public VectorBall(int x, int y, int diameter, Brush color)
 {
     position      = new Point(x, y);
     this.diameter = diameter;
     this.color    = color;
 }
 public VectorBall(int x, int y, int diameter, Brush color)
 {
     position = new Point(x, y);
     this.diameter = diameter;
     this.color = color;
 }
 public VectorBall(int x, int y, int diameter)
 {
     position      = new Point(x, y);
     this.diameter = diameter;
     color         = Brushes.CadetBlue;
 }
 public VectorBall(int x, int y, int diameter)
 {
     position = new Point(x,y);
     this.diameter = diameter;
     color = Brushes.CadetBlue;
 }