gluPerspective() after glOrtho

tmgergo
Unregistered
 
Post: #1
Hei Everybody!
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

glOrtho(-range,range,-range,range,-range,range)

it works without any troubles. But if I change to

gluPerspective(angle,aspect,1.0,2*range)
or
glFustrum(-range,range,-range,range,-range,range)

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?

Thx: tmgergo
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Luminary
Posts: 5,143
Joined: 2002.04
Post: #2
gluPerspective can't make the same view as Ortho, that's why there are two functions.

The eye will default to 0,0,0 looking at 0,0,1 (or is that 0,0,-1, I never remember) with a perspective.

You can change that however you like, but gluLookAt is one of the easiest ways to manage it.
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Moderator
Posts: 1,560
Joined: 2003.10
Post: #3
OneSadCookie Wrote:(or is that 0,0,-1, I never remember)

Yup, {0.0, 0.0, -1.0} is correct.

- Alex Diener
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