[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.cc

Index: webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.cc
diff --git a/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.cc b/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.cc
new file mode 100644
index 0000000000000000000000000000000000000000..dc76b67353b2085eb7f4bb606261170ea2cd172f
--- /dev/null
+++ b/webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.cc
@@ -0,0 +1,214 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/desktop_capture/screen_capturer_differ_wrapper.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/timeutils.h"
+#include "webrtc/modules/desktop_capture/desktop_geometry.h"
+#include "webrtc/modules/desktop_capture/differ_block.h"
+
+namespace webrtc {
+
+namespace {
+
+// Returns true if (0, 0) - (|width|, |height|) vector in |old_buffer| and
+// |new_buffer| are equal. |width| should be less than 32
+// (defined by kBlockSize), otherwise BlockDifference() should be used.
+bool PartialBlockDifference(const uint8_t* old_buffer,
+                            const uint8_t* new_buffer,
+                            int width,
+                            int height,
+                            int stride) {
+  RTC_DCHECK_LT(width, kBlockSize);
+  const int width_bytes = width * DesktopFrame::kBytesPerPixel;
+  for (int i = 0; i < height; i++) {
+    if (memcmp(old_buffer, new_buffer, width_bytes) != 0) {
+      return true;
+    }
+    old_buffer += stride;
+    new_buffer += stride;
+  }
+  return false;
+}
+
+// Compares columns in the range of [|left|, |right|), in a row in the
+// range of [|top|, |top| + |height|), starts from |old_buffer| and
+// |new_buffer|, and outputs updated regions into |output|. |stride| is the
+// DesktopFrame::stride().
+void CompareRow(const uint8_t* old_buffer,
+                const uint8_t* new_buffer,
+                const int left,
+                const int right,
+                const int top,
+                const int bottom,
+                const int stride,
+                DesktopRegion* const output) {
+  const int block_x_offset = kBlockSize * DesktopFrame::kBytesPerPixel;
+  const int width = right - left;
+  const int height = bottom - top;
+  const int block_count = (width - 1) / kBlockSize;
+  const int last_block_width = width - block_count * kBlockSize;
+  RTC_DCHECK(last_block_width <= kBlockSize && last_block_width > 0);
+
+  // The first block-column in a continuous dirty area in current block-row.
+  int first_dirty_x_block = -1;
+
+  // We always need to add dirty area into |output| in the last block, so handle
+  // it separatedly.
+  for (int x = 0; x < block_count; x++) {
+    if (BlockDifference(old_buffer, new_buffer, height, stride)) {
+      if (first_dirty_x_block == -1) {
+        // This is the first dirty block in a continuous dirty area.
+        first_dirty_x_block = x;
+      }
+    } else if (first_dirty_x_block != -1) {
+      // The block on the left is the last dirty block in a continuous
+      // dirty area.
+      output->AddRect(DesktopRect::MakeLTRB(
+          first_dirty_x_block * kBlockSize + left, top,
+          x * kBlockSize + left, bottom));
+      first_dirty_x_block = -1;
+    }
+    old_buffer += block_x_offset;
+    new_buffer += block_x_offset;
+  }
+
+  bool last_block_diff;
+  if (last_block_width < kBlockSize) {
+    // The last one is a partial vector.
+    last_block_diff = PartialBlockDifference(
+        old_buffer, new_buffer, last_block_width, height, stride);
+  } else {
+    last_block_diff =
+        BlockDifference(old_buffer, new_buffer, height, stride);
+  }
+  if (last_block_diff) {
+    if (first_dirty_x_block == -1) {
+      first_dirty_x_block = block_count;
+    }
+    output->AddRect(
+        DesktopRect::MakeLTRB(first_dirty_x_block * kBlockSize + left,
+                              top, right, bottom));
+  } else if (first_dirty_x_block != -1) {
+    output->AddRect(DesktopRect::MakeLTRB(
+        first_dirty_x_block * kBlockSize + left, top,
+        block_count * kBlockSize + left, bottom));
+  }
+}
+
+// Compares |rect| area in |old_frame| and |new_frame|, and outputs dirty
+// regions into |output|.
+void CompareFrames(const DesktopFrame& old_frame,
+                   const DesktopFrame& new_frame,
+                   DesktopRect rect,
+                   DesktopRegion* const output) {
+  RTC_DCHECK(old_frame.size().equals(new_frame.size()));
+  RTC_DCHECK_EQ(old_frame.stride(), new_frame.stride());
+  rect.IntersectWith(DesktopRect::MakeSize(old_frame.size()));
+
+  const int y_block_count = (rect.height() - 1) / kBlockSize;
+  const int last_y_block_height = rect.height() - y_block_count * kBlockSize;
+  // Offset from the start of one block-row to the next.
+  const int block_y_stride = old_frame.stride() * kBlockSize;
+  const uint8_t* prev_block_row_start =
+      old_frame.GetFrameDataAtPos(rect.top_left());
+  const uint8_t* curr_block_row_start =
+      new_frame.GetFrameDataAtPos(rect.top_left());
+
+  int top = rect.top();
+  // The last row may have a different height, so we handle it separately.
+  for (int y = 0; y < y_block_count; y++) {
+    CompareRow(prev_block_row_start, curr_block_row_start, rect.left(),
+               rect.right(), top, top + kBlockSize,
+               old_frame.stride(), output);
+    top += kBlockSize;
+    prev_block_row_start += block_y_stride;
+    curr_block_row_start += block_y_stride;
+  }
+  CompareRow(prev_block_row_start, curr_block_row_start, rect.left(),
+             rect.right(), top, top + last_y_block_height,
+             old_frame.stride(), output);
+}
+
+}  // namespace
+
+ScreenCapturerDifferWrapper::ScreenCapturerDifferWrapper(
+    std::unique_ptr<ScreenCapturer> base_capturer)
+    : base_capturer_(std::move(base_capturer)) {
+  RTC_DCHECK(base_capturer_);
+}
+
+ScreenCapturerDifferWrapper::~ScreenCapturerDifferWrapper() {}
+
+void ScreenCapturerDifferWrapper::Start(DesktopCapturer::Callback* callback) {
+  callback_ = callback;
+  base_capturer_->Start(this);
+}
+
+void ScreenCapturerDifferWrapper::SetSharedMemoryFactory(
+    std::unique_ptr<SharedMemoryFactory> shared_memory_factory) {
+  base_capturer_->SetSharedMemoryFactory(std::move(shared_memory_factory));
+}
+
+void ScreenCapturerDifferWrapper::Capture(const DesktopRegion& region) {
+  base_capturer_->Capture(region);
+}
+
+bool ScreenCapturerDifferWrapper::GetScreenList(ScreenList* screens) {
+  return base_capturer_->GetScreenList(screens);
+}
+
+bool ScreenCapturerDifferWrapper::SelectScreen(ScreenId id) {
+  return base_capturer_->SelectScreen(id);
+}
+
+void ScreenCapturerDifferWrapper::OnCaptureResult(
+    Result result,
+    std::unique_ptr<DesktopFrame> input_frame) {
+  int64_t start_time_nanos = rtc::TimeNanos();
+  if (!input_frame) {
+    callback_->OnCaptureResult(result, nullptr);
+    return;
+  }
+  RTC_DCHECK(result == Result::SUCCESS);
+
+  std::unique_ptr<SharedDesktopFrame> frame =
+      SharedDesktopFrame::Wrap(std::move(input_frame));
+  if (last_frame_ &&
+      (last_frame_->size().width() != frame->size().width() ||
+       last_frame_->size().height() != frame->size().height() ||
+       last_frame_->stride() != frame->stride())) {
+    last_frame_.reset();
+  }
+
+  if (last_frame_) {
+    DesktopRegion hints;
+    hints.Swap(frame->GetUnderlyingFrame()->mutable_updated_region());
+    for (DesktopRegion::Iterator it(hints); !it.IsAtEnd(); it.Advance()) {
+      CompareFrames(*last_frame_, *frame, it.rect(),
+                    frame->mutable_updated_region());
+    }
+  } else {
+    frame->mutable_updated_region()->SetRect(
+        DesktopRect::MakeSize(frame->size()));
+  }
+  last_frame_ = frame->Share();
+
+  frame->set_capture_time_ms(frame->GetUnderlyingFrame()->capture_time_ms() +
+                             (rtc::TimeNanos() - start_time_nanos) /
+                                 rtc::kNumNanosecsPerMillisec);
+  callback_->OnCaptureResult(result, std::move(frame));
+}
+
+}  // namespace webrtc