I used muti-viewport in my program. my view was use gluPerspective(45.0,aspect,4.0,vfar) code. In my sub-viewport, I wanna to draw a 2D-like background by using
I used gluUnproject(realx1,realy1,0.0,…x1,y1,z1) to get the value of x and y.
Well,when initially run, it seemed all right.But when I increased the value of vfar,the parameter of gluPerctive,the background of sub viewport suddenlly disappeared.