[HOpenGL] Confused about normals

Patrick Scheibe mai99dnn at studserv.uni-leipzig.de
Tue Oct 14 02:14:50 EDT 2003


First I want to thank Sven for solving
the problem with the missing normals.

But now I am a little bit confused. I'm sure to heard about that if you 
specify the vertexes of a polygon (with glBegin GL_POLYGON in c)
counterclockwise then the normalvector is set automatically.
That means if you look at a plane the normal vector points to you.

Is'nt that true?

My example problem seems to show that this is definitly not true. So if I want 
to use light (and that will be very often) and I have to specify these 
vectors by myself then I can't use the renderPrimitive Polygon or Quad in 
situ because the calculation of a normal vector of a polygon isnt that 
trivial.
The simplest way I see is to reduce this calculation to a normal vector 
calculation of a triangle. So I'm forced to define a new function 
makePoly taking a list of Points, calculating the normal and draw a polygon 
with this points. Otherwise I have to write down some points more then one 
time, the first time in the makenormal-function and in the secont at the 
render call.

1. Is this the way?
2. Where is it used that normals aren't right-angeled to the polygon-plan?
3. Exists there some higher-level function.

With best regards
Patrick


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