/**
* Creates the unit normal to the polygon by taking the cross product of the first two edges.
* Call with 'nsides' set to two if the polygon is visible from both sides.
*/
void setNormal() {
// We need three points to define two edges.
if (n < 3) return;
if (normal == null) normal = new float[3];
float[] p0 = {ps[points[0]], ps[points[0] + 1], ps[points[0] + 2]};
float[] p1 = {ps[points[1]], ps[points[1] + 1], ps[points[1] + 2]};
float[] p2 = {ps[points[2]], ps[points[2] + 1], ps[points[2] + 2]};
float[] e1 = new float[3];
float[] e2 = new float[3];
Tools3d.subtract(p1, p0, e1);
Tools3d.subtract(p2, p1, e2);
Tools3d.cross(e1, e2, normal);
Tools3d.makeUnit(normal);
dirtyNormal = false;
}
