Question

The code I’m using in my collision detection code is this:

(note: Vector3f is part of the LWJGL library.)

(Note2:Tri is a class composed of three of LWJGL’s Vector3fs. v1, v2, and v3.)

public Vector<Tri> getTrisTouching(Vector3f pos, float radius){
        Vector<Tri> tempVec = new Vector<Tri>();
        for(int i = 0; i < tris.size(); i++){
            Tri t = tris.get(i);

            Vector3f one_to_point = new Vector3f(0,0,0);
            Vector3f.sub(pos,t.v1,one_to_point);            //Storing vector A->P

            Vector3f one_to_two = new Vector3f(0,0,0);
            Vector3f.sub(t.v2,t.v1, one_to_two);            //Storing vector A->B

            Vector3f one_to_three = new Vector3f(0,0,0);
            Vector3f.sub(t.v3, t.v1, one_to_three);            //Storing vector A->C

            float q1 =  Vector3f.dot(one_to_point,  one_to_two) / one_to_two.lengthSquared();            // The normalized "distance" from a to
            float q2 =  Vector3f.dot(one_to_point,  one_to_three) / one_to_three.lengthSquared();            // The normalized "distance" from a to



            if (q1 > 0 && q2 > 0 && q1 + q2 < 1){
                tempVec.add(t);
            }
        }   

        return tempVec;
    }

My question is how do I correctly see if a point in space is touching one of my triangles?

Answer 1

To test if your point is inside the triangle, create a ray with its origin at the test point and extend it to infinity. A nice easy one would be a ray which is horizontal ( e.g. y constant, and x increases to infinity. Then count the number of times it intersects with one of your polygon edges. Zero or an even number of intersections means you are outside the triangle. The nice thing about this it works not just for triangles but any polygon.

http://erich.realtimerendering.com/ptinpoly/