Let there be two objects, one is at (x,y,0), the other is at (x,y,100), ie, right above the other one. By default, when I am moving them, I will not see them overlap, because of the viewing effects. Is there any way to make them overlap? Thanks.
what I meant was, opengl sets the view point as the middle of the window. so if I move them to the middle, they overlap. but when I put them on the lower-left side, the (x,y,0) appears to be to the lower-left of the (x,y,100), as (x,y,100) is closer to the viewing point.