WebXR: Tweak ARCore scheduling, add trace events

Update the ARCore scheduling to reduce latency, running GetFrameData and
ARCore's update with a delay when appropriate.

Use sliding averages to track timing for recent frames, and use that in
the heuristics.

Also add async trace events to mark Animating/Processing/Rendering
frames in the ArCoreGL timeline.

For background, see this presentation with some annotated trace events
explaining the new logic:

https://docs.google.com/presentation/d/e/2PACX-1vQTol3A0Y_LByOuMPSIb0qk-6FNQ7f5SpqO3GWfN-JY37LO7HPXTv1FrfK5e4Qerxx4CNzw9f90auCA/pub

Bug: 1136276
Change-Id: I0550ed3666c47d6f12b2708a1e5ef9a305b07f10
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464052
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816724}

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

@@ -17,6 +17,10 @@ FakeArCore::FakeArCore()
 
 FakeArCore::~FakeArCore() = default;
 
+ArCore::MinMaxRange FakeArCore::GetTargetFramerateRange() {
+  return {30.f, 30.f};
+}
+
 bool FakeArCore::Initialize(
     base::android::ScopedJavaLocalRef<jobject> application_context,
     const std::unordered_set<device::mojom::XRSessionFeature>&

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

@@ -26,6 +26,7 @@ class FakeArCore : public ArCore {
       base::android::ScopedJavaLocalRef<jobject> application_context,
       const std::unordered_set<device::mojom::XRSessionFeature>&
           enabled_features) override;
+  MinMaxRange GetTargetFramerateRange() override;
   void SetCameraTexture(uint32_t texture) override;
   void SetDisplayGeometry(const gfx::Size& frame_size,
                           display::Display::Rotation display_rotation) override;

device/vr/android/arcore/arcore.h

@@ -25,6 +25,14 @@ class COMPONENT_EXPORT(VR_ARCORE) ArCore {
  public:
   virtual ~ArCore() = default;
 
+  // Represents an inclusive range from min to max. (This is different from
+  // base::Interval which excludes the top end of the range, resulting in an
+  // empty interval if min==max.)
+  struct MinMaxRange {
+    float min;
+    float max;
+  };
+
   // Initializes the runtime and returns whether it was successful.
   // If successful, the runtime must be paused when this method returns.
   virtual bool Initialize(
@@ -32,6 +40,10 @@ class COMPONENT_EXPORT(VR_ARCORE) ArCore {
       const std::unordered_set<device::mojom::XRSessionFeature>&
           enabled_features) = 0;
 
+  // Returns the target framerate range in Hz. Actual capture frame rate will
+  // vary within this range, i.e. lower in low light to increase exposure time.
+  virtual MinMaxRange GetTargetFramerateRange() = 0;
+
   virtual void SetDisplayGeometry(
       const gfx::Size& frame_size,
       display::Display::Rotation display_rotation) = 0;

device/vr/android/arcore/arcore_gl.h

@@ -19,6 +19,7 @@
 #include "device/vr/public/mojom/isolated_xr_service.mojom.h"
 #include "device/vr/public/mojom/vr_service.mojom.h"
 #include "device/vr/util/fps_meter.h"
+#include "device/vr/util/sliding_average.h"
 #include "mojo/public/cpp/bindings/associated_receiver.h"
 #include "mojo/public/cpp/bindings/pending_associated_receiver.h"
 #include "mojo/public/cpp/bindings/pending_associated_remote.h"
@@ -180,6 +181,11 @@ class ArCoreGl : public mojom::XRFrameDataProvider,
 
   void GetRenderedFrameStats();
   void FinishRenderingFrame();
+  base::TimeDelta EstimatedArCoreFrameTime();
+  base::TimeDelta WaitTimeForArCoreUpdate();
+  base::TimeDelta WaitTimeForRenderCompletion();
+  void ScheduleGetFrameData();
+  void RunPendingGetFrameData();
 
   bool IsFeatureEnabled(mojom::XRSessionFeature feature);
 
@@ -251,6 +257,13 @@ class ArCoreGl : public mojom::XRFrameDataProvider,
 
   bool restrict_frame_data_ = false;
 
+  base::TimeTicks last_arcore_update_time_;
+  base::TimeDelta last_arcore_frame_timestamp_;
+
+  device::SlidingTimeDeltaAverage average_animate_time_;
+  device::SlidingTimeDeltaAverage average_process_time_;
+  device::SlidingTimeDeltaAverage average_render_time_;
+
   FPSMeter fps_meter_;
 
   mojo::Receiver<mojom::XRFrameDataProvider> frame_data_receiver_{this};

device/vr/android/arcore/arcore_impl.cc

@@ -430,7 +430,7 @@ bool ArCoreImpl::Initialize(
   return true;
 }
 
-bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) const {
+bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) {
   internal::ScopedArCoreObject<ArCameraConfigFilter*> camera_config_filter;
   ArCameraConfigFilter_create(
       ar_session, internal::ScopedArCoreObject<ArCameraConfigFilter*>::Receiver(
@@ -522,11 +522,16 @@ bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) const {
       ArCameraConfig_getDepthSensorUsage(ar_session, camera_config.get(),
                                          &depth_sensor_usage);
 
+      int32_t min_fps, max_fps;
+      ArCameraConfig_getFpsRange(ar_session, camera_config.get(), &min_fps,
+                                 &max_fps);
+
       DVLOG(3) << __func__
                << ": matching camera config found, texture dimensions="
                << tex_width << "x" << tex_height
                << ", image dimensions= " << img_width << "x" << img_height
-               << ", depth sensor usage=" << depth_sensor_usage;
+               << ", depth sensor usage=" << depth_sensor_usage
+               << ", min_fps=" << min_fps << ", max_fps=" << max_fps;
     }
 #endif
 
@@ -601,6 +606,11 @@ bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) const {
         }
       });
 
+  int32_t fps_min, fps_max;
+  ArCameraConfig_getFpsRange(ar_session, best_config->get(), &fps_min,
+                             &fps_max);
+  target_framerate_range_ = {fps_min, fps_max};
+
 #if DCHECK_IS_ON()
   {
     int32_t tex_width, tex_height;
@@ -617,7 +627,9 @@ bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) const {
     DVLOG(3) << __func__
              << ": selected camera config with texture dimensions=" << tex_width
              << "x" << tex_height << ", image dimensions=" << img_width << "x"
-             << img_height << ", depth sensor usage=" << depth_sensor_usage;
+             << img_height << ", depth sensor usage=" << depth_sensor_usage
+             << ", min_fps=" << target_framerate_range_.min
+             << ", max_fps=" << target_framerate_range_.max;
   }
 #endif
 
@@ -630,6 +642,10 @@ bool ArCoreImpl::ConfigureCamera(ArSession* ar_session) const {
   return true;
 }
 
+ArCore::MinMaxRange ArCoreImpl::GetTargetFramerateRange() {
+  return target_framerate_range_;
+}
+
 void ArCoreImpl::SetCameraTexture(uint32_t camera_texture_id) {
   DCHECK(IsOnGlThread());
   DCHECK(arcore_session_.is_valid());

device/vr/android/arcore/arcore_impl.h

@@ -110,6 +110,7 @@ class ArCoreImpl : public ArCore {
       base::android::ScopedJavaLocalRef<jobject> application_context,
       const std::unordered_set<device::mojom::XRSessionFeature>&
           enabled_features) override;
+  MinMaxRange GetTargetFramerateRange() override;
   void SetDisplayGeometry(const gfx::Size& frame_size,
                           display::Display::Rotation display_rotation) override;
   void SetCameraTexture(uint32_t camera_texture_id) override;
@@ -190,6 +191,9 @@ class ArCoreImpl : public ArCore {
   internal::ScopedArCoreObject<ArSession*> arcore_session_;
   internal::ScopedArCoreObject<ArFrame*> arcore_frame_;
 
+  // Target framerate reflecting the current camera configuration.
+  MinMaxRange target_framerate_range_ = {30.f, 30.f};
+
   // ArCore light estimation data
   internal::ScopedArCoreObject<ArLightEstimate*> arcore_light_estimate_;
 
@@ -291,7 +295,7 @@ class ArCoreImpl : public ArCore {
   // Helper, attempts to configure ArSession's camera for use. Note that this is
   // happening during initialization, before arcore_session_ is set.
   // Returns true if configuration succeeded, false otherwise.
-  bool ConfigureCamera(ArSession* ar_session) const;
+  bool ConfigureCamera(ArSession* ar_session);
 
   // Must be last.
   base::WeakPtrFactory<ArCoreImpl> weak_ptr_factory_{this};

device/vr/android/arcore/arcore_shim.cc

@@ -31,6 +31,7 @@ namespace {
   DO(ArCameraConfig_destroy)                                       \
   DO(ArCameraConfig_getDepthSensorUsage)                           \
   DO(ArCameraConfig_getFacingDirection)                            \
+  DO(ArCameraConfig_getFpsRange)                                   \
   DO(ArCameraConfig_getImageDimensions)                            \
   DO(ArCameraConfig_getTextureDimensions)                          \
   DO(ArCameraConfigFilter_create)                                  \
@@ -275,6 +276,14 @@ void ArCameraConfig_getFacingDirection(
       session, camera_config, out_facing);
 }
 
+void ArCameraConfig_getFpsRange(const ArSession* session,
+                                const ArCameraConfig* camera_config,
+                                int32_t* out_min_fps,
+                                int32_t* out_max_fps) {
+  return g_arcore_api->impl_ArCameraConfig_getFpsRange(
+      session, camera_config, out_min_fps, out_max_fps);
+}
+
 void ArCameraConfig_getImageDimensions(const ArSession* session,
                                        const ArCameraConfig* camera_config,
                                        int32_t* out_width,