/**
  * Returns the model space x value for an x, y, z coordinate.
  * <P>
  * This will give you a coordinate after it has been transformed
  * by translate(), rotate(), and camera(), but not yet transformed
  * by the projection matrix. For instance, his can be useful for
  * figuring out how points in 3D space relate to the edge
  * coordinates of a shape.
  */
 public float modelX(float x, float y, float z) {
   depthErrorXYZ("modelX");
   return 0;
 }

 protected void depthErrorXYZ(String method) {
   throw new RuntimeException(method + "(x, y, z) can only be used with " + "OPENGL or P3D, use " +                               method + "(x, y) instead.");}