Re: [Algorithms] portal engines in outdoor environments

[Brian P. <br...@va...>]

Bernd Kreimeier wrote:
> 
> John Ratcliff writes:
>  > If you had the ability to ask questions of the zbuffer like "is this
>  > bounding volume visable?" (yes/no) in an extremely high speed fashion then
>  > you could do gross culling on an object by object basis using the zbuffer
>  > contents during the render stage.  Some of the old spanbuffer software
>  > renderers could do this, because it was a fairly cheap question to ask,
>  > especially relative to the time it took to software render an entire 3d
>  > model.
>  >
>  > But, since you can't ask zbuffers these kinds of questions it's a moot
>  > point.
> 
> http://oss.sgi.com/projects/ogl-sample/registry/HP/occlusion_test.txt
> 
> Brian Paul mentioned that he is going to add that to Mesa
> using the Glide GR_STATS counters. I have no idea which Win32
> drivers offer this extension.


The actual value of this extension is questionable.  The problem
is you have to do a read-back from the hardware to get the
occlusion test result and the hit from doing that can be substantial.

The extension works now (in a development branch of the 3dfx DRI
driver) but I haven't done any performance analysis.

-Brian