Originally Posted by

**GClements**
Yes, provided that that the forward, up and right vectors are mutually perpendicular. Functions such as gluLookAt() normally use one vector directly then use cross products to generate the other two axes. So even if the vectors aren't perpendicular, you still get an orthogonal basis.

If you're using right and up (as opposed to forward and either right or up), the resulting quad should always be parallel to the projection plane, although it might be a parallelogram (rather than a rectangle) if the vectors aren't perpendicular.

When one of the vectors is a forward vector (as is the case for gluLookAt()), the forward direction (Z) is normally preserved, while the other two are generated using cross products. If the other vector isn't perpendicular to the forward vector, the resulting quad won't be parallel to the projection plane.