mapw(3G)

NAME
     mapw - maps a point on the screen into a line in 3-D world coordinates

FORTRAN 77 SPECIFICATION
     subroutine mapw(vobj, sx, sy, wx1,
    +    wy1, wz1, wx2, wy2, wz2)
     integer*4 vobj, sx, sy
     real wx1, wy1, wz1, wx2, wy2, wz2

PARAMETERS
     vobj   expects a viewing object containing the transformations that map
            the current displayed objects to the screen.

     sx     expects the x coordinate of the screen point to be mapped.

     sy     expects the y coordinate of the screen point to be mapped.

     wx1    returns the x world coordinate of one endpoint of a line.

     wy1    returns the y world coordinate of one endpoint of a line.

     wz1    returns the z world coordinate of one endpoint of a line.

     wx2    returns the x world coordinate of the remaining endpoint of a
            line.

     wy2    returns the y world coordinate of the remaining endpoint of a
            line.

     wz2    returns the z world coordinate of the remaining endpoint of a
            line.


DESCRIPTION
     mapw takes a pair of 2-D screen coordinates and maps them into 3-D world
     coordinates.  Since the z coordinate is missing from the screen
     coordinate system, the point becomes a line in world space.  mapw
     computes the inverse mapping from the viewing object, vobj.

     A viewing object is a graphical object that contains only routines that
     affect the model-view matrix, the projection matrix, or the viewport
     specification.  A correct mapping from screen coordinate to world
     coordinates requires that the viewing object contain the projection and
     viewing transformations that mapped the displayed object from world to
     screen coordinates.

     The system returns a world space line, which is computed from (sx, sy)
     and vobj, as two points and stores them in the locations addressed by
     wx1, wy1, wz1 and wx2, wy2, wz2.
SEE ALSO
     mapw2

NOTE
     This routine is available only in immediate mode.