\"Compute screen (sx, sy) - (sx + w, sy + h) to 3D unit square mapping.
The plane to map to is given in the z field of p. The observer is located at position vp (vp->z != 0.0).\"
In other words, this computes the projection of the point (x, y) to the plane z = p->z (
parallel to XY), from the vp point of view through the screen (sx, sy)->(sx +
w, sy + h)
| sx |
the abscissa of the upper-left screen rectangle. |
| sy |
the ordinate of the upper-left screen rectangle. |
| w |
the width of the screen rectangle. |
| h |
the height of the screen rectangle. |
| x |
the abscissa of the point in the screen rectangle to map. |
| y |
the ordinate of the point in the screen rectangle to map. |
| vp |
the position of the observer. |
| p |
the resulting point. |