// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "third_party/blink/renderer/modules/xr/xr_frame_provider.h"

#include <utility>

#include "build/build_config.h"
#include "third_party/blink/public/platform/platform.h"
#include "third_party/blink/renderer/bindings/core/v8/script_promise_resolver.h"
#include "third_party/blink/renderer/core/dom/document.h"
#include "third_party/blink/renderer/core/dom/dom_exception.h"
#include "third_party/blink/renderer/core/dom/frame_request_callback_collection.h"
#include "third_party/blink/renderer/core/frame/local_dom_window.h"
#include "third_party/blink/renderer/core/frame/local_frame.h"
#include "third_party/blink/renderer/core/frame/navigator.h"
#include "third_party/blink/renderer/core/imagebitmap/image_bitmap.h"
#include "third_party/blink/renderer/core/loader/document_loader.h"
#include "third_party/blink/renderer/core/timing/dom_window_performance.h"
#include "third_party/blink/renderer/modules/webgpu/gpu_device.h"
#include "third_party/blink/renderer/modules/webgpu/gpu_texture.h"
#include "third_party/blink/renderer/modules/xr/xr_gpu_binding.h"
#include "third_party/blink/renderer/modules/xr/xr_gpu_drawing_context.h"
#include "third_party/blink/renderer/modules/xr/xr_gpu_swap_chain.h"
#include "third_party/blink/renderer/modules/xr/xr_graphics_binding.h"
#include "third_party/blink/renderer/modules/xr/xr_layer_client.h"
#include "third_party/blink/renderer/modules/xr/xr_projection_layer.h"
#include "third_party/blink/renderer/modules/xr/xr_session.h"
#include "third_party/blink/renderer/modules/xr/xr_system.h"
#include "third_party/blink/renderer/modules/xr/xr_viewport.h"
#include "third_party/blink/renderer/modules/xr/xr_webgl_drawing_context.h"
#include "third_party/blink/renderer/modules/xr/xr_webgl_layer.h"
#include "third_party/blink/renderer/platform/graphics/gpu/xr_frame_transport_delegate.h"
#include "third_party/blink/renderer/platform/instrumentation/tracing/trace_event.h"
#include "third_party/perfetto/include/perfetto/tracing/track.h"
#include "ui/display/display.h"
#include "ui/gfx/geometry/transform.h"

namespace blink {

namespace {

class XRFrameProviderRequestCallback : public FrameCallback {
 public:
  explicit XRFrameProviderRequestCallback(XRFrameProvider* frame_provider)
      : frame_provider_(frame_provider) {}
  ~XRFrameProviderRequestCallback() override = default;
  void Invoke(double high_res_time_ms) override {
    frame_provider_->OnNonImmersiveVSync(high_res_time_ms);
  }

  void Trace(Visitor* visitor) const override {
    visitor->Trace(frame_provider_);
    FrameCallback::Trace(visitor);
  }

  Member<XRFrameProvider> frame_provider_;
};

gfx::RectF NormalizeViewport(gfx::Rect viewport,
                             uint32_t width,
                             uint32_t height) {
  return gfx::RectF(
      static_cast<float>(viewport.x()) / width,
      static_cast<float>(height - (viewport.y() + viewport.height())) / height,
      static_cast<float>(viewport.width()) / width,
      static_cast<float>(viewport.height()) / height);
}

}  // namespace

XRFrameProvider::XRFrameProvider(XRSystem* xr)
    : xr_(xr),
      frame_transport_(MakeGarbageCollected<XRFrameTransport>(
          xr->GetExecutionContext(),
          xr->GetExecutionContext()->GetTaskRunner(
              TaskType::kMiscPlatformAPI))),
      immersive_data_provider_(xr->GetExecutionContext()),
      immersive_presentation_provider_(xr->GetExecutionContext()),
      layer_manager_(xr->GetExecutionContext()),
      last_has_focus_(xr->IsFrameFocused()) {}

void XRFrameProvider::AddImmersiveSessionObserver(
    ImmersiveSessionObserver* observer) {
  immersive_observers_.insert(observer);
}

void XRFrameProvider::OnSessionStarted(
    XRSession* session,
    device::mojom::blink::XRSessionPtr session_ptr) {
  DCHECK(session);

  if (session->immersive()) {
    // Ensure we can only have one immersive session at a time.
    DCHECK(!immersive_session_);
    DCHECK(session_ptr->data_provider);
    DCHECK(session_ptr->submit_frame_sink);
    immersive_session_ = session;

    for (auto& observer : immersive_observers_) {
      observer->OnImmersiveSessionStart();
    }

    immersive_data_provider_.Bind(
        std::move(session_ptr->data_provider),
        xr_->GetExecutionContext()->GetTaskRunner(TaskType::kMiscPlatformAPI));
    immersive_data_provider_.set_disconnect_handler(
        BindOnce(&XRFrameProvider::OnProviderConnectionError,
                 WrapWeakPersistent(this), WrapWeakPersistent(session)));

    immersive_presentation_provider_.Bind(
        std::move(session_ptr->submit_frame_sink->provider),
        xr_->GetExecutionContext()->GetTaskRunner(TaskType::kMiscPlatformAPI));
    immersive_presentation_provider_.set_disconnect_handler(
        BindOnce(&XRFrameProvider::OnProviderConnectionError,
                 WrapWeakPersistent(this), WrapWeakPersistent(session)));

    frame_transport_->RegisterFrameTransferredCallback(blink::BindRepeating(
        &XRFrameProvider::OnTransferComplete, WrapWeakPersistent(this)));

    frame_transport_->RegisterFrameRenderedCallback(blink::BindRepeating(
        &XRFrameProvider::OnRenderComplete, WrapWeakPersistent(this)));

    if (session_ptr->layer_manager) {
      layer_manager_.Bind(std::move(session_ptr->layer_manager),
                          xr_->GetExecutionContext()->GetTaskRunner(
                              TaskType::kMiscPlatformAPI));
      layer_manager_.set_disconnect_handler(
          BindOnce(&XRFrameProvider::OnProviderConnectionError,
                   WrapWeakPersistent(this), WrapWeakPersistent(session)));
    }

    frame_transport_->BindSubmitFrameClient(
        std::move(session_ptr->submit_frame_sink->client_receiver));
    frame_transport_->SetTransportOptions(
        std::move(session_ptr->submit_frame_sink->transport_options));
    frame_transport_->PresentChange();

    last_frame_statistics_sent_time_ = base::TimeTicks::Now();

    repeating_timer_.Start(FROM_HERE, base::Seconds(1),
                           BindRepeating(&XRFrameProvider::SendFrameData,
                                         WrapWeakPersistent(this)));
  } else {
    // If a non-immersive session doesn't have a data provider, we don't
    // need to store a reference to it.
    if (!session_ptr->data_provider) {
      return;
    }

    HeapMojoRemote<device::mojom::blink::XRFrameDataProvider> data_provider(
        xr_->GetExecutionContext());
    data_provider.Bind(
        std::move(session_ptr->data_provider),
        xr_->GetExecutionContext()->GetTaskRunner(TaskType::kMiscPlatformAPI));
    data_provider.set_disconnect_handler(
        BindOnce(&XRFrameProvider::OnProviderConnectionError,
                 WrapWeakPersistent(this), WrapWeakPersistent(session)));

    non_immersive_data_providers_.insert(
        session, WrapDisallowNew(std::move(data_provider)));
  }
}

void XRFrameProvider::OnFocusChanged() {
  bool focus = xr_->IsFrameFocused();

  // If we are gaining focus, schedule a frame for magic window.  This accounts
  // for skipping RAFs in ProcessScheduledFrame.  Only do this when there are
  // magic window sessions but no immersive session. Note that immersive
  // sessions don't stop scheduling RAFs when focus is lost, so there is no need
  // to schedule immersive frames when focus is acquired.
  if (focus && !last_has_focus_ && requesting_sessions_.size() > 0 &&
      !immersive_session_) {
    ScheduleNonImmersiveFrame(nullptr);
  }
  last_has_focus_ = focus;
}

// Ends the immersive session when the presentation or immersive data provider
// got disconnected.
void XRFrameProvider::OnProviderConnectionError(XRSession* session) {
  DVLOG(2) << __func__;
  // This will call into |OnSessionEnded|, unless it has already ended.
  session->ForceEnd(XRSession::ShutdownPolicy::kImmediate);
}

void XRFrameProvider::OnSessionEnded(XRSession* session) {
  DVLOG(2) << __func__;
  if (session->immersive()) {
    DCHECK(session == immersive_session_);

    immersive_session_ = nullptr;
    pending_immersive_vsync_ = false;
    frame_id_ = -1;
    immersive_presentation_provider_.reset();
    immersive_data_provider_.reset();
    layer_manager_.reset();
    shared_images_.clear();

    first_immersive_frame_time_ = std::nullopt;
    first_immersive_frame_time_delta_ = std::nullopt;

    frame_transport_ = MakeGarbageCollected<XRFrameTransport>(
        session->GetExecutionContext(),
        session->GetExecutionContext()->GetTaskRunner(
            TaskType::kMiscPlatformAPI));

    repeating_timer_.Stop();
    for (auto& observer : immersive_observers_) {
      observer->OnImmersiveSessionEnd();
    }
  } else {
    non_immersive_data_providers_.erase(session);
    requesting_sessions_.erase(session);
  }
}

void XRFrameProvider::RestartNonImmersiveFrameLoop() {
  // When we no longer have an active immersive session schedule all the
  // outstanding frames that were requested while the immersive session was
  // active.
  if (immersive_session_ || requesting_sessions_.size() == 0)
    return;

  for (auto& session : requesting_sessions_) {
    RequestNonImmersiveFrameData(session.key.Get());
  }

  ScheduleNonImmersiveFrame(nullptr);
}

// Schedule a session to be notified when the next XR frame is available.
void XRFrameProvider::RequestFrame(XRSession* session) {
  DVLOG(3) << __func__;
  TRACE_EVENT0("gpu", "RequestFrame");
  DCHECK(session);

  auto options = device::mojom::blink::XRFrameDataRequestOptions::New();
  options->include_lighting_estimation_data = session->LightEstimationEnabled();
  options->stage_parameters_id = session->StageParametersId();
  options->depth_active = session->IsDepthActive();

  // Immersive frame logic.
  if (session->immersive()) {
    ScheduleImmersiveFrame(std::move(options));
    return;
  }

  // Non-immersive frame logic.

  // Duplicate frame requests are treated as a no-op.
  if (requesting_sessions_.Contains(session)) {
    DVLOG(2) << __func__ << ": session requested duplicate frame";
    return;
  }

  requesting_sessions_.insert(session, nullptr);

  // If there's an active immersive session save the request but suppress
  // processing it until the immersive session is no longer active.
  if (immersive_session_) {
    return;
  }

  RequestNonImmersiveFrameData(session);
  ScheduleNonImmersiveFrame(std::move(options));
}

void XRFrameProvider::ScheduleImmersiveFrame(
    device::mojom::blink::XRFrameDataRequestOptionsPtr options) {
  TRACE_EVENT0("gpu", "ScheduleImmersiveFrame");
  if (pending_immersive_vsync_)
    return;

  pending_immersive_vsync_ = true;
  frame_data_time_.StartTimer();
  // `this` is an okay TRACE ID here, since we are only allowed one immersive
  // session at a time.
  TRACE_EVENT_BEGIN(
      "xr", "RequestImmersiveFrame",
      perfetto::NamedTrack::FromPointer("blink::XRFrameProvider", this));
  immersive_data_provider_->GetFrameData(
      std::move(options), BindOnce(&XRFrameProvider::OnImmersiveFrameData,
                                   WrapWeakPersistent(this)));
}

void XRFrameProvider::ScheduleNonImmersiveFrame(
    device::mojom::blink::XRFrameDataRequestOptionsPtr options) {
  DVLOG(3) << __func__;
  TRACE_EVENT0("gpu", "ScheduleNonImmersiveFrame");

  DCHECK(!immersive_session_)
      << "Scheduling should be done via the exclusive session if present.";

  if (pending_non_immersive_vsync_) {
    DVLOG(3) << __func__ << ": non immersive vsync already pending";
    return;
  }

  LocalDOMWindow* window = xr_->DomWindow();
  if (!window)
    return;

  pending_non_immersive_vsync_ = true;

  // Calls |OnNonImmersiveVSync|
  window->document()->RequestAnimationFrame(
      MakeGarbageCollected<XRFrameProviderRequestCallback>(this),
      FrameCallbackType::kInternal);
}

void XRFrameProvider::OnImmersiveFrameData(
    device::mojom::blink::XRFrameDataPtr data) {
  frame_data_time_.StopTimer();
  TRACE_EVENT_END(
      "xr", /*RequestImmersiveFrame*/
      perfetto::NamedTrack::FromPointer("blink::XRFrameProvider", this));
  TRACE_EVENT0("gpu", "OnImmersiveFrameData");

  if (data.is_null()) {
    DVLOG(2) << __func__ << ": no data, current frame_id=" << frame_id_;
  } else {
    DVLOG(2) << __func__
             << ": have data, frame_id=" << data->render_info->frame_id;
  }

  // We may have lost the immersive session since the last VSync request.
  if (!immersive_session_) {
    DVLOG(1) << __func__ << ": immersive session lost";
    return;
  }

  if (!data) {
    DVLOG(3) << __func__ << ": frame data not received, re-requesting frame";
    // We have not received any frame data from the device. We could try to run
    // an XR animation frame [1], but that may cause issues with APIs that
    // receive state updates via XRFrameData (e.g. anchors, planes) for
    // maintaining their current state - they would behave as if all entities
    // lost tracking and got removed on the device. Let's behave as if we have
    // not received anything from the device and request a new frame.
    //
    // [1]  https://immersive-web.github.io/webxr/#xr-animation-frame)

    pending_immersive_vsync_ = false;
    RequestFrame(immersive_session_);
    return;
  }

  LocalDOMWindow* window = xr_->DomWindow();
  if (!window) {
    DVLOG(3) << __func__ << ": unable to get local DOM window!";
    return;
  }

  // Note: The |high_res_now_ms| is computed based on frame time returned from
  // immersive frame and eventually passed in to requestAnimationFrame callback
  // as `DOMHighResTimeStamp time`. This means that in case of immersive frames,
  // the `now` is the same as `frameTime` in XR animation frame algorithm [1].
  //
  // [1] https://immersive-web.github.io/webxr/#xr-animation-frame
  double high_res_now_ms = UpdateImmersiveFrameTime(window, *data);

  shared_images_.clear();

  frame_id_ = data->render_info->frame_id;
  if (data->buffer_shared_image.has_value()) {
    shared_images_.emplace_back(
        XRSharedImageSource::kBaseLayer, device::kInvalidLayerId,
        gpu::ClientSharedImage::ImportUnowned(
            std::move(data->buffer_shared_image.value())),
        data->buffer_sync_token.value());
  }

  if (data->camera_image_buffer_shared_image.has_value()) {
    shared_images_.emplace_back(
        XRSharedImageSource::kCamera, device::kInvalidLayerId,
        gpu::ClientSharedImage::ImportUnowned(
            std::move(data->camera_image_buffer_shared_image.value())),
        data->camera_image_buffer_sync_token.value());
  }

  // Cache composition layer buffers.
  if (data->composition_layers_data.has_value()) {
    base::span<const device::mojom::blink::XRLayerFrameDataPtr> layers_data =
        data->composition_layers_data.value();
    for (const auto& layer_data : layers_data) {
      shared_images_.emplace_back(
          XRSharedImageSource::kCompositionLayer, layer_data->layer_id,
          gpu::ClientSharedImage::ImportUnowned(
              std::move(layer_data->buffer_shared_image)),
          layer_data->buffer_sync_token);
    }
  }

  pending_immersive_vsync_ = false;

  for (auto& observer : immersive_observers_) {
    observer->OnImmersiveFrame();
  }

  // Post a task to handle scheduled animations after the current
  // execution context finishes, so that we yield to non-mojo tasks in
  // between frames. Executing mojo tasks back to back within the same
  // execution context caused extreme input delay due to processing
  // multiple frames without yielding, see crbug.com/701444.
  //
  // Used kInternalMedia since 1) this is not spec-ed and 2) this is media
  // related then tasks should not be throttled or frozen in background tabs.
  window->GetTaskRunner(blink::TaskType::kInternalMedia)
      ->PostTask(FROM_HERE,
                 BindOnce(&XRFrameProvider::ProcessScheduledFrame,
                          WrapWeakPersistent(this), std::move(data),
                          high_res_now_ms, ScheduledFrameType::kImmersive));
}

void XRFrameProvider::OnNonImmersiveVSync(double high_res_now_ms) {
  TRACE_EVENT0("gpu", "OnNonImmersiveVSync");
  DVLOG(2) << __func__;

  pending_non_immersive_vsync_ = false;

  // Suppress non-immersive vsyncs when there's an immersive session active.
  if (immersive_session_)
    return;

  LocalDOMWindow* window = xr_->DomWindow();
  if (!window)
    return;

  window->GetTaskRunner(blink::TaskType::kInternalMedia)
      ->PostTask(FROM_HERE,
                 BindOnce(&XRFrameProvider::ProcessScheduledFrame,
                          WrapWeakPersistent(this), nullptr, high_res_now_ms,
                          ScheduledFrameType::kInline));
}

void XRFrameProvider::OnNonImmersiveFrameData(
    XRSession* session,
    device::mojom::blink::XRFrameDataPtr frame_data) {
  TRACE_EVENT0("gpu", "OnNonImmersiveFrameData");
  DVLOG(2) << __func__;

  // TODO(https://crbug.com/837834): add unit tests for this code path.
  LocalDOMWindow* window = xr_->DomWindow();
  if (!window)
    return;

  // Look up the request for this session. The session may have ended between
  // when the request was sent and this callback, so skip it in that case.
  auto request = requesting_sessions_.find(session);
  if (request == requesting_sessions_.end()) {
    DVLOG(3) << __func__
             << ": request corresponding to received frame data not found";
    if (!session->ended()) {
      DVLOG(2) << __func__
               << ": the session's frame data provider missed the vsync";
    }

    return;
  }

  if (frame_data) {
    DVLOG(3) << __func__ << ": frame data for session stored";
    request->value = std::move(frame_data);
  } else {
    // Unexpectedly didn't get frame data, and we don't have a timestamp.
    // Try to request a regular animation frame to avoid getting stuck.
    DVLOG(1) << __func__ << ": NO FRAME DATA!";
    request->value = nullptr;
    window->document()->RequestAnimationFrame(
        MakeGarbageCollected<XRFrameProviderRequestCallback>(this),
        FrameCallbackType::kInternal);
  }
}

void XRFrameProvider::RequestNonImmersiveFrameData(XRSession* session) {
  DVLOG(3) << __func__;

  DCHECK(session);
  DCHECK(!session->immersive());
  DCHECK(!immersive_session_);

  // The requesting_sessions_ entry for this session must have already
  // been created in |RequestFrame|.
  auto request = requesting_sessions_.find(session);
  CHECK(request != requesting_sessions_.end());

  auto provider = non_immersive_data_providers_.find(session);
  if (provider == non_immersive_data_providers_.end()) {
    request->value = nullptr;
  } else {
    auto& data_provider = provider->value->Value();
    auto options = device::mojom::blink::XRFrameDataRequestOptions::New();
    options->include_lighting_estimation_data =
        session->LightEstimationEnabled();
    options->stage_parameters_id = session->StageParametersId();

    data_provider->GetFrameData(
        std::move(options),
        BindOnce(&XRFrameProvider::OnNonImmersiveFrameData,
                 WrapWeakPersistent(this), WrapWeakPersistent(session)));
  }
}

void XRFrameProvider::ProcessScheduledFrame(
    device::mojom::blink::XRFrameDataPtr frame_data,
    double high_res_now_ms,
    ScheduledFrameType frame_type) {
  DVLOG(2) << __func__ << ": frame_id_=" << frame_id_
           << ", high_res_now_ms=" << high_res_now_ms;

  TRACE_EVENT2("gpu", "XRFrameProvider::ProcessScheduledFrame", "frame",
               frame_id_, "timestamp", high_res_now_ms);

  LocalDOMWindow* window = xr_->DomWindow();
  if (!window)
    return;

  if (!xr_->IsFrameFocused() && !immersive_session_) {
    return;  // Not currently focused, so we won't expose poses (except to
             // immersive sessions).
  }

  if (immersive_session_) {
    if (frame_type != ScheduledFrameType::kImmersive) {
      DVLOG(1)
          << __func__
          << " Attempted to process non-immersive scheduled frame as immersive";
      return;
    }

    // Check if immersive session is still valid, it may have ended and be
    // waiting for shutdown acknowledgement.
    if (immersive_session_->ended()) {
      return;
    }

    bool emulated_position = false;
    if (frame_data && frame_data->render_info->mojo_from_viewer) {
      DVLOG(3) << __func__ << ": pose available, emulated_position="
               << frame_data->render_info->mojo_from_viewer->emulated_position;
      emulated_position =
          frame_data->render_info->mojo_from_viewer->emulated_position;
    } else {
      DVLOG(2) << __func__ << ": emulating immersive frame position";
      emulated_position = true;
    }

    immersive_session_->UpdatePresentationFrameState(
        high_res_now_ms, std::move(frame_data), frame_id_, emulated_position);

    // Check if immersive session is still set as any events dispatched to the
    // page may have allowed a ForceEndSession to be triggered.
    if (!immersive_session_ || immersive_session_->ended()) {
      return;
    }

#if DCHECK_IS_ON()
    // Sanity check: if drawing into a shared buffer, the optional shared image
    // must be present. Exception is the first immersive frame after a
    // transition where the frame ID wasn't set yet. In that case, drawing can
    // proceed, but the result will be discarded in SubmitWebGLLayer().
    if (frame_transport_->DrawingIntoSharedBuffer() && frame_id_ >= 0) {
      DCHECK(shared_images_.size());
    }
#endif
    // Run immersive_session_->OnFrame() in a posted task to ensure that
    // createAnchor promises get a chance to run - the presentation frame state
    // is already updated.
    window->GetTaskRunner(blink::TaskType::kInternalMedia)
        ->PostTask(FROM_HERE,
                   blink::BindOnce(&XRSession::OnFrame,
                                   WrapWeakPersistent(immersive_session_.Get()),
                                   high_res_now_ms, std::move(shared_images_)));
  } else {
    // In the process of fulfilling the frame requests for each session they are
    // extremely likely to request another frame. Work off of a separate list
    // from the requests to prevent infinite loops.
    decltype(requesting_sessions_) processing_sessions;

    DVLOG(3) << __func__ << ": clearing requesting_sessions_";
    swap(requesting_sessions_, processing_sessions);

    // Inform sessions with a pending request of the new frame
    for (auto& request : processing_sessions) {
      XRSession* session = request.key.Get();

      // If the session was terminated between requesting and now, we shouldn't
      // process anything further.
      if (session->ended()) {
        continue;
      }

      session->UpdatePresentationFrameState(
          high_res_now_ms, std::move(request.value), frame_id_,
          true /* Non-immersive positions are always emulated */);

      // If any events dispatched to the page caused this session to end, we
      // should stop processing.
      if (session->ended()) {
        continue;
      }

      // Run session->OnFrame() in a posted task to ensure that createAnchor
      // promises get a chance to run - the presentation frame state is already
      // updated.
      // Note that rather than call session->OnFrame() directly, we dispatch to
      // a helper method who can determine if the state requirements are still
      // met that would allow the frame to be served.
      window->GetTaskRunner(blink::TaskType::kInternalMedia)
          ->PostTask(FROM_HERE,
                     BindOnce(&XRFrameProvider::OnPreDispatchInlineFrame,
                              WrapWeakPersistent(this),
                              WrapWeakPersistent(session), high_res_now_ms));
    }
  }
}

void XRFrameProvider::OnPreDispatchInlineFrame(XRSession* session,
                                               double timestamp) {
  // Do nothing if the session was cleaned up or ended before we were schedueld.
  if (!session || session->ended())
    return;

  // If we have an immersive session, we shouldn't serve frames to the inline
  // session; however, we need to ensure that we don't stall out its frame loop,
  // so add a new frame request to get served after the immersive session exits.
  if (immersive_session_) {
    RequestFrame(session);
    return;
  }

  // If we still have the session and don't have an immersive session, then we
  // should serve the frame.
  session->OnFrame(timestamp, Vector<XRSharedImageData>());
}

double XRFrameProvider::UpdateImmersiveFrameTime(
    LocalDOMWindow* window,
    const device::mojom::blink::XRFrameData& data) {
  DVLOG(3) << __func__;

  // `data.time_delta` is in unspecified base. Because of that, we capture the
  // `time_delta` of the first frame we see (this gives us device_t_0), along
  // with the time we saw it (renderer_t_0). That allows us to translate from
  // device time to renderer time, so when we see frame N, we perform:
  // renderer_t_N = renderer_t_0 + (device_t_N - device_t_0)

  if (!first_immersive_frame_time_) {
    DCHECK(!first_immersive_frame_time_delta_);

    // This is the first time we got a frame data from an immersive session.
    // Let's capture device_t_0 and renderer_t_0.

    first_immersive_frame_time_ = base::TimeTicks::Now();
    first_immersive_frame_time_delta_ = data.time_delta;
  }

  // (device_t_N - device_t_0) is:
  base::TimeDelta current_frame_time_from_first_frame =
      data.time_delta - *first_immersive_frame_time_delta_;
  // renderer_t_N is then:
  base::TimeTicks current_frame_time =
      *first_immersive_frame_time_ + current_frame_time_from_first_frame;

  double high_res_now_ms =
      DOMWindowPerformance::performance(*window)
          ->MonotonicTimeToDOMHighResTimeStamp(current_frame_time);

  return high_res_now_ms;
}

void XRFrameProvider::SubmitLayer(device::LayerId layer_id,
                                  XrLayerClient* client,
                                  bool was_changed) {
  CHECK(client);
  std::unique_ptr<SharedImageHolder> image_ref = client->DoneWithSharedBuffer();

  CHECK(immersive_session_);
  CHECK(client->session());
  CHECK_EQ(client->session(), immersive_session_);

  if (!immersive_presentation_provider_.is_bound()) {
    return;
  }

  TRACE_EVENT1("gpu", "XRFrameProvider::SubmitLayer", "frame", frame_id_);
  DVLOG(3) << __func__ << ": frame=" << frame_id_;

  if (!was_changed) {
    return;
  }

  if (frame_id_ < 0) {
    // There is no valid frame_id_, and the browser side is not currently
    // expecting a frame to be submitted. That can happen for the first
    // immersive frame if the animation loop submits without a preceding
    // immersive GetFrameData response, in that case frame_id_ is -1 (see
    // https://crbug.com/855722).
    return;
  }

  if (frame_transport_->DrawingIntoSharedBuffer()) {
    // Image is written to shared buffer already. The layer now takes
    // ownership of the SharedImageHolder, which contains the SyncToken.
    DVLOG(3) << __func__ << ": FrameSubmit for SharedBuffer mode";
    any_layer_changed_ = true;
    layers_.emplace_back(layer_id, std::move(image_ref));
    return;
  } else {
    CHECK_NE(client->session()->GraphicsApi(), XRGraphicsBinding::Api::kWebGPU)
        << "WebGPU layers only support shared buffer submission modes";
  }

  image_ref = client->TransferToSharedImageHolder();

  if (!image_ref) {
    return;
  }

  any_layer_changed_ = true;
  layers_.emplace_back(layer_id, std::move(image_ref));
}

// TODO(bajones): This only works because we're restricted to a single layer at
// the moment. Will need an overhaul when we get more robust layering support.
void XRFrameProvider::UpdateWebGLLayerViewports(XRWebGLLayer* layer) {
  DCHECK(layer->session() == immersive_session_);
  DCHECK(immersive_presentation_provider_.is_bound());

  XRViewport* left =
      layer->GetViewportForEye(device::mojom::blink::XREye::kLeft);
  XRViewport* right =
      layer->GetViewportForEye(device::mojom::blink::XREye::kRight);
  float width = layer->framebufferWidth();
  float height = layer->framebufferHeight();

  // We may only have one eye view, i.e. in smartphone immersive AR mode.
  // Use all-zero bounds for unused views.
  // TODO(crbug.com/451876192): Investigate sending unnormalized coordinates
  // from here. We create TextureDrawQuads with unnormalized coordinates, so
  // removing this redundant normalization/unnormalization step would reduce
  // floating-point precision issues.
  gfx::RectF left_coords =
      left ? gfx::RectF(
                 static_cast<float>(left->x()) / width,
                 static_cast<float>(height - (left->y() + left->height())) /
                     height,
                 static_cast<float>(left->width()) / width,
                 static_cast<float>(left->height()) / height)
           : gfx::RectF();
  gfx::RectF right_coords =
      right ? gfx::RectF(
                  static_cast<float>(right->x()) / width,
                  static_cast<float>(height - (right->y() + right->height())) /
                      height,
                  static_cast<float>(right->width()) / width,
                  static_cast<float>(right->height()) / height)
            : gfx::RectF();

  immersive_presentation_provider_->UpdateLayerBounds(
      frame_id_, left_coords, right_coords, gfx::Size(width, height));
}

// TODO(bajones): This only works because we're restricted to a single layer at
// the moment. Will need an overhaul when we get more robust layering support.
void XRFrameProvider::UpdateLayerViewports(XRProjectionLayer* layer) {
  DCHECK(layer->session() == immersive_session_);
  DCHECK(immersive_presentation_provider_.is_bound());

  XRGraphicsBinding* binding = layer->binding();

  // TODO(crbug.com/359418629): Currently we have no way to submit texture
  // arrays to the compositor, so any array textures produced by the page will
  // be copied to a side-by-side texture prior to submission. That does mean
  // that we need to adjust the viewports from those reported to the page,
  // however, by altering the texture width here...
  float width = layer->textureWidth() * layer->textureArrayLength();
  float height = layer->textureHeight();

  gfx::RectF left_coords;
  gfx::RectF right_coords;
  if (immersive_session_->StereoscopicViews()) {
    XRViewData* left_view =
        immersive_session_->ViewDataForEye(device::mojom::blink::XREye::kLeft);
    XRViewData* right_view =
        immersive_session_->ViewDataForEye(device::mojom::blink::XREye::kRight);

    gfx::Rect left = binding->GetViewportForView(layer, left_view);
    gfx::Rect right = binding->GetViewportForView(layer, right_view);

    // (continued from prior comment) ...and offsetting the viewports here.
    if (layer->textureArrayLength() > 1) {
      right.set_x(right.x() + layer->textureWidth());
    }

    left_coords = NormalizeViewport(left, width, height);
    right_coords = NormalizeViewport(right, width, height);
  } else {
    XRViewData* mono_view =
        immersive_session_->ViewDataForEye(device::mojom::blink::XREye::kNone);
    gfx::Rect viewport = binding->GetViewportForView(layer, mono_view);

    left_coords = NormalizeViewport(viewport, width, height);

    // Non-stereo modes (i.e. smartphone immersive AR mode)
    // use the default all-zero bounds for right view.
  }

  immersive_presentation_provider_->UpdateLayerBounds(
      frame_id_, left_coords, right_coords, gfx::Size(width, height));
}

void XRFrameProvider::ClearCachedLayersData() {
  any_layer_changed_ = false;
  layers_.clear();
}

void XRFrameProvider::SubmitFrame(XRFrameTransportDelegate* transport_delegate,
                                  gpu::SharedImageExportResult export_result) {
  CHECK(transport_delegate);

  if (!immersive_presentation_provider_.is_bound()) {
    return;
  }

  TRACE_EVENT1("gpu", "XRFrameProvider::SubmitFrame", "frame", frame_id_);
  DVLOG(3) << __func__ << ": frame=" << frame_id_;

  // Ensure temporary data is always reset.
  bool was_any_layer_changed = any_layer_changed_;
  any_layer_changed_ = false;

  if (frame_id_ < 0) {
    // There is no valid frame_id_, and the browser side is not currently
    // expecting a frame to be submitted. That can happen for the first
    // immersive frame if the animation loop submits without a preceding
    // immersive GetFrameData response, in that case frame_id_ is -1 (see
    // https://crbug.com/855722).
    return;
  }

  auto this_frame_id = frame_id_;

  // Reset an active frame id, since anything we'd want to do (resizing/etc) can
  // no-longer happen to this frame.
  frame_id_ = -1;

  if (!immersive_presentation_provider_.is_bound()) {
    return;
  }

  if (!was_any_layer_changed) {
    // Just tell the device side that there was no submitted frame instead of
    // executing the implicit end-of-frame submit.
    frame_transport_->FrameSubmitMissing(immersive_presentation_provider_.get(),
                                         std::move(export_result),
                                         this_frame_id);
    dropped_frames_++;

    return;
  }

  frame_transport_->FramePreImage(transport_delegate);

  // The backend expects layer ID list to contain a single element (i.e. the
  // base layer) if the 'layers' feature is not enabled.
  if (!layer_manager_.is_bound()) {
    // At this case, only a single layer should exist since the
    // layers feature is not enabled.
    CHECK_EQ(layers_.size(), 1U);
  }

  bool succeeded = frame_transport_->FrameSubmit(
      immersive_presentation_provider_.get(), transport_delegate,
      std::move(layers_), std::move(export_result), this_frame_id);

  succeeded ? num_frames_++ : dropped_frames_++;
  if (succeeded) {
    submit_frame_time_.StartTimer();
  }
}

void XRFrameProvider::Dispose() {
  DVLOG(2) << __func__;
  immersive_presentation_provider_.reset();
  immersive_data_provider_.reset();
  // Reset layers data.
  ClearCachedLayersData();
  if (immersive_session_)
    immersive_session_->ForceEnd(XRSession::ShutdownPolicy::kImmediate);
  // TODO(bajones): Do something for outstanding frame requests?
}

void XRFrameProvider::SendFrameData() {
  if (!immersive_session_) {
    return;
  }

  device::mojom::blink::XrFrameStatisticsPtr xr_frame_stat =
      device::mojom::blink::XrFrameStatistics::New();

  xr_frame_stat->trace_id = immersive_session_->GetTraceId();

  base::TimeTicks now = base::TimeTicks::Now();
  xr_frame_stat->duration = now - last_frame_statistics_sent_time_;
  last_frame_statistics_sent_time_ = now;

  xr_frame_stat->num_frames = num_frames_;
  xr_frame_stat->dropped_frames = dropped_frames_;

  num_frames_ = 0;
  dropped_frames_ = 0;

  xr_frame_stat->frame_data_time = frame_data_time_.TakeAverageMicroseconds();

  xr_frame_stat->page_animation_frame_time =
      immersive_session()->TakeAnimationFrameTimerAverage();

  xr_frame_stat->submit_frame_time =
      submit_frame_time_.TakeAverageMicroseconds();

  if (xr_->GetWebXrInternalsRendererListener()) {
    xr_->GetWebXrInternalsRendererListener()->OnFrameData(
        std::move(xr_frame_stat));
  }
}

void XRFrameProvider::OnTransferComplete(
    bool succeeded,
    const Vector<device::LayerId>& layer_ids) {
  if (succeeded && immersive_session_) {
    immersive_session_->OnTransferComplete(layer_ids);
  }
}

void XRFrameProvider::OnRenderComplete() {
  submit_frame_time_.StopTimer();
}

bool XRFrameProvider::DrawingIntoSharedBuffer() const {
  return frame_transport_->DrawingIntoSharedBuffer();
}

void XRFrameProvider::Trace(Visitor* visitor) const {
  visitor->Trace(xr_);
  visitor->Trace(frame_transport_);
  visitor->Trace(immersive_session_);
  visitor->Trace(immersive_data_provider_);
  visitor->Trace(immersive_presentation_provider_);
  visitor->Trace(non_immersive_data_providers_);
  visitor->Trace(requesting_sessions_);
  visitor->Trace(immersive_observers_);
  visitor->Trace(layer_manager_);
}

}  // namespace blink