Question

For a 3D game engine I’m working on I need to calculate if two 3D triangles are on the same plane to display it accordingly. How do I calculate the angles of a triangle in 3D space?

Would calculating a surface normal and comparing those ever give me 2 equivalent normals?

Answer 1

Why do you want to do that? What is the number of triangle you expect to test? It seems a little bit complex for a real time rendering algorithm!

Anyway:

Compute the normal n of the triangle. Then compute the plane equation:
a.x + b.y + c.z + d = 0 with (a,b,c) being your triangle normal and d = - dot(n,P) (P is one of your triangle vertex). Do the same for the second triangle.

The two planes are the same if the four valuesabcd are equals or opposite (all together).