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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 "ScrollVelocityQueue.h"
#include "mozilla/StaticPrefs_apz.h"
#include "mozilla/StaticPrefs_layout.h"
#include "nsPresContext.h"
#include "nsRefreshDriver.h"
namespace mozilla {
namespace layout {
void ScrollVelocityQueue::Sample(const nsPoint& aScrollPosition) {
float flingSensitivity =
StaticPrefs::layout_css_scroll_snap_prediction_sensitivity();
int maxVelocity =
StaticPrefs::layout_css_scroll_snap_prediction_max_velocity();
maxVelocity = nsPresContext::CSSPixelsToAppUnits(maxVelocity);
int maxOffset = maxVelocity * flingSensitivity;
TimeStamp currentRefreshTime =
mPresContext->RefreshDriver()->MostRecentRefresh();
if (mSampleTime.IsNull()) {
mAccumulator = nsPoint();
} else {
uint32_t durationMs = (currentRefreshTime - mSampleTime).ToMilliseconds();
if (durationMs > StaticPrefs::apz_velocity_relevance_time_ms()) {
mAccumulator = nsPoint();
mQueue.Clear();
} else if (durationMs == 0) {
mAccumulator += aScrollPosition - mLastPosition;
} else {
nsPoint velocity = mAccumulator * 1000 / durationMs;
velocity.Clamp(maxVelocity);
mQueue.AppendElement(std::make_pair(durationMs, velocity));
mAccumulator = aScrollPosition - mLastPosition;
}
}
mAccumulator.Clamp(maxOffset);
mSampleTime = currentRefreshTime;
mLastPosition = aScrollPosition;
TrimQueue();
}
void ScrollVelocityQueue::TrimQueue() {
if (mSampleTime.IsNull()) {
// There are no samples, nothing to do here.
return;
}
TimeStamp currentRefreshTime =
mPresContext->RefreshDriver()->MostRecentRefresh();
uint32_t timeDelta = (currentRefreshTime - mSampleTime).ToMilliseconds();
for (int i = mQueue.Length() - 1; i >= 0; i--) {
timeDelta += mQueue[i].first;
if (timeDelta >= StaticPrefs::apz_velocity_relevance_time_ms()) {
// The rest of the samples have expired and should be dropped
for (; i >= 0; i--) {
mQueue.RemoveElementAt(0);
}
}
}
}
void ScrollVelocityQueue::Reset() {
mAccumulator = nsPoint();
mSampleTime = TimeStamp();
mQueue.Clear();
}
/**
Calculate the velocity of the scroll frame, in appunits / second.
*/
nsPoint ScrollVelocityQueue::GetVelocity() {
TrimQueue();
if (mQueue.Length() == 0) {
// If getting the scroll velocity before any scrolling has occurred,
// the velocity must be (0, 0)
return nsPoint();
}
nsPoint velocity;
for (int i = mQueue.Length() - 1; i >= 0; i--) {
velocity += mQueue[i].second;
}
return velocity / mQueue.Length();
;
}
} // namespace layout
} // namespace mozilla