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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */
#include "AsyncScrollBase.h"
#include "gfxPrefs.h"
using namespace mozilla;
AsyncScrollBase::AsyncScrollBase(nsPoint aStartPos)
: mIsFirstIteration(true)
, mStartPos(aStartPos)
{
}
void
AsyncScrollBase::Update(TimeStamp aTime,
nsPoint aDestination,
const nsSize& aCurrentVelocity)
{
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;
}
TimeDuration
AsyncScrollBase::ComputeDuration(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 * mIntervalRatio, mOriginMinMS, mOriginMaxMS);
return TimeDuration::FromMilliseconds(durationMS);
}
void
AsyncScrollBase::InitializeHistory(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(mOriginMaxMS / mIntervalRatio);
mPrevEventTime[0] = aTime - maxDelta;
mPrevEventTime[1] = mPrevEventTime[0] - maxDelta;
mPrevEventTime[2] = mPrevEventTime[1] - maxDelta;
}
void
AsyncScrollBase::InitTimingFunction(nsSMILKeySpline& aTimingFunction,
nscoord aCurrentPos,
nscoord aCurrentVelocity,
nscoord aDestination)
{
if (aDestination == aCurrentPos || gfxPrefs::SmoothScrollCurrentVelocityWeighting() == 0) {
aTimingFunction.Init(0, 0, 1 - gfxPrefs::SmoothScrollStopDecelerationWeighting(), 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 * gfxPrefs::SmoothScrollCurrentVelocityWeighting();
double dxy = slope / normalization * gfxPrefs::SmoothScrollCurrentVelocityWeighting();
aTimingFunction.Init(dt, dxy, 1 - gfxPrefs::SmoothScrollStopDecelerationWeighting(), 1);
}
nsPoint
AsyncScrollBase::PositionAt(TimeStamp aTime) const
{
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
AsyncScrollBase::VelocityAt(TimeStamp aTime) const
{
double timeProgress = ProgressAt(aTime);
return nsSize(VelocityComponent(timeProgress, mTimingFunctionX,
mStartPos.x, mDestination.x),
VelocityComponent(timeProgress, mTimingFunctionY,
mStartPos.y, mDestination.y));
}
nscoord
AsyncScrollBase::VelocityComponent(double aTimeProgress,
const nsSMILKeySpline& 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));
}
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