diff -r 000000000000 -r 6474c204b198 widget/windows/nsScreenWin.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/windows/nsScreenWin.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,167 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsScreenWin.h"
+#include "nsCoord.h"
+#include "gfxWindowsPlatform.h"
+#include "nsIWidget.h"
+
+
+nsScreenWin :: nsScreenWin ( HMONITOR inScreen )
+  : mScreen(inScreen)
+{
+#ifdef DEBUG
+  HDC hDCScreen = ::GetDC(nullptr);
+  NS_ASSERTION(hDCScreen,"GetDC Failure");
+  NS_ASSERTION ( ::GetDeviceCaps(hDCScreen, TECHNOLOGY) == DT_RASDISPLAY, "Not a display screen");
+  ::ReleaseDC(nullptr,hDCScreen);
+#endif
+
+  // nothing else to do. I guess we could cache a bunch of information
+  // here, but we want to ask the device at runtime in case anything
+  // has changed.
+}
+
+
+nsScreenWin :: ~nsScreenWin()
+{
+  // nothing to see here.
+}
+
+
+NS_IMETHODIMP
+nsScreenWin :: GetRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
+  BOOL success = FALSE;
+  if ( mScreen ) {
+    MONITORINFO info;
+    info.cbSize = sizeof(MONITORINFO);
+    success = ::GetMonitorInfoW( mScreen, &info );
+    if ( success ) {
+      *outLeft = info.rcMonitor.left;
+      *outTop = info.rcMonitor.top;
+      *outWidth = info.rcMonitor.right - info.rcMonitor.left;
+      *outHeight = info.rcMonitor.bottom - info.rcMonitor.top;
+    }
+  }
+  if (!success) {
+     HDC hDCScreen = ::GetDC(nullptr);
+     NS_ASSERTION(hDCScreen,"GetDC Failure");
+    
+     *outTop = *outLeft = 0;
+     *outWidth = ::GetDeviceCaps(hDCScreen, HORZRES);
+     *outHeight = ::GetDeviceCaps(hDCScreen, VERTRES); 
+     
+     ::ReleaseDC(nullptr, hDCScreen);
+  }
+  return NS_OK;
+
+} // GetRect
+
+
+NS_IMETHODIMP
+nsScreenWin :: GetAvailRect(int32_t *outLeft, int32_t *outTop, int32_t *outWidth, int32_t *outHeight)
+{
+  BOOL success = FALSE;
+
+  if ( mScreen ) {
+    MONITORINFO info;
+    info.cbSize = sizeof(MONITORINFO);
+    success = ::GetMonitorInfoW( mScreen, &info );
+    if ( success ) {
+      *outLeft = info.rcWork.left;
+      *outTop = info.rcWork.top;
+      *outWidth = info.rcWork.right - info.rcWork.left;
+      *outHeight = info.rcWork.bottom - info.rcWork.top;
+    }
+  }
+  if (!success) {
+    RECT workArea;
+    ::SystemParametersInfo(SPI_GETWORKAREA, 0, &workArea, 0);
+    *outLeft = workArea.left;
+    *outTop = workArea.top;
+    *outWidth = workArea.right - workArea.left;
+    *outHeight = workArea.bottom - workArea.top;
+  }
+
+  return NS_OK;
+  
+} // GetAvailRect
+
+static double
+GetDPIScale()
+{
+  double dpiScale= nsIWidget::DefaultScaleOverride();
+  if (dpiScale <= 0.0) {
+    dpiScale = gfxWindowsPlatform::GetPlatform()->GetDPIScale(); 
+  }
+  return dpiScale;
+}
+
+NS_IMETHODIMP
+nsScreenWin::GetRectDisplayPix(int32_t *outLeft,  int32_t *outTop,
+                               int32_t *outWidth, int32_t *outHeight)
+{
+  int32_t left, top, width, height;
+  nsresult rv = GetRect(&left, &top, &width, &height);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  double scaleFactor = 1.0 / GetDPIScale();
+  *outLeft = NSToIntRound(left * scaleFactor);
+  *outTop = NSToIntRound(top * scaleFactor);
+  *outWidth = NSToIntRound(width * scaleFactor);
+  *outHeight = NSToIntRound(height * scaleFactor);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScreenWin::GetAvailRectDisplayPix(int32_t *outLeft,  int32_t *outTop,
+                                    int32_t *outWidth, int32_t *outHeight)
+{
+  int32_t left, top, width, height;
+  nsresult rv = GetAvailRect(&left, &top, &width, &height);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  double scaleFactor = 1.0 / GetDPIScale();
+  *outLeft = NSToIntRound(left * scaleFactor);
+  *outTop = NSToIntRound(top * scaleFactor);
+  *outWidth = NSToIntRound(width * scaleFactor);
+  *outHeight = NSToIntRound(height * scaleFactor);
+  return NS_OK;
+}
+
+
+NS_IMETHODIMP 
+nsScreenWin :: GetPixelDepth(int32_t *aPixelDepth)
+{
+  //XXX not sure how to get this info for multiple monitors, this might be ok...
+  HDC hDCScreen = ::GetDC(nullptr);
+  NS_ASSERTION(hDCScreen,"GetDC Failure");
+
+  int32_t depth = ::GetDeviceCaps(hDCScreen, BITSPIXEL);
+  if (depth == 32) {
+    // If a device uses 32 bits per pixel, it's still only using 8 bits
+    // per color component, which is what our callers want to know.
+    // (Some devices report 32 and some devices report 24.)
+    depth = 24;
+  }
+  *aPixelDepth = depth;
+
+  ::ReleaseDC(nullptr, hDCScreen);
+  return NS_OK;
+
+} // GetPixelDepth
+
+
+NS_IMETHODIMP 
+nsScreenWin :: GetColorDepth(int32_t *aColorDepth)
+{
+  return GetPixelDepth(aColorDepth);
+
+} // GetColorDepth
+
+