用中点画圆法画一个圆，其生成的速度快，存储结构比较简单-Drawcircle paintings by the mid-point of a circle, which generates fast, relatively simple storage structure

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 co