[cairo] problem with BitBlt

[Michael Gurnett]

I have the following bit of code

bckgrnd = new Graphics::TBitmap;
   bckgrnd->Width = ClientWidth;
   bckgrnd->Height = ClientHeight;
 HDC hdc;
 hdc=bckgrnd->Canvas->Handle;
  cairo_pattern_t *pat;
 cairo_surface_t *surface;

 surface = cairo_win32_surface_create (hdc);
 background = cairo_create (surface);

....


The idea is the to draw on the background surface and BitBlt it on my paint routine. However, with the code above it appears that the initial drawing space is filled white (guessing rgba are all 1). Is there a way to get the initial drawing region to be transparant. 

Thanks

Michael
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