[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h

Index: webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h
diff --git a/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h b/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h
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index 0000000000000000000000000000000000000000..55fa136b48dd60f2d78f0fda9bc7261552028610
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+++ b/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h
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+/*
+ *  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_SCREEN_CAPTURER_DIFFER_WRAPPER_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURER_DIFFER_WRAPPER_H_
+
+#include <memory>
+
+#include "webrtc/modules/desktop_capture/screen_capturer.h"
+#include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
+
+namespace webrtc {
+
+// A ScreenCapturer implementation to forward capture requests to the underlying
+// implementation, and help to calculate the dirty region.

[Sergey Ulanov, 2016/08/12 05:25:51]

suggest rewording:
// ScreenCapturer wrapper that calculates updated_region() by comparing frames
// content.

[Hzj_jie, 2016/08/15 00:38:06]

Done.

+// This class has several restrictions,
+// 1. Underlying capturer should use SharedDesktopFrame to return captured

[Sergey Ulanov, 2016/08/12 05:25:51]

I think it's better to avoid this restriction by always wrapping returned frames
in a new SharedDesktopFrame. 

[Hzj_jie, 2016/08/15 00:38:06]

Done.

+// instances of DesktopFrame.
+// 2. If the underlying capturer provides updated_region() as hints, it expects

[Sergey Ulanov, 2016/08/12 05:25:51]

I don't think this needs to be mentioned here. Valid ScreenCapturer
implementation should never return updated_region() that outside of the screen
boundaries. It's also easy to make this class deal with this.

[Hzj_jie, 2016/08/15 00:38:06]

Done.

+// the region won't excceed DesktopFrame::size().
+class ScreenCapturerDifferWrapper : public ScreenCapturer,
+                                    public DesktopCapturer::Callback {
+ public:
+  // Creates a ScreenCapturerDifferWrapper with a ScreenCapturer implementation,
+  // and takes its ownership. If |diff_entire_frame| is true, this class will
+  // assume underlying capturer won't update DesktopFrame::updated_region() by
+  // discarding it, and always compare entire frame. Otherwise, this class will
+  // use DesktopFrame::updated_region() returned by underlying capturer as hints
+  // to improve the performance to calculate the dirty region.
+  explicit ScreenCapturerDifferWrapper(
+      std::unique_ptr<ScreenCapturer> base_capturer,
+      bool diff_entire_frame);
+  ~ScreenCapturerDifferWrapper() override;
+
+  // ScreenCapturer interface.
+  void Start(DesktopCapturer::Callback* callback) override;
+  void SetSharedMemoryFactory(
+      std::unique_ptr<SharedMemoryFactory> shared_memory_factory) override;
+  void Capture(const DesktopRegion& region) override;
+  bool GetScreenList(ScreenList* screens) override;
+  bool SelectScreen(ScreenId id) override;
+
+ private:
+  // DesktopCapturer::Callback interface.
+  void OnCaptureResult(Result result,
+                       std::unique_ptr<DesktopFrame> frame) override;
+
+  const std::unique_ptr<ScreenCapturer> base_capturer_;
+  const bool diff_entire_frame_;
+  DesktopCapturer::Callback* callback_;
+  std::unique_ptr<SharedDesktopFrame> last_frame_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_SCREEN_CAPTURER_DIFFER_WRAPPER_H_