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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 "SmoothMsdScrollAnimation.h"
#include "AsyncPanZoomController.h"
namespace mozilla {
namespace layers {
AsyncPanZoomController& aApzc, const CSSPoint& aInitialPosition,
const CSSPoint& aInitialVelocity, const CSSPoint& aDestination,
double aSpringConstant, double aDampingRatio,
ScrollSnapTargetIds&& aSnapTargetIds,
ScrollTriggeredByScript aTriggeredByScript)
: mApzc(aApzc),
mXAxisModel(aInitialPosition.x, aDestination.x, aInitialVelocity.x,
aSpringConstant, aDampingRatio),
mYAxisModel(aInitialPosition.y, aDestination.y, aInitialVelocity.y,
aSpringConstant, aDampingRatio),
mTriggeredByScript(aTriggeredByScript) {}
bool SmoothMsdScrollAnimation::DoSample(FrameMetrics& aFrameMetrics,
const TimeDuration& aDelta) {
CSSToParentLayerScale zoom(aFrameMetrics.GetZoom());
if (zoom == CSSToParentLayerScale(0)) {
return false;
CSSPoint oneParentLayerPixel =
ParentLayerPoint(1, 1) / aFrameMetrics.GetZoom();
if (mXAxisModel.IsFinished(oneParentLayerPixel.x) &&
mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
// Set the scroll offset to the exact destination. If we allow the scroll
// offset to end up being a bit off from the destination, we can get
// artefacts like "scroll to the next snap point in this direction"
// scrolling to the snap point we're already supposed to be at.
CSSPoint(mXAxisModel.GetDestination(), mYAxisModel.GetDestination()));
return false;
CSSPoint position =
CSSPoint(mXAxisModel.GetPosition(), mYAxisModel.GetPosition());
CSSPoint css_velocity =
CSSPoint(mXAxisModel.GetVelocity(), mYAxisModel.GetVelocity());
// Convert from pixels/second to pixels/ms
ParentLayerPoint velocity =
ParentLayerPoint(css_velocity.x, css_velocity.y) / 1000.0f;
// Keep the velocity updated for the Axis class so that any animations
// chained off of the smooth scroll will inherit it.
if (mXAxisModel.IsFinished(oneParentLayerPixel.x)) {
} else {
if (mYAxisModel.IsFinished(oneParentLayerPixel.y)) {
} else {
// If we overscroll, hand off to a fling animation that will complete the
// spring back.
ParentLayerPoint displacement =
(position - aFrameMetrics.GetVisualScrollOffset()) * zoom;
ParentLayerPoint overscroll;
ParentLayerPoint adjustedOffset;
mApzc.mX.AdjustDisplacement(displacement.x, adjustedOffset.x, overscroll.x);
mApzc.mY.AdjustDisplacement(displacement.y, adjustedOffset.y, overscroll.y);
mApzc.ScrollBy(adjustedOffset / zoom);
// The smooth scroll may have caused us to reach the end of our scroll
// range. This can happen if either the
// layout.css.scroll-behavior.damping-ratio preference is set to less than 1
// (underdamped) or if a smooth scroll inherits velocity from a fling
// gesture.
if (!IsZero(overscroll / zoom)) {
// Hand off a fling with the remaining momentum to the next APZC in the
// overscroll handoff chain.
// We may have reached the end of the scroll range along one axis but
// not the other. In such a case we only want to hand off the relevant
// component of the fling.
if (mApzc.IsZero(overscroll.x)) {
velocity.x = 0;
} else if (mApzc.IsZero(overscroll.y)) {
velocity.y = 0;
// To hand off the fling, we attempt to find a target APZC and start a new
// fling with the same velocity on that APZC. For simplicity, the actual
// overscroll of the current sample is discarded rather than being handed
// off. The compositor should sample animations sufficiently frequently
// that this is not noticeable. The target APZC is chosen by seeing if
// there is an APZC further in the handoff chain which is pannable; if
// there isn't, we take the new fling ourselves, entering an overscrolled
// state.
// Note: APZC is holding mRecursiveMutex, so directly calling
// HandleSmoothScrollOverscroll() (which acquires the tree lock) would
// violate the lock ordering. Instead we schedule
// HandleSmoothScrollOverscroll() to be called after mRecursiveMutex is
// released.
mDeferredTasks.AppendElement(NewRunnableMethod<ParentLayerPoint, SideBits>(
"layers::AsyncPanZoomController::HandleSmoothScrollOverscroll", &mApzc,
&AsyncPanZoomController::HandleSmoothScrollOverscroll, velocity,
return false;
return true;
void SmoothMsdScrollAnimation::SetDestination(
const CSSPoint& aNewDestination, ScrollSnapTargetIds&& aSnapTargetIds,
ScrollTriggeredByScript aTriggeredByScript) {
mSnapTargetIds = std::move(aSnapTargetIds);
mTriggeredByScript = aTriggeredByScript;
CSSPoint SmoothMsdScrollAnimation::GetDestination() const {
return CSSPoint(mXAxisModel.GetDestination(), mYAxisModel.GetDestination());
SmoothMsdScrollAnimation::AsSmoothMsdScrollAnimation() {
return this;
} // namespace layers
} // namespace mozilla