Re: Clip-Mapping

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Rick Weyrauch (rweyrauch++at++camus.paradigmsim.com)
Wed, 16 Apr 1997 08:10:07 -0500

On Apr 10, 5:28pm, Jeff Brickley wrote:
> Subject: Clip-Mapping
>
> As I understand it, Clipmapping is/was available with Performer 2.1 on
> the IR level machines. What is the largest clipmap successfully used with
> geometry (no 2 triangle scenes)? What was the polygon count? What was the
> level of machine? We are finally getting started on clipmaps, but the
> results are not looking good in so far as speed. Our normal Database
> consists of two databases of 32,000 polygons in the same scene (side by
> side) and our normal imagery was one 2048x2048x1 texture on one DB and one
> 4096x4096x1 texture on the other DB and we have always been able to maintain
> 20hz. This is without clipmapping, now clipmapping one DB in a scene (the
> other removed) at 4096x4096x1, we've had to reduce the polygon count to
> support it.... Is this normal for clipmapping? We are actually trying to
> support the current Beta releases of Performer 2.2, but I have no comparison
> to what has actually been accomplished with Performer 2.1....
>
> Jeffry J. Brickley
> Lockheed Martin
> White Sands Missile Range
>-- End of excerpt from Jeff Brickley

Are you using the Performer utility library code to compute the clip-texture
center point? The pfu code traverses every clip-textured polygon to compute
the clip-texture center point. (Looking at the stats is you APP time large?)
This is fine for a 2-poly demo but does not work with more complex database.
 There are a couple of solutions. The first is to compute the clip-texture
center point by traversing a lower resolution representation of the
clip-texture models. The low resolution model does need to be added to the
sccene graph. The other option is to compute the center point by defining a
function that maps world coordinates into clip-texture coordinates.

Rick

-- 


Rick Weyrauch				voice: (972) 960-2301
Paradigm Simulation Inc.		fax:   (972) 960-2303
14900 Landmark Blvd., Suite 400		rweyrauch++at++paradigmsim.com
Dallas TX 75240				www.paradigmsim.com
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