opengl 画的2d图形，可以实现1缩小，2放大，g恢复，物体自己旋转，并沿着自己的轨道旋转-opengl draw the 2d graphics, you can achieve a narrow, two zoom, g recovery, object own rotation, and rotation along its orbit

opengl 做的 3个立体的指向箭头，可以用方向键控制旋转-opengl to do three-dimensional pointing arrow, you can use the arrow keys to control the rotation

学生作业，实现opengl颜色叠加的简单演示-for OpenGL