Bug 629866. Part 1: Create a DIB for a Win32 surface that's similar to a parent surface with alpha, even if the parent surface doesn't have a DIB. r=jrmuizel

--HG--
extra : rebase_source : 95240f4f4f2d7f7fa453a1eb3ca020c1839160c7

gfx/thebes/gfxWindowsSurface.cpp

@@ -130,6 +130,43 @@ gfxWindowsSurface::InitWithDC(PRUint32 flags)
     }
 }
 
+already_AddRefed<gfxASurface>
+gfxWindowsSurface::CreateSimilarSurface(gfxContentType aContent,
+                                        const gfxIntSize& aSize)
+{
+    if (!mSurface || !mSurfaceValid) {
+        return nsnull;
+    }
+
+    cairo_surface_t *surface;
+    if (GetContentType() == CONTENT_COLOR_ALPHA) {
+        // When creating a similar surface to a transparent surface, ensure
+        // the new surface uses a DIB. cairo_surface_create_similar won't
+        // use  a DIB for a CONTENT_COLOR surface if this surface doesn't
+        // have a DIB (e.g. if we're a transparent window surface). But
+        // we need a DIB to perform well if the new surface is composited into
+        // a surface that's the result of create_similar(CONTENT_COLOR_ALPHA)
+        // (e.g. a backbuffer for the window) --- that new surface *would*
+        // have a DIB.
+        surface =
+          cairo_win32_surface_create_with_dib(cairo_format_t(gfxASurface::FormatFromContent(aContent)),
+                                              aSize.width, aSize.height);
+    } else {
+        surface =
+          cairo_surface_create_similar(mSurface, cairo_content_t(aContent),
+                                       aSize.width, aSize.height);
+    }
+
+    if (cairo_surface_status(surface)) {
+        cairo_surface_destroy(surface);
+        return nsnull;
+    }
+
+    nsRefPtr<gfxASurface> result = Wrap(surface);
+    cairo_surface_destroy(surface);
+    return result.forget();
+}
+
 gfxWindowsSurface::~gfxWindowsSurface()
 {
     if (mOwnsDC) {

gfx/thebes/gfxWindowsSurface.h

@@ -67,6 +67,9 @@ public:
 
     gfxWindowsSurface(cairo_surface_t *csurf);
 
+    virtual already_AddRefed<gfxASurface> CreateSimilarSurface(gfxContentType aType,
+                                                               const gfxIntSize& aSize);
+
     void InitWithDC(PRUint32 flags);
 
     virtual ~gfxWindowsSurface();