Bug 1435022 - Make the Composite function private and document/clean it. r=sotaro

MozReview-Commit-ID: 3UQKwwC3Fav

--HG--
extra : rebase_source : 19737ed1c2ab40d7656257adbac10626ace1d9e7

gfx/layers/ipc/CompositorVsyncScheduler.cpp

@@ -211,24 +211,28 @@ void
 CompositorVsyncScheduler::Composite(TimeStamp aVsyncTimestamp)
 {
   MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
-  {
+  MOZ_ASSERT(mVsyncSchedulerOwner);
+
+  { // scope lock
     MonitorAutoLock lock(mCurrentCompositeTaskMonitor);
     mCurrentCompositeTask = nullptr;
   }
 
-  if ((aVsyncTimestamp < mLastCompose) && !mAsapScheduling) {
-    // We can sometimes get vsync timestamps that are in the past
-    // compared to the last compose with force composites.
-    // In those cases, wait until the next vsync;
-    return;
-  }
+  if (!mAsapScheduling) {
+    // Some early exit conditions if we're not in ASAP mode
+    if (aVsyncTimestamp < mLastCompose) {
+      // We can sometimes get vsync timestamps that are in the past
+      // compared to the last compose with force composites.
+      // In those cases, wait until the next vsync;
+      return;
+    }
 
-  MOZ_ASSERT(mVsyncSchedulerOwner);
-  if (!mAsapScheduling && mVsyncSchedulerOwner->IsPendingComposite()) {
-    // If previous composite is still on going, finish it and does a next
-    // composite in a next vsync.
-    mVsyncSchedulerOwner->FinishPendingComposite();
-    return;
+    if (mVsyncSchedulerOwner->IsPendingComposite()) {
+      // If previous composite is still on going, finish it and wait for the
+      // next vsync.
+      mVsyncSchedulerOwner->FinishPendingComposite();
+      return;
+    }
   }
 
   DispatchTouchEvents(aVsyncTimestamp);
@@ -236,7 +240,10 @@ CompositorVsyncScheduler::Composite(TimeStamp aVsyncTimestamp)
   if (mNeedsComposite || mAsapScheduling) {
     mNeedsComposite = 0;
     mLastCompose = aVsyncTimestamp;
+
+    // Tell the owner to do a composite
     mVsyncSchedulerOwner->CompositeToTarget(nullptr, nullptr);
+
     mVsyncNotificationsSkipped = 0;
 
     TimeDuration compositeFrameTotal = TimeStamp::Now() - aVsyncTimestamp;

gfx/layers/ipc/CompositorVsyncScheduler.h

@@ -58,7 +58,6 @@ public:
   void ScheduleComposition();
   void CancelCurrentCompositeTask();
   bool NeedsComposite();
-  void Composite(TimeStamp aVsyncTimestamp);
   void ForceComposeToTarget(gfx::DrawTarget* aTarget, const gfx::IntRect* aRect);
 
   const TimeStamp& GetLastComposeTime()
@@ -87,6 +86,10 @@ private:
   // such a task already queued. Can be called from any thread.
   void PostVRTask(TimeStamp aTimestamp);
 
+  // This gets run at vsync time and "does" a composite (which really means
+  // update internal state and call the owner to do the composite).
+  void Composite(TimeStamp aVsyncTimestamp);
+
   void NotifyCompositeTaskExecuted();
   void ObserveVsync();
   void UnobserveVsync();