User Clip Planes is mechanism provided by OpenGL that allows application to provide information about additional clipping planes, against which rendered geometry will be clipped. Each user specified clip plane can be turned on and off separately, and for each of them four plane equation coefficients can be provided using OpenGL API: void glEnable(GLenum  cap); where cap is GL_CLIP_DISTANCEi ( i == 0 to N-1 ) void glClipPlane(GLenum  plane, const GLdouble *  equation); where plane is GL_CLIP_PLANEi (.. Read More