[SDL] Re: sdl GL with stencil buffer

Franck Guillaud fguillaud at mailivs.ivs.fr
Thu Apr 27 04:48:41 PDT 2000

Oliver Batchelor wrote:
> Would a two passes algorithm be twice as slow ?
> I am trying to make this quite fast for use in flying over a
> landscape type thing ...
> I have display lists for all the objects
> and to do that I would need to stop using them...

  If display list are correctly managed by the driver (cached), you can
do the
second pass at virtually no cost. The algorithm would be :

1) Calculate shadow texture
2) first Pass : render scene 
3) second pass : render scene with projected shadow texture

 However, if you first rendering is fill rate limited, the second
pass may have a non negligeable cost.

> To do the shadow and reflection I would still need stencil buffer or
> it would go there no matter what even if nothing was there wouldnt it
> ?
> so basically it would be better to do a double rendering rather than
> use the gl multi texture ARB thing's.

  I'm surprised that Voodoo 3 doesn't support multitexture.

  Did you try to run the Mesa multi-texture demo ? Which GL driver are
you using ?


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