ScrollAnimationBezierPhysics.h

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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 http://mozilla.org/MPL/2.0/. */

#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 {

 public:

  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;

 protected:

  double ProgressAt(const TimeStamp& aTime) const {

    return std::clamp((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_