Hello. I have a really small question regarding how to implement normal mapping. All the model files I have already have per-vertex normals stored in them. All the tutorials/articles I've found computes all three of the normals, tangents and bitangents per vertex by averaging the triangles the vertex is part of and then orthogonalizing them. However, I can't find any information on what I should do with the already existing per-vertex normals. What are 3D programs that generate normal maps etc expecting me to do? Should I ignore the per vertex normals, can I assume that they're already what I need (calculated the same way the tutorials/articles tell me to) or do I need to take them into consideration in some special way?