97 lines
2.7 KiB
C++
97 lines
2.7 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "ScrollVelocityQueue.h"
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#include "gfxPrefs.h"
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#include "nsPresContext.h"
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#include "nsRefreshDriver.h"
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namespace mozilla {
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namespace layout {
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void
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ScrollVelocityQueue::Sample(const nsPoint& aScrollPosition)
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{
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float flingSensitivity = gfxPrefs::ScrollSnapPredictionSensitivity();
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int maxVelocity = gfxPrefs::ScrollSnapPredictionMaxVelocity();
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maxVelocity = nsPresContext::CSSPixelsToAppUnits(maxVelocity);
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int maxOffset = maxVelocity * flingSensitivity;
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TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
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if (mSampleTime.IsNull()) {
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mAccumulator = nsPoint();
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} else {
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uint32_t durationMs = (currentRefreshTime - mSampleTime).ToMilliseconds();
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if (durationMs > gfxPrefs::APZVelocityRelevanceTime()) {
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mAccumulator = nsPoint();
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mQueue.Clear();
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} else if (durationMs == 0) {
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mAccumulator += aScrollPosition - mLastPosition;
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} else {
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nsPoint velocity = mAccumulator * 1000 / durationMs;
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velocity.Clamp(maxVelocity);
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mQueue.AppendElement(std::make_pair(durationMs, velocity));
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mAccumulator = aScrollPosition - mLastPosition;
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}
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}
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mAccumulator.Clamp(maxOffset);
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mSampleTime = currentRefreshTime;
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mLastPosition = aScrollPosition;
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TrimQueue();
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}
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void
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ScrollVelocityQueue::TrimQueue()
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{
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if (mSampleTime.IsNull()) {
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// There are no samples, nothing to do here.
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return;
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}
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TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
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nsPoint velocity;
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uint32_t timeDelta = (currentRefreshTime - mSampleTime).ToMilliseconds();
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for (int i = mQueue.Length() - 1; i >= 0; i--) {
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timeDelta += mQueue[i].first;
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if (timeDelta >= gfxPrefs::APZVelocityRelevanceTime()) {
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// The rest of the samples have expired and should be dropped
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for (; i >= 0; i--) {
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mQueue.RemoveElementAt(0);
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}
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}
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}
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}
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void
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ScrollVelocityQueue::Reset()
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{
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mAccumulator = nsPoint();
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mSampleTime = TimeStamp();
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mQueue.Clear();
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}
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/**
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Calculate the velocity of the scroll frame, in appunits / second.
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*/
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nsPoint
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ScrollVelocityQueue::GetVelocity()
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{
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TrimQueue();
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if (mQueue.Length() == 0) {
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// If getting the scroll velocity before any scrolling has occurred,
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// the velocity must be (0, 0)
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return nsPoint();
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}
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nsPoint velocity;
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for (int i = mQueue.Length() - 1; i >= 0; i--) {
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velocity += mQueue[i].second;
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}
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return velocity / mQueue.Length();;
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}
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} // namespace layout
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} // namespace mozilla
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