BlankDetectorDesktopCapturerWrapper to detect a blank DesktopFrame

webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h

Index: webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h
diff --git a/webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h b/webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h
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+/*
+ *  Copyright (c) 2017 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_BLANK_DETECTOR_DESKTOP_CAPTURER_WRAPPER_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_BLANK_DETECTOR_DESKTOP_CAPTURER_WRAPPER_H_
+
+#include <memory>
+
+#include "webrtc/modules/desktop_capture/desktop_capturer.h"
+#include "webrtc/modules/desktop_capture/rgba_color.h"
+
+namespace webrtc {
+
+// A DesktopCapturer wrapper detects the return value of its owned
+// DesktopCapturer implementation. If sampled pixels returned by the
+// DesktopCapturer implementation all equal to the blank pixel, this wrapper
+// returns ERROR_TEMPORARY. If the DesktopCapturer implementation fails for too
+// many times, this wrapper returns ERROR_PERMANENT.
+class BlankDetectorDesktopCapturerWrapper final
+    : public DesktopCapturer,
+      public DesktopCapturer::Callback {
+ public:
+  // Creates BlankDetectorDesktopCapturerWrapper. BlankDesktopCapturerWrapper
+  // takes ownership of |capturer|. The |blank_pixel| is the unmodified color
+  // returned by the |capturer|. |permanent_failure_threshold| controls how
+  // many frames BlankDetectorDesktopCapturerWrapper checks before returning a
+  // permanent error. Setting |permanent_failure_threshold| to negative value to
+  // disable this function, i.e. BlankDetectorDesktopCapturerWrapper will check
+  // every frame, and never return permanent error.

[Sergey Ulanov, 2017/03/02 23:45:51]

Do we actually need this feature? It adds complexity, but I don't see a case
when it can be useful.

[Hzj_jie, 2017/03/03 02:29:41]

I am OK to remove the permanent_failure_threshold. Once we need it, an
individual capturer wrapper can help to reduce the complexity.

+  BlankDetectorDesktopCapturerWrapper(std::unique_ptr<DesktopCapturer> capturer,
+                                      RgbaColor blank_pixel,

[Sergey Ulanov, 2017/03/02 23:45:51]

Do we need this parameter? Will we even need to pass anything other then 0?

[Hzj_jie, 2017/03/03 02:29:41]

If we use this class with GDI capturer on Windows 10, we need to provide 0xff
instead of 0x00. So it looks like a useful parameter. Unlike
permanent_failure_threshold, it does not make the logic complex, we always need
to compare the pixel with a color. So I would prefer to keep it.

+                                      int permanent_failure_threshold);
+  ~BlankDetectorDesktopCapturerWrapper() override;
+
+  // DesktopCapturer interface.
+  void Start(DesktopCapturer::Callback* callback) override;
+  void SetSharedMemoryFactory(
+      std::unique_ptr<SharedMemoryFactory> shared_memory_factory) override;
+  void CaptureFrame() override;
+  void SetExcludedWindow(WindowId window) override;
+  bool GetSourceList(SourceList* sources) override;
+  bool SelectSource(SourceId id) override;
+  bool FocusOnSelectedSource() override;
+
+ private:
+  // DesktopCapturer::Callback interface.
+  void OnCaptureResult(Result result,
+                       std::unique_ptr<DesktopFrame> frame) override;
+
+  bool IsBlankFrame(const DesktopFrame& frame) const;
+
+  // Detects whether pixel at (x, y) equals to |blank_pixel_|.
+  bool IsBlankPixel(const DesktopFrame& frame, int x, int y) const;
+
+  // Whether permanent failure has been enabled by this instance, i.e.
+  // |permanent_failure_threshold_| >= 0.
+  bool permanent_failure_enabled() const;
+
+  // Whether permanent error should be returned by this instance for current
+  // frame.
+  bool permanent_failure_reached() const;
+
+  // Returns a permanent error to |callback_|.
+  void ReturnPermanentError();
+
+  const std::unique_ptr<DesktopCapturer> capturer_;
+  const RgbaColor blank_pixel_;
+
+  // The count of failures before this wrapper returns an ERROR_PERMANENT. Set
+  // this value to negative to always return ERROR_TEMPORARY.
+  const int permanent_failure_threshold_;
+
+  // The count of blank frames received in a sequence.
+  int failure_count_ = 0;
+
+  // Whether a non-blank frame has been received.
+  bool non_blank_frame_received_ = false;
+
+  // Whether the last frame is blank.
+  bool last_frame_is_blank_ = false;
+
+  // Whether current frame is the first frame.
+  bool is_first_frame_ = true;
+
+  DesktopCapturer::Callback* callback_ = nullptr;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_BLANK_DETECTOR_DESKTOP_CAPTURER_WRAPPER_H_