masking a window - having a window with transparent borders?

[Akos Maroy <darkeye tyrell hu>]

hi,

I'm trying to create a custom window, what would have rounded edges. to 
create this effect, I'm having transparent PNG files for the edges. 
unfortunately, drawing these with Gdk::Pixbuf::render_to_drawable() 
doesn't honor the transparent parts of the PNG.

I saw that one has to create a Gdk::Bitmap, that would be the mask for 
the window. but how would I create such a mask for the very window I'd 
like to draw? should I try to render the whole window into a pixmap 
first, somehow create the mask from that, and than apply that mask on 
the window?

what would I use to achieve this? would I use 
Pixbuf::render_pixmap_and_mask(), or something similar? if so, what 
would the alpha treshhold values mean?


Akos