Introduction - If you have any usage issues, please Google them yourself
Experimental requirements: 1, respectively, the parameters used to generate a round and Bresenham algorithm drawcircle 2, call the circle and ellipse drawing function to draw the right tips: openGL in glrotatef function by the rotation of coordinate system, such as around the Z axis Rotate 45 degrees (equivalent to XY-plane graphics rotate 45 degrees around the origin) through glrotatef (45,0,0,1) to achieve.