Re: Shadow problems on RE2 with IRISGL
Mario Veraart (rioj7++at++fel.tno.nl)
Thu, 11 Jun 1998 15:24:30 +0200 (MET DST)
Angus Dorbie wrote:
>
> Mario Veraart wrote:
> >
> > Hello pfUsers,
> >
> > I try to get shadows with Iris Performer 2.0 on an Onyx Re2 with
> > IRISGL.
> >
> > I have used shadows.c as a start but has found that there are a few
> > problems. I have made a terrain with a couple of cubes on it.
> >
> > You can find this text with a couple of pictures at the following URL
> >
> > http://vtd.fel.tno.nl/~fveraart/shadow/problem.html
> >
> > In the following pictures the small green cube is the position of the
> > lightsource.
> > On the terrrain are a few large red cubes with a small green cube next
> > to it. The large terrain square is 80x80 meters and I have used a shadow map
> > size of 512 pixels.
> >
> > 1)
> > For a setting off the light I see that the small green cubes don't
> > cast any shadow.
> >
> > 2)
> > Depending on the distance of the large cube to the light the geometry
> > that is in shadow
> > is further away from the object. All of the small green cubes should
> > be in shadow.
> >
> > 3)
> > The objects that are in shadow are not lit with the ambient lighting
> > term. They are drawn black.
> >
> > 4)
> > The back side of the cubes are not in shadow.
> >
> > If anyone can help me solve these problems?
>
>
> The problem is the relative positions of the depth image and
> projected r coordinate.
>
> An offset is required to avoid what ammounts to resolution
> dependent z fighting in the projected light space. Your offset
> is grossly large. You should try a shadow map frustum with near
> and far clip planes closer,
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?
> 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?
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.
Mario
>
> See www.dorbie.com for my projective depth map shadow
> adventures in th 'UAV' section.
>
> Cheers,Angus.
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on Mon Aug 10 1998 - 17:57:32 PDT