What are the normals for 3d cube as used in OpenGL ES?

Question

I have a cube defined as :

  float vertices[] = {
            //Vertices according to faces
                -1.0f, -1.0f, 1.0f, //Vertex 0
                1.0f,          


        

Answer 1

The normal of a surface is simply a direction vector. Since the normal will be the same for two surfaces that are coplanar, you will only need 6 surface normals. However, often, it's the case that normals are expected to be defined per vertex, in which case you'll need 36 (one for each vertex of each triangle on each face of the cube).

To compute the normals, simply use the following calculation: http://www.opengl.org/wiki/Calculating_a_Surface_Normal