Re: Destination alpha?

Around 16 o'clock on Jun 4, Mark Vojkovich wrote:

>    I think maybe fewer 32bpp hardware can do destination alpha than
> you realize.

It's not so much a matter of "doing" destination alpha than of having 
storage for any intermediate alpha values used in pixel computations.  As 
long as the frame buffer provides 4 bytes of storage for each pixel, the 
Render code can use the additional storage for destination alpha data.
Whether rendering with the destination alpha is accelerated in hardware is 
a separate issue.

Of course, for destinations which don't have storage, the application can 
create an external alpha buffer.  Render happily uses separate pixmaps to 
store alpha data.

Keith Packard        XFree86 Core Team        HP Cambridge Research Lab