I agree that the non-uniform scaling probably has a lot to do with it,
because I noticed that the effect got worse the more I scaled the
geometry. For instance, the cylinders that still looked like cylinders
had no problem, but those that were scaled down into disks a few pixels
thick had serious problems.
Unfortunately, I have to scale everything to the proper size in the
application I'm writing. At least setting the specular color to black
and the shininess to 1 removes the specular color artifact for now.

Florin, did you scale your shapes up or down? That is, did you make them
appear bigger or smaller than the original geometry size? In this
application the shapes are always being scaled down. The original
cylinder shape is much larger and longer in proportion than any of the
cylinders in this application. I wonder whether scaling a shape down
makes the specular color much brighter while scaling a shape up makes
the colors much darker...

Anyways, maybe I'll have fewer problems if I start with a VRML shape
file that is closer to the eventual size of the shape that will be
displayed, so that the scaling is less extreme. I'll try that next.

Monica

Florin Herinean wrote:

"All of the cylinders share the same geometry and appearance, and each are
scaled down using a transform group to the wanted size."

That was *my* problem. The scaling was non-uniform, meaning that different
scales were applied in different directions. Since the shared geometry
contained also the computed normals, the later ones were affected by the
non-uniform scaling, resulting in a strage effect, opposite to the one
described by Monica, some of the surfaces were always dark, regardless of
the position of the light, just if like the specular colour was reduced to
10% of the intensity.

So I think that Monica may be running into similar problems.



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