[osg-users] From post-perspective space to world space (GLSL)

[Joakim Simonsson]

Hi,

In GLSL, a point is transformed from world-space to post-perspective
camera space like this:

ftransform();
OR
gl_ModelViewProjectionMatrix * gl_Vertex;
OR
gl_ProjectionMatrix * gl_ModelViewMatrix * gl_Vertex;
OR
gl_ProjectionMatrix * osg_ViewMatrix * gl_Vertex;

It seems that the osg-provided uniform, osg_ViewMatrix, is equivalent with
gl_ModelViewMatrix.

What I am looking for is to transform a point from post-perspective space
to world-space.

A document that I've read says that this is done by the following
equations:

(I am using the ' symbol for denoting an inverse (^-1) )

Eq 1:
     M_Projector = (M_View * M_Perspective)'

If I have understood things correctly, this is the inverse of
ModelViewProjectionMatrix. (?)

Eq 2:
     p_world = M_Projector * p_projector

M are the camera matrices. p is a point in homogenous three-dimensional
space.

If (M_View * M_Perspective)' is the the inverse of
ModelViewProjectionMatrix it would be equivalent to,
osg_ViewMatrixInverse * gl_ProjectionMatrix', as B'A'=(AB)' .  (?)

osg_ViewMatrixInverse is provided by osg, so the only thing I have to do
is to calculate the inverse of gl_ProjectionMatrix.

Are there a more convenient way make this calculation?



-- 
Joakim Simonsson