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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 */
#ifndef mozilla_layout_ScrollAnimationBezierPhysics_h_
#define mozilla_layout_ScrollAnimationBezierPhysics_h_
#include "ScrollAnimationPhysics.h"
#include "mozilla/SMILKeySpline.h"
namespace mozilla {
struct ScrollAnimationBezierPhysicsSettings {
// These values are minimum and maximum animation duration per event,
// and a global ratio which defines how longer is the animation's duration
// compared to the average recent events intervals (such that for a relatively
// consistent events rate, the next event arrives before current animation
// ends)
int32_t mMinMS;
int32_t mMaxMS;
double mIntervalRatio;
// This class implements a cubic bezier timing function and automatically
// adapts the animation duration based on the scrolling rate.
class ScrollAnimationBezierPhysics final : public ScrollAnimationPhysics {
explicit ScrollAnimationBezierPhysics(
const nsPoint& aStartPos,
const ScrollAnimationBezierPhysicsSettings& aSettings);
void Update(const TimeStamp& aTime, const nsPoint& aDestination,
const nsSize& aCurrentVelocity) override;
void ApplyContentShift(const CSSPoint& aShiftDelta) override;
// Get the velocity at a point in time in nscoords/sec.
nsSize VelocityAt(const TimeStamp& aTime) override;
// Returns the expected scroll position at a given point in time, in app
// units, relative to the scroll frame.
nsPoint PositionAt(const TimeStamp& aTime) override;
bool IsFinished(const TimeStamp& aTime) override {
return aTime > mStartTime + mDuration;
double ProgressAt(const TimeStamp& aTime) const {
return clamped((aTime - mStartTime) / mDuration, 0.0, 1.0);
nscoord VelocityComponent(double aTimeProgress,
const SMILKeySpline& aTimingFunction,
nscoord aStart, nscoord aDestination) const;
// Calculate duration, possibly dynamically according to events rate and
// event origin. (also maintain previous timestamps - which are only used
// here).
TimeDuration ComputeDuration(const TimeStamp& aTime);
// Initializes the timing function in such a way that the current velocity is
// preserved.
void InitTimingFunction(SMILKeySpline& aTimingFunction, nscoord aCurrentPos,
nscoord aCurrentVelocity, nscoord aDestination);
// Initialize event history.
void InitializeHistory(const TimeStamp& aTime);
// Cached Preferences values.
ScrollAnimationBezierPhysicsSettings mSettings;
// mPrevEventTime holds previous 3 timestamps for intervals averaging (to
// reduce duration fluctuations). When AsyncScroll is constructed and no
// previous timestamps are available (indicated with mIsFirstIteration),
// initialize mPrevEventTime using imaginary previous timestamps with maximum
// relevant intervals between them.
TimeStamp mPrevEventTime[3];
TimeStamp mStartTime;
nsPoint mStartPos;
nsPoint mDestination;
TimeDuration mDuration;
SMILKeySpline mTimingFunctionX;
SMILKeySpline mTimingFunctionY;
bool mIsFirstIteration;
} // namespace mozilla
#endif // mozilla_layout_ScrollAnimationBezierPhysics_h_