HELP: Cameras and Billboards

[Anton1]

I need help. I'm doing a basic graphic engine for high school project. I've been using Irrlicht as a reference. But I'm stuck with the camera and billboard thing.

I want to do a billboard node, but the irrlicht camera uses the lookat method. i don't to think to long about it, so i ask you how can i get the upvector, eye and center from just a matrix xyz rotation. I'd prefer to know it this way.
Thanks

[vitek]

If you have the view matrix, you can get all the information you need pretty easily. Assuming you are using a row major matrix, it would look like this...

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[ 0  1  2  3]
[ 4  5  6  7]
[ 8  9 10 11]
[12 13 14 15]

You can easily extract the following information from the view matrix...

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 x axis       = (M[0], M[4], M[8])
 y axis       = (M[1], M[5], M[9])
 z axis       = (M[2], M[6], M[10])
 eye position = (M[12], M[13], M[14])

If you use a right hand coordinate system with +Z into the screen and +Y up, then the Z axis is the look direction vector and Y is the up vector. +X would point to the left.

Travis