cast: support cursor rendering for tab capture

content/browser/media/capture/cursor_renderer.h

+// Copyright (c) 2015 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_MEDIA_CAPTURE_CURSOR_RENDERER_H_
+#define CONTENT_BROWSER_MEDIA_CAPTURE_CURSOR_RENDERER_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "content/common/content_export.h"
+#include "media/base/video_frame.h"
+#include "skia/ext/image_operations.h"
+#include "ui/aura/window.h"
+#include "ui/base/cursor/cursor.h"
+#include "ui/events/event_handler.h"
+#include "ui/gfx/geometry/point.h"
+#include "ui/gfx/geometry/rect.h"
+#include "ui/gfx/geometry/size.h"
+#include "ui/gfx/native_widget_types.h"
+
+namespace content {
+
+enum {
+  ENABLE_MOUSE_EVENTS = 1

[miu, 2015/10/20 02:12:44]

I suggest removing this for a number of technical reasons (comments below). 
However, when it comes to the user experience, do you ever NOT want to disable
the mouse cursor when there is no movement?

[xjz, 2015/10/20 17:12:08]

I think we want to disable the mouse cursor while playing video. But may want to
show cursor during presentation even when there is no mouse movement.

[Irfan, 2015/10/21 23:01:07]

Have gone with keeping the same code for all cases right now.

[Irfan, 2015/10/21 23:01:08]

I did consider keeping the mouse rendering logic for all cases, but ended up
adding this as an afterthought to retain existing behavior in other cases. I
think we can keep the behavior consistent.

+};
+
+// Tracks state for making decisions on cursor display on a captured video
+// frame
+class CONTENT_EXPORT CursorRenderer : public ui::EventHandler {
+ public:
+  explicit CursorRenderer(aura::Window* window,

[miu, 2015/10/20 02:12:44]

Please comment that |window| is expected to out-live CursorRenderer.

However, for the ContentCaptureSubscription (tab capture case), I'm worried the
|window| could be destroyed somehow before the CursorRenderer.  Perhaps
CursorRenderer should also be a WindowObserver so that it can call
Window::RemovePreTargetHandler() when WindowObserver::OnWindowDestroying()?

[Irfan, 2015/10/21 23:01:07]

Done.

+                          bool enable_mouse_events = false);

[miu, 2015/10/20 02:12:44]

Just need the |window| argument.  If it's not null, do the mouse event
listening.  If null, don't.

[Irfan, 2015/10/21 23:01:07]

Done.

+  ~CursorRenderer() override;
+  void Clear();
+  bool Update(const gfx::Rect& region_in_frame);
+  void RenderOnVideoFrame(const scoped_refptr<media::VideoFrame>& target) const;
+  // Overridden from ui::EventHandler to make decision on when
+  // cursor gets rendered on a captured video frame
+  void OnMouseEvent(ui::MouseEvent* event) override;
+
+ private:
+  ui::Cursor last_cursor_;
+  gfx::Size window_size_when_cursor_last_updated_;
+  gfx::Point cursor_position_in_frame_;
+  SkBitmap scaled_cursor_bitmap_;
+  aura::Window* window_;
+
+  // This flag enables mouse event tracking for the purpose of disabling
+  // cursor rendering when there is no movement
+  const bool enable_mouse_events_;

[miu, 2015/10/20 02:12:44]

ditto here: No need for a bool since |window_| will either be null or not null.

+
+  enum {
+    // Minium movement before cursor is rendered on frame
+    MIN_MOVEMENT = 15
+  };
+  enum {

[miu, 2015/10/20 02:12:44]

nit: These can both be in one enum block.

[Irfan, 2015/10/21 23:01:08]

I had kept them separate since the values do not mean the same thing, but adding
units to name will clarify it

+    // Maximum idle time allowed before we stop rendering the cursor
+    // on frame
+    MAX_IDLE_TIME = 2

[miu, 2015/10/20 02:12:44]

Please add units to naming of these two enums (i.e., ..._PIXELS and
..._SECONDS).

[Irfan, 2015/10/21 23:01:07]

Done.

+  };
+
+  base::TimeDelta last_mouse_movement_timestamp_;
+  float last_mouse_position_x_;

[miu, 2015/10/20 02:12:44]

The two floats and bool need initialization in the ctor.

[xjz, 2015/10/20 17:12:08]

Are these two the mouse location? Why they are float?

[Irfan, 2015/10/21 23:01:07]

Done.

[Irfan, 2015/10/21 23:01:08]

those are the units in which MouseEVent tracks x and y

+  float last_mouse_position_y_;
+  bool cursor_displayed_;
+  DISALLOW_COPY_AND_ASSIGN(CursorRenderer);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_CAPTURE_CURSOR_RENDERER_H_