Calculating angle between 2 vectors in 3D

I suspect you don't actually want that answer though, since you mentioned deferred lightning. You probably just want the matrix that would transform your model into the correct space for the rendering. This is just going to be some combination of inverted and multiplied matricies for your model, camera, and light depending on what space you are coming from and what one you want to go to (world? camera? screen?).

But, the direct answer is that you can get the angle from:
acos( dot( vec1, vec2 ) )
And then rotate it about the axis:
normalize( cross( vec1, vec2 ) )

But which axis?

Quote:

Original post by KulSeran acos( dot( vec1, vec2 ) )

This only works if vec1 and vec2 are unit vectors. More generally, you have:

vec1 dot vec2 = |vec1| * |vec2| * cos(angle)

where |vec| denotes the length of the vector.

Edit: The axis to rotate around is given by the last equation in KulSeran's post.

Em, i dont understand. I m getting only 1 angle from acos( dot( vec1, vec2 ) ) and
how can i use it for example in glRotatef()?

The result of a cross product of two vectors is a vector perpendicular to both vectors. When normalized, that can be used as the axis of rotation for a rotation from one vector orientation to the other.

Thx, now i understand:) So i m going back to my code