// IN SETUP(), WE ADD ONE LINE OF CODE TO MAKE OUR LISTENER LISTEN TO OUR CURRENT WINDOW this.addMouseWheelListener(new CMouseWheelEvent());
float wheelScalingFactor=1.1;  //magnification factor
class CMouseWheelEvent implements MouseWheelListener {
  public CMouseWheelEvent() {}
  public void mouseWheelMoved(MouseWheelEvent e) {
    int notches = e.getWheelRotation();
    if (notches < 0)     C.scaleByG( wheelScalingFactor);// mouse scroll up
    else C.scaleByG( 1./wheelScalingFactor); // mouse scroll down
  }
}