How can I draw an object in openGL that always faces the camera?

Question

Possible Duplicate:
Inverting rotation in 3D, to make an object always face the camera?

I have some 2D images in 3D space that I would like to face the camera at all times. These objects are inside a stack of transformations (since I want them to move relative to another object, to keep a long story short). What would be the easiest way to implement this?

Solution

I answered this already here: Inverting rotation in 3D, to make an object always face the camera?

Comments

[Nick Weaver]

Mathematics, it's been too long, so this won't suffice for an answer. You can use the surface normal of your 2d images to point to the camera. Assuming that your 2D images are on a simple plane.

[datenwolf]

While this would work in principle, this method is a lot more complicated, than it needs to be. See my post.

[pmr]

So why not mark the question as a duplicate and vote to close?

[datenwolf]

@pmr: Good point, I wish I could delete it; now that it has been accepted I can't…