From e45770707bd843805e500b81a6a70badc062e755 Mon Sep 17 00:00:00 2001
From: Mason Chang <mchang@mozilla.com>
Date: Fri, 6 Mar 2015 13:58:22 -0800
Subject: [PATCH] Bug 1138502. Reset vsync unobserve count if a force composite
 occurs. r=mstange

---
 gfx/layers/ipc/CompositorParent.cpp | 21 +++++++++++++++++++++
 gfx/layers/ipc/CompositorParent.h   |  1 +
 2 files changed, 22 insertions(+)

diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
index 44244ebd0be9..76d34928cf09 100644
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -343,6 +343,23 @@ CompositorVsyncObserver::Composite(TimeStamp aVsyncTimestamp)
   DispatchTouchEvents(aVsyncTimestamp);
 }
 
+void
+CompositorVsyncObserver::OnForceComposeToTarget()
+{
+  /**
+   * bug 1138502 - There are cases such as during long-running window resizing events
+   * where we receive many sync RecvFlushComposites. We also get vsync notifications which
+   * will increment mVsyncNotificationsSkipped because a composite just occurred. After
+   * enough vsyncs and RecvFlushComposites occurred, we will disable vsync. Then at the next
+   * ScheduleComposite, we will enable vsync, then get a RecvFlushComposite, which will
+   * force us to unobserve vsync again. On some platforms, enabling/disabling vsync is not
+   * free and this oscillating behavior causes a performance hit. In order to avoid this problem,
+   * we reset the mVsyncNotificationsSkipped counter to keep vsync enabled.
+   */
+  MOZ_ASSERT(CompositorParent::IsInCompositorThread());
+  mVsyncNotificationsSkipped = 0;
+}
+
 bool
 CompositorVsyncObserver::NeedsComposite()
 {
@@ -1040,6 +1057,10 @@ CompositorParent::ForceComposeToTarget(DrawTarget* aTarget, const nsIntRect* aRe
   PROFILER_LABEL("CompositorParent", "ForceComposeToTarget",
     js::ProfileEntry::Category::GRAPHICS);
 
+  if (mCompositorVsyncObserver) {
+    mCompositorVsyncObserver->OnForceComposeToTarget();
+  }
+
   AutoRestore<bool> override(mOverrideComposeReadiness);
   mOverrideComposeReadiness = true;
 
diff --git a/gfx/layers/ipc/CompositorParent.h b/gfx/layers/ipc/CompositorParent.h
index 88c87fc71b1b..8a4f12697886 100644
--- a/gfx/layers/ipc/CompositorParent.h
+++ b/gfx/layers/ipc/CompositorParent.h
@@ -106,6 +106,7 @@ public:
   bool NeedsComposite();
   void CancelCurrentCompositeTask();
   void Destroy();
+  void OnForceComposeToTarget();
 
 private:
   virtual ~CompositorVsyncObserver();