transparency

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Lance R. Marrou (marrou++at++vsl.ist.ucf.edu)
Fri, 20 Jan 1995 16:04:47 -0500 (EST)

I get a different result from using this:

    pfGStateMode( exp_gstate, PFSTATE_TRANSPARENCY,
                  PFTR_ON|PFTR_NO_OCCLUDE );

as opposed to:

  long exp_trans_state;
  long PreDraw(pfTraverser *trav, void *data)
  {
    exp_trans_state = pfGetTransparency();
    pfTransparency(PFTR_ON|PFTR_NO_OCCLUDE);
    return PFTRAV_CONT;
  }

  long PostDraw(pfTraverser *trav, void *data)
  {
    pfTransparency(exp_trans_state);
    return PFTRAV_CONT;
  }

The pre-draw and post-draw function callback technique provides
the correct transparent geoset (of course the alpha values are
set correctly). However, setting the state mode works for
allowing transparency, but it makes the geoset occlude other
transparent geometry. I have attempted just about every combination
of state mode to get it to work the same, but no luck. Obviously,
I could just stick to the function callbacks, but I want to know
why setting the state doesn't work.

I have images which show the results of both methods for those
interested to see them.

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