I just started to study OpenGL and have some problems with perspective projection.
I have a program in which a cube bouncing on the screen. If I create my 3D space like
it works without any troubles. But if I change to
Either I can't see anything in my window or I can notice that my viewing-point is somewhere 'in the created space' and the cube can go 'behind me'.
How could I manage to see the same space just like with glOrtho?
Is it necessary to use gluLookAt(...) with glPerspective? What is the default viewing-point after creating a space with gluPerspective? Is there a process to calculate gluPerspective() from glOrtho?