camera parameters

Hi all,

I’m looking for a way to “extract” the camera parameters from the OpenGL modelview matrix. These parameters are the ones used with gluLookAt like camera position, up vector,…

anyone have any ideas?

You can do like this I think:
Create a look-at vector (called l here) that is pointing from the world origin down the positive z-axis (the default look-at vector). This vector can be of any length, but unit length is a “standard” length. l=(0,0,1,1)
Create the upvector (called u here) that is pointing from the world origin, and upwards along the positive y-axis (the default up-vector). u=(0,1,0,1)

Then multiply these two vectors with the current modelview matrix, and you should have the look-at vector and upvector in world coordinates.

I think you also can multiply the origin o=(0,0,0,1) with the modelview matrix to get the current viewposition.

[This message has been edited by Bob (edited 09-19-2000).]