Suppose to be in NormalizedDeviceCoordinate: I need to transform in world-coordinates a simple vector that starts at the center of the unit-cube and ends on the right plane of the unit-cube (right vector).

I think I would have to calculate:

(M^-1)*(P^-1)*(1,0,0) right???

where M and P are MODELVIEW and PROJECTION.

If I am right, how I can calculate the inverse of the projection matrix??