*/
protected Group createKnobSurface(final double startAngle, final double centerX,
final double centerY, final double radiusX, final double radiusY,
final Color... colors) {
Group group = new Group();
final Shape background = new Ellipse(centerX, centerY, radiusX, radiusY);
background.setFill(new RadialGradient(0, 0, this.centerX, this.centerY,
Math.max(radiusX, radiusY), false, CycleMethod.NO_CYCLE,
new Stop(0, Color.BLACK), new Stop(0.95d, Color.DARKGRAY.darker()),
new Stop(0.97d, Color.GRAY.brighter())));
group.getChildren().add(background);
double startRadians = startAngle * 2d * Math.PI;