Sounds like you are reversing the winding on some parts. That's easily done if you calculate the vertices for just part of the sphere then use reflections to find the rest of the vertices. If you're using back face culling try turning it off and it will be easier to tell what is happening. Just drawing a hemisphere will also make it easier to figure out what is going wrong as well.

Quote:Original post by Conqueran
I tried inverting the normal.. The sphere points are held in a data file, I simply draw the polygons from the data file and calculate the normals for each.. I tried normalizing the vectors myself, I get the same result.

A depth buffer problem? I'm not sure what u mean by culling back surfaces..

Polygons are considered to be front-facing or back-facing if their vertices appear in counter-clockwise or clockwise order (respectively). You can enable culling so that back-facing polygons aren't drawn. For details, see Chapter 2 of the Red Book. The depth buffer is also explained in that chapter.

I assume you are using the vertex normals of the sphere, i.e. direction from the center to the vertex. Try checking those against face normals, i.e. cross product of two consecutive edges of a face. The dot product of the vertex and face normal should be positive. If it's negative your winding is reversed.

It might seem intuitive that the normal should specify the front face, but it doesn't. If the user is suppose to be inside the sphere then the front face is the inside faces, but the normals would still point out.

Easiest is really to just turn off back face culling and set differant colors for the front and back faces. Without a picture the best guess is that front faces are inside faces on some polygons and outside faces on others.

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That seems odd. Sounds like you don't have a depth buffer. I've had it fail to give me a depth buffer when I asked for a higher bit depth than available. If you requested a depth buffer then try calling glGetIntegerv with GL_DEPTH_BITS to verify that you actually got a depth buffer. If you got a depth buffer make sure you didn't use too small a zNear, i.e. under 0.1.