tangent shader rayshadow artifacts

Hi All,

I’m getting nasty shadow artifacts when I use raytraced shadows on tangent shaded materials.

All I did here is add a new material and enabled tangent (on the left), the sphere on the right simply has the default material…

No amount of UV unwrapping, OSA, Bias or anything can get rid of it…
I’m using a CVS of blender but i’ve tried in 2.45 and it produces worse artifacts
help please…
i wanna use tangent shaders and raytraced soft shadows in a project but cant with these uglies :frowning:

[xp sp2, python 2.5, intel quad 2.6, geeforce8800ultra]

I see the same behavior here.
It seems the problem comes from raytraced shadows.
I modified my spot to use buffered shadows instead of raytraced and the artifacts (almost) go away.

you’d be correct there oxben… it is only ray shadows that cause this, so for now i am using buffer spots. but i’d much rather use the new raytraced soft shadows in the cvs cuz they prettier :smiley:

i wonder if it’s an inherent blender “bug” or if there is some way to fix it…

Oh what i do to avoid this is use a few raytrace shadow lights… By taking out the ray tracing of a few lights… And just let like a few select lights do the shadow tracing. and just let the others luminate but not cast shadows.

That is a fundamental problem in rendering. It’s not noticeable on a lot of materials because the surface light is at zero before it reaches that boundary. On materials that are light even on polys facing away from the light, you cannot properly render self-shadows.

Under the Shaders tab, you can turn off “Shadow” that way it can still cast shadows, but no shadows will show up on that material - unfortunately not from other objects either.

To get the shadows to look completely right will require multiple passes and compositing.

Yep, the tangent shader is really not physically correct - you might want to try turning the spec down and turn on ray reflections - since you already have tangent shading switched on, if you pull down the gloss and make the reflection a bit blurry, you’ll get anisotropic reflections, which is what the tangent shading is trying to reproduce.