smooth shading problem

As I understood, you want to draw a surface, right? Then, if you want to do it by hands, specifying normal to each quad, you'll have to create a LOT of those quads to approximate surface. In OpenGL there are evaluators for these things. If you still want to draw a surface without them, I advise you to refer to NeHe tutorials. There is an example of flag. It's just a simple sin surface, created in cycle.

Why don't you throw us a screen shot with the smooth shading?

Without a pic, the first question I thought I'd ask was: how are you calculating the vertex normals? I'd say its most likely that there is an error in there which is causing your object to look weird. It's actually really simple, you calculate the face normals with a cross product, and average the face normals of faces which share a vertex for each vertex in your mesh.

Just post back with an answer to the first question and we can step you through the whole process if you have any difficulty understanding.

Yes I want to draw a surface(toroid) and i'm calculating the vertex normals using the parametric superquadratic function. When I use glShadeModel(GL_SMOOTH), the shape looks like the one at right. It's shading each quad one by one however I want the whole object to be shaded but I'm missing something.

Here's the image
http://www.geocities.com/concentrator2/toroid.jpg

1 - Double check your normals. I find it helps to actually draw the normals (pretty simple to do) for easy sanity checks.
2 - Are the normals at the verticies the surface normal of the quad? It almost looks like you're just applying the surface normal of the quad at the verticies, instead of finding and using the vertex normal (which would be the average of all the surface normals of the quads the vertex is a part of).

Quote:

Original post by concentrator Yes I want to draw a surface(toroid) and i'm calculating the vertex normals using the parametric superquadratic function. When I use glShadeModel(GL_SMOOTH), the shape looks like the one at right. It's shading each quad one by one however I want the whole object to be shaded but I'm missing something. Here's the image http://www.geocities.com/concentrator2/toroid.jpg

OpenGL can't magically smoothly shade all you model. The gouraud shading happens per triangle, however if you have one normal for every shared vertex the surface of your model will look smooth. So, the normal at the bottom left of quad A must equal to the normal at the bottom right of the quad left to quad A, and so on.

Concentrator, there is something fundamentally wrong here. In smooth shading, each vertex has one constant normal. Let me explain better what is wrong:

Say quadrilaterals 1, 2, 3 and 4 share vertex # 47. When you are drawing these quads, you are specifying a different normal for vertex # 47 each time. That doesn't give you smooth shading.

To be safe, you should make a vertex struct, and make it have 2 member vectors, one for the position coords of the vertex, another for the direction of the normal. But the problem at the moment is with your calculations. If it helps, what should look like a convex bulge for each quad is looking like a concave depression.

Personally, I think it would be easier to average the face normals and store it once and for all in your vertex struct.