code: protected void setRegion(float cx, float cy) {
  		x0 = cx - radius;
  		y0 = cy - radius;
  
  		if( x0 < 0 ) { x0 = 0;}
  		else if( x0+width > image.width ) { x0 = image.width-width; }
  		if( y0 < 0 ) { y0 = 0;}
  		else if( y0+width > image.height ) { y0 = image.height-width; }
  
  	}
docs: Updates the location of the rectangular bounding box
  @param cx Image center x-axis
  @param cy Image center y-axis