Lighting stationary wrt to view -- how?

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Scott McMillan (scott++at++ht.com)
Wed, 10 Apr 1996 17:15:54 -0400 (EDT)

I am having a problem with a headlight attached to the viewing position,
looking in the same direction as the view. Essentially, my app is flying
inside a piece of geometry according to a constrained path. The viewpoint
changes every frame. What i would like is a lightsource that lights
whatever the camera is looking at with the ability to define falloffs - a
miner's headlight if you will. I am using the C++ api and performer 2.0.
My basic code fragment is:

    // set up the headlight - this is the only real light in the scene
    ViewState->headlight = new pfLightSource();
    // make it a local light source - set at orgin for now
    ViewState->headlight->setPos(0.0f,0.0f,0.0f,1.0f);

    scene->addChild(ViewState->headlight);

to initialize the light. The code that updates the view gets an eye point
(eye) a lookat point (lookat) and an up point. After computing the new
view matrix from these, I tried this approach:

    ViewState->headlight->setPos(eye[PF_X],eye[PF_Y],eye[PF_Z],1.0f);
    ViewState->headlight->setSpotDir(lookat[PF_X],lookat[PF_Y],lookat[PF_Z]);
    ViewState->headlight->setSpotCone(5.0f,55.0f);

to move the light to the new pose.

This did not work. The view pose works flawlessly, but the light remained
at the origin (I saw it as I flew past).

I then tried this idea for the move:

    ViewState->headlight->setPos(eye[PF_X],eye[PF_Y],eye[PF_Z],1.0f);
    pfPushIdentMatrix();
    ViewState->headlight->setSpotDir(lookat[PF_X],lookat[PF_Y],lookat[PF_Z]);
    ViewState->headlight->setSpotCone(5.0f,90.0f);
    ViewState->headlight->on();
    pfPopMatrix();

which also had no effect on the position or orientation. So I attempted to
ensure that the light was not being culled by doing the following in the
initialization stage:

    /* set a large empty sphere for the bounding sphere of the light,
       keeping it from being culled
    */
    pfSphere * sph = new pfSphere();
    sph->makeEmpty();
    sph->radius = (float)PF_HUGEVAL;
    ViewState->headlight->setBound(sph,PFBOUND_STATIC);

which again had no effect.

My question is has anyone done this who would be willing to share code? Am I
on the right track (and just have some small error), am I on a totally wrong
track or is it a case of "this should work" and therefore there must be
something else in my application which is causing the problem? Any help would
be greatly appreciated.

Thanks in advance,

--


Paul Sherman


Please CC responses to paul++at++ht.com as well...thanks.



-- 
Scott McMillan / scott++at++ht.com / (301)984-3706 x250 / FAX (301)984-2104
                      High Techsplanations Inc. 
       6001 Montrose Road, Suite 902 / Rockville, MD 20852-4874 















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