Fix potential duplicated StartFrame() call (#3047)

Author: MortimerGoro

app/src/main/cpp/BrowserWorld.cpp

@@ -1422,10 +1422,12 @@ BrowserWorld::TickImmersive() {
   m.device->SetRenderMode(device::RenderMode::Immersive);
 
   const bool supportsFrameAhead = m.device->SupportsFramePrediction(DeviceDelegate::FramePrediction::ONE_FRAME_AHEAD);
+  auto framePrediction = DeviceDelegate::FramePrediction::ONE_FRAME_AHEAD;
   VRB_GL_CHECK(glDepthMask(GL_FALSE));
   if (!supportsFrameAhead || (m.externalVR->GetVRState() != ExternalVR::VRState::Rendering)) {
       // Do not use one frame ahead prediction if not supported or we are rendering the spinner.
-      m.device->StartFrame(DeviceDelegate::FramePrediction::NO_FRAME_AHEAD);
+      framePrediction = DeviceDelegate::FramePrediction::NO_FRAME_AHEAD;
+      m.device->StartFrame(framePrediction);
       m.externalVR->PushFramePoses(m.device->GetHeadTransform(), m.controllers->GetControllers(),
                                    m.context->GetTimestamp());
   }
@@ -1435,15 +1437,15 @@ BrowserWorld::TickImmersive() {
   m.externalVR->GetFrameResult(surfaceHandle, textureWidth, textureHeight, leftEye, rightEye);
   ExternalVR::VRState state = m.externalVR->GetVRState();
   if (supportsFrameAhead) {
-      if (m.externalVR->WasFirstPresentingFrame()) {
+      if (framePrediction != DeviceDelegate::FramePrediction::ONE_FRAME_AHEAD) {
           // StartFrame() has been already called to render the spinner, do not call it again.
           // Instead, repeat the XR frame and render the spinner while we transition
           // to one frame ahead prediction.
           state = ExternalVR::VRState::Loading;
       } else {
           // Predict poses for one frame ahead and push the data to shmem so Gecko
           // can start the next XR RAF ASAP.
-          m.device->StartFrame(DeviceDelegate::FramePrediction::ONE_FRAME_AHEAD);
+          m.device->StartFrame(framePrediction);
       }
       m.externalVR->PushFramePoses(m.device->GetHeadTransform(), m.controllers->GetControllers(),
               m.context->GetTimestamp());

app/src/main/cpp/ExternalVR.cpp

@@ -127,7 +127,6 @@ struct ExternalVR::State {
   vrb::Vector eyeOffsets[device::EyeCount];
   uint64_t lastFrameId = 0;
   bool firstPresentingFrame = false;
-  bool wasFirstPresentingFrame = false;
   bool compositorEnabled = false;
   bool waitingForExit = false;
 
@@ -456,7 +455,6 @@ ExternalVR::WaitFrameResult() {
   m.PullBrowserStateWhileLocked();
   while (true) {
     if (!IsPresenting() || m.browser.layerState[0].layer_stereo_immersive.frameId != m.lastFrameId) {
-      m.wasFirstPresentingFrame = m.firstPresentingFrame;
       m.firstPresentingFrame = false;
       m.system.displayState.lastSubmittedFrameSuccessful = true;
       m.system.displayState.lastSubmittedFrameId = m.browser.layerState[0].layer_stereo_immersive.frameId;
@@ -482,10 +480,6 @@ ExternalVR::WaitFrameResult() {
   return true;
 }
 
-bool ExternalVR::WasFirstPresentingFrame() const {
-  return m.wasFirstPresentingFrame;
-}
-
 void
 ExternalVR::CompleteEnumeration()
 {

app/src/main/cpp/ExternalVR.h

@@ -55,7 +55,6 @@ class ExternalVR : public ImmersiveDisplay {
   VRState GetVRState() const;
   void PushFramePoses(const vrb::Matrix& aHeadTransform, const std::vector<Controller>& aControllers, const double aTimestamp);
   bool WaitFrameResult();
-  bool WasFirstPresentingFrame() const;
   void GetFrameResult(int32_t& aSurfaceHandle,
                       int32_t& aTextureWidth,
                       int32_t& aTextureHeight,