Prevent WebVR from reprojecting with invalid poses

chrome/browser/android/vr_shell/vr_shell.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 "chrome/browser/android/vr_shell/vr_shell.h"
 
 #include "base/metrics/histogram_macros.h"
 #include "chrome/browser/android/vr_shell/ui_elements.h"
 #include "chrome/browser/android/vr_shell/ui_interface.h"
 #include "chrome/browser/android/vr_shell/ui_scene.h"
@@ skipping 520 matching lines @@
 
     // When using async reprojection, we need to know which pose was used in
     // the WebVR app for drawing this frame. Due to unknown amounts of
     // buffering in the compositor and SurfaceTexture, we read the pose number
     // from a corner pixel. There's no point in doing this for legacy
     // distortion rendering since that doesn't need a pose, and reading back
     // pixels is an expensive operation. TODO(klausw): stop doing this once we
     // have working no-compositor rendering for WebVR.
     if (gvr_api_->GetAsyncReprojectionEnabled()) {
       uint32_t webvr_pose_frame = GetPixelEncodedPoseIndex();
-      head_pose = webvr_head_pose_[webvr_pose_frame % kPoseRingBufferSize];
+      // If we don't get a valid frame ID back we shouldn't attempt to reproject
+      // by an invalid matrix, so turn of reprojection instead.
+      if (webvr_pose_frame == 0) {
+        webvr_left_viewport_->SetReprojection(GVR_REPROJECTION_NONE);
+        webvr_right_viewport_->SetReprojection(GVR_REPROJECTION_NONE);
+      } else {
+        webvr_left_viewport_->SetReprojection(GVR_REPROJECTION_FULL);
+        webvr_right_viewport_->SetReprojection(GVR_REPROJECTION_FULL);
+        head_pose = webvr_head_pose_[webvr_pose_frame % kPoseRingBufferSize];
+      }
     }
   }
 
   DrawVrShell(head_pose, frame);
 
   frame.Unbind();
   frame.Submit(*buffer_viewport_list_, head_pose);
 }
 
 void VrShell::DrawVrShell(const gvr::Mat4f& head_pose,
@@ skipping 347 matching lines @@
            const JavaParamRef<jobject>& ui_web_contents,
            jlong ui_window_android) {
   return reinterpret_cast<intptr_t>(new VrShell(
       env, obj, content::WebContents::FromJavaWebContents(content_web_contents),
       reinterpret_cast<ui::WindowAndroid*>(content_window_android),
       content::WebContents::FromJavaWebContents(ui_web_contents),
       reinterpret_cast<ui::WindowAndroid*>(ui_window_android)));
 }
 
 }  // namespace vr_shell