Encode frame number in pixel data for pose sync

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 <thread>
 
 #include "chrome/browser/android/vr_shell/ui_scene.h"
 #include "chrome/browser/android/vr_shell/vr_compositor.h"
@@ skipping 256 matching lines @@
       bool is_inside = x >= 0.0f && x < 1.0f && y >= 0.0f && y < 1.0f;
       if (is_inside) {
         closest_element = distance_to_plane;
         target_point_ = plane_intersection_point;
         target_element_ = &plane;
       }
     }
   }
 }
 
+void VrShell::SetGvrPoseForWebVr(gvr::Mat4f pose, uint32_t pose_num) {
+  webvr_head_pose_[pose_num % POSE_QUEUE_SIZE] = pose;
+  webvr_newest_pose_num_ = pose_num;
+}
+
+int32_t GetPixelEncodedFrameNumber() {
+  // Read the frame number encoded in a bottom left pixel as color values.
+  // See also third_party/WebKit/Source/modules/vr/VRDisplay.cpp which
+  // encodes the frame number, and device/vr/android/gvr/gvr_device.cc
+  // which tracks poses.
+  uint8_t pixels[4];
+  // Assume we're reading from the frambebuffer we just wrote to.
+  // That's true currently, we may need to use glReadBuffer(GL_BACK)
+  // or equivalent if the rendering setup changes in the future.
+  glReadPixels(0, 0, 1, 1, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
+  return pixels[0] | (pixels[1] << 8) | (pixels[2] << 16);
+}
+
 void VrShell::DrawFrame(JNIEnv* env, const JavaParamRef<jobject>& obj) {
   buffer_viewport_list_->SetToRecommendedBufferViewports();
 
   gvr::Frame frame = swap_chain_->AcquireFrame();
   gvr::ClockTimePoint target_time = gvr::GvrApi::GetTimePointNow();
   target_time.monotonic_system_time_nanos += kPredictionTimeWithoutVsyncNanos;
   gvr::Mat4f head_pose = gvr_api_->GetHeadSpaceFromStartSpaceRotation(target_time);
   head_pose = gvr_api_->ApplyNeckModel(head_pose, 1.0f);
 
   // Bind back to the default framebuffer.
   frame.BindBuffer(0);
 
   if (webvr_mode_) {
     DrawWebVr();
     if (!webvr_secure_origin_) {
       DrawWebVrOverlay(target_time.monotonic_system_time_nanos);
     }
+
+    int32_t webvr_pose_frame = GetPixelEncodedFrameNumber();
+    // LOG << "klausw: newest_pose=" << webvr_newest_pose_num_ <<
+    //     " pixel=" << webvr_pose_frame <<
+    //     "(" << webvr_pose_frame - webvr_newest_pose_num_ << ")";
+
+    head_pose = webvr_head_pose_[webvr_pose_frame % POSE_QUEUE_SIZE];
   } else {
     DrawVrShell(head_pose);
   }
 
   frame.Unbind();
   frame.Submit(*buffer_viewport_list_, head_pose);
 }
 
 void VrShell::DrawVrShell(const gvr::Mat4f& head_pose) {
   float screen_tilt = desktop_screen_tilt_ * M_PI / 180.0f;
@@ skipping 205 matching lines @@
   SetIdentityM(icon_pos);
   const float small_icon_width =
       kWebVrWarningPermanentRect.width / 1000.f * kWebVrWarningDistance;
   const float small_icon_height =
       kWebVrWarningPermanentRect.height / 1000.f * kWebVrWarningDistance;
   const float small_icon_angle =
       kWebVrWarningPermanentAngle * M_PI / 180.f;  // Degrees to radians.
   ScaleM(icon_pos, icon_pos, small_icon_width, small_icon_height, 1.0f);
   TranslateM(icon_pos, icon_pos, 0.0f, 0.0f, -kWebVrWarningDistance);
   icon_pos = MatrixMul(
-      QuatToMatrix(QuatFromAxisAngle(1.f, 0.f, 0.f, small_icon_angle)),
+      QuatToMatrix(QuatFromAxisAngle({1.f, 0.f, 0.f}, small_icon_angle)),
       icon_pos);
   gvr::Mat4f combined = MatrixMul(projection_matrix,
                                   MatrixMul(view_matrix, icon_pos));
   vr_shell_renderer_->GetTexturedQuadRenderer()->Draw(
       ui_texture_id_, combined, MakeUiGlCopyRect(kWebVrWarningPermanentRect));
 
   // Check if we also need to show the transient warning.
   if (present_time_nanos > webvr_warning_end_nanos_) {
     return;
   }
@@ skipping 139 matching lines @@
       content::WebContents::FromJavaWebContents(content_web_contents));
   content::ContentViewCore* ui_core = content::ContentViewCore::FromWebContents(
       content::WebContents::FromJavaWebContents(ui_web_contents));
   return reinterpret_cast<intptr_t>(new VrShell(
       env, obj, c_core,
       reinterpret_cast<ui::WindowAndroid*>(content_window_android), ui_core,
       reinterpret_cast<ui::WindowAndroid*>(ui_window_android)));
 }
 
 }  // namespace vr_shell