[Xorg] XComposite, XDamage Extension with Xvideo or GL

Alan Cox alan at lxorguk.ukuu.org.uk
Sat Aug 7 08:32:58 PDT 2004

On Gwe, 2004-08-06 at 18:45, Keith Packard wrote:
> Around 19 o'clock on Aug 6, "Amir Bukhari" wrote:
> > Redirect OpenGL application to backing store pixmap does not work with
> > Composite Extension (in Manual Mode) (Xserver always draw).
> Correct.  Fixing GLX to draw to off-screen memory will require additional 
> work.

Not a huge amount on the GL side. Generally the GL applications in
direct mode are already drawing off screen anyway and then blitting to
the front display. A redirected OpenGL window would mean allocating
another back buffer somewhere (probably on the X side since only X can
deal with the "out of memory" failure sequence) and changing GL_FRONT to
use it if neccessary.

I suspect (GL hackers correct me) that it could even be deferred to the
point the app uses GL_FRONT.

Fixing X to know when and how to composite and do damage with it is the
fun side.

> For simple decoration and animation hacks, the overlays will "work", but 
> for more sophisticated manipulation, the drivers need to be modified to 
> use the 3D texturing engine to convert the YUV image to RGB data in the 

Most TV capture cards already can do RGB capture modes in 15, 16, 24 and
32bit, as well as a 240 colour 8bit palette (which might be interesting
for textures). 

Other question I have on Damage/Composite - how does it interact with


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