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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
#include "ScrollAnimationBezierPhysics.h"
#include "mozilla/StaticPrefs_general.h"
using namespace mozilla;
ScrollAnimationBezierPhysics::ScrollAnimationBezierPhysics(
const nsPoint& aStartPos,
const ScrollAnimationBezierPhysicsSettings& aSettings)
: mSettings(aSettings), mStartPos(aStartPos), mIsFirstIteration(true) {}
void ScrollAnimationBezierPhysics::Update(const TimeStamp& aTime,
const nsPoint& aDestination,
const nsSize& aCurrentVelocity) {
if (mIsFirstIteration) {
InitializeHistory(aTime);
}
TimeDuration duration = ComputeDuration(aTime);
nsSize currentVelocity = aCurrentVelocity;
if (!mIsFirstIteration) {
// If an additional event has not changed the destination, then do not let
// another minimum duration reset slow things down. If it would then
// instead continue with the existing timing function.
if (aDestination == mDestination &&
aTime + duration > mStartTime + mDuration) {
return;
}
currentVelocity = VelocityAt(aTime);
mStartPos = PositionAt(aTime);
}
mStartTime = aTime;
mDuration = duration;
mDestination = aDestination;
InitTimingFunction(mTimingFunctionX, mStartPos.x, currentVelocity.width,
aDestination.x);
InitTimingFunction(mTimingFunctionY, mStartPos.y, currentVelocity.height,
aDestination.y);
mIsFirstIteration = false;
}
void ScrollAnimationBezierPhysics::ApplyContentShift(
const CSSPoint& aShiftDelta) {
nsPoint shiftDelta = CSSPoint::ToAppUnits(aShiftDelta);
mStartPos += shiftDelta;
mDestination += shiftDelta;
}
TimeDuration ScrollAnimationBezierPhysics::ComputeDuration(
const TimeStamp& aTime) {
// Average last 3 delta durations (rounding errors up to 2ms are negligible
// for us)
int32_t eventsDeltaMs = (aTime - mPrevEventTime[2]).ToMilliseconds() / 3;
mPrevEventTime[2] = mPrevEventTime[1];
mPrevEventTime[1] = mPrevEventTime[0];
mPrevEventTime[0] = aTime;
// Modulate duration according to events rate (quicker events -> shorter
// durations). The desired effect is to use longer duration when scrolling
// slowly, such that it's easier to follow, but reduce the duration to make it
// feel more snappy when scrolling quickly. To reduce fluctuations of the
// duration, we average event intervals using the recent 4 timestamps (now +
// three prev -> 3 intervals).
int32_t durationMS =
clamped<int32_t>(eventsDeltaMs * mSettings.mIntervalRatio,
mSettings.mMinMS, mSettings.mMaxMS);
return TimeDuration::FromMilliseconds(durationMS);
}
void ScrollAnimationBezierPhysics::InitializeHistory(const TimeStamp& aTime) {
// Starting a new scroll (i.e. not when extending an existing scroll
// animation), create imaginary prev timestamps with maximum relevant
// intervals between them.
// Longest relevant interval (which results in maximum duration)
TimeDuration maxDelta = TimeDuration::FromMilliseconds(
mSettings.mMaxMS / mSettings.mIntervalRatio);
mPrevEventTime[0] = aTime - maxDelta;
mPrevEventTime[1] = mPrevEventTime[0] - maxDelta;
mPrevEventTime[2] = mPrevEventTime[1] - maxDelta;
}
void ScrollAnimationBezierPhysics::InitTimingFunction(
SMILKeySpline& aTimingFunction, nscoord aCurrentPos,
nscoord aCurrentVelocity, nscoord aDestination) {
if (aDestination == aCurrentPos ||
StaticPrefs::general_smoothScroll_currentVelocityWeighting() == 0) {
aTimingFunction.Init(
0, 0, 1 - StaticPrefs::general_smoothScroll_stopDecelerationWeighting(),
1);
return;
}
const TimeDuration oneSecond = TimeDuration::FromSeconds(1);
double slope =
aCurrentVelocity * (mDuration / oneSecond) / (aDestination - aCurrentPos);
double normalization = sqrt(1.0 + slope * slope);
double dt = 1.0 / normalization *
StaticPrefs::general_smoothScroll_currentVelocityWeighting();
double dxy = slope / normalization *
StaticPrefs::general_smoothScroll_currentVelocityWeighting();
aTimingFunction.Init(
dt, dxy,
1 - StaticPrefs::general_smoothScroll_stopDecelerationWeighting(), 1);
}
nsPoint ScrollAnimationBezierPhysics::PositionAt(const TimeStamp& aTime) {
if (IsFinished(aTime)) {
return mDestination;
}
double progressX = mTimingFunctionX.GetSplineValue(ProgressAt(aTime));
double progressY = mTimingFunctionY.GetSplineValue(ProgressAt(aTime));
return nsPoint(NSToCoordRound((1 - progressX) * mStartPos.x +
progressX * mDestination.x),
NSToCoordRound((1 - progressY) * mStartPos.y +
progressY * mDestination.y));
}
nsSize ScrollAnimationBezierPhysics::VelocityAt(const TimeStamp& aTime) {
if (IsFinished(aTime)) {
return nsSize(0, 0);
}
double timeProgress = ProgressAt(aTime);
return nsSize(VelocityComponent(timeProgress, mTimingFunctionX, mStartPos.x,
mDestination.x),
VelocityComponent(timeProgress, mTimingFunctionY, mStartPos.y,
mDestination.y));
}
nscoord ScrollAnimationBezierPhysics::VelocityComponent(
double aTimeProgress, const SMILKeySpline& aTimingFunction, nscoord aStart,
nscoord aDestination) const {
double dt, dxy;
aTimingFunction.GetSplineDerivativeValues(aTimeProgress, dt, dxy);
if (dt == 0) return dxy >= 0 ? nscoord_MAX : nscoord_MIN;
const TimeDuration oneSecond = TimeDuration::FromSeconds(1);
double slope = dxy / dt;
return NSToCoordRound(slope * (aDestination - aStart) /
(mDuration / oneSecond));
}