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I've tried Vista and XP Professional - Light goes through the bottom edges

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Steve:
The reason the shadow bias has to be set this high is because without it the flat faces polygons used in Anim8or could not be made to look smooth.  Smoothing out the normals introduces an inconsistency in the geometry.  The physical surface (perfectly flat faces) and the apparent surface (smoothly lit curved shapes) are not in agreement.  Ray traced shadows follow the true geometry and would make very ugly dark jagged edges where a curved surface goes from light to shadow.  Adding a disproportionally large shadow bias reduces the probelm so that it's seldom visible.

Here's an example of a default sphere and an infinite light.

To fix it simply increase the number of divisions used for the sphere.

Tanzim:
Hey Steve, is the huge shadow bias problem only something Anim8or has, or do all CG software have this problem?

onespirit5777:
Thank you - I'll see what I can figure out and find a way around this if possible.

Steve:
It's fundamental to polygonal modeling and raytracing.  The way to get around it is to tesselate your model into more, smaller faces in the areas where the true geometrical normal differs more from then interpolated "smooth" normal.  The example I show above is a sphere with the default 8x12 faces.  The geometry is flat on each face but the smooth lighting tries to hide this.  The dark artifacts are in a geometric shadow but the interpolated (smooth) normal says it should be lit.  Increasing the shadow bias will make this go away but that would cause problems like onespirit5777 has to get much worse.  If you give the wall thickness it should help.

Note: this problem is also in the scanline shader.  But because the view point is known I can be a lot smarter about hiding it.  This is tricky code to write though.  Getting all these values right for the scanline renderer delayed it's release by well over 3 months and made my first attempt at a ray tracer useless (only about a year of coding thrown away, no big deal :-)

onespirit5777:
Ouch! That bites - What I haven't tried is make each wall by it's self but using a cube to set the depth. That should work and thanks again for the info. It really helps to understand certain things as it will help me be a better 3d artist. I still have a long way to go, but I'll be there some day if I stick to it.

This program is so easy to use and so powerful in its' simplicity. Truespace isn't too bad, but this program has spoiled me and I don't like to use the others because of you. With just a few simple clicks of the mouse and it's done. You just can't beat that!!!

They hate you - don't they. HA HA HA HA!

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