Android WebView: flush input events during onVSync

content/browser/renderer_host/render_widget_host_view_android.cc

Index: content/browser/renderer_host/render_widget_host_view_android.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_android.cc b/content/browser/renderer_host/render_widget_host_view_android.cc
index dd65887f78db5d47ad01b2adc5b5da168d243a18..f587c252d7dbd6fd14e97a719040c0ccb97658b9 100644
--- a/content/browser/renderer_host/render_widget_host_view_android.cc
+++ b/content/browser/renderer_host/render_widget_host_view_android.cc
@@ -201,9 +201,9 @@ RenderWidgetHostViewAndroid::RenderWidgetHostViewAndroid(
       using_synchronous_compositor_(SynchronousCompositorImpl::FromID(
                                         widget_host->GetProcess()->GetID(),
                                         widget_host->GetRoutingID()) != NULL),
+      vsync_subscribers_bitmask_(0),
       frame_evictor_(new DelegatedFrameEvictor(this)),
-      locks_on_frame_count_(0),
-      observing_root_window_(false) {
+      locks_on_frame_count_(0) {
   host_->SetView(this);
   SetContentViewCore(content_view_core);
   ImageTransportFactoryAndroid::AddObserver(this);
@@ -260,9 +260,8 @@ void RenderWidgetHostViewAndroid::WasShown() {
   host_->WasShown(ui::LatencyInfo());
 
   if (content_view_core_ && !using_synchronous_compositor_) {
-    content_view_core_->GetWindowAndroid()->AddObserver(this);
+    SubscribeToVSync(INPUT | BEGIN_FRAME);
     content_view_core_->GetWindowAndroid()->RequestVSyncUpdate();
-    observing_root_window_ = true;
   }
 }
 
@@ -276,10 +275,8 @@ void RenderWidgetHostViewAndroid::WasHidden() {
   // utilization.
   host_->WasHidden();
 
-  if (content_view_core_ && !using_synchronous_compositor_) {
-    content_view_core_->GetWindowAndroid()->RemoveObserver(this);
-    observing_root_window_ = false;
-  }
+  if (content_view_core_ && !using_synchronous_compositor_)
+    UnsubscribeToVSync(INPUT | BEGIN_FRAME);

[jdduke (slow), 2014/08/20 04:11:53]

Hmm, this isn't quite what I had in mind. I was thinking/hoping the subscriber
types would replace the various ad-hoc flags that track how a given vsync signal
should be dispatched (flush_input_requested_, needs_begin_frame_), and the
ad-hoc way in which a vsync signal is requested (via RequestVSyncupdate). Lazily
adding |this| as an observer to the window is a nice fall-out from that
approach, but not really the main motivation, if that makes sense. 

[hush (inactive), 2014/08/20 18:06:50]

I see.
I will remove |flush_input_requested_| and |needs_begin_frame_|, and just use
the bit mask.

Also I will move almost every "requestVSyncUpdate" into SubscribeToVSync

On 2014/08/20 04:11:53, jdduke wrote:

 }
 
 void RenderWidgetHostViewAndroid::WasResized() {
@@ -811,6 +808,10 @@ void RenderWidgetHostViewAndroid::ShowDisambiguationPopup(
 
 scoped_ptr<SyntheticGestureTarget>
 RenderWidgetHostViewAndroid::CreateSyntheticGestureTarget() {
+  DCHECK(content_view_core_);
+  if (using_synchronous_compositor_)
+    SubscribeToVSync(INPUT);
+
   return scoped_ptr<SyntheticGestureTarget>(new SyntheticGestureTargetAndroid(
       host_, content_view_core_->CreateTouchEventSynthesizer()));
 }
@@ -1440,10 +1441,8 @@ void RenderWidgetHostViewAndroid::DidStopFlinging() {
 void RenderWidgetHostViewAndroid::SetContentViewCore(
     ContentViewCoreImpl* content_view_core) {
   RemoveLayers();
-  if (observing_root_window_ && content_view_core_) {
-    content_view_core_->GetWindowAndroid()->RemoveObserver(this);
-    observing_root_window_ = false;
-  }
+  if (vsync_subscribers_bitmask_ && content_view_core_)
+    UnsubscribeToVSync(INPUT | BEGIN_FRAME);
 
   bool resize = false;
   if (content_view_core != content_view_core_) {
@@ -1470,8 +1469,7 @@ void RenderWidgetHostViewAndroid::SetContentViewCore(
     return;
 
   if (!using_synchronous_compositor_) {
-    content_view_core_->GetWindowAndroid()->AddObserver(this);
-    observing_root_window_ = true;
+    SubscribeToVSync(INPUT | BEGIN_FRAME);
     if (needs_begin_frame_)
       content_view_core_->GetWindowAndroid()->RequestVSyncUpdate();
   }
@@ -1518,17 +1516,36 @@ void RenderWidgetHostViewAndroid::OnDetachCompositor() {
   RunAckCallbacks();
 }
 
+void RenderWidgetHostViewAndroid::SubscribeToVSync(uint32 type) {
+  if (!vsync_subscribers_bitmask_)
+    content_view_core_->GetWindowAndroid()->AddObserver(this);
+
+  vsync_subscribers_bitmask_ |= type;
+  // Synchronous compositor does not request begin frames OnVSync.
+  DCHECK(!using_synchronous_compositor_ ||
+         !(vsync_subscribers_bitmask_ & BEGIN_FRAME));
+}
+
+void RenderWidgetHostViewAndroid::UnsubscribeToVSync(uint32 type) {
+  vsync_subscribers_bitmask_ &= ~type;
+  if (!vsync_subscribers_bitmask_)
+    content_view_core_->GetWindowAndroid()->RemoveObserver(this);
+}
+
 void RenderWidgetHostViewAndroid::OnVSync(base::TimeTicks frame_time,
                                           base::TimeDelta vsync_period) {
   TRACE_EVENT0("cc", "RenderWidgetHostViewAndroid::OnVSync");
   if (!host_)
     return;
 
-  if (flush_input_requested_) {
+  if (vsync_subscribers_bitmask_ & INPUT & flush_input_requested_) {
     flush_input_requested_ = false;
     host_->FlushInput();
   }
 
+  if (!(vsync_subscribers_bitmask_ & BEGIN_FRAME))
+    return;
+
   TRACE_EVENT0("cc", "RenderWidgetHostViewAndroid::SendBeginFrame");
   base::TimeTicks display_time = frame_time + vsync_period;