WebVR: avoid race conditions for partially-initialized display

device/vr/android/gvr/gvr_device.cc

 // 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 "device/vr/android/gvr/gvr_device.h"
 
 #include <math.h>
 #include <algorithm>
 
 #include "base/time/time.h"
@@ skipping 37 matching lines @@
   device->rightEye = mojom::VREyeParameters::New();
   mojom::VREyeParametersPtr& left_eye = device->leftEye;
   mojom::VREyeParametersPtr& right_eye = device->rightEye;
 
   left_eye->fieldOfView = mojom::VRFieldOfView::New();
   right_eye->fieldOfView = mojom::VRFieldOfView::New();
 
   left_eye->offset.resize(3);
   right_eye->offset.resize(3);
 
-  // TODO(bajones): GVR has a bug that causes it to return bad render target
-  // sizes when the phone is in portait mode. Send arbitrary,
-  // not-horrifically-wrong values instead.
-  //  gvr::Sizei render_target_size = gvr_api->GetRecommendedRenderTargetSize();
-  gvr::Sizei render_target_size = kFallbackRenderTargetSize;
+  // Set the render target size to "invalid" to indicate that
+  // we can't render into it yet. Other code uses this to check
+  // for valid state.
+  gvr::Sizei render_target_size = kInvalidRenderTargetSize;
   left_eye->renderWidth = render_target_size.width / 2;
   left_eye->renderHeight = render_target_size.height;
 
   right_eye->renderWidth = left_eye->renderWidth;
   right_eye->renderHeight = left_eye->renderHeight;
 
   gvr::GvrApi* gvr_api = GetGvrApi();
   if (!gvr_api) {
     // We may not be able to get an instance of GvrApi right away, so
     // stub in some data till we have one.
@@ skipping 10 matching lines @@
     right_eye->fieldOfView->rightDegrees = 45;
 
     left_eye->offset[0] = -0.0;
     left_eye->offset[1] = -0.0;
     left_eye->offset[2] = -0.03;
 
     right_eye->offset[0] = 0.0;
     right_eye->offset[1] = 0.0;
     right_eye->offset[2] = 0.03;
 
-    delegate_->SetWebVRRenderSurfaceSize(2 * left_eye->renderWidth,
-                                         left_eye->renderHeight);
+    // Tell the delegate not to draw yet, to avoid a race condition
+    // (and visible wobble) on entering VR.
+    delegate_->SetWebVRRenderSurfaceSize(0, 0);

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

nit: use constant

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

Done.

 
     return device;
   }
 
   // In compositor mode, we have to use the current compositor window's
   // surface size. Would be nice to change it, but that needs more browser
   // internals to be modified. TODO(klausw,crbug.com/655722): remove this once
   // we can pick our own surface size.
   gvr::Sizei compositor_size = delegate_->GetWebVRCompositorSurfaceSize();
   left_eye->renderWidth = compositor_size.width / 2;
@@ skipping 163 matching lines @@
 }
 
 gvr::GvrApi* GvrDevice::GetGvrApi() {
   if (!delegate_)
     return nullptr;
 
   return delegate_->gvr_api();
 }
 
 }  // namespace device