Xgl and direct rendering

[Allen Akin]

On Wed, Mar 01, 2006 at 05:24:25PM +0100, Matthias Hopf wrote:
| OpenGL overlay is something similar for OpenGL, and it hurts my brain
| when I think of it. It is something used for user interfaces in ancient
| OpenGL applications...

It was (and still is, in some apps) used for menus and cursors.  But
it's also used for more complex things like non-destructive annotations
on "expensive" imagery (e.g. high-res satellite images with dynamic
mapping overlays, or ultrasound systems), and for stand-ins that can be
manipulated interactively when the fully-rendered objects they represent
are too complex for that.

Overlay is cheap to implement and extremely effective.  Some large apps
are heavily dependent on it, so it's not going to vanish anytime soon.
Eventually it can be replaced by more general mechanisms like
compositing, when all systems of interest have large video memories and
GPUs that can composite 1GPix/sec or better.  When this will happen in
each of the various market segments served by XOrg is open to debate.

Allen