利用给定的可用函数(可用一部分)，生成地球围绕太阳旋转的动画。(无需生 成太阳，无需考虑光照和纹理。) 假定地球的公转平面为 XOY 平面，公转半径 为 100.0，地球半径为 10.0，并且假定地球自转轴的方向始终为 Z 轴方向。在程 序中需要维持两个全局变量 rot 和 rov，分别表示当前的自转角和公转角。-Use of a given function (or part) are available, and generate the animation of the earth revolves around the sun. (no born into the sun, without considering the illumination and texture.) Assumes that the revolution of the earth plane as XOY, orbital radius of 100.0, the radius of the earth is 10.0, and the direction of the earth s spin axis is always assumed to be the Z axis. Need to maintain two global variables in the process sequence rot and the rov, respectively according to the current　the corner and around the corner.