but we
    // still want to use the actual non-scrollable metrics from the layer.
    metrics = LayerMetricsWrapper::BottommostMetrics(aLayer);

  // We must apply the resolution scale before a pan/zoom transform, so we call
  // GetTransform here.
  LayerToParentLayerMatrix4x4 oldTransform = aLayer->GetTransformTyped() *

  CSSToLayerScale geckoZoom = metrics.LayersPixelsPerCSSPixel().ToScaleFactor();

  LayerIntPoint scrollOffsetLayerPixels = RoundedToInt(metrics.GetScrollOffset() * geckoZoom);

  if (mIsFirstPaint) {
    mContentRect = metrics.GetScrollableRect();
    mIsFirstPaint = false;
  } else if (!metrics.GetScrollableRect().IsEqualEdges(mContentRect)) {
    mContentRect = metrics.GetScrollableRect();

  // We synchronise the viewport information with Java after sending the above
  // notifications, so that Java can take these into account in its response.
  // Calculate the absolute display port to send to Java
  LayerIntRect displayPort = RoundedToInt(
      ? metrics.GetDisplayPort()
      : metrics.GetCriticalDisplayPort()
    ) * geckoZoom);
  displayPort += scrollOffsetLayerPixels;

  ScreenMargin fixedLayerMargins(0, 0, 0, 0);

  // Ideally we would initialize userZoom to AsyncPanZoomController::CalculateResolution(metrics)
  // but this causes a reftest-ipc test to fail (see bug 883646 comment 27). The reason for this
  // appears to be that metrics.mZoom is poorly initialized in some scenarios. In these scenarios,
  // however, we can assume there is no async zooming in progress and so the following statement
  // works fine.
  CSSToParentLayerScale userZoom(metrics.GetDevPixelsPerCSSPixel()
                                 // This function only applies to the root scrollable frame,
                                 // for which we can assume that x and y scales are equal.
                               * metrics.GetCumulativeResolution().ToScaleFactor()
                               * LayerToParentLayerScale(1));
  ParentLayerRect userRect(metrics.GetScrollOffset() * userZoom,
  SyncViewportInfo(displayPort, geckoZoom, mLayersUpdated, mPaintSyncId,
                   userRect, userZoom, fixedLayerMargins);
  mLayersUpdated = false;
  mPaintSyncId = 0;

  // Handle transformations for asynchronous panning and zooming. We determine the
  // zoom used by Gecko from the transformation set on the root layer, and we
  // determine the scroll offset used by Gecko from the frame metrics of the
  // primary scrollable layer. We compare this to the user zoom and scroll
  // offset in the view transform we obtained from Java in order to compute the
  // transformation we need to apply.
  ParentLayerPoint geckoScroll(0, 0);
  if (metrics.IsScrollable()) {
    geckoScroll = metrics.GetScrollOffset() * userZoom;

  LayerToParentLayerScale asyncZoom = userZoom / metrics.LayersPixelsPerCSSPixel().ToScaleFactor();
  ParentLayerPoint translation = userRect.TopLeft() - geckoScroll;
  AsyncTransformComponentMatrix treeTransform = AsyncTransform(asyncZoom, -translation);

  // Apply the tree transform on top of GetLocalTransform() here (rather than
  // GetTransform()) in case the OMTA code in SampleAnimations already set a
  // shadow transform; in that case we want to apply ours on top of that one
  // rather than clobber it.
  SetShadowTransform(aLayer, aLayer->GetLocalTransformTyped() * treeTransform);

  // Make sure that overscroll and under-zoom are represented in the old
  // transform so that fixed position content moves and scales accordingly.
  // These calculations will effectively scale and offset fixed position layers
  // in screen space when the compensatory transform is performed in
  // AlignFixedAndStickyLayers.
  ParentLayerRect contentScreenRect = mContentRect * userZoom;
  Point3D overscrollTranslation;
  if (userRect.x < contentScreenRect.x) {
    overscrollTranslation.x = contentScreenRect.x - userRect.x;
  } else if (userRect.XMost() > contentScreenRect.XMost()) {
    overscrollTranslation.x = contentScreenRect.XMost() - userRect.XMost();
  if (userRect.y < contentScreenRect.y) {
    overscrollTranslation.y = contentScreenRect.y - userRect.y;
  } else if (userRect.YMost() > contentScreenRect.YMost()) {
    overscrollTranslation.y = contentScreenRect.YMost() - userRect.YMost();

  gfx::Size underZoomScale(1.0f, 1.0f);
  if (mContentRect.width * userZoom.scale < metrics.GetCompositionBounds().width) {
    underZoomScale.width = (mContentRect.width * userZoom.scale) /
  if (mContentRect.height * userZoom.scale < metrics.GetCompositionBounds().height) {
    underZoomScale.height = (mContentRect.height * userZoom.scale) /
  oldTransform.PreScale(underZoomScale.width, underZoomScale.height, 1);

  // Make sure fixed position layers don't move away from their anchor points
  // when we're asynchronously panning or zooming
  AlignFixedAndStickyLayers(aLayer, aLayer, metrics.GetScrollId(), oldTransform,
                            fixedLayerMargins, false);

  ExpandRootClipRect(aLayer, fixedLayerMargins);

AsyncCompositionManager::GetFrameUniformity(FrameUniformityData* aOutData)

AsyncCompositionManager::TransformShadowTree(TimeStamp aCurrentFrame,
                                             TransformsToSkip aSkip)
  PROFILER_LABEL("AsyncCompositionManager", "TransformShadowTree",

  Layer* root = mLayerManager->GetRoot();
  if (!root) {
    return false;

  // First, compute and set the shadow transforms from OMT animations.
  // NB: we must sample animations *before* sampling pan/zoom
  // transforms.
  bool wantNextFrame = SampleAnimations(root, aCurrentFrame);

  if (!(aSkip & TransformsToSkip::APZ)) {
    // FIXME/bug 775437: unify this interface with the ~native-fennec
    // derived code
    // Attempt to apply an async content transform to any layer that has
    // an async pan zoom controller (which means that it is rendered
    // async using Gecko). If this fails, fall back to transforming the
    // primary scrollable layer.  "Failing" here means that we don't
    // find a frame that is async scrollable.  Note that the fallback
    // code also includes Fennec which is rendered async.  Fennec uses
    // its own platform-specific async rendering that is done partially
    // in Gecko and partially in Java.
    bool foundRoot = false;
    Maybe<ParentLayerIntRect> clipDeferredFromChildren;
    if (ApplyAsyncContentTransformToTree(root, &foundRoot, clipDeferredFromChildren)) {
#if defined(MOZ_ANDROID_APZ)
      if (foundRoot && mFixedLayerMargins != ScreenMargin()) {
        MoveScrollbarForLayerMargin(root, mRootScrollableId, mFixedLayerMargins);
    } else {
      AutoTArray<Layer*,1> scrollableLayers;

      for (uint32_t i = 0; i < scrollableLayers.Length(); i++) {
        if (scrollableLayers[i]) {

    // Advance APZ animations to the next expected vsync timestamp, if we can
    // get it.
    TimeStamp nextFrame = aCurrentFrame;
    TimeDuration vsyncrate = gfxPlatform::GetPlatform()->GetHardwareVsync()->GetGlobalDisplay().GetVsyncRate();
    if (vsyncrate != TimeDuration::Forever()) {
      nextFrame += vsyncrate;
    wantNextFrame |= SampleAPZAnimations(LayerMetricsWrapper(root), nextFrame);

  LayerComposite* rootComposite = root->AsLayerComposite();

  gfx::Matrix4x4 trans = rootComposite->GetShadowBaseTransform();
  trans *= gfx::Matrix4x4::From2D(mWorldTransform);

  if (gfxPrefs::CollectScrollTransforms()) {

  return wantNextFrame;

AsyncCompositionManager::SetFirstPaintViewport(const LayerIntPoint& aOffset,
                                               const CSSToLayerScale& aZoom,
                                               const CSSRect& aCssPageRect)
  AndroidBridge::Bridge()->SetFirstPaintViewport(aOffset, aZoom, aCssPageRect);

AsyncCompositionManager::SetPageRect(const CSSRect& aCssPageRect)

AsyncCompositionManager::SyncViewportInfo(const LayerIntRect& aDisplayPort,
                                          const CSSToLayerScale& aDisplayResolution,
                                          bool aLayersUpdated,
                                          int32_t aPaintSyncId,
                                          ParentLayerRect& aScrollRect,
                                          CSSToParentLayerScale& aScale,
                                          ScreenMargin& aFixedLayerMargins)

AsyncCompositionManager::SyncFrameMetrics(const ParentLayerPoint& aScrollOffset,
                                          const CSSToParentLayerScale& aZoom,
                                          const CSSRect& aCssPageRect,
                                          const CSSRect& aDisplayPort,
                                          const CSSToLayerScale& aPaintedResolution,
                                          bool aLayersUpdated,
                                          int32_t aPaintSyncId,
                                          ScreenMargin& aFixedLayerMargins)
  AndroidBridge::Bridge()->SyncFrameMetrics(aScrollOffset, aZoom, aCssPageRect,
                                            aDisplayPort, aPaintedResolution,
                                            aLayersUpdated, aPaintSyncId,

} // namespace layers
} // namespace mozilla