WebVR: avoid race conditions for partially-initialized display

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 e6515a2eda78795122935ded775a9c85d462cb79..c286f069f65efba7d5c194963e6b69a5bd3a168b 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
@@ -75,6 +75,7 @@ VRDisplay::VRDisplay(NavigatorVR* navigatorVR,
     : m_navigatorVR(navigatorVR),
       m_isConnected(false),
       m_isPresenting(false),
+      m_isValidDeviceForPresenting(true),
       m_canUpdateFramePose(true),
       m_capabilities(new VRDisplayCapabilities()),
       m_eyeParametersLeft(new VREyeParameters()),
@@ -108,6 +109,13 @@ void VRDisplay::update(const device::mojom::blink::VRDisplayInfoPtr& display) {
   m_capabilities->setCanPresent(display->capabilities->canPresent);
   m_capabilities->setMaxLayers(display->capabilities->canPresent ? 1 : 0);
 
+  // Ignore non presenting delegate
+  bool isValid = display->leftEye->renderWidth > 0;
+  bool needOnPresentChange = false;
+  if (m_isPresenting && isValid && !m_isValidDeviceForPresenting) {
+    needOnPresentChange = true;
+  }
+  m_isValidDeviceForPresenting = isValid;
   m_eyeParametersLeft->update(display->leftEye);
   m_eyeParametersRight->update(display->rightEye);
 
@@ -118,6 +126,10 @@ void VRDisplay::update(const device::mojom::blink::VRDisplayInfoPtr& display) {
   } else {
     m_stageParameters = nullptr;
   }
+
+  if (needOnPresentChange) {
+    OnPresentChange();
+  }
 }
 
 void VRDisplay::disconnected() {
@@ -496,10 +508,10 @@ void VRDisplay::forceExitPresent() {
     } else {
       // Can't get into this presentation mode, so nothing to do here.
     }
+    m_isPresenting = false;

[mthiesse, 2016/12/01 21:46:57]

why this change?

[klausw, 2016/12/01 23:08:56]

OnPresentChange() looks at m_isPresenting to tell if presentation is
starting or stopping. The rest of the code was consistent in changing 
the flag before calling OnPresentChange, but this method did it the 
other way around. I just moved the existing assignment, the overall
effect is the same. (There's no need to set m_isPresenting to false
in the "else" branch where it's false already.)

     OnPresentChange();
   }
 
-  m_isPresenting = false;
   m_renderingContext = nullptr;
   m_contextGL = nullptr;
 }
@@ -619,6 +631,10 @@ Document* VRDisplay::document() {
 }
 
 void VRDisplay::OnPresentChange() {
+  if (m_isPresenting && !m_isValidDeviceForPresenting) {
+    VLOG(1) << __FUNCTION__ << ": device not valid, not sending event";
+    return;
+  }
   m_navigatorVR->enqueueVREvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplaypresentchange, true, false, this, ""));
 }