利用中点画圆算法绘制一个圆,中点画圆法是利用圆心在坐标原点圆的方程，将每个像素的中点坐标代入圆的方程得到d,再通过d的值来确定中点与圆的位置。-Utilization of stipple round draw a circle algorithm。Stipple the center circle method is to use in the origin of coordinates the equation of circle, the midpoint of each pixel coordinates into the equation of circle d, then through the d value determines the location of the middle and round.