Source code

Revision control

Other Tools

/* -*- 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 */
#include "mozilla/layers/AsyncCompositionManager.h"
#include <stdint.h> // for uint32_t
#include "LayerManagerComposite.h" // for LayerManagerComposite, etc
#include "Layers.h" // for Layer, ContainerLayer, etc
#include "gfxPoint.h" // for gfxPoint, gfxSize
#include "mozilla/ProfilerLabels.h"
#include "mozilla/ServoBindings.h" // for Servo_AnimationValue_GetOpacity, etc
#include "mozilla/ScopeExit.h" // for MakeScopeExit
#include "mozilla/StaticPrefs_apz.h"
#include "mozilla/StaticPrefs_gfx.h"
#include "mozilla/WidgetUtils.h" // for ComputeTransformForRotation
#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/AnimationHelper.h"
#include "mozilla/layers/APZSampler.h" // for APZSampler
#include "mozilla/layers/APZUtils.h" // for CompleteAsyncTransform
#include "mozilla/layers/Compositor.h" // for Compositor
#include "mozilla/layers/CompositorAnimationStorage.h" // for CompositorAnimationStorage
#include "mozilla/layers/CompositorBridgeParent.h" // for CompositorBridgeParent, etc
#include "mozilla/layers/CompositorThread.h"
#include "mozilla/layers/LayerAnimationUtils.h" // for TimingFunctionToComputedTimingFunction
#include "mozilla/layers/LayerMetricsWrapper.h" // for LayerMetricsWrapper
#include "mozilla/layers/SampleTime.h"
#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 nsTArray
#include "UnitTransforms.h" // for TransformTo
# include <android/log.h>
# include "mozilla/layers/UiCompositorControllerParent.h"
# include "mozilla/widget/AndroidCompositorWidget.h"
#include "FrameUniformityData.h"
#include "TreeTraversal.h" // for ForEachNode, BreadthFirstSearch
#include "VsyncSource.h"
namespace mozilla {
namespace layers {
using namespace mozilla::gfx;
static bool IsSameDimension(hal::ScreenOrientation o1,
hal::ScreenOrientation o2) {
bool isO1portrait = (o1 == hal::eScreenOrientation_PortraitPrimary ||
o1 == hal::eScreenOrientation_PortraitSecondary);
bool isO2portrait = (o2 == hal::eScreenOrientation_PortraitPrimary ||
o2 == hal::eScreenOrientation_PortraitSecondary);
return !(isO1portrait ^ isO2portrait);
static bool ContentMightReflowOnOrientationChange(const IntRect& rect) {
return rect.Width() != rect.Height();
CompositorBridgeParent* aParent, HostLayerManager* aManager)
: mLayerManager(aManager),
mCompositorBridge(aParent) {
AsyncCompositionManager::~AsyncCompositionManager() = default;
void AsyncCompositionManager::ResolveRefLayers(
CompositorBridgeParent* aCompositor, bool* aHasRemoteContent) {
if (aHasRemoteContent) {
*aHasRemoteContent = false;
if (!mLayerManager->GetRoot()) {
mReadyForCompose = true;
bool hasRemoteContent = false;
ForEachNode<ForwardIterator>(mLayerManager->GetRoot(), [&](Layer* layer) {
RefLayer* refLayer = layer->AsRefLayer();
if (!refLayer) {
hasRemoteContent = true;
const CompositorBridgeParent::LayerTreeState* state =
if (!state) {
Layer* referent = state->mRoot;
if (!referent) {
if (!refLayer->GetLocalVisibleRegion().IsEmpty()) {
hal::ScreenOrientation chromeOrientation = mTargetConfig.orientation();
hal::ScreenOrientation contentOrientation =
if (!IsSameDimension(chromeOrientation, contentOrientation) &&
mTargetConfig.naturalBounds())) {
mReadyForCompose = false;
if (aHasRemoteContent) {
*aHasRemoteContent = hasRemoteContent;
void AsyncCompositionManager::DetachRefLayers() {
if (!mLayerManager->GetRoot()) {
mReadyForCompose = false;
mLayerManager->GetRoot(), [&](Layer* layer) {
RefLayer* refLayer = layer->AsRefLayer();
if (!refLayer) {
const CompositorBridgeParent::LayerTreeState* state =
if (!state) {
Layer* referent = state->mRoot;
if (referent) {
void AsyncCompositionManager::ComputeRotation() {
if (!mTargetConfig.naturalBounds().IsEmpty()) {
mWorldTransform = ComputeTransformForRotation(mTargetConfig.naturalBounds(),
static void GetBaseTransform(Layer* aLayer, Matrix4x4* aTransform) {
// Start with the animated transform if there is one
*aTransform = (aLayer->AsHostLayer()->GetShadowTransformSetByAnimation()
? aLayer->GetLocalTransform()
: aLayer->GetTransform());
static void TransformClipRect(
Layer* aLayer, const ParentLayerToParentLayerMatrix4x4& aTransform) {
const Maybe<ParentLayerIntRect>& clipRect =
if (clipRect) {
ParentLayerIntRect transformed = TransformBy(aTransform, *clipRect);
// Similar to TransformFixedClip(), but only transforms the fixed part of the
// clip.
static void TransformFixedClip(
Layer* aLayer, const ParentLayerToParentLayerMatrix4x4& aTransform,
AsyncCompositionManager::ClipParts& aClipParts) {
if (aClipParts.mFixedClip) {
*aClipParts.mFixedClip = TransformBy(aTransform, *aClipParts.mFixedClip);
* 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(), 1);
aTransform.PostScale(1.0f / aLayer->GetPostXScale(),
1.0f / aLayer->GetPostYScale(), 1);
static void TranslateShadowLayer(
Layer* aLayer, const ParentLayerPoint& aTranslation, bool aAdjustClipRect,
AsyncCompositionManager::ClipPartsCache* aClipPartsCache) {
// 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.
SetShadowTransform(aLayer, layerTransform);
if (aAdjustClipRect) {
auto transform =
// If we're passed a clip parts cache, only transform the fixed part of
// the clip.
if (aClipPartsCache) {
auto iter = aClipPartsCache->find(aLayer);
MOZ_ASSERT(iter != aClipPartsCache->end());
TransformFixedClip(aLayer, transform, iter->second);
} else {
TransformClipRect(aLayer, transform);
// 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, aClipPartsCache);
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;
* 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, ScrollableLayerGuid::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, ScrollableLayerGuid::ViewID aFixedWithRespectTo,
Layer* aTransformedLayer, ScrollableLayerGuid::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,
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;
// If |aLayer| is fixed or sticky, returns the scroll id of the scroll frame
// that it's fixed or sticky to. Otherwise, returns Nothing().
static Maybe<ScrollableLayerGuid::ViewID> IsFixedOrSticky(Layer* aLayer) {
bool isRootOfFixedSubtree = aLayer->GetIsFixedPosition() &&
if (isRootOfFixedSubtree) {
return Some(aLayer->GetFixedPositionScrollContainerId());
if (aLayer->GetIsStickyPosition()) {
return Some(aLayer->GetStickyScrollContainerId());
return Nothing();
void AsyncCompositionManager::AlignFixedAndStickyLayers(
Layer* aTransformedSubtreeRoot, Layer* aStartTraversalAt,
SideBits aStuckSides, ScrollableLayerGuid::ViewID aTransformScrollId,
const LayerToParentLayerMatrix4x4& aPreviousTransformForRoot,
const LayerToParentLayerMatrix4x4& aCurrentTransformForRoot,
const ScreenMargin& aFixedLayerMargins, ClipPartsCache& aClipPartsCache,
const ScreenMargin& aGeckoFixedLayerMargins) {
Layer* layer = aStartTraversalAt;
bool needsAsyncTransformUnapplied = false;
if (Maybe<ScrollableLayerGuid::ViewID> fixedTo = IsFixedOrSticky(layer)) {
needsAsyncTransformUnapplied = AsyncTransformShouldBeUnapplied(
layer, *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 = layer->GetFirstChild(); child;
child = child->GetNextSibling()) {
AlignFixedAndStickyLayers(aTransformedSubtreeRoot, child, aStuckSides,
aTransformScrollId, aPreviousTransformForRoot,
aCurrentTransformForRoot, aFixedLayerMargins,
aClipPartsCache, aGeckoFixedLayerMargins);
AdjustFixedOrStickyLayer(aTransformedSubtreeRoot, layer, aStuckSides,
aTransformScrollId, aPreviousTransformForRoot,
aCurrentTransformForRoot, aFixedLayerMargins,
aClipPartsCache, aGeckoFixedLayerMargins);
// Determine the amount of overlap between the 1D vector |aTranslation|
// and the interval [aMin, aMax].
static gfxFloat IntervalOverlap(gfxFloat aTranslation, gfxFloat aMin,
gfxFloat aMax) {
if (aTranslation > 0) {
return std::max(0.0, std::min(aMax, aTranslation) - std::max(aMin, 0.0));
return std::min(0.0, std::max(aMin, aTranslation) - std::min(aMax, 0.0));
void AsyncCompositionManager::AdjustFixedOrStickyLayer(
Layer* aTransformedSubtreeRoot, Layer* aFixedOrSticky, SideBits aStuckSides,
ScrollableLayerGuid::ViewID aTransformScrollId,
const LayerToParentLayerMatrix4x4& aPreviousTransformForRoot,
const LayerToParentLayerMatrix4x4& aCurrentTransformForRoot,
const ScreenMargin& aFixedLayerMargins, ClipPartsCache& aClipPartsCache,
const ScreenMargin& aGeckoFixedLayerMargins) {
Layer* layer = aFixedOrSticky;
// 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;
if (layer != aTransformedSubtreeRoot) {
AccumulateLayerTransforms(layer->GetParent(), aTransformedSubtreeRoot,
// A transform creates a containing block for fixed-position descendants,
// so there shouldn't be a transform in between the fixed layer and
// the subtree root layer.
if (layer->GetIsFixedPosition()) {
// Calculate the cumulative transforms between the subtree root with the
// old transform and the current transform.
// For coordinate purposes, we'll treat the subtree root layer as the
// "parent" layer, even though it could be a farther ancestor.
auto oldCumulativeTransform = ViewAs<LayerToParentLayerMatrix4x4>(
ancestorTransform * aPreviousTransformForRoot.ToUnknownMatrix());
auto newCumulativeTransform = ViewAs<LayerToParentLayerMatrix4x4>(
ancestorTransform * aCurrentTransformForRoot.ToUnknownMatrix());
// We're going to be inverting |newCumulativeTransform|. If it's singular,
// there's nothing we can do.
if (newCumulativeTransform.IsSingular()) {
// Since we create container layers for fixed layers, there shouldn't
// a local CSS or OMTA transform on the fixed layer, either (any local
// transform would go onto a descendant layer inside the container
// layer).
#ifdef DEBUG
Matrix4x4 localTransform;
GetBaseTransform(layer, &localTransform);
// 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 transform is applied).
LayerPoint anchor = layer->GetFixedPositionAnchor();
SideBits sideBits = layer->GetFixedPositionSides();
if (layer->GetIsStickyPosition()) {
// For sticky items, it may be that only some of the sides are actively
// stuck. Only take into account those sides.
sideBits &= aStuckSides;
// Offset the layer's anchor point to make sure fixed position content
// respects content document fixed position margins.
ScreenPoint offset = apz::ComputeFixedMarginsOffset(
aFixedLayerMargins, sideBits,
// For sticky layers, we don't need to factor aGeckoFixedLayerMargins
// because Gecko doesn't shift the position of sticky elements for dynamic
// toolbar movements.
layer->GetIsStickyPosition() ? ScreenMargin() : aGeckoFixedLayerMargins);
// Fixed margins only apply to layers fixed to the root, so we can view
// the offset in layer space.
LayerPoint offsetAnchor =
anchor + ViewAs<LayerPixel>(
offset, PixelCastJustification::ScreenIsParentLayerForRoot);
// Additionally transform the anchor to compensate for the change
// from the old transform to the new 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 transform
// to bring it back to layer space.
ParentLayerPoint offsetAnchorInSubtreeRootSpace =
LayerPoint transformedAnchor =
// We want to translate the layer by the difference between
// |transformedAnchor| and |anchor|.
LayerPoint translation = transformedAnchor - anchor;
// A fixed layer will "consume" (be unadjusted by) the entire translation
// calculated above. A sticky layer may consume all, part, or none of it,
// depending on where we are relative to its sticky scroll range.
// The remainder of the translation (the unconsumed portion) needs to
// be propagated to descendant fixed/sticky layers.
LayerPoint unconsumedTranslation;
if (layer->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 LayerRectAbsolute& stickyOuter = layer->GetStickyScrollRangeOuter();
const LayerRectAbsolute& stickyInner = layer->GetStickyScrollRangeInner();
LayerPoint originalTranslation = translation;
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());
unconsumedTranslation = translation - originalTranslation;
// 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.
true, &aClipPartsCache);
// Propragate the unconsumed portion of the translation to descendant
// fixed/sticky layers.
if (unconsumedTranslation != LayerPoint()) {
// Take the computations we performed to derive |translation| from
// |aCurrentTransformForRoot|, and perform them in reverse, keeping other
// quantities fixed, to come up with a new transform |newTransform| that
// would produce |unconsumedTranslation|.
LayerPoint newTransformedAnchor = unconsumedTranslation + anchor;
ParentLayerPoint newTransformedAnchorInSubtreeRootSpace =
LayerToParentLayerMatrix4x4 newTransform = aPreviousTransformForRoot;
newTransform.PostTranslate(newTransformedAnchorInSubtreeRootSpace -
// Propagate this new transform to our descendants as the new value of
// |aCurrentTransformForRoot|. This allows them to consume the unconsumed
// translation.
for (Layer* child = layer->GetFirstChild(); child;
child = child->GetNextSibling()) {
AlignFixedAndStickyLayers(aTransformedSubtreeRoot, child, aStuckSides,
aTransformScrollId, aPreviousTransformForRoot,
newTransform, aFixedLayerMargins,
aClipPartsCache, aGeckoFixedLayerMargins);
bool AsyncCompositionManager::SampleAnimations(Layer* aLayer,
TimeStamp aCurrentFrameTime) {
CompositorAnimationStorage* storage =
return storage->SampleAnimations(aLayer, mCompositorBridge,
mPreviousFrameTimeStamp, aCurrentFrameTime);
void AsyncCompositionManager::RecordShadowTransforms(Layer* aLayer) {
ForEachNodePostOrder<ForwardIterator>(aLayer, [this](Layer* layer) {
for (uint32_t i = 0; i < layer->GetScrollMetadataCount(); i++) {
if (!layer->GetFrameMetrics(i).IsScrollable()) {
gfx::Matrix4x4 shadowTransform =
if (!shadowTransform.Is2D()) {
Matrix transform = shadowTransform.As2D();
if (transform.IsTranslation() && !shadowTransform.IsIdentity()) {
Point translation = transform.GetTranslation();
mLayerTransformRecorder.RecordTransform(layer, 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->AsHostLayer()->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 =
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, ScrollableLayerGuid::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<ReverseIterator>(aRoot, [aRootScrollId](Layer* aNode) {
return (aNode->GetScrollbarData().IsThumb() &&
aNode->GetScrollbarData().mDirection.isSome() &&
*aNode->GetScrollbarData().mDirection ==
ScrollDirection::eHorizontal &&
aNode->GetScrollbarData().mTargetViewId == 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.
ParentLayerPoint(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);
bool AsyncCompositionManager::ApplyAsyncContentTransformToTree(
Layer* aLayer, bool* aOutFoundRoot) {
bool appliedTransform = false;
std::stack<Maybe<ParentLayerIntRect>> stackDeferredClips;
std::stack<LayersId> layersIds;
// Maps layers to their ClipParts. The parts are not stored individually
// on the layer, but during AlignFixedAndStickyLayers we need access to
// the individual parts for descendant layers.
ClipPartsCache clipPartsCache;
Layer* zoomContainer = nullptr;
Maybe<LayerMetricsWrapper> zoomedMetrics;
[&](Layer* layer) {
if (layer->AsRefLayer()) {
// If we encounter the async zoom container, find the corresponding
// APZC and stash it into |zoomedMetrics|.
// (We stash it in the form of a LayerMetricsWrapper because
// APZSampler requires going through that rather than using the APZC
// directly.)
// We do this on the way down the tree (i.e. here in the pre-action)
// so that by the time we encounter the layers with the RCD-RSF's
// scroll metadata (which will be descendants of the async zoom
// container), we can check for it and know we should only apply the
// scroll portion of the async transform to those layers (as the zoom
// portion will go on the async zoom container).
if (Maybe<ScrollableLayerGuid::ViewID> zoomedScrollId =
layer->GetAsyncZoomContainerId()) {
zoomContainer = layer;
[zoomedScrollId, &zoomedMetrics](LayerMetricsWrapper aWrapper) {
// Do not descend into layer subtrees with a different layers
// id.
if (aWrapper.AsRefLayer()) {
return TraversalFlag::Skip;
if (aWrapper.Metrics().GetScrollId() == *zoomedScrollId) {
zoomedMetrics = Some(aWrapper);
return TraversalFlag::Abort;
return TraversalFlag::Continue;
[&](Layer* layer) {
Maybe<ParentLayerIntRect> clipDeferredFromChildren =;
LayersId currentLayersId =;
LayerToParentLayerMatrix4x4 oldTransform =
layer->GetTransformTyped() * AsyncTransformMatrix();
AsyncTransformComponentMatrix combinedAsyncTransform;
bool hasAsyncTransform = false;
// Only set on the root layer for Android.
ScreenMargin fixedLayerMargins;
// Each layer has multiple clips:
// - Its local clip, which is fixed to the layer contents, i.e. it
// moves with those async transforms which the layer contents move
// with.
// - Its scrolled clip, which moves with all async transforms.
// - For each ScrollMetadata on the layer, a scroll clip. This
// includes the composition bounds and any other clips induced by
// layout. This moves with async transforms from ScrollMetadatas
// above it.
// In this function, these clips are combined into two shadow clip
// parts:
// - The fixed clip, which consists of the local clip only, initially
// transformed by all async transforms.
// - The scrolled clip, which consists of the other clips, transformed
// by the appropriate transforms.
// These two parts are kept separate for now, because for fixed layers,
// we need to adjust the fixed clip (to cancel out some async
// transforms). The parts are kept in a cache which is cleared at the
// beginning of every composite. The final shadow clip for the layer is
// the intersection of the (possibly adjusted) fixed clip and the
// scrolled clip.
ClipParts& clipParts = clipPartsCache[layer];
clipParts.mFixedClip = layer->GetClipRect();
clipParts.mScrolledClip = layer->GetScrolledClipRect();
// If we are a perspective transform ContainerLayer, apply the clip
// deferred from our child (if there is any) before we iterate over our
// frame metrics, because this clip is subject to all async transforms
// of this layer. Since this clip came from the a scroll clip on the
// child, it becomes part of our scrolled clip.
clipParts.mScrolledClip = IntersectMaybeRects(clipDeferredFromChildren,
// 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;
// The layer's scrolled clip can have an ancestor mask layer as well,
// which is moved by all async scrolls on this layer.
if (const Maybe<LayerClip>& scrolledClip = layer->GetScrolledClip()) {
if (scrolledClip->GetMaskLayerIndex()) {
if (RefPtr<APZSampler> sampler = mCompositorBridge->GetAPZSampler()) {
for (uint32_t i = 0; i < layer->GetScrollMetadataCount(); i++) {
LayerMetricsWrapper wrapper(layer, i);
if (!wrapper.GetApzc()) {
const FrameMetrics& metrics = wrapper.Metrics();
hasAsyncTransform = true;
AsyncTransformComponents asyncTransformComponents =
(zoomedMetrics &&
sampler->GetGuid(*zoomedMetrics) == sampler->GetGuid(wrapper))
? AsyncTransformComponents{AsyncTransformComponent::eLayout}
: LayoutAndVisual;
AsyncTransformComponentMatrix asyncTransform =
wrapper, asyncTransformComponents);
Maybe<CompositionPayload> payload =
// The scroll latency should be measured between composition and the
// first scrolling event. Otherwise we observe metrics with <16ms
// latency even when frame.delay is enabled.
if (payload.isSome()) {
if (!layer->IsScrollableWithoutContent()) {
const ScrollMetadata& scrollMetadata = wrapper.Metadata();
// 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 */
(layer->GetParent() == nullptr && /* rootmost metrics */
i + 1 >= layer->GetScrollMetadataCount());
if (*aOutFoundRoot) {
mRootScrollableId = metrics.GetScrollId();
Compositor* compositor = mLayerManager->GetCompositor();
if (CompositorBridgeParent* bridge =
compositor->GetCompositorBridgeParent()) {
LayersId rootLayerTreeId = bridge->RootLayerTreeId();
GeckoViewMetrics gvMetrics =
if (mIsFirstPaint || GeckoViewMetricsHaveUpdated(gvMetrics)) {
if (RefPtr<UiCompositorControllerParent> uiController =
GetFromRootLayerTreeId(rootLayerTreeId)) {
mLastMetrics = gvMetrics;
if (mIsFirstPaint) {
if (RefPtr<UiCompositorControllerParent> uiController =
GetFromRootLayerTreeId(rootLayerTreeId)) {
mIsFirstPaint = false;
if (mLayersUpdated) {
LayersId rootLayerTreeId = bridge->RootLayerTreeId();
if (RefPtr<UiCompositorControllerParent> uiController =
GetFromRootLayerTreeId(rootLayerTreeId)) {
mLayersUpdated = false;
fixedLayerMargins = GetFixedLayerMargins();
*aOutFoundRoot = false;
// Non-Android platforms still care about this flag being cleared
// after the first call to TransformShadowTree().
mIsFirstPaint = false;
// Transform the current local clips by this APZC's async transform.
if (clipParts.mFixedClip) {
*clipParts.mFixedClip =
TransformBy(asyncTransform, *clipParts.mFixedClip);
if (clipParts.mScrolledClip) {
*clipParts.mScrolledClip =
TransformBy(asyncTransform, *clipParts.mScrolledClip);
// Note: we don't set the layer's shadow clip rect property yet;
// AlignFixedAndStickyLayers will use the clip parts from the clip
// parts cache.
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 =
layer->GetTransformTyped() *
CompleteAsyncTransform(AdjustForClip(asyncTransform, layer));
// See bug 1630274 for why we pass eNone here; fixing that bug will
// probably end up changing this to be more correct.
AlignFixedAndStickyLayers(layer, layer, SideBits::eNone,
metrics.GetScrollId(), oldTransform,
fixedLayerMargins, clipPartsCache,
// 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.HasScrollClip()) {
ParentLayerIntRect clip =
if (layer->GetParent() &&
layer->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.)
} else {
clipParts.mScrolledClip =
IntersectMaybeRects(Some(clip), clipParts.mScrolledClip);
// 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.HasScrollClip()) {
const LayerClip& scrollClip = scrollMetadata.ScrollClip();
if (scrollClip.GetMaskLayerIndex()) {
size_t maskLayerIndex = scrollClip.GetMaskLayerIndex().value();
Layer* ancestorMaskLayer =
if (Maybe<ScrollableLayerGuid::ViewID> zoomedScrollId =
layer->GetAsyncZoomContainerId()) {
if (zoomedMetrics) {
AsyncTransformComponentMatrix zoomTransform =
*zoomedMetrics, {AsyncTransformComponent::eVisual});
hasAsyncTransform = true;
combinedAsyncTransform *= zoomTransform;
} else {
// TODO: Is this normal? It happens on some pages, such as
// about:config on mobile, for just one frame or so, before the
// scroll metadata for zoomedScrollId appears in the layer tree.
auto IsFixedToZoomContainer = [&](Layer* aFixedLayer) {
if (!zoomedMetrics) {
return false;
ScrollableLayerGuid::ViewID targetId =
MOZ_ASSERT(targetId != ScrollableLayerGuid::NULL_SCROLL_ID);
ScrollableLayerGuid rootContent = sampler->GetGuid(*zoomedMetrics);
return rootContent.mScrollId == targetId &&
rootContent.mLayersId == currentLayersId;
auto SidesStuckToZoomContainer = [&](Layer* aLayer) -> SideBits {
SideBits result = SideBits::eNone;
if (!zoomedMetrics) {
return result;
if (!aLayer->GetIsStickyPosition()) {
return result;
ScrollableLayerGuid::ViewID targetId =
if (targetId == ScrollableLayerGuid::NULL_SCROLL_ID) {
return result;
ScrollableLayerGuid rootContent = sampler->GetGuid(*zoomedMetrics);
if (rootContent.mScrollId != targetId ||
rootContent.mLayersId != currentLayersId) {
return result;
ParentLayerPoint translation =
*zoomedMetrics, {AsyncTransformComponent::eLayout})
if (apz::IsStuckAtBottom(translation.y,
aLayer->GetStickyScrollRangeOuter())) {
result |= SideBits::eBottom;
if (apz::IsStuckAtTop(translation.y,
aLayer->GetStickyScrollRangeOuter())) {
result |= SideBits::eTop;
return result;
// Layers fixed to the RCD-RSF no longer need
// AdjustFixedOrStickyLayer() to scroll them by the eVisual transform,
// as that's now applied to the async zoom container itself. However,
// we still need to adjust them by the fixed layer margins to
// account for dynamic toolbar transitions. This is also handled by
// AdjustFixedOrStickyLayer(), so we now call it with empty transforms
// to get it to perform just the fixed margins adjustment.
SideBits stuckSides = SidesStuckToZoomContainer(layer);
if (zoomedMetrics && ((layer->GetIsFixedPosition() &&
!layer->GetParent()->GetIsFixedPosition() &&
IsFixedToZoomContainer(layer)) ||
stuckSides != SideBits::eNone)) {
LayerToParentLayerMatrix4x4 emptyTransform;
ScreenMargin marginsForFixedLayer = GetFixedLayerMargins();
AdjustFixedOrStickyLayer(zoomContainer, layer, stuckSides,
emptyTransform, emptyTransform,
marginsForFixedLayer, clipPartsCache,
bool clipChanged = (hasAsyncTransform || clipDeferredFromChildren ||
if (clipChanged) {
// Intersect the two clip parts and apply them to the layer.
// During ApplyAsyncContentTransformTree on an ancestor layer,
// AlignFixedAndStickyLayers may overwrite this with a new clip it
// computes from the clip parts, but if that doesn't happen, this
// is the layer's final clip rect.
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.
layer->GetLocalTransformTyped() *
AdjustForClip(combinedAsyncTransform, layer));
// Do the same for the layer's own mask layer, if it has one.
if (Layer* maskLayer = layer->GetMaskLayer()) {
SetShadowTransform(maskLayer, maskLayer->GetLocalTransformTyped() *
appliedTransform = true;
ExpandRootClipRect(layer, fixedLayerMargins);
if (layer->GetScrollbarData().mScrollbarLayerType ==
layers::ScrollbarLayerType::Thumb) {
if (layer->AsRefLayer()) {
MOZ_ASSERT(layersIds.size() > 1);
return appliedTransform;
bool AsyncCompositionManager::GeckoViewMetricsHaveUpdated(
const GeckoViewMetrics& aMetrics) {
return RoundedToInt(mLastMetrics.mVisualScrollOffset) !=
RoundedToInt(aMetrics.mVisualScrollOffset) ||
mLastMetrics.mZoom != aMetrics.mZoom;
static bool LayerIsScrollbarTarget(const LayerMetricsWrapper& aTarget,
Layer* aScrollbar) {
if (!aTarget.GetApzc()) {
return false;
const FrameMetrics& metrics = aTarget.Metrics();
if (metrics.GetScrollId() != aScrollbar->GetScrollbarData().mTargetViewId) {
return false;
return !metrics.IsScrollInfoLayer();
static void ApplyAsyncTransformToScrollbarForContent(
const RefPtr<APZSampler>& aSampler, Layer* aScrollbar,
const LayerMetricsWrapper& aContent, bool aScrollbarIsDescendant) {
AsyncTransformComponentMatrix clipTransform;
LayerToParentLayerMatrix4x4 transform =
aScrollbar->GetLocalTransformTyped(), aContent,
aScrollbar->GetScrollbarData(), aScrollbarIsDescendant,
if (aScrollbarIsDescendant) {
// 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, clipTransform);
SetShadowTransform(aScrollbar, transform);
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);
LayerMetricsWrapper scrolledLayer;
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.
ForEachNode<ForwardIterator>(root, [&root, &scrolledLayer, &aScrollbar](
LayerMetricsWrapper aLayerMetrics) {
// Do not recurse into RefLayers, since our initial aSubtreeRoot is the
// root (or RefLayer root) of a single layer space to search.
if (root != aLayerMetrics && aLayerMetrics.AsRefLayer()) {
return TraversalFlag::Skip;
if (LayerIsScrollbarTarget(aLayerMetrics, aScrollbar)) {
scrolledLayer = aLayerMetrics;
return TraversalFlag::Abort;
return TraversalFlag::Continue;
return scrolledLayer;
void 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) {
aLayer, scrollTarget, isAncestor);
void AsyncCompositionManager::GetFrameUniformity(
FrameUniformityData* aOutData) {
bool AsyncCompositionManager::TransformShadowTree(
const SampleTime& aCurrentFrame, TimeDuration aVsyncRate,
CompositorBridgeParentBase::TransformsToSkip aSkip) {
AUTO_PROFILER_LABEL("AsyncCompositionManager::TransformShadowTree", GRAPHICS);
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.Time());
// Advance animations to the next expected vsync timestamp, if we can
// get it.
SampleTime nextFrame = aCurrentFrame;
MOZ_ASSERT(aVsyncRate != TimeDuration::Forever());
if (aVsyncRate != TimeDuration::Forever()) {
nextFrame = nextFrame + aVsyncRate;
// Reset the previous time stamp if we don't already have any running
// animations to avoid using the time which is far behind for newly
// started animations.
mPreviousFrameTimeStamp = wantNextFrame ? aCurrentFrame.Time() : TimeStamp();
if (!(aSkip & CompositorBridgeParentBase::TransformsToSkip::APZ)) {
bool apzAnimating = false;
if (RefPtr<APZSampler> apz = mCompositorBridge->GetAPZSampler()) {
apzAnimating = apz->AdvanceAnimations(nextFrame);
wantNextFrame |= apzAnimating;
// Apply an async content transform to any layer that has
// an async pan zoom controller.
bool foundRoot = false;
if (ApplyAsyncContentTransformToTree(root, &foundRoot)) {
if (foundRoot && GetFixedLayerMargins() != ScreenMargin()) {
MoveScrollbarForLayerMargin(root, mRootScrollableId,
HostLayer* rootComposite = root->AsHostLayer();
gfx::Matrix4x4 trans = rootComposite->GetShadowBaseTransform();
trans *= gfx::Matrix4x4::From2D(mWorldTransform);
if (StaticPrefs::gfx_vsync_collect_scroll_transforms()) {
return wantNextFrame;
void AsyncCompositionManager::SetFixedLayerMargins(ScreenIntCoord aTop,
ScreenIntCoord aBottom) { = aTop;
mFixedLayerMargins.bottom = aBottom;
ScreenMargin AsyncCompositionManager::GetFixedLayerMargins() const {
ScreenMargin result = mFixedLayerMargins;
if (StaticPrefs::apz_fixed_margin_override_enabled()) { = StaticPrefs::apz_fixed_margin_override_top();
result.bottom = StaticPrefs::apz_fixed_margin_override_bottom();
return result;
} // namespace layers
} // namespace mozilla