3
Given a list of vertices and a list of indices..
// Some standard mesh information that you should have lying around.
// vertex is your vertex structure that just contains a normal and position here.
// vertices is a pointer to the first vertex
// indices is a pointer to the first index
// num_verts is number of vertices
// num_indices is number of indices
// each face of the mesh is made up of three vertices.
std::vector<Vector3>* normal_buffer = new std::vector<Vector3>[num_vertices];
for( int i = 0; i < num_indices; i += 3 )
{
// get the three vertices that make the faces
Vector3 p1 = vertices[indices[i+0]];
Vector3 p2 = vertices[indices[i+1]];
Vector3 p3 = vertices[indices[i+2]];
Vector3 v1 = p2 - p1;
Vector3 v2 = p3 - p1;
Vector3 normal = v1.Cross( v2 );
normal.Normalize();
// Store the face's normal for each of the vertices that make up the face.
normal_buffer[indices[i+0]].push_back( normal );
normal_buffer[indices[i+1]].push_back( normal );
normal_buffer[indices[i+2]].push_back( normal );
}
// Now loop through each vertex vector, and avarage out all the normals stored.
for( int i = 0; i < num_vertices; ++i )
{
for( int j = 0; j < normal_buffer[i].size(); ++j )
vertices[i].normal += normal_buffer[i][j];
vertices[i].normal /= normal_buffer[i].size();
}
Bevelled cube is perfect example why you should take the area into account, because that's a straight example from real world artists use on models to make the lighting look better. If you wouldn't take the area into account you would have to add extra edges on polys next to bevelled edge to get expected result.
