WebVR: flush before requesting sync token for mailbox

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/vr/VRDisplay.h"
 
 #include "core/css/StylePropertySet.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/FrameRequestCallback.h"
 #include "core/dom/ScriptedAnimationController.h"
@@ skipping 505 matching lines @@
     return;
   }
 
   // No frame Id to write before submitting the frame.
   if (vr_frame_id_ < 0) {
     // TODO(klausw): There used to be a submitFrame here, but we can't
     // submit without a frameId and associated pose data. Just drop it.
     return;
   }
 
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::Flush_1");
   context_gl_->Flush();
+  TRACE_EVENT_END0("gpu", "VRDisplay::Flush_1");
 
   // Check if the canvas got resized, if yes send a bounds update.
   int current_width = rendering_context_->drawingBufferWidth();
   int current_height = rendering_context_->drawingBufferHeight();
   if ((current_width != source_width_ || current_height != source_height_) &&
       current_width != 0 && current_height != 0) {
     source_width_ = current_width;
     source_height_ = current_height;
     UpdateLayerBounds();
   }
@@ skipping 16 matching lines @@
   if (wait_for_previous_transfer_to_finish) {
     TRACE_EVENT0("gpu", "VRDisplay::waitForPreviousTransferToFinish");
     while (pending_submit_frame_) {
       if (!submit_frame_client_binding_.WaitForIncomingMethodCall()) {
         DLOG(ERROR) << "Failed to receive SubmitFrame response";
         break;
       }
     }
   }
 
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::GetImage");
   RefPtr<Image> image_ref = rendering_context_->GetImage(
       kPreferAcceleration, kSnapshotReasonCreateImageBitmap);
+  TRACE_EVENT_END0("gpu", "VRDisplay::GetImage");
 
   // Hardware-accelerated rendering should always be texture backed,
   // as implemented by AcceleratedStaticBitmapImage. Ensure this is
   // the case, don't attempt to render if using an unexpected drawing
   // path.
   if (!image_ref.Get() || !image_ref->IsTextureBacked()) {
     NOTREACHED() << "WebVR requires hardware-accelerated rendering to texture";
     return;
   }
 
   // The AcceleratedStaticBitmapImage must be kept alive until the
   // mailbox is used via createAndConsumeTextureCHROMIUM, the mailbox
   // itself does not keep it alive. We must keep a reference to the
   // image until the mailbox was consumed.
   StaticBitmapImage* static_image =
       static_cast<StaticBitmapImage*>(image_ref.Get());
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::EnsureMailbox");
   static_image->EnsureMailbox();
+  TRACE_EVENT_END0("gpu", "VRDisplay::EnsureMailbox");
 
   if (wait_for_previous_transfer_to_finish) {
     // Save a reference to the image to keep it alive until next frame,
     // where we'll wait for the transfer to finish before overwriting
     // it.
     previous_image_ = std::move(image_ref);
   }
 
+  // Create mailbox and sync token for transfer.
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::GetMailbox");
+  auto mailbox = static_image->GetMailbox();
+  TRACE_EVENT_END0("gpu", "VRDisplay::GetMailbox");
+  // Flush to avoid black screen flashes which appear to be related to
+  // "fence sync must be flushed before generating sync token" GL errors.
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::Flush_2");
+  context_gl_->Flush();
+  TRACE_EVENT_END0("gpu", "VRDisplay::Flush_2");
+  auto sync_token = static_image->GetSyncToken();
+
   // Wait for the previous render to finish, to avoid losing frames in the
   // Android Surface / GLConsumer pair. TODO(klausw): make this tunable?
-  // Other devices may have different preferences.
+  // Other devices may have different preferences. Do this step as late
+  // as possible before SubmitFrame to ensure we can do as much work as
+  // possible in parallel with the previous frame's rendering.
   {
     TRACE_EVENT0("gpu", "waitForPreviousRenderToFinish");
     while (pending_previous_frame_render_) {
       if (!submit_frame_client_binding_.WaitForIncomingMethodCall()) {
         DLOG(ERROR) << "Failed to receive SubmitFrame response";
         break;
       }
     }
   }
 
   pending_previous_frame_render_ = true;
   pending_submit_frame_ = true;
-  display_->SubmitFrame(
-      vr_frame_id_,
-      gpu::MailboxHolder(static_image->GetMailbox(),
-                         static_image->GetSyncToken(), GL_TEXTURE_2D));
+
+  TRACE_EVENT_BEGIN0("gpu", "VRDisplay::SubmitFrame");
+  display_->SubmitFrame(vr_frame_id_,
+                        gpu::MailboxHolder(mailbox, sync_token, GL_TEXTURE_2D));
+  TRACE_EVENT_END0("gpu", "VRDisplay::SubmitFrame");
 
   // If preserveDrawingBuffer is false, must clear now. Normally this
   // happens as part of compositing, but that's not active while
   // presenting, so run the responsible code directly.
   rendering_context_->MarkCompositedAndClearBackbufferIfNeeded();
 
   // If we're not deferring the wait for transferring the mailbox,
   // we need to wait for it now to prevent the image going out of
   // scope before its mailbox is retrieved.
   if (!wait_for_previous_transfer_to_finish) {
@@ skipping 262 matching lines @@
   visitor->Trace(stage_parameters_);
   visitor->Trace(eye_parameters_left_);
   visitor->Trace(eye_parameters_right_);
   visitor->Trace(layer_);
   visitor->Trace(rendering_context_);
   visitor->Trace(scripted_animation_controller_);
   visitor->Trace(pending_present_resolvers_);
 }
 
 }  // namespace blink