此程序的功能是实现基本的openGL中的画线算法，总共有四个算法。DDA画线算法，中点Bresenham算法画直线，改进Bresenham算法画直线以及 四分法绘制椭圆-Feature of this program is to achieve the basic openGL draw lines in the algorithm, a total of four algorithms. DDA line drawing algorithm, Bresenham midpoint line d