Re: Shadow problems on RE2 with IRISGL

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Angus Dorbie (dorbie++at++sgi.com)
Thu, 11 Jun 1998 09:31:28 -0700

Mario Veraart wrote:
>

> If I increase the near plane close to the scene the resulting shadow
> is much better. The shadow edge is still not smooth at the back side
> of the cubes. It looks like a z-resolution problem.
>
> > and more zbuffer precision if you
> is this done by getting a visual with more z-buffer bits?

Yes, but you should also try and minimize the distance between
near and far clip in the projective channel.

>
> > have i and a smaller displacement in r on the texture matrix.
> I use the pfLightSource for the shadows. How do I set a smaller
> displacement for r?
>

>From the pfLightSource man page:

     For best results, SHADOW lighting requires that the scene be
slightly
     displaced in depth when rendering the shadow map. This reduces
artifacts
     such as "self-shadowing". The PFLS_SHADOW_DISPLACE_SCALE and
     PFLS_SHADOW_DISPLACE_OFFSET tokens to pfLightSource::setVal specify
     displacement values. The default values are respectively: for
IrisGL 1.0
     and 256.0 for OpenGL 1.0 and .0019 but experimentation is required
for
     best results (both values should be positive).

> Is there some text on how the shadow algorithm works based on IrisGL calls?
> This way I might get an impression what is going on behind the scene
> and have a clue on what the parameters might do that I can adjust.
>

www.dorbie.com explains what's going on in the UAV section, the
OpenGL and IrisGL implementations are almost exactly equivalent
and there's enough information on these pages.

Also, read the 1987 Siggraph (the one with Luxo Jr on the cover)
paper by the folks at Pixar, William Reeves et.al. on rendering
anti-aliased shadows using depth maps......my favourite paper of
all time (if you don't count the jello paper).

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


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