[WebRTC] Implement Windows ScreenDrawer to test ScreenCapturer*

webrtc/modules/desktop_capture/screen_drawer_linux.cc

+/*
+ *  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_drawer_linux.h"
+
+#include <memory>
+
+namespace webrtc {
+
+ScreenDrawerX11::ScreenDrawerX11()
+    : ScreenDrawer(),
+      display_(SharedXDisplay::CreateDefault()),
+      screen_(DefaultScreenOfDisplay(display_->display())),
+      screen_num_(DefaultScreen(display_->display())),
+      rect_(DesktopRect::MakeWH(screen_->width, screen_->height)),
+      window_(
+          XCreateSimpleWindow(display_->display(),

[Sergey Ulanov, 2016/08/09 17:43:01]

I'd prefer moving all this initialization logic out of the initializer list.
Many of these operation may fail (e.g. test running outside of XWindow) and so
you need to check the results.

[Hzj_jie, 2016/08/11 18:42:03]

Done.

+                              RootWindow(display_->display(), screen_num_),
+                              0,
+                              0,
+                              rect_.width(),
+                              rect_.height(),
+                              0,
+                              BlackPixel(display_->display(), screen_num_),
+                              BlackPixel(display_->display(), screen_num_))) {
+  XSelectInput(display_->display(), window_, StructureNotifyMask);
+  XMapWindow(display_->display(), window_);

[Sergey Ulanov, 2016/08/09 17:43:01]

Verify that these succeed. Since this is test-only code just CHECK()'ing the
result is appropriate.

[Hzj_jie, 2016/08/11 18:42:04]

I believe the return value of these functions are not so useful. X11 uses a
different error handling mechanism. By default, it will print error message and
force quite. I have redirected the error to RTC_CHECK, so we can catch them in
the logs.

+  while (true) {
+    XEvent event;
+    XNextEvent(display_->display(), &event);
+    if (event.type == MapNotify) {
+      break;
+    }
+  }
+  XFlush(display_->display());
+  context_ = DefaultGC(display_->display(), screen_num_);
+  colormap_ = DefaultColormap(display_->display(), screen_num_);
+}
+
+ScreenDrawerX11::~ScreenDrawerX11() {
+  XUnmapWindow(display_->display(), window_);
+  XDestroyWindow(display_->display(), window_);
+}
+
+DesktopRect ScreenDrawerX11::DrawableRegion() {
+  return rect_;
+}
+
+void ScreenDrawerX11::DrawRectangle(DesktopRect rect, uint32_t rgba) {
+  const char* rgba_array = reinterpret_cast<const char*>(&rgba);
+  int r = rgba_array[0];
+  int g = rgba_array[1];
+  int b = rgba_array[2];

[Sergey Ulanov, 2016/08/09 17:43:01]

r = rgba & 0xff;
g = (rgba & 0xff00) >> 8;
b = (rgba & 0xff0000) >> 8;

This would work correctly on big-endian cpus

[Hzj_jie, 2016/08/11 18:42:04]

Good point. Done.

+  // X11 does not support Alpha.
+  XColor color;
+  color.red = r << 8;

[Sergey Ulanov, 2016/08/09 17:43:01]

r * 256 would be more readable as it makes it clearer what happens here.

[Hzj_jie, 2016/08/11 18:42:04]

Done.

+  color.green = g << 8;
+  color.blue = b << 8;
+  color.flags = DoRed | DoGreen | DoBlue;
+  XAllocColor(display_->display(), colormap_, &color);
+  XSetForeground(display_->display(), context_, color.pixel);
+  XFillRectangle(display_->display(), window_, context_, rect.left(),
+                 rect.top(), rect.width(), rect.height());
+  XFlush(display_->display());
+}
+
+// static
+std::unique_ptr<ScreenDrawer> ScreenDrawer::Create() {
+  return std::unique_ptr<ScreenDrawer>(new ScreenDrawerX11());
+}
+
+}  // namespace webrtc