帮助学习opengl视角变换的程序，还有camera类的使用-Help learning program opengl perspective transformation, as well as the use of camera class

对一副图片内的四边形进行透视变换，可以得到四边形的四个点坐标以及对应的转换矩阵H。-A four-point coordinate of the quadrilateral and the corresponding transformation matrix H can be obtained by perspective transformation of the quadrilaterals in a picture.