Monitor the intersection of video and viewport.

media/remoting/remoting_controller.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 "media/remoting/remoting_controller.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback_helpers.h"
 #include "base/logging.h"
@@ skipping 124 matching lines @@
   UpdateAndMaybeSwitch();
 }
 
 void RemotingController::OnExitedFullscreen() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   is_fullscreen_ = false;
   UpdateAndMaybeSwitch();
 }
 
+void RemotingController::OnVideoViewportRatioChanged(double ratio) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+
+  is_fullscreen_ = ratio > 0.85;

[miu, 2016/11/05 02:47:46]

Need "debouncing" logic here. Something like "no changes in ratio for 5 seconds"
before we attempt to start remoting:

void RemotingController::OnVideoViewportRatioChanged(double ratio) {
  // Reset on any notification, since this indicates the user is scrolling
  // around in the document, the document is changing layout, etc.
  viewport_fill_debouncer_timer_.Reset();

  // Dropping below the threshold should instantly stop remote rendering.
  if (ratio < 0.85) {
    if (is_mostly_filling_viewport_) {
      is_mostly_filling_viewport_ = false;
      UpdateAndMaybeSwitch();
    }
    return;
  }

  // Meeting/Exceeding the threshold should hold steady for 5 seconds before
  // starting remote rendering.
  if (!is_mostly_filling_viewport_) {
    viewport_fill_debouncer_timer_.Start(
        ..., 5 seconds, this,
        &RemotingController::OnViewportMostlyFilledAndUnchanging);
  }
}

void RemotingController::OnViewportMostlyFilledAndUnchanging() {
  is_mostly_filling_viewport_ = true;
  UpdateAndMaybeSwitch();
}

Note: |viewport_fill_debouncer_timer_| is a base::OneShotTimer. I also suggest
using a separate flag for this (i.e., don't re-use |is_fullscreen_|).

[xjz, 2016/11/09 02:24:28]

Done.

+  UpdateAndMaybeSwitch();
+}
+
 void RemotingController::OnSetCdm(CdmContext* cdm_context) {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   // TODO(xjz): Not implemented. Will add in up-coming change.
   NOTIMPLEMENTED();
 }
 
 void RemotingController::SetSwitchRendererCallback(
     const SwitchRendererCallback& cb) {
   DCHECK(task_runner_->BelongsToCurrentThread());
@@ skipping 108 matching lines @@
     // |swithc_renderer_cb_.Run()| will be called after remoting is started
     // successfully.
     remoter_->Start();
   } else {
     switch_renderer_cb_.Run();
     remoter_->Stop(mojom::RemotingStopReason::LOCAL_PLAYBACK);
   }
 }
 
 }  // namespace media