Remove Sync GetPose VRService call, implement VRVSyncProvider

chrome/browser/android/vr_shell/vr_shell_gl.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_gl.h"
 
 #include "base/android/jni_android.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/android/vr_shell/ui_elements.h"
 #include "chrome/browser/android/vr_shell/ui_scene.h"
 #include "chrome/browser/android/vr_shell/vr_controller.h"
 #include "chrome/browser/android/vr_shell/vr_gl_util.h"
 #include "chrome/browser/android/vr_shell/vr_input_manager.h"
 #include "chrome/browser/android/vr_shell/vr_math.h"
 #include "chrome/browser/android/vr_shell/vr_shell.h"
 #include "chrome/browser/android/vr_shell/vr_shell_renderer.h"
+#include "device/vr/android/gvr/gvr_device.h"
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
-#include "ui/gfx/vsync_provider.h"
 #include "ui/gl/android/scoped_java_surface.h"
 #include "ui/gl/android/surface_texture.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/init/gl_factory.h"
 
 namespace vr_shell {
 
 namespace {
-// Constant taken from treasure_hunt demo.
+// TODO(mthiesse): If gvr::PlatformInfo().GetPosePredictionTime() is ever
+// exposed, use that instead (it defaults to 50ms on most platforms).
 static constexpr long kPredictionTimeWithoutVsyncNanos = 50000000;
 
 static constexpr float kZNear = 0.1f;
 static constexpr float kZFar = 1000.0f;
 
 // Screen angle in degrees. 0 = vertical, positive = top closer.
 static constexpr float kDesktopScreenTiltDefault = 0;
 
 static constexpr float kReticleWidth = 0.025f;
 static constexpr float kReticleHeight = 0.025f;
@@ skipping 93 matching lines @@
   return mouse_event;
 }
 
 enum class ViewerType {
   UNKNOWN_TYPE = 0,
   CARDBOARD = 1,
   DAYDREAM = 2,
   VIEWER_TYPE_MAX,
 };
 
-int GetPixelEncodedPoseIndexByte() {
-  TRACE_EVENT0("gpu", "VrShellGl::GetPixelEncodedPoseIndex");
-  // Read the pose index encoded in a bottom left pixel as color values.
-  // See also third_party/WebKit/Source/modules/vr/VRDisplay.cpp which
-  // encodes the pose index, and device/vr/android/gvr/gvr_device.cc
-  // which tracks poses. Returns the low byte (0..255) if valid, or -1
-  // if not valid due to bad magic number.
-  uint8_t pixels[4];
-  // Assume we're reading from the framebuffer 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);
-
-  // Check for the magic number written by VRDevice.cpp on submit.
-  // This helps avoid glitches from garbage data in the render
-  // buffer that can appear during initialization or resizing. These
-  // often appear as flashes of all-black or all-white pixels.
-  if (pixels[1] == kWebVrPosePixelMagicNumbers[0] &&
-      pixels[2] == kWebVrPosePixelMagicNumbers[1]) {
-    // Pose is good.
-    return pixels[0];
-  }
-  VLOG(1) << "WebVR: reject decoded pose index " << (int)pixels[0] <<
-      ", bad magic number " << (int)pixels[1] << ", " << (int)pixels[2];
-  return -1;
-}
-
 int64_t TimeInMicroseconds() {
   return std::chrono::duration_cast<std::chrono::microseconds>(
       std::chrono::steady_clock::now().time_since_epoch()).count();
 }
 
-void WaitForSwapAck(const base::Closure& callback, gfx::SwapResult result) {
-  callback.Run();
-}
-
 }  // namespace
 
 VrShellGl::VrShellGl(
     const base::WeakPtr<VrShell>& weak_vr_shell,
     const base::WeakPtr<VrInputManager>& content_input_manager,
     const base::WeakPtr<VrInputManager>& ui_input_manager,
     scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner,
     gvr_context* gvr_api,
     bool initially_web_vr,
     bool reprojected_rendering)
       : web_vr_mode_(initially_web_vr),
         surfaceless_rendering_(reprojected_rendering),
         task_runner_(base::ThreadTaskRunnerHandle::Get()),
+        binding_(this),
         weak_vr_shell_(weak_vr_shell),
         content_input_manager_(content_input_manager),
         ui_input_manager_(ui_input_manager),
         main_thread_task_runner_(std::move(main_thread_task_runner)),
         weak_ptr_factory_(this) {
   GvrInit(gvr_api);
 }
 
 VrShellGl::~VrShellGl() {
-  draw_task_.Cancel();
+  vsync_task_.Cancel();
 }
 
 void VrShellGl::Initialize() {
-  gvr::Mat4f identity;
-  SetIdentityM(identity);
-  webvr_head_pose_.resize(kPoseRingBufferSize, identity);
-  webvr_head_pose_valid_.resize(kPoseRingBufferSize, false);
-
   scene_.reset(new UiScene);
 
   if (surfaceless_rendering_) {
     // If we're rendering surfaceless, we'll never get a java surface to render
     // into, so we can initialize GL right away.
     InitializeGl(nullptr);
   }
 }
 
 void VrShellGl::InitializeGl(gfx::AcceleratedWidget window) {
@@ skipping 22 matching lines @@
     LOG(ERROR) << "gl::init::CreateGLContext failed";
     ForceExitVr();
     return;
   }
   if (!context_->MakeCurrent(surface_.get())) {
     LOG(ERROR) << "gl::GLContext::MakeCurrent() failed";
     ForceExitVr();
     return;
   }
 
-  // TODO(mthiesse): We don't appear to have a VSync provider ever here. This is
-  // sort of okay, because the GVR swap chain will block if we render too fast,
-  // but we should address this properly.
-  if (surface_->GetVSyncProvider()) {
-    surface_->GetVSyncProvider()->GetVSyncParameters(base::Bind(
-        &VrShellGl::UpdateVSyncParameters, weak_ptr_factory_.GetWeakPtr()));
-  } else {
-    LOG(ERROR) << "No VSync Provider";
-  }
-
   unsigned int textures[2];
   glGenTextures(2, textures);
   ui_texture_id_ = textures[0];
   content_texture_id_ = textures[1];
   ui_surface_texture_ = gl::SurfaceTexture::Create(ui_texture_id_);
   content_surface_texture_ = gl::SurfaceTexture::Create(content_texture_id_);
   ui_surface_.reset(new gl::ScopedJavaSurface(ui_surface_texture_.get()));
   content_surface_.reset(new gl::ScopedJavaSurface(
       content_surface_texture_.get()));
   ui_surface_texture_->SetFrameAvailableCallback(base::Bind(
         &VrShellGl::OnUIFrameAvailable, weak_ptr_factory_.GetWeakPtr()));
   content_surface_texture_->SetFrameAvailableCallback(base::Bind(
         &VrShellGl::OnContentFrameAvailable, weak_ptr_factory_.GetWeakPtr()));
 
   content_surface_texture_->SetDefaultBufferSize(
       content_tex_physical_size_.width, content_tex_physical_size_.height);
   ui_surface_texture_->SetDefaultBufferSize(ui_tex_physical_size_.width,
                                             ui_tex_physical_size_.height);
 
   main_thread_task_runner_->PostTask(FROM_HERE, base::Bind(
       &VrShell::SurfacesChanged, weak_vr_shell_,
       content_surface_->j_surface().obj(),
       ui_surface_->j_surface().obj()));
 
   InitializeRenderer();
 
-  draw_task_.Reset(base::Bind(&VrShellGl::DrawFrame, base::Unretained(this)));
-  ScheduleNextDrawFrame();
+  vsync_task_.Reset(base::Bind(&VrShellGl::OnVSync, base::Unretained(this)));
+  OnVSync();
 
   ready_to_draw_ = true;
 }
 
 void VrShellGl::OnUIFrameAvailable() {
   ui_surface_texture_->UpdateTexImage();
 }
 
 void VrShellGl::OnContentFrameAvailable() {
   content_surface_texture_->UpdateTexImage();
+  received_frame_ = true;
+}
+
+bool VrShellGl::GetPixelEncodedPoseIndexByte(int* pose_index) {
+  TRACE_EVENT0("gpu", "VrShellGl::GetPixelEncodedPoseIndex");
+  if (!received_frame_) {
+    *pose_index = last_pose_;
+    return true;
+  }
+  received_frame_ = false;
+
+  // Read the pose index encoded in a bottom left pixel as color values.
+  // See also third_party/WebKit/Source/modules/vr/VRDisplay.cpp which
+  // encodes the pose index, and device/vr/android/gvr/gvr_device.cc
+  // which tracks poses. Returns the low byte (0..255) if valid, or -1
+  // if not valid due to bad magic number.
+  uint8_t pixels[4];
+  // Assume we're reading from the framebuffer 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);
+
+  // Check for the magic number written by VRDevice.cpp on submit.
+  // This helps avoid glitches from garbage data in the render
+  // buffer that can appear during initialization or resizing. These
+  // often appear as flashes of all-black or all-white pixels.
+  if (pixels[1] == kWebVrPosePixelMagicNumbers[0] &&
+      pixels[2] == kWebVrPosePixelMagicNumbers[1]) {
+    // Pose is good.
+    *pose_index = pixels[0];
+    last_pose_ = pixels[0];
+    return true;
+  }
+  VLOG(1) << "WebVR: reject decoded pose index " << (int)pixels[0]
+          << ", bad magic number " << (int)pixels[1] << ", "
+          << (int)pixels[2];
+  return false;
 }
 
 void VrShellGl::GvrInit(gvr_context* gvr_api) {
   gvr_api_ = gvr::GvrApi::WrapNonOwned(gvr_api);
   controller_.reset(new VrController(gvr_api));
 
   ViewerType viewerType;
   switch (gvr_api_->GetViewerType()) {
     case gvr::ViewerType::GVR_VIEWER_TYPE_DAYDREAM:
       viewerType = ViewerType::DAYDREAM;
       break;
     case gvr::ViewerType::GVR_VIEWER_TYPE_CARDBOARD:
       viewerType = ViewerType::CARDBOARD;
       break;
     default:
       NOTREACHED();
       viewerType = ViewerType::UNKNOWN_TYPE;
       break;
   }
   UMA_HISTOGRAM_ENUMERATION("VRViewerType", static_cast<int>(viewerType),
       static_cast<int>(ViewerType::VIEWER_TYPE_MAX));
 }
 
 void VrShellGl::InitializeRenderer() {
   // While WebVR is going through the compositor path, it shares
   // the same texture ID. This will change once it gets its own
   // surface, but store it separately to avoid future confusion.
   // TODO(klausw,crbug.com/655722): remove this.
   webvr_texture_id_ = content_texture_id_;
-  // Out of paranoia, explicitly reset the "pose valid" flags to false
-  // from the GL thread. The constructor ran in the UI thread.
-  // TODO(klausw,crbug.com/655722): remove this.
-  webvr_head_pose_valid_.assign(kPoseRingBufferSize, false);
 
   gvr_api_->InitializeGl();
+  webvr_head_pose_.assign(kPoseRingBufferSize,
+                          gvr_api_->GetHeadSpaceFromStartSpaceRotation(
+                              gvr::GvrApi::GetTimePointNow()));
+
   std::vector<gvr::BufferSpec> specs;
   // For kFramePrimaryBuffer (primary VrShell and WebVR content)
   specs.push_back(gvr_api_->CreateBufferSpec());
   render_size_primary_ = specs[kFramePrimaryBuffer].GetSize();
 
   // For kFrameHeadlockedBuffer (for WebVR insecure content warning).
   // Set this up at fixed resolution, the (smaller) FOV gets set below.
   specs.push_back(gvr_api_->CreateBufferSpec());
   specs.back().SetSize(kHeadlockedBufferDimensions);
   render_size_headlocked_ = specs[kFrameHeadlockedBuffer].GetSize();
@@ skipping 239 matching lines @@
   DCHECK(input_target != InputTarget::NONE);
   const base::WeakPtr<VrInputManager>& weak_ptr =
       input_target == InputTarget::CONTENT ? content_input_manager_
                                            : ui_input_manager_;
   main_thread_task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&VrInputManager::ProcessUpdatedGesture, weak_ptr,
                  base::Passed(std::move(event))));
 }
 
-void VrShellGl::SetGvrPoseForWebVr(const gvr::Mat4f& pose, uint32_t pose_num) {
-  webvr_head_pose_[pose_num % kPoseRingBufferSize] = pose;
-  webvr_head_pose_valid_[pose_num % kPoseRingBufferSize] = true;
-}
-
-bool VrShellGl::WebVrPoseByteIsValid(int pose_index_byte) {
-  if (pose_index_byte < 0) {
-    return false;
-  }
-  if (!webvr_head_pose_valid_[pose_index_byte % kPoseRingBufferSize]) {
-    VLOG(1) << "WebVR: reject decoded pose index " << pose_index_byte <<
-        ", not a valid pose";
-    return false;
-  }
-  return true;
-}
-
 void VrShellGl::DrawFrame() {
   TRACE_EVENT0("gpu", "VrShellGl::DrawFrame");
+
   // Reset the viewport list to just the pair of viewports for the
   // primary buffer each frame. Head-locked viewports get added by
   // DrawVrShell if needed.
   buffer_viewport_list_->SetToRecommendedBufferViewports();
 
   gvr::Frame frame = swap_chain_->AcquireFrame();
-  gvr::ClockTimePoint target_time = gvr::GvrApi::GetTimePointNow();
-  target_time.monotonic_system_time_nanos += kPredictionTimeWithoutVsyncNanos;
+  if (!frame.is_valid()) {
+    return;
+  }
+  frame.BindBuffer(kFramePrimaryBuffer);
+  if (web_vr_mode_) {
+    DrawWebVr();
+  }
 
-  gvr::Mat4f head_pose =
-      gvr_api_->GetHeadSpaceFromStartSpaceRotation(target_time);
+  int pose_index;
+  gvr::Mat4f head_pose;
+
+  // 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,crbug.com/655722): stop
+  // doing this once we have working no-compositor rendering for WebVR.
+  if (web_vr_mode_ && gvr_api_->GetAsyncReprojectionEnabled() &&
+      GetPixelEncodedPoseIndexByte(&pose_index)) {
+    head_pose = webvr_head_pose_[pose_index % kPoseRingBufferSize];
+  } else {
+    gvr::ClockTimePoint target_time = gvr::GvrApi::GetTimePointNow();
+    target_time.monotonic_system_time_nanos += kPredictionTimeWithoutVsyncNanos;
+    head_pose = gvr_api_->GetHeadSpaceFromStartSpaceRotation(target_time);
+  }
 
   gvr::Vec3f position = GetTranslation(head_pose);
   if (position.x == 0.0f && position.y == 0.0f && position.z == 0.0f) {
     // This appears to be a 3DOF pose without a neck model. Add one.
     // The head pose has redundant data. Assume we're only using the
     // object_from_reference_matrix, we're not updating position_external.
     // TODO: Not sure what object_from_reference_matrix is. The new api removed
     // it. For now, removing it seems working fine.
     gvr_api_->ApplyNeckModel(head_pose, 1.0f);
   }
 
-  frame.BindBuffer(kFramePrimaryBuffer);
-
   // Update the render position of all UI elements (including desktop).
   const float screen_tilt = kDesktopScreenTiltDefault * M_PI / 180.0f;
   scene_->UpdateTransforms(screen_tilt, TimeInMicroseconds());
 
   UpdateController(GetForwardVector(head_pose));
 
-  if (web_vr_mode_) {
-    DrawWebVr();
-
-    // 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,crbug.com/655722): stop
-    // doing this once we have working no-compositor rendering for WebVR.
-    if (gvr_api_->GetAsyncReprojectionEnabled()) {
-      int pose_index_byte = GetPixelEncodedPoseIndexByte();
-      if (WebVrPoseByteIsValid(pose_index_byte)) {
-        // We have a valid pose, use it for reprojection.
-        webvr_left_viewport_->SetReprojection(GVR_REPROJECTION_FULL);
-        webvr_right_viewport_->SetReprojection(GVR_REPROJECTION_FULL);
-        head_pose = webvr_head_pose_[pose_index_byte % kPoseRingBufferSize];
-        // We can't mark the used pose as invalid since unfortunately
-        // we have to reuse them. The compositor will re-submit stale
-        // frames on vsync, and we can't tell that this has happened
-        // until we've read the pose index from it, and at that point
-        // it's too late to skip rendering.
-      } else {
-        // If we don't get a valid frame ID back we shouldn't attempt
-        // to reproject by an invalid matrix, so turn off reprojection
-        // instead. Invalid poses can permanently break reprojection
-        // for this GVR instance: http://crbug.com/667327
-        webvr_left_viewport_->SetReprojection(GVR_REPROJECTION_NONE);
-        webvr_right_viewport_->SetReprojection(GVR_REPROJECTION_NONE);
-      }
-    }
-  }
-
   DrawVrShell(head_pose, frame);
 
   frame.Unbind();
   frame.Submit(*buffer_viewport_list_, head_pose);
 
   // No need to swap buffers for surfaceless rendering.
-  if (surfaceless_rendering_) {
-    ScheduleNextDrawFrame();
-    return;
-  }
-
-  if (surface_->SupportsAsyncSwap()) {
-    surface_->SwapBuffersAsync(base::Bind(&WaitForSwapAck, base::Bind(
-        &VrShellGl::ScheduleNextDrawFrame, weak_ptr_factory_.GetWeakPtr())));
-  } else {
+  if (!surfaceless_rendering_) {
+    // TODO(mthiesse): Support asynchronous SwapBuffers.
     surface_->SwapBuffers();
-    ScheduleNextDrawFrame();
   }
 }
 
 void VrShellGl::DrawVrShell(const gvr::Mat4f& head_pose,
                             gvr::Frame &frame) {
   TRACE_EVENT0("gpu", "VrShellGl::DrawVrShell");
   std::vector<const ContentRectangle*> head_locked_elements;
   std::vector<const ContentRectangle*> world_elements;
   for (const auto& rect : scene_->GetUiElements()) {
     if (!rect->visible) {
@@ skipping 203 matching lines @@
   buffer_viewport_list_->SetBufferViewport(GVR_RIGHT_EYE,
                                            *webvr_right_viewport_);
 }
 
 void VrShellGl::OnTriggerEvent() {
   // Set a flag to handle this on the render thread at the next frame.
   touch_pending_ = true;
 }
 
 void VrShellGl::OnPause() {
-  draw_task_.Cancel();
+  vsync_task_.Cancel();
   controller_->OnPause();
   gvr_api_->PauseTracking();
 }
 
 void VrShellGl::OnResume() {
   gvr_api_->RefreshViewerProfile();
   gvr_api_->ResumeTracking();
   controller_->OnResume();
   if (ready_to_draw_) {
-    draw_task_.Reset(base::Bind(&VrShellGl::DrawFrame, base::Unretained(this)));
-    ScheduleNextDrawFrame();
+    vsync_task_.Reset(base::Bind(&VrShellGl::OnVSync, base::Unretained(this)));
+    OnVSync();
   }
 }
 
 void VrShellGl::SetWebVrMode(bool enabled) {
   web_vr_mode_ = enabled;
 }
 
 void VrShellGl::UpdateWebVRTextureBounds(const gvr::Rectf& left_bounds,
                                          const gvr::Rectf& right_bounds) {
   webvr_left_viewport_->SetSourceUv(left_bounds);
@@ skipping 26 matching lines @@
   if (ui_surface_texture_.get())
     ui_surface_texture_->SetDefaultBufferSize(width, height);
   ui_tex_physical_size_.width = width;
   ui_tex_physical_size_.height = height;
 }
 
 base::WeakPtr<VrShellGl> VrShellGl::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
-void VrShellGl::UpdateVSyncParameters(const base::TimeTicks timebase,
-                                      const base::TimeDelta interval) {
-  vsync_timebase_ = timebase;
-  vsync_interval_ = interval;
-}
-
-void VrShellGl::ScheduleNextDrawFrame() {
+void VrShellGl::OnVSync() {
   base::TimeTicks now = base::TimeTicks::Now();
   base::TimeTicks target;
 
-  if (vsync_interval_.is_zero()) {
-    target = now;
+  // Don't send VSyncs until we have a timebase/interval.
+  if (vsync_interval_.is_zero())
+    return;
+  target = now + vsync_interval_;
+  int64_t intervals = (target - vsync_timebase_) / vsync_interval_;
+  target = vsync_timebase_ + intervals * vsync_interval_;
+  task_runner_->PostDelayedTask(FROM_HERE, vsync_task_.callback(),
+                                target - now);
+
+  double time = (intervals * vsync_interval_).InSecondsF();
+  if (!callback_.is_null()) {
+    callback_.Run(GetPose(), time);
+    callback_.Reset();
   } else {
-    target = now + vsync_interval_;
-    int64_t intervals = (target - vsync_timebase_) / vsync_interval_;
-    target = vsync_timebase_ + intervals * vsync_interval_;
+    pending_vsync_ = true;
+    pending_time_ = time;
   }
+  DrawFrame();
+}
 
-  task_runner_->PostDelayedTask(FROM_HERE, draw_task_.callback(), target - now);
+void VrShellGl::OnRequest(device::mojom::VRVSyncProviderRequest request) {
+  binding_.Close();
+  binding_.Bind(std::move(request));
+}
+
+void VrShellGl::GetVSync(const GetVSyncCallback& callback) {
+  if (!pending_vsync_) {
+    callback_ = std::move(callback);

[dcheng, 2017/01/12 09:56:56]

One thing I'm not certain about is if it's OK to just drop pending callbacks and
never invoke them inside an impl. I would expect that the calling side would
need to track some mapping of outstanding calls to the result callbacks, and not
invoking them at all would cause those to never be freed.

[mthiesse, 2017/01/12 15:49:03]

It's not okay to just drop pending callbacks. I've addressed this by calling any
outstanding callback in the destructor.

Given that this is a send->ack->send->ack loop we'll never have more than one
outstanding callback. (just added a CHECK to verify this)

+    return;
+  }
+  pending_vsync_ = false;
+  callback.Run(GetPose(), pending_time_);
+}
+
+void VrShellGl::UpdateVSyncInterval(long timebase_nanos,
+                                    double interval_seconds) {
+  vsync_timebase_ = base::TimeTicks();
+  vsync_timebase_ += base::TimeDelta::FromMicroseconds(timebase_nanos / 1000);
+  vsync_interval_ = base::TimeDelta::FromSecondsD(interval_seconds);
+  vsync_task_.Reset(base::Bind(&VrShellGl::OnVSync, base::Unretained(this)));
+  OnVSync();
 }
 
 void VrShellGl::ForceExitVr() {
   main_thread_task_runner_->PostTask(
       FROM_HERE, base::Bind(&VrShell::ForceExitVr, weak_vr_shell_));
 }
 
 void VrShellGl::UpdateScene(std::unique_ptr<base::ListValue> commands) {
   scene_->HandleCommands(std::move(commands), TimeInMicroseconds());
 }
 
+device::mojom::VRPosePtr VrShellGl::GetPose() {
+  TRACE_EVENT0("input", "VrShellGl::GetPose");
+
+  gvr::ClockTimePoint target_time = gvr::GvrApi::GetTimePointNow();
+  target_time.monotonic_system_time_nanos += kPredictionTimeWithoutVsyncNanos;
+
+  gvr::Mat4f head_mat =
+      gvr_api_->GetHeadSpaceFromStartSpaceRotation(target_time);
+  head_mat = gvr_api_->ApplyNeckModel(head_mat, 1.0f);
+
+  uint32_t pose_index = pose_index_++;
+  webvr_head_pose_[pose_index % kPoseRingBufferSize] = head_mat;
+
+  return VrShell::VRPosePtrFromGvrPose(head_mat, pose_index);
+}
+
 }  // namespace vr_shell