Ok when using gl lighting, you need to specify normals. I was wondering, is there one normal per vertex, one normal per triangle, or one normal per vertex per triangle? I would think that the normal would be the same at each vertex of a triangle, since the triangle is flat (one normal per triangle then, passed 3 times). But I''ve seen an awful lot of code that specifies normals per vertex. Whats the deal? Thanks!

In OpenGL, each vertex has a corresponding normal.

If you want the triangles to be flat-shaded and have defined edges then you only need to supply one normal - this is then used to render each of the 3 vertices. You can get the normal for a triangle by taking the cross product of 2 vectors that lie on the same plane as the triangle.

If you want a smooth-shaded look to your model/terrain/whatever then you need to take the average of the normals for all the triangles that meet at that vertex.

Hope this helps

Yes they told you everything...

In geometry, a plane (or a polygon) has one and only one normal.

In OpenGL you can use this normal by specifying the same normal for every vertex (that is the same by specyfing it one time).
In this case you have flat-shaded poly...if you specify different normal for each vertex you can smooth spheres or cylinders as 666_1337 shown! Note that you can render a smoothed cylinders with only 6-8 edges and create the illusion of a real cyl!
These normals can be used in different ways: one methos is to compute the color for each vertex using its own normal and then do a color interpolation to fill the poly (gourad shading?).
Another method is to interpolate the normals on the texels (phong shading?).
And independently you can apply different lightning models.

In bump mapping (or similar algorithms) you can specify different normals for each pixel...