Exemple #1
0
    /**
     * 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;
    }
Exemple #2
0
    /**
     * Decides if this polygon is a 'back face'. A back face is a polygon that is facing away from
     * the camera and therefore should not be drawn. If this polygon is double sided then it can not
     * be a back face. In such a case this routine has the side effect of ensuring that the normal
     * points towards the camera eye rather than away from it.
     *
     * @see Obj3d#draw(Graphics)
     */
    boolean isBackFace(final float[] eye) {

      if (dirtyNormal) {
        setNormal();
      }

      p[0] = ps[points[0]];
      p[1] = ps[points[0] + 1];
      p[2] = ps[points[0] + 2];

      Tools3d.subtract(p, eye, ray);

      if (doubleSided) {
        // flip the normal if necessary so this is NOT a backface
        if (Tools3d.dot(normal, ray) >= 0) {
          Tools3d.scaleBy(normal, -1);
        }
        return false;
      } else {
        return (Tools3d.dot(normal, ray) >= 0);
      }
    }