Implement screen capturer for MediaStream API.

content/browser/renderer_host/media/screen_capturer.h

+// Copyright (c) 2012 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.
+
+#ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_SCREEN_CAPTURER_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_SCREEN_CAPTURER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/threading/thread.h"
+#include "base/timer.h"
+#include "content/common/content_export.h"
+#include "media/video/capture/video_capture_device.h"
+#include "remoting/capturer/video_frame_capturer.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+
+namespace content {
+
+class CONTENT_EXPORT ScreenCapturer
+    : public media::VideoCaptureDevice,
+      public NON_EXPORTED_BASE(remoting::VideoFrameCapturer::Delegate) {
+ public:
+
+  ScreenCapturer();
+  virtual ~ScreenCapturer();
+
+  // Helper used in tests to supply a fake capturer.
+  void set_test_frame_capturer(
+      scoped_ptr<remoting::VideoFrameCapturer> capturer) {
+    video_frame_capturer_ = capturer.Pass();
+  }
+
+  // media::VideoCaptureDevice interface.
+  virtual void Allocate(int width, int height,
+                        int frame_rate,
+                        EventHandler* event_handler) OVERRIDE;
+  virtual void Start() OVERRIDE;
+  virtual void Stop() OVERRIDE;
+  virtual void DeAllocate() OVERRIDE;
+  virtual const Name& device_name() OVERRIDE;
+
+  // VideoFrameCapturer::Delegate interface.

[Wez, 2013/01/10 00:58:14]

nit: Add a comment to clarify that these run on the internal capture thread.

[Sergey Ulanov, 2013/01/11 23:46:20]

Done.

+  virtual void OnCaptureCompleted(
+      scoped_refptr<remoting::CaptureData> capture_data) OVERRIDE;
+  virtual void OnCursorShapeChanged(
+      scoped_ptr<remoting::MouseCursorShape> cursor_shape) OVERRIDE;
+
+ private:
+  // Helper methods that run on the |capture_thread_|.
+  void DoAllocate(int frame_rate, EventHandler* event_handler);

[Wez, 2013/01/10 00:58:14]

Could you fold these helpers into the calls themselves with a thread-trampoline?

If not then I'd suggest making clear in the comment that these directly mirror
the methods in VideoCaptureDevice.

[Sergey Ulanov, 2013/01/11 23:46:20]

Don't think I can use trampoline approach with worker pool. Done.

+  void DoStart();
+  void DoStop();
+  void DoDeAllocate();
+  void DoCapture();

[Wez, 2013/01/10 00:58:14]

Add a separate comment for DoCapture() to explain what triggers it / what it
does, since it doesn't directly mirror a VideoCaptureDevice API.

[Sergey Ulanov, 2013/01/11 23:46:20]

Done.

+
+  base::Thread capture_thread_;

[Wez, 2013/01/10 00:58:14]

You're relying on |capture_thread_| stopping during tear-down to make
base::Unretained() safe - for that I think you need the thread to be the
last-constructed/first-deleted member?

[Sergey Ulanov, 2013/01/11 23:46:20]

Removed the thread. Now using worker pool.

+
+  Name name_;
+  EventHandler* event_handler_;
+  int frame_rate_;

[Wez, 2013/01/10 00:58:14]

Add a comment to indicate that these are parameters from Allocate(), and to
explain where |name_| comes from.

[Sergey Ulanov, 2013/01/11 23:46:20]

Done.

+
+  scoped_ptr<remoting::VideoFrameCapturer> video_frame_capturer_;
+  bool capture_pending_;

[Wez, 2013/01/10 00:58:14]

Add comments to state explicitly what these are for, please.

e.g. For capture_pending_, explain that we only want to capture a single frame
at a time.

[Sergey Ulanov, 2013/01/11 23:46:20]

Done.

+
+  // After Allocate() is called we need to call OnFrameInfo() method of the
+  // |evant_handler_| to specify the size of the frames this capturer will

[Wez, 2013/01/10 00:58:14]

typo: event_handler

[Sergey Ulanov, 2013/01/11 23:46:20]

Done.

+  // produce. In order to get screen size from |video_frame_capturer_| we need
+  // to capture at least one frame. Once screen size is known it's stored in
+  // |frame_size_|.
+  bool waiting_frame_size_;

[Wez, 2013/01/10 00:58:14]

Can't you indicate this implicitly via |frame_size_| being empty?

[Sergey Ulanov, 2013/01/11 23:46:20]

It's better to have an explicit flag, e.g. for the case when DeAllocate() is
called shortly after Allocate(), before we get first frame captured. It also
makes code more readable.

+  SkISize frame_size_;
+  SkBitmap resized_bitmap_;
+
+  scoped_ptr<base::RepeatingTimer<ScreenCapturer> > timer_;

[Wez, 2013/01/10 00:58:14]

Add comment to explain this, e.g. why it needs to be a scoped_ptr rather than a
straight member.

[Sergey Ulanov, 2013/01/11 23:46:20]

Not using timer anymore.

+  bool started_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScreenCapturer);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_SCREEN_CAPTURER_H_