Jakob Kristianse #1 / 1

Vector question
What formula/function do I use to update a vector to reflect the difference between two other vectors? I am moving a point across/above a face, and when entering a new face (tested using Intersect) i want to update the directionvector of the point to reflect the difference between the normals of the two faces (in order to get my point to maintain a fixed path, parallel to the faces it passes). These two facenormals I calculate by averaging (+normalizing) the normals of the face's 3 vectornormals (by the way, is this the correct way to do that?) Thanks for helping (and please forgive my poor math).... Jakob
