layout/generic/ScrollAnimationBezierPhysics.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_layout_ScrollAnimationBezierPhysics_h_
   8 #define mozilla_layout_ScrollAnimationBezierPhysics_h_
   9
  10 #include "ScrollAnimationPhysics.h"
  11 #include "mozilla/SMILKeySpline.h"
  12
  13 namespace mozilla {
  14
  15 struct ScrollAnimationBezierPhysicsSettings {
  16   // These values are minimum and maximum animation duration per event,
  17   // and a global ratio which defines how longer is the animation's duration
  18   // compared to the average recent events intervals (such that for a relatively
  19   // consistent events rate, the next event arrives before current animation
  20   // ends)
  21   int32_t mMinMS;
  22   int32_t mMaxMS;
  23   double mIntervalRatio;
  24 };
  25
  26 // This class implements a cubic bezier timing function and automatically
  27 // adapts the animation duration based on the scrolling rate.
  28 class ScrollAnimationBezierPhysics final : public ScrollAnimationPhysics {
  29  public:
  30   explicit ScrollAnimationBezierPhysics(
  31       const nsPoint& aStartPos,
  32       const ScrollAnimationBezierPhysicsSettings& aSettings);
  33
  34   void Update(const TimeStamp& aTime, const nsPoint& aDestination,
  35               const nsSize& aCurrentVelocity) override;
  36
  37   void ApplyContentShift(const CSSPoint& aShiftDelta) override;
  38
  39   // Get the velocity at a point in time in nscoords/sec.
  40   nsSize VelocityAt(const TimeStamp& aTime) override;
  41
  42   // Returns the expected scroll position at a given point in time, in app
  43   // units, relative to the scroll frame.
  44   nsPoint PositionAt(const TimeStamp& aTime) override;
  45
  46   bool IsFinished(const TimeStamp& aTime) override {
  47     return aTime > mStartTime + mDuration;
  48   }
  49
  50  protected:
  51   double ProgressAt(const TimeStamp& aTime) const {
  52     return clamped((aTime - mStartTime) / mDuration, 0.0, 1.0);
  53   }
  54
  55   nscoord VelocityComponent(double aTimeProgress,
  56                             const SMILKeySpline& aTimingFunction,
  57                             nscoord aStart, nscoord aDestination) const;
  58
  59   // Calculate duration, possibly dynamically according to events rate and
  60   // event origin. (also maintain previous timestamps - which are only used
  61   // here).
  62   TimeDuration ComputeDuration(const TimeStamp& aTime);
  63
  64   // Initializes the timing function in such a way that the current velocity is
  65   // preserved.
  66   void InitTimingFunction(SMILKeySpline& aTimingFunction, nscoord aCurrentPos,
  67                           nscoord aCurrentVelocity, nscoord aDestination);
  68
  69   // Initialize event history.
  70   void InitializeHistory(const TimeStamp& aTime);
  71
  72   // Cached Preferences values.
  73   ScrollAnimationBezierPhysicsSettings mSettings;
  74
  75   // mPrevEventTime holds previous 3 timestamps for intervals averaging (to
  76   // reduce duration fluctuations). When AsyncScroll is constructed and no
  77   // previous timestamps are available (indicated with mIsFirstIteration),
  78   // initialize mPrevEventTime using imaginary previous timestamps with maximum
  79   // relevant intervals between them.
  80   TimeStamp mPrevEventTime[3];
  81
  82   TimeStamp mStartTime;
  83
  84   nsPoint mStartPos;
  85   nsPoint mDestination;
  86   TimeDuration mDuration;
  87   SMILKeySpline mTimingFunctionX;
  88   SMILKeySpline mTimingFunctionY;
  89   bool mIsFirstIteration;
  90 };
  91
  92 }  // namespace mozilla
  93
  94 #endif  // mozilla_layout_ScrollAnimationBezierPhysics_h_