[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/desktop_frame_generator.h

Index: webrtc/modules/desktop_capture/desktop_frame_generator.h
diff --git a/webrtc/modules/desktop_capture/desktop_frame_generator.h b/webrtc/modules/desktop_capture/desktop_frame_generator.h
new file mode 100644
index 0000000000000000000000000000000000000000..9348e6ed36eb437294a00108a932c4944a523b24
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+++ b/webrtc/modules/desktop_capture/desktop_frame_generator.h
@@ -0,0 +1,112 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_FRAME_GENERATOR_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_FRAME_GENERATOR_H_
+
+#include <memory>
+
+#include "webrtc/modules/desktop_capture/desktop_frame.h"
+#include "webrtc/modules/desktop_capture/desktop_geometry.h"
+#include "webrtc/modules/desktop_capture/desktop_region.h"
+#include "webrtc/modules/desktop_capture/shared_memory.h"
+
+namespace webrtc {
+
+// A functor to generate a DesktopFrame.
+class DesktopFrameGenerator {
+ public:
+  DesktopFrameGenerator();
+  virtual ~DesktopFrameGenerator();
+
+  virtual std::unique_ptr<DesktopFrame> operator()(

[Sergey Ulanov, 2016/08/18 05:07:58]

style guide discourages operator overloading.
https://google.github.io/styleguide/cppguide.html#Operator_Overloading .
Operator() specifically makes the calling code rather confusing, and there is no
good reason you need it here. Call this method GetNextFrame()?

[Hzj_jie, 2016/08/23 00:54:59]

Done.

+      SharedMemoryFactory* factory) = 0;
+};
+
+// A base implementation of DesktopFrameGenerator to take care about the
+// DesktopFrame
+// size, filling updated_region(), etc, but only requires derived classes to
+// implement the Paint() function.
+class BaseDesktopFrameGenerator : public DesktopFrameGenerator {

[Sergey Ulanov, 2016/08/18 05:07:58]

I don't think you really need inheritance here. Style guide says that
composition should be preferred:
https://google.github.io/styleguide/cppguide.html#Inheritance
In this case this class can simply take a pointer or rtc::Callback<> to the
Paint() function

[Hzj_jie, 2016/08/23 00:54:59]

I think you must mean the BlackWhiteDesktopFrameGenerator. I have changed it to
BlackWhiteDesktopFramePainter.

+ public:
+  BaseDesktopFrameGenerator();
+  ~BaseDesktopFrameGenerator() override;
+
+  std::unique_ptr<DesktopFrame> operator()(SharedMemoryFactory* factory) final;
+
+  // Sets the size of the frame which will be returned in next operator()
+  // call.
+  DesktopSize* size();
+
+  // Decides whether BaseDesktopFrameGenerator returns a frame in next Capture()
+  // callback. If return_frame_ is true, BaseDesktopFrameGenerator will create a
+  // frame according to both size_ and SharedMemoryFactory input, and uses
+  // Paint() function to paint it.
+  void set_return_frame(bool return_frame);
+
+  // Decides whether MockScreenCapturer returns a frame with updated regions.
+  // MockScreenCapturer will keep DesktopFrame::updated_region() empty if this
+  // field is false.
+  void set_provide_updated_region_hints(bool provide_updated_region_hints);
+
+  // Decides whether MockScreenCapturer randomly enlarges updated regions in the
+  // DesktopFrame. Set this field to true to simulate an inaccurate updated
+  // regions' return from OS APIs.
+  void set_enlarge_updated_region(bool enlarge_updated_region);
+
+  // The range to enlarge a updated region if |enlarge_updated_region_| is true.
+  // If this field is less than zero, it will be treated as zero, and
+  // |enlarge_updated_region_| will be ignored.
+  void set_enlarge_range(int enlarge_range);
+
+  // Decides whether BaseDesktopFrameGenerator randomly add some updated regions
+  // in the
+  // DesktopFrame. Set this field to true to simulate an inaccurate updated
+  // regions' return from OS APIs.
+  void set_add_random_updated_region(bool add_random_updated_region);
+
+ private:
+  // Paints on the |frame|, and updates |updated_region| to indicate
+  // rectangles painted. If this function returns false,
+  // BaseDesktopFrameGenerator will
+  // returns a nullptr from operator() call.
+  virtual bool Paint(DesktopFrame* frame, DesktopRegion* updated_region) = 0;
+
+  DesktopSize size_;
+  bool return_frame_;
+  bool provide_updated_region_hints_;
+  bool enlarge_updated_region_;
+  int enlarge_range_;
+  bool add_random_updated_region_;
+};
+
+// An implementation of BaseDesktopFrameGenerator to paint block on
+// mutable_updated_region(), and white elsewhere.
+class BlackWhiteDesktopFrameGenerator : public BaseDesktopFrameGenerator {
+ public:
+  BlackWhiteDesktopFrameGenerator();
+  ~BlackWhiteDesktopFrameGenerator() override;
+
+  // The black regions of the frame which will be returned in next operator()
+  // call. BlackWhiteDesktopFrameGenerator will return a white frame, with black
+  // in the
+  // updated_region_. Each operator() call with return_frame_ as true will
+  // consume updated_region_.
+  DesktopRegion* updated_region();
+
+ private:
+  bool Paint(DesktopFrame* frame, DesktopRegion* updated_region) override;
+
+  DesktopRegion updated_region_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_DESKTOP_FRAME_GENERATOR_H_