🚀 go-pugleaf

In article <1992Dec16.215009.24896@Princeton.EDU> smulgund@phoenix.Princeton.EDU (Sandeep Shriram Mulgund) writes:
>I'm trying to use a 4D/35 Iris running under Irix 4.0.5 to generate an
>out-of-window display for a flight simulator.  I'm having trouble trying
>to relate the angles that define the aircraft's orientation with the
>parameters of the "lookat" command.  Specifically, there's an argument
>to lookat called "twist" that defines the angle of twist about the line
>of sight.  I haven't for the life of me been able to figure out what
>this variable really is, and how it relates to other variables I do know.
>Does anybody out there have any experience using this command?  Any help
>would be appreciated.
>
>Thanks!

lookat has caused confusion for many people.  check out

/usr/people/4Dgifts/examples/grafix/{upat-main.c, upat.c} 

for a tres swank alternative to lookat.  from the grafix dir's README:

  -->  upat.c,           this set implements an alternative approach to
       upat-main.c       LOOKAT(3G) where, instead of viewing the scene
                         with the default up-axis being Y, the user can
                         easily specify the up-axis in any direction desired.

upat-main.c's top:
 *
 *  NOTE:  the core routine itself--upat--exists separately in the upat.c
 *         file.  this is so that it can be employed more easily as a
 *         stand-alone module.
 *

upat.c's top:
/*
 *   upat.c:
 *
 *    This module contains all the code necessary to hook the routine upat()
 *  into any application wanting to take advantage of "user-defined up-axis"
 *  functionality.  Excluding its seventh parameter--twist--upat() can be
 *  thought of as a superset of the LOOKAT(3G) function (the first six
 *  parameters are identical to the first six parameters of LOOKAT(3G)).
 *
 * C SPECIFICATION
 *     void upat(vx, vy, vz, px, py, pz, ux, uy, uz)
 *     float vx, vy, vz, px, py, pz, ux, uy, uz;
 *
 * PARAMETERS
 *     vx, vy, vz   is the viewpoint, the point the eye is looking from
 *     px, py, pz   is the reference point, the point the eye is looking at
 *     ux, uy, uz   is the up vector





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