提供直线的三种算法；提供圆的算法；提供画任意圆弧的算法-Three algorithms to provide a straight line provide round algorithm provide painting arc arbitrary algorithm

通过程序实现Bresenham画线算法，中点画圆算法以及中点画椭圆的算法-Achieved through the process Bresenham line algorithm, the midpoint circle algorithm, and the dotted ellipse algorithm