I'm implementing smooth groups for our lightmapper. This means each face's normal needs to be interpolated across a face for the lighting equation, instead of just using the flat polygon normal.
Our lightmapper works on BSP-style, where each side is coplanar and can have any number of sides.
So my question is, is there a simple way to do Gouraud or Phong shading on a coplanar polygon? Is there any other routine that can calculate this? I tried messing around with a vertex distance method, but I don't think that will work.