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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/. */
#include "SimpleVelocityTracker.h"
#include "mozilla/ServoStyleConsts.h" // for StyleComputedTimingFunction
#include "mozilla/StaticPrefs_apz.h"
#include "mozilla/StaticPtr.h" // for StaticAutoPtr
static mozilla::LazyLogModule sApzSvtLog("apz.simplevelocitytracker");
#define SVT_LOG(...) MOZ_LOG(sApzSvtLog, LogLevel::Debug, (__VA_ARGS__))
namespace mozilla {
namespace layers {
// When we compute the velocity we do so by taking two input events and
// dividing the distance delta over the time delta. In some cases the time
// delta can be really small, which can make the velocity computation very
// volatile. To avoid this we impose a minimum time delta below which we do
// not recompute the velocity.
const TimeDuration MIN_VELOCITY_SAMPLE_TIME = TimeDuration::FromMilliseconds(5);
extern StaticAutoPtr<StyleComputedTimingFunction> gVelocityCurveFunction;
SimpleVelocityTracker::SimpleVelocityTracker(Axis* aAxis)
: mAxis(aAxis), mVelocitySamplePos(0) {}
void SimpleVelocityTracker::StartTracking(ParentLayerCoord aPos,
TimeStamp aTimestamp) {
Clear();
mVelocitySampleTime = aTimestamp;
mVelocitySamplePos = aPos;
}
Maybe<float> SimpleVelocityTracker::AddPosition(ParentLayerCoord aPos,
TimeStamp aTimestamp) {
if (aTimestamp <= mVelocitySampleTime + MIN_VELOCITY_SAMPLE_TIME) {
// See also the comment on MIN_VELOCITY_SAMPLE_TIME.
// We don't update either mVelocitySampleTime or mVelocitySamplePos so that
// eventually when we do get an event with the required time delta we use
// the corresponding distance delta as well.
SVT_LOG("%p|%s skipping velocity computation for small time delta %f ms\n",
mAxis->OpaqueApzcPointer(), mAxis->Name(),
(aTimestamp - mVelocitySampleTime).ToMilliseconds());
return Nothing();
}
float newVelocity =
(float)(mVelocitySamplePos - aPos) /
(float)(aTimestamp - mVelocitySampleTime).ToMilliseconds();
newVelocity = ApplyFlingCurveToVelocity(newVelocity);
SVT_LOG("%p|%s updating velocity to %f with touch\n",
mAxis->OpaqueApzcPointer(), mAxis->Name(), newVelocity);
mVelocitySampleTime = aTimestamp;
mVelocitySamplePos = aPos;
AddVelocityToQueue(aTimestamp, newVelocity);
return Some(newVelocity);
}
Maybe<float> SimpleVelocityTracker::ComputeVelocity(TimeStamp aTimestamp) {
float velocity = 0;
int count = 0;
for (const auto& e : mVelocityQueue) {
TimeDuration timeDelta = (aTimestamp - e.first);
if (timeDelta < TimeDuration::FromMilliseconds(
StaticPrefs::apz_velocity_relevance_time_ms())) {
count++;
velocity += e.second;
}
}
mVelocityQueue.Clear();
if (count > 1) {
velocity /= count;
}
return Some(velocity);
}
void SimpleVelocityTracker::Clear() { mVelocityQueue.Clear(); }
void SimpleVelocityTracker::AddVelocityToQueue(TimeStamp aTimestamp,
float aVelocity) {
mVelocityQueue.AppendElement(std::make_pair(aTimestamp, aVelocity));
if (mVelocityQueue.Length() >
StaticPrefs::apz_max_velocity_queue_size_AtStartup()) {
mVelocityQueue.RemoveElementAt(0);
}
}
float SimpleVelocityTracker::ApplyFlingCurveToVelocity(float aVelocity) const {
float newVelocity = aVelocity;
if (StaticPrefs::apz_max_velocity_inches_per_ms() > 0.0f) {
bool velocityIsNegative = (newVelocity < 0);
newVelocity = fabs(newVelocity);
float maxVelocity =
mAxis->ToLocalVelocity(StaticPrefs::apz_max_velocity_inches_per_ms());
newVelocity = std::min(newVelocity, maxVelocity);
if (StaticPrefs::apz_fling_curve_threshold_inches_per_ms() > 0.0f &&
StaticPrefs::apz_fling_curve_threshold_inches_per_ms() <
StaticPrefs::apz_max_velocity_inches_per_ms()) {
float curveThreshold = mAxis->ToLocalVelocity(
StaticPrefs::apz_fling_curve_threshold_inches_per_ms());
if (newVelocity > curveThreshold) {
// here, 0 < curveThreshold < newVelocity <= maxVelocity, so we apply
// the curve
float scale = maxVelocity - curveThreshold;
float funcInput = (newVelocity - curveThreshold) / scale;
float funcOutput =
gVelocityCurveFunction->At(funcInput, /* aBeforeFlag = */ false);
float curvedVelocity = (funcOutput * scale) + curveThreshold;
SVT_LOG("%p|%s curving up velocity from %f to %f\n",
mAxis->OpaqueApzcPointer(), mAxis->Name(), newVelocity,
curvedVelocity);
newVelocity = curvedVelocity;
}
}
if (velocityIsNegative) {
newVelocity = -newVelocity;
}
}
return newVelocity;
}
} // namespace layers
} // namespace mozilla
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