/** * 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; }