richr@etl.ARPA (Richard Rosenthal) (05/05/88)
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Does anyone have any programs, including source code, that
demonstrate the use of lighting models (lighting models as
described in Graphics Library User's Guide, Chapter 14,
Lighting Models) on SGI IRIS 4D/60T?
The programs liquid, light, and sdisp appear not to use
these facilities. Please, please, correct me if I am wrong
or, better yet, explain how these programs work.
Obviously, I am trying to teach myself about lighting.
Thanks.
--
Richard Rosenthal | ARPANET: richr@etl.arpa
US Army Engineer Topographic Laboratories | UUCP: ???
Ft. Belvoir, VA 22060-5546 | PHONE: +1 202 355 2830grose@camax01.UUCP (Larry Grose) (05/09/88)
A warning concerning SGI's implementation of their lighting model. In order to differentiate between when transformations are intended to modify just the model and when they are intended to modify both the model and the lights, they have added an mmode() call, which is described in section 14.4 of the Graphics Library User's Guide. It claims that the calls perspective, window, ortho, and ortho2 work under both MVIEWING and MPROJECTION modes. However, when I was out at their headquarters porting to the GT and scratching my head over why my lighting model code no longer worked (normals appeared to be reversed), I talked to one of their software gurus, who helped implement the lighting model for the GT. He pointed out I wasn't using MPROJECTION mode with the above calls and I pointed him to SGI's documentation. He politely said 'ouch', and admitted that it was wrong for the GT (ie, perspective, window, ortho, and ortho2 must be used under MPROJECTION mode only). Unfortunately, the buck apparently stopped there, because the new documentation that came with 3.0 still has the same error. In the 4 examples provided in section 14.6 for using mmode, only the first one will work on the GT (all 4 work for non-GT's). To the best of my knowledge, the rest of the lighting model documentation is correct, though admittedly it is not very tutorial in nature.