1 files changed, 378 insertions, 0 deletions
diff --git a/gfx/layers/composite/ImageComposite.cpp b/gfx/layers/composite/ImageComposite.cpp
new file mode 100644
index 0000000000..7c36519843
--- /dev/null
+++ b/gfx/layers/composite/ImageComposite.cpp
@@ -0,0 +1,378 @@
+/* -*- 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 "ImageComposite.h"
+
+#include <inttypes.h>
+
+#include "mozilla/ProfilerMarkers.h"
+#include "gfxPlatform.h"
+#include "nsPrintfCString.h"
+
+namespace mozilla {
+
+using namespace gfx;
+
+namespace layers {
+
+/* static */ const float ImageComposite::BIAS_TIME_MS = 1.0f;
+
+ImageComposite::ImageComposite() = default;
+
+ImageComposite::~ImageComposite() = default;
+
+TimeStamp ImageComposite::GetBiasedTime(const TimeStamp& aInput) const {
+  switch (mBias) {
+    case ImageComposite::BIAS_NEGATIVE:
+      return aInput - TimeDuration::FromMilliseconds(BIAS_TIME_MS);
+    case ImageComposite::BIAS_POSITIVE:
+      return aInput + TimeDuration::FromMilliseconds(BIAS_TIME_MS);
+    default:
+      return aInput;
+  }
+}
+
+void ImageComposite::UpdateBias(size_t aImageIndex, bool aFrameChanged) {
+  MOZ_ASSERT(aImageIndex < ImagesCount());
+
+  TimeStamp compositionTime = GetCompositionTime();
+  TimeStamp compositedImageTime = mImages[aImageIndex].mTimeStamp;
+  TimeStamp nextImageTime = aImageIndex + 1 < ImagesCount()
+                                ? mImages[aImageIndex + 1].mTimeStamp
+                                : TimeStamp();
+
+  if (profiler_thread_is_being_profiled_for_markers() && compositedImageTime &&
+      nextImageTime) {
+    TimeDuration offsetCurrent = compositedImageTime - compositionTime;
+    TimeDuration offsetNext = nextImageTime - compositionTime;
+    nsPrintfCString str("current %.2lfms, next %.2lfms",
+                        offsetCurrent.ToMilliseconds(),
+                        offsetNext.ToMilliseconds());
+    PROFILER_MARKER_TEXT("Video frame offsets", GRAPHICS, {}, str);
+  }
+
+  if (compositedImageTime.IsNull()) {
+    mBias = ImageComposite::BIAS_NONE;
+    return;
+  }
+  TimeDuration threshold = TimeDuration::FromMilliseconds(1.5);
+  if (compositionTime - compositedImageTime < threshold &&
+      compositionTime - compositedImageTime > -threshold) {
+    // The chosen frame's time is very close to the composition time (probably
+    // just before the current composition time, but due to previously set
+    // negative bias, it could be just after the current composition time too).
+    // If the inter-frame time is almost exactly equal to (a multiple of)
+    // the inter-composition time, then we're in a dangerous situation because
+    // jitter might cause frames to fall one side or the other of the
+    // composition times, causing many frames to be skipped or duplicated.
+    // Try to prevent that by adding a negative bias to the frame times during
+    // the next composite; that should ensure the next frame's time is treated
+    // as falling just before a composite time.
+    mBias = ImageComposite::BIAS_NEGATIVE;
+    return;
+  }
+  if (!nextImageTime.IsNull() && nextImageTime - compositionTime < threshold &&
+      nextImageTime - compositionTime > -threshold) {
+    // The next frame's time is very close to our composition time (probably
+    // just after the current composition time, but due to previously set
+    // positive bias, it could be just before the current composition time too).
+    // We're in a dangerous situation because jitter might cause frames to
+    // fall one side or the other of the composition times, causing many frames
+    // to be skipped or duplicated.
+    // Specifically, the next composite is at risk of picking the "next + 1"
+    // frame rather than the "next" frame, which would cause the "next" frame to
+    // be skipped. Try to prevent that by adding a positive bias to the frame
+    // times during the next composite; if the inter-frame time is almost
+    // exactly equal to the inter-composition time, that should ensure that the
+    // next + 1 frame falls just *after* the next composition time, and the next
+    // composite should then pick the next frame rather than the next + 1 frame.
+    mBias = ImageComposite::BIAS_POSITIVE;
+    return;
+  }
+  if (aFrameChanged) {
+    // The current and next video frames are a sufficient distance from the
+    // composition time and we can reliably pick the right frame without bias.
+    // Reset the bias.
+    // We only do this when the frame changed. Otherwise, when playing a 30fps
+    // video on a 60fps display, we'd keep resetting the bias during the "middle
+    // frames".
+    mBias = ImageComposite::BIAS_NONE;
+  }
+}
+
+int ImageComposite::ChooseImageIndex() {
+  // ChooseImageIndex is called for all images in the layer when it is visible.
+  // Change to this behaviour would break dropped frames counting calculation:
+  // We rely on this assumption to determine if during successive runs an
+  // image is returned that isn't the one following immediately the previous one
+  if (mImages.IsEmpty()) {
+    return -1;
+  }
+
+  TimeStamp compositionTime = GetCompositionTime();
+  auto compositionOpportunityId = GetCompositionOpportunityId();
+  if (compositionTime &&
+      compositionOpportunityId != mLastChooseImageIndexComposition) {
+    // We are inside a composition, in the first call to ChooseImageIndex during
+    // this composition.
+    // Find the newest frame whose biased timestamp is at or before
+    // `compositionTime`.
+    uint32_t imageIndex = 0;
+    while (imageIndex + 1 < mImages.Length() &&
+           mImages[imageIndex + 1].mTextureHost->IsValid() &&
+           GetBiasedTime(mImages[imageIndex + 1].mTimeStamp) <=
+               compositionTime) {
+      ++imageIndex;
+    }
+
+    if (!mImages[imageIndex].mTextureHost->IsValid()) {
+      // Still not ready to be shown.
+      return -1;
+    }
+
+    bool wasVisibleAtPreviousComposition =
+        compositionOpportunityId == mLastChooseImageIndexComposition.Next();
+
+    bool frameChanged =
+        UpdateCompositedFrame(imageIndex, wasVisibleAtPreviousComposition);
+    UpdateBias(imageIndex, frameChanged);
+
+    mLastChooseImageIndexComposition = compositionOpportunityId;
+
+    return imageIndex;
+  }
+
+  // We've been called before during this composition, or we're not in a
+  // composition. Just return the last image we picked (if it's one of the
+  // current images).
+  for (uint32_t i = 0; i < mImages.Length(); ++i) {
+    if (mImages[i].mFrameID == mLastFrameID &&
+        mImages[i].mProducerID == mLastProducerID) {
+      return i;
+    }
+  }
+
+  return 0;
+}
+
+const ImageComposite::TimedImage* ImageComposite::ChooseImage() {
+  int index = ChooseImageIndex();
+  return index >= 0 ? &mImages[index] : nullptr;
+}
+
+void ImageComposite::RemoveImagesWithTextureHost(TextureHost* aTexture) {
+  for (int32_t i = mImages.Length() - 1; i >= 0; --i) {
+    if (mImages[i].mTextureHost == aTexture) {
+      aTexture->UnbindTextureSource();
+      mImages.RemoveElementAt(i);
+    }
+  }
+}
+
+void ImageComposite::ClearImages() { mImages.Clear(); }
+
+void ImageComposite::SetImages(nsTArray<TimedImage>&& aNewImages) {
+  if (!aNewImages.IsEmpty()) {
+    DetectTimeStampJitter(&aNewImages[0]);
+
+    // Frames older than the first frame in aNewImages that we haven't shown yet
+    // will never be shown.
+    CountSkippedFrames(&aNewImages[0]);
+
+    if (profiler_thread_is_being_profiled_for_markers()) {
+      int len = aNewImages.Length();
+      const auto& first = aNewImages[0];
+      const auto& last = aNewImages.LastElement();
+      nsPrintfCString str("%d %s, frameID %" PRId32 " (prod %" PRId32
+                          ") to frameID %" PRId32 " (prod %" PRId32 ")",
+                          len, len == 1 ? "image" : "images", first.mFrameID,
+                          first.mProducerID, last.mFrameID, last.mProducerID);
+      PROFILER_MARKER_TEXT("ImageComposite::SetImages", GRAPHICS, {}, str);
+    }
+  }
+  mImages = std::move(aNewImages);
+}
+
+// Returns whether the frame changed.
+bool ImageComposite::UpdateCompositedFrame(
+    int aImageIndex, bool aWasVisibleAtPreviousComposition) {
+  MOZ_RELEASE_ASSERT(aImageIndex >= 0);
+  MOZ_RELEASE_ASSERT(aImageIndex < static_cast<int>(mImages.Length()));
+  const TimedImage& image = mImages[aImageIndex];
+
+  auto compositionOpportunityId = GetCompositionOpportunityId();
+  TimeStamp compositionTime = GetCompositionTime();
+  MOZ_RELEASE_ASSERT(compositionTime,
+                     "Should only be called during a composition");
+
+  nsCString descr;
+  if (profiler_thread_is_being_profiled_for_markers()) {
+    nsCString relativeTimeString;
+    if (image.mTimeStamp) {
+      relativeTimeString.AppendPrintf(
+          " [relative timestamp %.1lfms]",
+          (image.mTimeStamp - compositionTime).ToMilliseconds());
+    }
+    int remainingImages = mImages.Length() - 1 - aImageIndex;
+    static const char* kBiasStrings[] = {"NONE", "NEGATIVE", "POSITIVE"};
+    descr.AppendPrintf(
+        "frameID %" PRId32 " (producerID %" PRId32 ") [composite %" PRIu64
+        "] [bias %s] [%d remaining %s]%s",
+        image.mFrameID, image.mProducerID, compositionOpportunityId.mId,
+        kBiasStrings[mBias], remainingImages,
+        remainingImages == 1 ? "image" : "images", relativeTimeString.get());
+    if (mLastProducerID != image.mProducerID) {
+      descr.AppendPrintf(", previous producerID: %" PRId32, mLastProducerID);
+    } else if (mLastFrameID != image.mFrameID) {
+      descr.AppendPrintf(", previous frameID: %" PRId32, mLastFrameID);
+    } else {
+      descr.AppendLiteral(", no change");
+    }
+  }
+  PROFILER_MARKER_TEXT("UpdateCompositedFrame", GRAPHICS, {}, descr);
+
+  if (mLastFrameID == image.mFrameID && mLastProducerID == image.mProducerID) {
+    // The frame didn't change.
+    return false;
+  }
+
+  CountSkippedFrames(&image);
+
+  int32_t dropped = mSkippedFramesSinceLastComposite;
+  mSkippedFramesSinceLastComposite = 0;
+
+  if (!aWasVisibleAtPreviousComposition) {
+    // This video was not part of the on-screen scene during the previous
+    // composition opportunity, for example it may have been scrolled off-screen
+    // or in a background tab, or compositing might have been paused.
+    // Ignore any skipped frames and don't count them as dropped.
+    dropped = 0;
+  }
+
+  if (dropped > 0) {
+    mDroppedFrames += dropped;
+    if (profiler_thread_is_being_profiled_for_markers()) {
+      const char* frameOrFrames = dropped == 1 ? "frame" : "frames";
+      nsPrintfCString text("%" PRId32 " %s dropped: %" PRId32 " -> %" PRId32
+                           " (producer %" PRId32 ")",
+                           dropped, frameOrFrames, mLastFrameID, image.mFrameID,
+                           mLastProducerID);
+      PROFILER_MARKER_TEXT("Video frames dropped", GRAPHICS, {}, text);
+    }
+  }
+
+  mLastFrameID = image.mFrameID;
+  mLastProducerID = image.mProducerID;
+  mLastFrameUpdateComposition = compositionOpportunityId;
+
+  return true;
+}
+
+void ImageComposite::OnFinishRendering(int aImageIndex,
+                                       const TimedImage* aImage,
+                                       base::ProcessId aProcessId,
+                                       const CompositableHandle& aHandle) {
+  if (mLastFrameUpdateComposition != GetCompositionOpportunityId()) {
+    // The frame did not change in this composition.
+    return;
+  }
+
+  if (aHandle) {
+    ImageCompositeNotificationInfo info;
+    info.mImageBridgeProcessId = aProcessId;
+    info.mNotification = ImageCompositeNotification(
+        aHandle, aImage->mTimeStamp, GetCompositionTime(), mLastFrameID,
+        mLastProducerID);
+    AppendImageCompositeNotification(info);
+  }
+}
+
+const ImageComposite::TimedImage* ImageComposite::GetImage(
+    size_t aIndex) const {
+  if (aIndex >= mImages.Length()) {
+    return nullptr;
+  }
+  return &mImages[aIndex];
+}
+
+void ImageComposite::CountSkippedFrames(const TimedImage* aImage) {
+  if (aImage->mProducerID != mLastProducerID) {
+    // Switched producers.
+    return;
+  }
+
+  if (mImages.IsEmpty() || aImage->mFrameID <= mLastFrameID + 1) {
+    // No frames were skipped.
+    return;
+  }
+
+  uint32_t targetFrameRate = gfxPlatform::TargetFrameRate();
+  if (targetFrameRate == 0) {
+    // Can't know whether we could have reasonably displayed all video frames.
+    return;
+  }
+
+  double targetFrameDurationMS = 1000.0 / targetFrameRate;
+
+  // Count how many images in mImages were skipped between mLastFrameID and
+  // aImage.mFrameID. Only count frames for which we can estimate a duration by
+  // looking at the next frame's timestamp, and only if the video frame rate is
+  // no faster than the target frame rate.
+  int32_t skipped = 0;
+  for (size_t i = 0; i + 1 < mImages.Length(); i++) {
+    const auto& img = mImages[i];
+    if (img.mProducerID != aImage->mProducerID ||
+        img.mFrameID <= mLastFrameID || img.mFrameID >= aImage->mFrameID) {
+      continue;
+    }
+
+    // We skipped img! Estimate img's time duration.
+    const auto& next = mImages[i + 1];
+    if (next.mProducerID != aImage->mProducerID) {
+      continue;
+    }
+
+    MOZ_ASSERT(next.mFrameID > img.mFrameID);
+    TimeDuration duration = next.mTimeStamp - img.mTimeStamp;
+    if (floor(duration.ToMilliseconds()) >= floor(targetFrameDurationMS)) {
+      // Count the frame.
+      skipped++;
+    }
+  }
+
+  mSkippedFramesSinceLastComposite += skipped;
+}
+
+void ImageComposite::DetectTimeStampJitter(const TimedImage* aNewImage) {
+  if (!profiler_thread_is_being_profiled_for_markers() ||
+      aNewImage->mTimeStamp.IsNull()) {
+    return;
+  }
+
+  // Find aNewImage in mImages and compute its timestamp delta, if found.
+  // Ideally, a given video frame should never change its timestamp (jitter
+  // should be zero). However, we re-adjust video frame timestamps based on the
+  // audio clock. If the audio clock drifts compared to the system clock, or if
+  // there are bugs or inaccuracies in the computation of these timestamps,
+  // jitter will be non-zero.
+  Maybe<TimeDuration> jitter;
+  for (const auto& img : mImages) {
+    if (img.mProducerID == aNewImage->mProducerID &&
+        img.mFrameID == aNewImage->mFrameID) {
+      if (!img.mTimeStamp.IsNull()) {
+        jitter = Some(aNewImage->mTimeStamp - img.mTimeStamp);
+      }
+      break;
+    }
+  }
+  if (jitter) {
+    nsPrintfCString text("%.2lfms", jitter->ToMilliseconds());
+    PROFILER_MARKER_TEXT("VideoFrameTimeStampJitter", GRAPHICS, {}, text);
+  }
+}
+
+}  // namespace layers
+}  // namespace mozilla