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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 */
#include "CompositableHost.h" // for CompositableTextureHostRef
#include "mozilla/gfx/2D.h"
#include "mozilla/TimeStamp.h" // for TimeStamp
#include "nsTArray.h"
namespace mozilla {
namespace layers {
* Implements Image selection logic.
class ImageComposite {
static const float BIAS_TIME_MS;
explicit ImageComposite();
virtual ~ImageComposite();
int32_t GetFrameID() {
const TimedImage* img = ChooseImage();
return img ? img->mFrameID : -1;
int32_t GetProducerID() {
const TimedImage* img = ChooseImage();
return img ? img->mProducerID : -1;
int32_t GetLastFrameID() const { return mLastFrameID; }
int32_t GetLastProducerID() const { return mLastProducerID; }
uint32_t GetDroppedFramesAndReset() {
uint32_t dropped = mDroppedFrames;
mDroppedFrames = 0;
return dropped;
enum Bias {
// Don't apply bias to frame times
// Apply a negative bias to frame times to keep them before the vsync time
// Apply a positive bias to frame times to keep them after the vsync time
virtual TimeStamp GetCompositionTime() const = 0;
virtual CompositionOpportunityId GetCompositionOpportunityId() const = 0;
virtual void AppendImageCompositeNotification(
const ImageCompositeNotificationInfo& aInfo) const = 0;
struct TimedImage {
CompositableTextureHostRef mTextureHost;
TimeStamp mTimeStamp;
gfx::IntRect mPictureRect;
int32_t mFrameID;
int32_t mProducerID;
* ChooseImage is guaranteed to return the same TimedImage every time it's
* called during the same composition, up to the end of Composite() ---
* it depends only on mImages, mCompositor->GetCompositionTime(), and mBias.
* mBias is updated at the end of Composite().
const TimedImage* ChooseImage();
int ChooseImageIndex();
const TimedImage* GetImage(size_t aIndex) const;
size_t ImagesCount() const { return mImages.Length(); }
const nsTArray<TimedImage>& Images() const { return mImages; }
void RemoveImagesWithTextureHost(TextureHost* aTexture);
void ClearImages();
void SetImages(nsTArray<TimedImage>&& aNewImages);
// Send ImageComposite notifications and update the ChooseImage bias.
void OnFinishRendering(int aImageIndex, const TimedImage* aImage,
base::ProcessId aProcessId,
const CompositableHandle& aHandle);
int32_t mLastFrameID = -1;
int32_t mLastProducerID = -1;
nsTArray<TimedImage> mImages;
TimeStamp GetBiasedTime(const TimeStamp& aInput) const;
// Called when we know that frames older than aImage will never get another
// chance to be displayed.
// Counts frames in mImages that were skipped, and adds the skipped count to
// mSkippedFramesSinceLastComposite.
void CountSkippedFrames(const TimedImage* aImage);
// Update mLastFrameID and mLastProducerID, and report dropped frames.
// Returns whether the frame changed.
bool UpdateCompositedFrame(int aImageIndex,
bool aWasVisibleAtPreviousComposition);
void UpdateBias(size_t aImageIndex, bool aFrameUpdated);
// Emit a profiler marker about video frame timestamp jitter.
void DetectTimeStampJitter(const TimedImage* aNewImage);
* Bias to apply to the next frame.
Bias mBias = BIAS_NONE;
// Video frames that were in mImages but that will never reach the screen.
// This count is reset in UpdateCompositedFrame.
int32_t mSkippedFramesSinceLastComposite = 0;
// The number of dropped frames since the last call to
// GetDroppedFramesAndReset(). Not all skipped frames are considered "dropped"
// - for example, videos that are scrolled out of view or videos in background
// tabs are expected to skip frames, and those skipped frames are not counted
// as dropped frames.
uint32_t mDroppedFrames = 0;
// The composition opportunity IDs of the last calls to ChooseImageIndex and
// UpdateCompositedFrame, respectively.
CompositionOpportunityId mLastChooseImageIndexComposition;
CompositionOpportunityId mLastFrameUpdateComposition;
} // namespace layers
} // namespace mozilla