Use ARCore camera frame time to estimate frame intervals

This should be more accurate than using wallclock time, but
is a bit clunky since unfortunately ARCore uses an unspecified
time base, so it's not directly compatible with base::TimeTicks.

Bug: 1064629
Change-Id: If4a73f26b7b5aaa7e87a615a15ad4b9031f5aa32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2119637
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753410}

chrome/browser/android/vr/arcore_device/arcore.h

@@ -45,6 +45,10 @@ class ArCore {
   // when the camera image was updated successfully.
   virtual mojom::VRPosePtr Update(bool* camera_updated) = 0;
 
+  // Camera image timestamp. This returns TimeDelta instead of TimeTicks since
+  // ARCore internally uses an arbitrary and unspecified time base.
+  virtual base::TimeDelta GetFrameTimestamp() = 0;
+
   // Return latest estimate for the floor height.
   virtual float GetEstimatedFloorHeight() = 0;
 

chrome/browser/android/vr/arcore_device/arcore_gl.cc

@@ -363,13 +363,13 @@ void ArCoreGl::GetFrameData(
   base::TimeTicks arcore_update_started = base::TimeTicks::Now();
   mojom::VRPosePtr pose = arcore_->Update(&camera_updated);
   base::TimeTicks now = base::TimeTicks::Now();
-  if (!arcore_update_completed_.is_null()) {
-    arcore_update_interval_ = now - arcore_update_completed_;
-    arcore_update_next_expected_ = now + arcore_update_interval_;
+  base::TimeDelta frame_timestamp = arcore_->GetFrameTimestamp();
+  if (!arcore_last_frame_timestamp_.is_zero()) {
+    arcore_frame_interval_ = frame_timestamp - arcore_last_frame_timestamp_;
+    arcore_update_next_expected_ = now + arcore_frame_interval_;
   }
-  arcore_update_completed_ = now;
-  base::TimeDelta arcore_update_elapsed =
-      arcore_update_completed_ - arcore_update_started;
+  arcore_last_frame_timestamp_ = frame_timestamp;
+  base::TimeDelta arcore_update_elapsed = now - arcore_update_started;
   TRACE_COUNTER1("gpu", "ARCore update elapsed (ms)",
                  arcore_update_elapsed.InMilliseconds());
 

chrome/browser/android/vr/arcore_device/arcore_gl.h

@@ -232,9 +232,9 @@ class ArCoreGl : public mojom::XRFrameDataProvider,
 
   bool restrict_frame_data_ = false;
 
-  base::TimeTicks arcore_update_completed_;
   base::TimeTicks arcore_update_next_expected_;
-  base::TimeDelta arcore_update_interval_;
+  base::TimeDelta arcore_last_frame_timestamp_;
+  base::TimeDelta arcore_frame_interval_;
   FPSMeter fps_meter_;
 
   mojo::Receiver<mojom::XRFrameDataProvider> frame_data_receiver_{this};

chrome/browser/android/vr/arcore_device/arcore_impl.cc

@@ -465,6 +465,15 @@ mojom::VRPosePtr ArCoreImpl::Update(bool* camera_updated) {
   return GetMojomVRPoseFromArPose(arcore_session_.get(), arcore_pose.get());
 }
 
+base::TimeDelta ArCoreImpl::GetFrameTimestamp() {
+  DCHECK(arcore_session_.is_valid());
+  DCHECK(arcore_frame_.is_valid());
+  int64_t out_timestamp_ns;
+  ArFrame_getTimestamp(arcore_session_.get(), arcore_frame_.get(),
+                       &out_timestamp_ns);
+  return base::TimeDelta::FromNanoseconds(out_timestamp_ns);
+}
+
 mojom::XRPlaneDetectionDataPtr ArCoreImpl::GetDetectedPlanesData() {
   DVLOG(2) << __func__;
 

chrome/browser/android/vr/arcore_device/arcore_impl.h

@@ -64,6 +64,7 @@ class ArCoreImpl : public ArCore {
       const base::span<const float> uvs) override;
   gfx::Transform GetProjectionMatrix(float near, float far) override;
   mojom::VRPosePtr Update(bool* camera_updated) override;
+  base::TimeDelta GetFrameTimestamp() override;
 
   mojom::XRPlaneDetectionDataPtr GetDetectedPlanesData() override;
 

chrome/browser/android/vr/arcore_device/arcore_shim.cc

@@ -34,6 +34,7 @@ namespace {
   DO(ArFrame_create)                                               \
   DO(ArFrame_destroy)                                              \
   DO(ArFrame_getLightEstimate)                                     \
+  DO(ArFrame_getTimestamp)                                         \
   DO(ArFrame_getUpdatedAnchors)                                    \
   DO(ArFrame_getUpdatedTrackables)                                 \
   DO(ArFrame_hitTestRay)                                           \
@@ -275,6 +276,13 @@ void ArFrame_getLightEstimate(const ArSession* session,
                                                      out_light_estimate);
 }
 
+void ArFrame_getTimestamp(const ArSession* session,
+                          const ArFrame* frame,
+                          int64_t* out_timestamp_ns) {
+  return g_arcore_api->impl_ArFrame_getTimestamp(session, frame,
+                                                 out_timestamp_ns);
+}
+
 void ArFrame_getUpdatedAnchors(const ArSession* session,
                                const ArFrame* frame,
                                ArAnchorList* out_anchor_list) {

chrome/browser/android/vr/arcore_device/fake_arcore.cc

@@ -196,6 +196,10 @@ mojom::VRPosePtr FakeArCore::Update(bool* camera_updated) {
   return pose;
 }
 
+base::TimeDelta FakeArCore::GetFrameTimestamp() {
+  return base::TimeTicks::Now() - base::TimeTicks();
+}
+
 float FakeArCore::GetEstimatedFloorHeight() {
   return 2.0;
 }

chrome/browser/android/vr/arcore_device/fake_arcore.h

@@ -31,6 +31,7 @@ class FakeArCore : public ArCore {
       const base::span<const float> uvs) override;
   gfx::Transform GetProjectionMatrix(float near, float far) override;
   mojom::VRPosePtr Update(bool* camera_updated) override;
+  base::TimeDelta GetFrameTimestamp() override;
 
   void Pause() override;
   void Resume() override;