Re: Pixmap question

["Timothy M. Shead" <tshead k-3d com>]

Paul Barton-Davis wrote:

> > I need to develop Display window which can a number of coloured layers.
> > ( the various layers used in IC design).
> >
> > Where each layer overlaps another, I want to see the correct ANDING of
> > the colours.
> >
> > I need to be able to repaint with an odd layer removed from display.
> >
> > I can see that if I have multiple pixmaps (one for each layer to be
> > displayed), but just sending the desired pixmaps to the screen I should 
> > be able to achieve this.
>
>
> 1) I believe that no part of X (or GDK) current supports such
>    things. This generally goes by the name "alpha channel", and X
>    doesn't support it. A pixel in a Drawable is either completely
>    transparent or completely opaque (with its own particular color).

The X Render extension should support these types of operations (with 
hardware support, when available). However, you're talking about 
bleeding edge (it only just appeared in XFree86 4.0.2) X calls - no 
support from GTK+, etc. Check out the release notes and link at 
http://www.xfree86.org

Regards,
Tim