Re: Pixmaps & transparency

[Tristan Van Berkom <tvb gnome org>]

Peter Zhelezniakov wrote:
> Hello GTK developers,
>
> I have an external library that draws possibly transparent/translucent 
> images to a GdkDrawable only. I want to capture these images in a 
> pixbuf, but when i try to copy pixels from the drawable (a pixmap), all 
> information about transparency is lost. So far i can think of two ways 
> to solve this:
>
> - Draw every image to two pixmaps with different backgrounds, then 
> compare results
> - Extend GdkPixmap somehow (isn't Gdk an object system, after all?) and 
> override painting methods so that they keep track of transparency. I'm 
> not sure this is feasible however.
>
> Could anyone please comment on this, or come up with better ideas?

    If your external library uses gdk_draw_pixbuf () to draw to the
said drawables, you could hold a reference to the passed pixbuf by
overriding the GdkPixmap implementation of "->draw_pixbuf()" in your
GdkPixmap derivative, it doesn't sound elegant but if your stuck with
that functionality; it'll do the trick.

Cheers,
                                   -Tristan