Several minor improvements of DirectX capturer

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc

Index: webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
diff --git a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
index 0276f6b94155065c3b9898789332c4da8ba63165..edf054d6efcc55026bbcfc6ca3dcffa40d5bdd4e 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
+++ b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.cc
@@ -11,6 +11,7 @@
 #include "webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h"
 
 #include <windows.h>
+#include <ShellScalingApi.h>
 
 #include <algorithm>
 
@@ -18,12 +19,29 @@
 
 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();
@@ -119,6 +137,14 @@ 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;
@@ -142,13 +168,6 @@ bool DxgiDuplicatorController::DoInitialize() {
     }
   }
 
-  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;
 }