Billboarding

OpenGL OpenGL: Basic Coding
1

Hello,

I am trying to get billboarding to work. I needed a little clarification. This is the way i tried:

From the modelview, i obtain the following:


--             --
| x1  y1  z1   -| 
| x2  y2  z2   -|
| x3  y3  z3   -|
| -   -   -    -|
--             --

[(x1, x2, x3) is the vector that provides the X orientation]
[ ** ‘-’ implies i’m not using that part of the matrix]

Using the x vector, find the angle between that and
[0, 0, -1] So, this would be the angle i need to rotate the billboard on the y axis.

Let this angle be “Ang”

So, what i’m trying is:

  1. Rotate scene by “rot” angle on the Y axis.

  2. Using the modelview, obtain “Ang” Now, rot will be equal to Ang. So, i just do a negative rotation of Ang on the Y axis.

ie.

. Rotate scene by rot
. Obtain Ang
. Rotate object by -Ang

This seems to work. I am trying for billboarding on only one axis. Is there a better way? Or is this method fine?

Thanks!