Find the normal angle of the face of a triangle in 3D, given the co-ordinates of its vertices

Question

As you may be able to tell from this screenshot, I am trying to make a physics engine for a platformer I am working on, but I have run into a definite problem: I need to be able

Answer 1

The cross product is the right answer. Dont forget to normalise the result, and dont forget that if the triangle has zero area, the result is invalid because there is no well defined normal. Basically, if your three vertices are p0, p1 and p2:

vector temp = cross(p1 - p0, p2 - p0);
if (length(temp) < epsilon) then
    Degenerate_triangle_error;
else
    return normalize(temp);

Also, as the other answer says, whether you get the 'up facing' or 'down facing' normal will depend on the ordering of your vertices.