/**
* Draw a filled diamond of side length 2r, centred on (x, y).
*
* @param x the x-coordinate of the centre of the diamond
* @param y the y-coordinate of the centre of the diamond
* @param r radius is half the length of any side of the diamond
* @throws RuntimeException if r is negative
*/
public static void filledDiamond(double x, double y, double r) {
offscreen.fill(ShapeAssist.diamond(x, y, r));
draw();
}
