Several minor improvements of DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.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/win/dxgi_duplicator_controller.h"
 
 #include <windows.h>
+#include <ShellScalingApi.h>
 
 #include <algorithm>
 
 #include "webrtc/base/checks.h"
 
 namespace webrtc {
 
+namespace {
+
+// A one-time initialization to disable Windows from scaling the resolution.
+struct DpiAwareness {
+  DpiAwareness();
+};
+
+DpiAwareness::DpiAwareness() {
+  // for Windows 8 or earlier
+  SetProcessDPIAware();
+  // for Windows 8.1 or later
+  SetProcessDpiAwareness(PROCESS_PER_MONITOR_DPI_AWARE);

[Jamie, 2016/09/16 21:54:10]

According to
https://msdn.microsoft.com/en-us/library/windows/desktop/ms633543(v=vs.85).aspx,
use of these functions is discouraged; we should set this in the manifest
instead. If that's not possible for some reason, then I think this should be
done explicitly somewhere early in main(), rather than as a side-effect of
creating a DxgiDuplicatorController. WDYT?

[Hzj_jie, 2016/09/16 22:37:53]

I have just talked with Joe, the manifest has already embedded in our binary.
And I believe Chrome is also enabled DPI awareness, so I do not need to do it
here.
What I really need to do is to embed the same manifest in
it2me_standalone_host_main.

+}
+
+}  // namespace
+
 DxgiDuplicatorController::Context::~Context() {
   DxgiDuplicatorController::Instance()->Unregister(this);
 }
 
 // static
 DxgiDuplicatorController* DxgiDuplicatorController::Instance() {
+  const static DpiAwareness one_time_initialization;
   // The static instance won't be deleted to ensure it can be used by other
   // threads even during program exiting.
   static DxgiDuplicatorController* instance = new DxgiDuplicatorController();
   return instance;
 }
 
 DxgiDuplicatorController::DxgiDuplicatorController() = default;
 
 DxgiDuplicatorController::~DxgiDuplicatorController() {
   rtc::CritScope lock(&lock_);
@@ skipping 75 matching lines @@
     return true;
   }
   Deinitialize();
   return false;
 }
 
 bool DxgiDuplicatorController::DoInitialize() {
   RTC_DCHECK(desktop_rect_.is_empty());
   RTC_DCHECK(duplicators_.empty());
 
+  // DPI is used by DxgiOutputDuplicator, so initialize it first.
+  HDC hdc = GetDC(nullptr);
+  // Use old DPI value if failed.
+  if (hdc) {
+    dpi_.set(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
+    ReleaseDC(nullptr, hdc);
+  }
+
   std::vector<D3dDevice> devices = D3dDevice::EnumDevices();
   if (devices.empty()) {
     return false;
   }
 
   for (size_t i = 0; i < devices.size(); i++) {
     duplicators_.emplace_back(devices[i]);
     if (!duplicators_.back().Initialize()) {
       return false;
     }
     if (desktop_rect_.is_empty()) {
       desktop_rect_ = duplicators_.back().desktop_rect();
     } else {
       const DesktopRect& left = desktop_rect_;
       const DesktopRect& right = duplicators_.back().desktop_rect();
       desktop_rect_ =
           DesktopRect::MakeLTRB(std::min(left.left(), right.left()),
                                 std::min(left.top(), right.top()),
                                 std::max(left.right(), right.right()),
                                 std::max(left.bottom(), right.bottom()));
     }
   }
 
-  HDC hdc = GetDC(nullptr);
-  // Use old DPI value if failed.
-  if (hdc) {
-    dpi_.set(GetDeviceCaps(hdc, LOGPIXELSX), GetDeviceCaps(hdc, LOGPIXELSY));
-    ReleaseDC(nullptr, hdc);
-  }
-
   identity_++;
   return true;
 }
 
 void DxgiDuplicatorController::Deinitialize() {
   desktop_rect_ = DesktopRect();
   duplicators_.clear();
 }
 
 bool DxgiDuplicatorController::ContextExpired(
@@ skipping 63 matching lines @@
       Deinitialize();
       return false;
     }
   }
   // id >= ScreenCount(). This is a user error, so we do not need to
   // deinitialize.
   return false;
 }
 
 }  // namespace webrtc