说明：  计算机图形学OPENGL直线生成算法的实现程序: 1.采用键盘输入的方式输入直线段的两端点 2.实现BRESENHAM直线生成算法
(Computer Graphics OPENGL linear algorithm to generate the procedure: 1. The use of keyboard input enter the two end points of line segment 2. The realization of a straight line Bresenham Algorithm)