Re: Shadow problems on RE2 with IRISGL
Angus Dorbie (dorbie++at++sgi.com)
Tue, 05 May 1998 10:18:25 -0700
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, and more zbuffer precision if you
have i and a smaller displacement in r on the texture matrix.
See www.dorbie.com for my projective depth map shadow
adventures in th 'UAV' section.
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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on Mon Aug 10 1998 - 17:57:22 PDT