windows窗口的透明边缘

  if (rtc::rtc_win::GetVersion() >= rtc::rtc_win::Version::VERSION_WIN8 ||
      is_maximized) {
    // Only apply this cropping to windows with a resize border (otherwise,
    // it'd clip the edges of captured pop-up windows without this border).
    LONG style = GetWindowLong(window, GWL_STYLE);
    if (style & WS_THICKFRAME || style & DS_MODALFRAME) {
      int width = GetSystemMetrics(SM_CXSIZEFRAME);
      int bottom_height = GetSystemMetrics(SM_CYSIZEFRAME);
      const int visible_border_height = GetSystemMetrics(SM_CYBORDER);
      int top_height = visible_border_height;

      // If requested, avoid cropping the visible window border. This is used
      // for pop-up windows to include their border, but not for the outermost
      // window (where a partially-transparent border may expose the
      // background a bit).
      if (avoid_cropping_border) {
        width = std::max(0, width - GetSystemMetrics(SM_CXBORDER));
        bottom_height = std::max(0, bottom_height - visible_border_height);
        top_height = 0;
      }
      cropped_rect->Extend(-width, -top_height, -width, -bottom_height);
    }
  }

    RECT frame;
    auto hr = DwmGetWindowAttribute(window, DWMWA_EXTENDED_FRAME_BOUNDS, &frame,
                                    sizeof(RECT));
    if (hr == S_OK) {
      // it/s means the window has no transparent borders;
      if (frame.left == window_rect.left()) {
        return true;
      }
    }