BlankDetectorDesktopCapturerWrapper to detect a blank DesktopFrame

webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h

+/*
+ *  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"

[Sergey Ulanov, 2017/03/01 22:18:32]

Comments for RgbaColor say that it's for tests only and that was my
understanding as well. Do we really need to use it here? This class could just
detect black frames, I don't think we need to pass blank_pixel as a parameter.

[Hzj_jie, 2017/03/01 23:31:38]

AFAICT, on Linux, the blank pixel is 0xff, and on Windows 8, it's 0x00, on
Windows 10, it's 0xff. But DX APIs return 0x00. So it's easy for us to use
different RgbaColors for different platforms.

+
+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:
+  BlankDetectorDesktopCapturerWrapper(std::unique_ptr<DesktopCapturer> capturer,
+                                      RgbaColor blank_pixel,
+                                      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.
+  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();
+
+  // Returns a temporary error to |callback_|.
+  void ReturnTemporaryError();
+
+  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_