Joachim Diepstraten wrote:
> > I may regret taking such a strong stance, but while a face normal is
> > *generally* calculated to be perpendicular to the plane formed by 3 points,
> > it is *not* mandatory. Normals and windings have nothing to do with each
> Okay that's right. But this will lead into quite false lightning
> calculation. Okay only if the normal is extremly different to the true
> surface normal
No, wrong. Lighting calcs have *nothing* to do with backface culling.
They are two completely separate operations. Culling uses the winding
information to determine the "front" of the polygon. That is the removed
if needed. In another stage of the rendering pipeline lighting is
performed. This uses the supplied normals to they perform shading and
colouring of the remaining surfaces.
> > But regardless... Java3d and OpenGL do *no* backface culling based on
> > normals. They *only* consider the windings.
> Which I thought is just a cheap speedup trick which leads to wrong
> solutions :). Especialy if you do rotation arround z-axis. (?)
No, it has nothing whatsoever to do with speedup and is not a wrong
solution. Consider a surface that has vertex normals. Two diametrically
opposite vertices point away from the viewer, two towards. Are you
supposed to render this polygon or not? If so, what happens at the point
that the normal swaps directions? This becomes an impossible to compute
value (infinite value). What color is it?
--
Justin Couch http://www.vlc.com.au/~justin/
Freelance Java Consultant http://www.yumetech.com/
Author, Java 3D FAQ Maintainer http://www.j3d.org/
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Neither man nor woman is the measure of all things. Every organism
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