WebVR: process animations from posted task to yield for other events

third_party/WebKit/Source/modules/vr/VRDisplay.cpp

Index: third_party/WebKit/Source/modules/vr/VRDisplay.cpp
diff --git a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
index cc8f1038aae5d967f3865cc8b9a1881194dcb3d9..7c76114d50501e017583313962039ed7914c5333 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
@@ -27,6 +27,7 @@
 #include "modules/webgl/WebGLRenderingContextBase.h"
 #include "platform/Histogram.h"
 #include "platform/UserGestureIndicator.h"
+#include "platform/instrumentation/tracing/TraceEvent.h"
 #include "public/platform/Platform.h"
 #include "wtf/AutoReset.h"
 #include "wtf/Time.h"
@@ -676,6 +677,14 @@ void VRDisplay::OnDeactivate(
       EventTypeNames::vrdisplaydeactivate, true, false, this, reason));
 }
 
+void VRDisplay::processScheduledAnimations(double timestamp) {
+  TRACE_EVENT1("gpu", "VRDisplay::OnVSync", "frame", m_vrFrameId);
+
+  AutoReset<bool> animating(&m_inAnimationFrame, true);
+  m_pendingRaf = false;
+  m_scriptedAnimationController->serviceScriptedAnimations(timestamp);
+}
+
 void VRDisplay::OnVSync(device::mojom::blink::VRPosePtr pose,
                         mojo::common::mojom::blink::TimeDeltaPtr time,
                         int16_t frameId,
@@ -704,12 +713,21 @@ void VRDisplay::OnVSync(device::mojom::blink::VRPosePtr pose,
     m_timebase = WTF::monotonicallyIncreasingTime() - timeDelta.InSecondsF();
   }
 
-  AutoReset<bool> animating(&m_inAnimationFrame, true);
   m_framePose = std::move(pose);
   m_vrFrameId = frameId;
-  m_pendingRaf = false;
-  m_scriptedAnimationController->serviceScriptedAnimations(
-      m_timebase + timeDelta.InSecondsF());
+
+  // Post a task to handle scheduled animations after the current
+  // execution context finishes, so that we yield to non-mojo tasks in
+  // between frames. Executing mojo tasks back to back within the same
+  // execution context caused extreme input delay due to processing
+  // multiple frames without yielding, see crbug.com/701444. I suspect
+  // this is due to WaitForIncomingMethodCall receiving the OnVSync
+  // but queueing it for immediate execution since it doesn't match
+  // the interface being waited on.
+  Platform::current()->currentThread()->getWebTaskRunner()->postTask(

[haraken, 2017/03/24 01:16:06]

The default task runner is going to be deprecated. Use
TaskRunnerHelper::postTask() instead.

See
https://cs.chromium.org/chromium/src/third_party/WebKit/public/platform/WebTh...

+      BLINK_FROM_HERE,
+      WTF::bind(&VRDisplay::processScheduledAnimations,
+                wrapWeakPersistent(this), m_timebase + timeDelta.InSecondsF()));
 }
 
 void VRDisplay::ConnectVSyncProvider() {