Bug 577200. Part 2: When painting a Win32 transparent widget with GDI (Aero Glass), tell gfxWindowsSurface our HDC surface is transparent. r=roc

gfx/thebes/gfxWindowsSurface.cpp

@@ -63,7 +63,11 @@ gfxWindowsSurface::gfxWindowsSurface(HDC dc, PRUint32 flags) :
         mForPrinting = PR_TRUE;
     } else
 #endif
+    if (flags & FLAG_IS_TRANSPARENT) {
+        Init(cairo_win32_surface_create_with_alpha(mDC));
+    } else {
         Init(cairo_win32_surface_create(mDC));
+    }
 }
 
 gfxWindowsSurface::gfxWindowsSurface(const gfxIntSize& size, gfxImageFormat imageFormat) :

gfx/thebes/gfxWindowsSurface.h

@@ -49,7 +49,8 @@ class THEBES_API gfxWindowsSurface : public gfxASurface {
 public:
     enum {
         FLAG_TAKE_DC = (1 << 0),
-        FLAG_FOR_PRINTING = (1 << 1)
+        FLAG_FOR_PRINTING = (1 << 1),
+        FLAG_IS_TRANSPARENT = (1 << 2),
     };
 
     gfxWindowsSurface(HWND wnd);

widget/src/windows/nsWindowGfx.cpp

@@ -436,7 +436,9 @@ PRBool nsWindow::OnPaint(HDC aDC)
           if (!targetSurface &&
               IsRenderMode(gfxWindowsPlatform::RENDER_GDI))
           {
-            targetSurfaceWin = new gfxWindowsSurface(hDC);
+            PRUint32 flags = (mTransparencyMode == eTransparencyOpaque) ? 0 :
+                gfxWindowsSurface::FLAG_IS_TRANSPARENT;
+            targetSurfaceWin = new gfxWindowsSurface(hDC, flags);
             targetSurface = targetSurfaceWin;
           }
 #ifdef CAIRO_HAS_D2D_SURFACE