实现直线、圆、椭圆和区域填充，其中直线和圆的生成分别用DDA算法、中点画线法和Bresenham算法，扫描转换和区域填充用多边形扫描转换的扫描线算法和种子填充算法。-To achieve a straight line, round, oval and the area filling, in which the generation of linear and circular respectively DDA algorithm, the stipple line method and Br