[cairo] how to use alpha blending by cairo?

[Kristian Høgsberg]

On 6/27/06, lao wb <laowenbo at gmail.com> wrote:
> Hi
>    I am using GTK+ to do with my application. I have a bitmap without alpha
> channel as my background, another bitmap with alpha channel to show above
> through to see the background. At first, I tried to use gdk to do this,
> still not succeed yet, always  show only the last one gdk_draw_pixbuf
> invokes in the expose handler.

To do this with cairo, you can say something like:

  cr = gdk_cairo_create (widget->window);
  gdk_cairo_set_source_pixbuf (cr, pixbuf, 0, 0);
  cairo_paint (cr);
  cairo_destroy (cr);

But I suspect the problem is you're loading an xpm file to a drawable
and converting that to a pixbuf.  Consider storing the overlay image
as a PNG file and load it using gdk_pixbuf_new_from_file().

cheers,
Kristian