[cairo] problem with BitBlt

[Michael Gurnett]

Am I right in guessing thas it is BitBlt that doesn't support alpha values, and if so is there a better alternative?

Michael
  ----- Original Message ----- 
  From: Michael Gurnett 
  To: cairo at cairographics.org 
  Sent: Sunday, August 31, 2008 2:27 AM
  Subject: [cairo] problem with BitBlt


  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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