Is it possible to create an opengl space without glortho or glu perspective

OpenGL OpenGL: Basic Coding
1

Hi,

is it possible to create an opengl space without glortho or glu perspective?

i have an opengl code which draws a 3d object but it doesnt have anyone of these to functions.

So where does it specify the size of the frustum?

2

OpenGL has defaults for all states.
The default for all matrices is the identity which makes the default viewing frustum to be identical to glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0).

Read the OpenGL programming guide (search for redbook.pdf) and the OpenGL 2.0 specs.

3

Originally posted by tirengarfio:
[b]
is it possible to create an opengl space without glortho or glu perspective?

So where does it specify the size of the frustum? [/b]
Both those functions only modify current matrix. The program can calculate the projection matrix in its own way and use the glLoadMatrix function to upload the resulting matrix.

4

And of course there is glFrustum :wink:

5

yes the size of your space is always a 2x2x2 cube centered at the origin and your transformation matrix maps coordinates into that space, so with the identity matrix ana point (x,y,z) with an x value of -1 gets mapped to the left side of the vieport, x=1 to the right, y=-1 is the bottom, y=1 is the top, z=1 is closest to you, and z=-1 is the firthest away.

Note, when you load the identity transformation matrix, the x axis points to the right, y points up and z towards you, but after glOrtho(-1, 1, -1, 1, -1, 1) z points away from you.