Bug 1270954 - When Win10 Anniversary Update APIs are available, enable automatic scaling of the non-client area when a window is on a secondary display with different DPI. r=emk, a=kwierso

--HG--
extra : amend_source : 7eabc4033b2455549c74936c373aeea07a473cef

widget/windows/WinUtils.cpp

@@ -487,6 +487,17 @@ WinUtils::Initialize()
   }
 }
 
+// static
+LRESULT WINAPI
+WinUtils::NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
+                                            WPARAM wParam, LPARAM lParam)
+{
+  if (msg == WM_NCCREATE && sEnableNonClientDpiScaling) {
+    sEnableNonClientDpiScaling(hWnd);
+  }
+  return ::DefWindowProcW(hWnd, msg, wParam, lParam);
+}
+
 // static
 void
 WinUtils::LogW(const wchar_t *fmt, ...)

widget/windows/WinUtils.h

@@ -174,6 +174,12 @@ public:
     DPI_AWARENESS_CONTEXT mPrevContext;
   };
 
+  // Wrapper for DefWindowProc that will enable non-client dpi scaling on the
+  // window during creation.
+  static LRESULT WINAPI
+  NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
+                                    WPARAM wParam, LPARAM lParam);
+
   /**
    * Get the system's default logical-to-physical DPI scaling factor,
    * which is based on the primary display. Note however that unlike

widget/windows/nsWindow.cpp

@@ -799,7 +799,7 @@ nsWindow::RegisterWindowClass(const wchar_t* aClassName,
   }
 
   wc.style         = CS_DBLCLKS | aExtraStyle;
-  wc.lpfnWndProc   = ::DefWindowProcW;
+  wc.lpfnWndProc   = WinUtils::NonClientDpiScalingDefWindowProcW;
   wc.cbClsExtra    = 0;
   wc.cbWndExtra    = 0;
   wc.hInstance     = nsToolkit::mDllInstance;