зеркало из https://github.com/mozilla/gecko-dev.git
123 строки
4.1 KiB
C++
123 строки
4.1 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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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 "ImageComposite.h"
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namespace mozilla {
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using namespace gfx;
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namespace layers {
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/* static */ const float ImageComposite::BIAS_TIME_MS = 1.0f;
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ImageComposite::ImageComposite()
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: mLastFrameID(-1)
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, mLastProducerID(-1)
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, mBias(BIAS_NONE)
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{}
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ImageComposite::~ImageComposite()
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{
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}
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/* static */ TimeStamp
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ImageComposite::GetBiasedTime(const TimeStamp& aInput, ImageComposite::Bias aBias)
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{
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switch (aBias) {
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case ImageComposite::BIAS_NEGATIVE:
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return aInput - TimeDuration::FromMilliseconds(BIAS_TIME_MS);
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case ImageComposite::BIAS_POSITIVE:
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return aInput + TimeDuration::FromMilliseconds(BIAS_TIME_MS);
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default:
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return aInput;
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}
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}
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/* static */ ImageComposite::Bias
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ImageComposite::UpdateBias(const TimeStamp& aCompositionTime,
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const TimeStamp& aCompositedImageTime,
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const TimeStamp& aNextImageTime, // may be null
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ImageComposite::Bias aBias)
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{
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if (aCompositedImageTime.IsNull()) {
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return ImageComposite::BIAS_NONE;
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}
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TimeDuration threshold = TimeDuration::FromMilliseconds(1.0);
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if (aCompositionTime - aCompositedImageTime < threshold &&
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aCompositionTime - aCompositedImageTime > -threshold) {
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// The chosen frame's time is very close to the composition time (probably
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// just before the current composition time, but due to previously set
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// negative bias, it could be just after the current composition time too).
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// If the inter-frame time is almost exactly equal to (a multiple of)
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// the inter-composition time, then we're in a dangerous situation because
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// jitter might cause frames to fall one side or the other of the
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// composition times, causing many frames to be skipped or duplicated.
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// Try to prevent that by adding a negative bias to the frame times during
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// the next composite; that should ensure the next frame's time is treated
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// as falling just before a composite time.
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return ImageComposite::BIAS_NEGATIVE;
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}
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if (!aNextImageTime.IsNull() &&
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aNextImageTime - aCompositionTime < threshold &&
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aNextImageTime - aCompositionTime > -threshold) {
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// The next frame's time is very close to our composition time (probably
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// just after the current composition time, but due to previously set
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// positive bias, it could be just before the current composition time too).
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// We're in a dangerous situation because jitter might cause frames to
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// fall one side or the other of the composition times, causing many frames
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// to be skipped or duplicated.
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// Try to prevent that by adding a negative bias to the frame times during
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// the next composite; that should ensure the next frame's time is treated
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// as falling just before a composite time.
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return ImageComposite::BIAS_POSITIVE;
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}
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return ImageComposite::BIAS_NONE;
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}
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int
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ImageComposite::ChooseImageIndex() const
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{
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if (mImages.IsEmpty()) {
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return -1;
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}
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TimeStamp now = GetCompositionTime();
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if (now.IsNull()) {
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// Not in a composition, so just return the last image we composited
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// (if it's one of the current images).
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for (uint32_t i = 0; i < mImages.Length(); ++i) {
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if (mImages[i].mFrameID == mLastFrameID &&
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mImages[i].mProducerID == mLastProducerID) {
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return i;
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}
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}
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return -1;
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}
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uint32_t result = 0;
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while (result + 1 < mImages.Length() &&
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GetBiasedTime(mImages[result + 1].mTimeStamp, mBias) <= now) {
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++result;
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}
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return result;
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}
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const ImageComposite::TimedImage* ImageComposite::ChooseImage() const
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{
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int index = ChooseImageIndex();
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return index >= 0 ? &mImages[index] : nullptr;
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}
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ImageComposite::TimedImage* ImageComposite::ChooseImage()
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{
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int index = ChooseImageIndex();
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return index >= 0 ? &mImages[index] : nullptr;
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}
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} // namespace layers
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} // namespace mozilla
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