Bug 890156 - patch 2 - Expose DevicePixelsPerDesktopPixel through nsIBaseWindow and its implementations. r=emk

docshell/base/nsDocShell.cpp

@@ -5782,6 +5782,23 @@ nsDocShell::GetUnscaledDevicePixelsPerCSSPixel(double* aScale)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDocShell::GetDevicePixelsPerDesktopPixel(double* aScale)
+{
+  if (mParentWidget) {
+    *aScale = mParentWidget->GetDesktopToDeviceScale().scale;
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIBaseWindow> ownerWindow(do_QueryInterface(mTreeOwner));
+  if (ownerWindow) {
+    return ownerWindow->GetDevicePixelsPerDesktopPixel(aScale);
+  }
+
+  *aScale = 1.0;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsDocShell::SetPosition(int32_t aX, int32_t aY)
 {

embedding/browser/nsDocShellTreeOwner.cpp

@@ -560,6 +560,17 @@ nsDocShellTreeOwner::GetUnscaledDevicePixelsPerCSSPixel(double* aScale)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDocShellTreeOwner::GetDevicePixelsPerDesktopPixel(double* aScale)
+{
+  if (mWebBrowser) {
+    return mWebBrowser->GetDevicePixelsPerDesktopPixel(aScale);
+  }
+
+  *aScale = 1.0;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsDocShellTreeOwner::SetPosition(int32_t aX, int32_t aY)
 {

embedding/browser/nsWebBrowser.cpp

@@ -1294,6 +1294,14 @@ nsWebBrowser::GetUnscaledDevicePixelsPerCSSPixel(double* aScale)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsWebBrowser::GetDevicePixelsPerDesktopPixel(double* aScale)
+{
+  *aScale = mParentWidget ? mParentWidget->GetDesktopToDeviceScale().scale
+                          : 1.0;
+  return NS_OK;
+}
+
 NS_IMETHODIMP
 nsWebBrowser::SetPosition(int32_t aX, int32_t aY)
 {

widget/nsIBaseWindow.idl

@@ -21,7 +21,7 @@ typedef voidPtr nativeWindow;
  * but rather a common set that nearly all windowed objects support.    
  */
 
-[scriptable, uuid(9DA319F3-EEE6-4504-81A5-6A19CF6215BF)]
+[scriptable, uuid(ca635529-a977-4552-9b8a-66187e54d882)]
 interface nsIBaseWindow : nsISupports
 {
 	/*
@@ -192,6 +192,20 @@ interface nsIBaseWindow : nsISupports
 	*/
 	readonly attribute double unscaledDevicePixelsPerCSSPixel;
 
+	/*
+	The number of device pixels per display pixel on this window's current
+	screen. (The meaning of "display pixel" varies across OS environments;
+	it is the pixel units used by the desktop environment to manage screen
+	real estate and window positioning, which may correspond to (per-screen)
+	device pixels, or may be a virtual coordinate space that covers a multi-
+	monitor, mixed-dpi desktop space.)
+	This is the value returned by DevicePixelsPerDesktopPixel() of the underlying
+	widget.
+	Note that this may change if the window is moved between screens with
+	differing resolutions.
+	*/
+	readonly attribute double devicePixelsPerDesktopPixel;
+
 	/**
 	* Give the window focus.
 	*/

xpfe/appshell/nsChromeTreeOwner.cpp

@@ -382,6 +382,12 @@ NS_IMETHODIMP nsChromeTreeOwner::GetUnscaledDevicePixelsPerCSSPixel(double *aSca
    return mXULWindow->GetUnscaledDevicePixelsPerCSSPixel(aScale);
 }
 
+NS_IMETHODIMP nsChromeTreeOwner::GetDevicePixelsPerDesktopPixel(double *aScale)
+{
+   NS_ENSURE_STATE(mXULWindow);
+   return mXULWindow->GetDevicePixelsPerDesktopPixel(aScale);
+}
+
 NS_IMETHODIMP nsChromeTreeOwner::SetPosition(int32_t x, int32_t y)
 {
    NS_ENSURE_STATE(mXULWindow);

xpfe/appshell/nsContentTreeOwner.cpp

@@ -621,6 +621,12 @@ NS_IMETHODIMP nsContentTreeOwner::GetUnscaledDevicePixelsPerCSSPixel(double* aSc
    return mXULWindow->GetUnscaledDevicePixelsPerCSSPixel(aScale);
 }
 
+NS_IMETHODIMP nsContentTreeOwner::GetDevicePixelsPerDesktopPixel(double* aScale)
+{
+   NS_ENSURE_STATE(mXULWindow);
+   return mXULWindow->GetDevicePixelsPerDesktopPixel(aScale);
+}
+
 NS_IMETHODIMP nsContentTreeOwner::SetPosition(int32_t aX, int32_t aY)
 {
    NS_ENSURE_STATE(mXULWindow);

xpfe/appshell/nsXULWindow.cpp

@@ -557,6 +557,12 @@ NS_IMETHODIMP nsXULWindow::Destroy()
   return NS_OK;
 }
 
+NS_IMETHODIMP nsXULWindow::GetDevicePixelsPerDesktopPixel(double *aScale)
+{
+  *aScale = mWindow ? mWindow->GetDesktopToDeviceScale().scale : 1.0;
+  return NS_OK;
+}
+
 NS_IMETHODIMP nsXULWindow::GetUnscaledDevicePixelsPerCSSPixel(double *aScale)
 {
   *aScale = mWindow ? mWindow->GetDefaultScale().scale : 1.0;