BlankDetectorDesktopCapturerWrapper to detect a blank DesktopFrame

webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.cc

+/*
+ *  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.
+ */
+
+#include "webrtc/modules/desktop_capture/blank_detector_desktop_capturer_wrapper.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/modules/desktop_capture/desktop_geometry.h"
+
+namespace webrtc {
+
+BlankDetectorDesktopCapturerWrapper::BlankDetectorDesktopCapturerWrapper(
+    std::unique_ptr<DesktopCapturer> capturer,
+    RgbaColor blank_pixel)
+    : capturer_(std::move(capturer)),
+      blank_pixel_(blank_pixel) {
+  RTC_DCHECK(capturer_);
+}
+
+BlankDetectorDesktopCapturerWrapper::~BlankDetectorDesktopCapturerWrapper() =
+    default;
+
+void BlankDetectorDesktopCapturerWrapper::Start(
+    DesktopCapturer::Callback* callback) {
+  capturer_->Start(this);
+  callback_ = callback;
+}
+
+void BlankDetectorDesktopCapturerWrapper::SetSharedMemoryFactory(
+    std::unique_ptr<SharedMemoryFactory> shared_memory_factory) {
+  capturer_->SetSharedMemoryFactory(std::move(shared_memory_factory));
+}
+
+void BlankDetectorDesktopCapturerWrapper::CaptureFrame() {
+  RTC_DCHECK(callback_);
+  capturer_->CaptureFrame();
+}
+
+void BlankDetectorDesktopCapturerWrapper::SetExcludedWindow(WindowId window) {
+  capturer_->SetExcludedWindow(window);
+}
+
+bool BlankDetectorDesktopCapturerWrapper::GetSourceList(SourceList* sources) {
+  return capturer_->GetSourceList(sources);
+}
+
+bool BlankDetectorDesktopCapturerWrapper::SelectSource(SourceId id) {
+  return capturer_->SelectSource(id);
+}
+
+bool BlankDetectorDesktopCapturerWrapper::FocusOnSelectedSource() {
+  return capturer_->FocusOnSelectedSource();
+}
+
+void BlankDetectorDesktopCapturerWrapper::OnCaptureResult(
+    Result result,
+    std::unique_ptr<DesktopFrame> frame) {
+  RTC_DCHECK(callback_);
+  if (result != Result::SUCCESS || non_blank_frame_received_) {
+    callback_->OnCaptureResult(result, std::move(frame));
+    return;
+  }
+
+  RTC_DCHECK(frame);
+
+  // If nothing has been changed in current frame, we do not need to check it
+  // again.
+  if (!frame->updated_region().is_empty() || is_first_frame_) {
+    last_frame_is_blank_ = IsBlankFrame(*frame);
+    is_first_frame_ = false;
+  }
+  if (!last_frame_is_blank_) {
+    non_blank_frame_received_ = true;
+    callback_->OnCaptureResult(Result::SUCCESS, std::move(frame));
+    return;
+  }
+
+  callback_->OnCaptureResult(Result::ERROR_TEMPORARY,
+                             std::unique_ptr<DesktopFrame>());
+}
+
+bool BlankDetectorDesktopCapturerWrapper::IsBlankFrame(
+    const DesktopFrame& frame) const {
+  // We will check 7489 pixels for a frame with 1024 x 768 resolution.
+  for (int i = 0; i < frame.size().width() * frame.size().height(); i += 105) {
+    const int x = i % frame.size().width();
+    const int y = i / frame.size().width();
+    if (!IsBlankPixel(frame, x, y)) {
+      return false;
+    }
+  }
+
+  // We are verifying the pixel in the center as well.
+  return IsBlankPixel(frame, frame.size().width() / 2,
+                      frame.size().height() / 2);
+}
+
+bool BlankDetectorDesktopCapturerWrapper::IsBlankPixel(
+    const DesktopFrame& frame,
+    int x,
+    int y) const {
+  uint8_t* pixel_data = frame.GetFrameDataAtPos(DesktopVector(x, y));
+  return RgbaColor(pixel_data) == blank_pixel_;
+}
+
+}  // namespace webrtc