Composite extension and 30bit TrueColor visuals...

Roland Mainz roland.mainz at
Sat Dec 4 19:37:03 PST 2004

Keith Packard wrote:
> > How will the Composite extension deal with 30bit TrueColor visuals
> > (=having 10bit per R-, G-, B-gun) ? Doesn't that mean that there are
> > only two bits left for the alpha channel ?
> You could use two bits for alpha in this visual. Alternatively, you could
> just let those windows be opaque and create 8-8-8-8 windows for
> translucent applications.
> It's also the case that Render supports external alpha channels; it's quite
> possible to create a convention for Compositing Mangers to identify the
> pixmap associated with that external alpha channel for a particular window.

It may be the better to make a seperate pixmap the default for the
composite extension. Too many applications have problems with the new
ARGB visuals so moving the alpha channel out of the line of fire (e.g.
into a seperate pixmap) may solve both problems (for 24bit visuals the
8bit alpha channel can still be in the upper 8bit of a 32bit word, just
the addressing would be seperate (e.g. accesses to RGB values go into
the first 24bit, accesses to the alpha pixmap to into the upper 8bit)).



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