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/* -*- 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 "SampledAPZCState.h"
#include "APZUtils.h"
namespace mozilla {
namespace layers {
SampledAPZCState::SampledAPZCState() {}
SampledAPZCState::SampledAPZCState(const FrameMetrics& aMetrics)
: mLayoutViewport(aMetrics.GetLayoutViewport()),
mZoom(aMetrics.GetZoom()) {
SampledAPZCState::SampledAPZCState(const FrameMetrics& aMetrics,
Maybe<CompositionPayload>&& aPayload,
APZScrollGeneration aGeneration)
: mLayoutViewport(aMetrics.GetLayoutViewport()),
mGeneration(aGeneration) {
bool SampledAPZCState::operator==(const SampledAPZCState& aOther) const {
// The payload doesn't factor into equality, that just comes along for
// the ride.
return mLayoutViewport.IsEqualEdges(aOther.mLayoutViewport) &&
mVisualScrollOffset == aOther.mVisualScrollOffset &&
mZoom == aOther.mZoom;
bool SampledAPZCState::operator!=(const SampledAPZCState& aOther) const {
return !(*this == aOther);
Maybe<CompositionPayload> SampledAPZCState::TakeScrollPayload() {
return std::move(mScrollPayload);
void SampledAPZCState::UpdateScrollProperties(const FrameMetrics& aMetrics) {
mLayoutViewport = aMetrics.GetLayoutViewport();
mVisualScrollOffset = aMetrics.GetVisualScrollOffset();
void SampledAPZCState::UpdateScrollPropertiesWithRelativeDelta(
const FrameMetrics& aMetrics, const CSSPoint& aRelativeDelta) {
mVisualScrollOffset += aRelativeDelta;
void SampledAPZCState::UpdateZoomProperties(const FrameMetrics& aMetrics) {
mZoom = aMetrics.GetZoom();
void SampledAPZCState::ClampVisualScrollOffset(const FrameMetrics& aMetrics) {
// Make sure that we use the local mZoom to do these calculations, because the
// one on aMetrics might be newer.
CSSRect scrollRange = FrameMetrics::CalculateScrollRange(
aMetrics.GetScrollableRect(), aMetrics.GetCompositionBounds(), mZoom);
mVisualScrollOffset = scrollRange.ClampPoint(mVisualScrollOffset);
void SampledAPZCState::ZoomBy(float aScale) { mZoom.scale *= aScale; }
void SampledAPZCState::RemoveFractionalAsyncDelta() {
// This function is a performance hack. With non-WebRender, having small
// fractional deltas between the layout offset and scroll offset on
// container layers can trigger the creation of a temporary surface during
// composition, because it produces a non-integer translation that doesn't
// play well with layer clips. So we detect the case where the delta is
// uselessly small (0.01 parentlayer pixels or less) and tweak the sampled
// scroll offset to eliminate it. By doing this here at sample time rather
// than elsewhere in the pipeline we are least likely to break assumptions
// and invariants elsewhere in the code, since sampling effectively takes
// a snapshot of APZ state (decoupling it from APZ assumptions) and provides
// it as an input to the compositor (so all compositor state should be
// internally consistent based on this input).
if (mLayoutViewport.TopLeft() == mVisualScrollOffset) {
const ParentLayerCoord EPSILON = 0.01;
ParentLayerPoint paintedOffset = mLayoutViewport.TopLeft() * mZoom;
ParentLayerPoint asyncOffset = mVisualScrollOffset * mZoom;
if (FuzzyEqualsAdditive(paintedOffset.x, asyncOffset.x, EPSILON) &&
FuzzyEqualsAdditive(paintedOffset.y, asyncOffset.y, EPSILON)) {
mVisualScrollOffset = mLayoutViewport.TopLeft();
void SampledAPZCState::KeepLayoutViewportEnclosingVisualViewport(
const FrameMetrics& aMetrics) {
aMetrics.GetCompositionBounds(), mZoom)),
aMetrics.GetScrollableRect(), mLayoutViewport);
} // namespace layers
} // namespace mozilla