alpha and rib files on the NeXT.

[munzner]

> > Alpha information is ignored if transparency is not enabled. By
> > default, transparency is off. You want a command like this:
>  (merge-ap g1 appearance { +transparent material {alpha .2}})
>Thanks. 
>Unfortunately it still doesn't seem to work exactly.  

Aha. The answer is that your ND colormap had alpha 1 everywhere and
was overriding the alpha value you gave at the apperance level. Since
you can't have more than one colormap per camera window, the only way
to have a scene with some objects transparent and some opaque is to
turn off the ND colormap on one type of object, with the "keepcolor"
appearance option:

  (merge-ap g1 appearance {keepcolor +transparent material {alpha .2}})
                           ^^^^^^^^^

One could, of course, use a colormap with alpha < 1:

(ND-color "xyz" (
	( (0 0 0 1 0 0)
		-1	0.1 0.1 1 .2
		-0.833	0 0.5 1 .2
		.....)))

instead of

(ND-color "xyz" (
	( (0 0 0 1 0 0)
		-1	0.1 0.1 1 1
		-0.833	0 0.5 1 1
		.....)))



>I might point out, in the spirit of a (possibly) helpful suggestion,  
>that (as far as I can tell) "+transparent" is not documented in the  
>manual.  In a way I see why--the SGI pannel has a button for this  
>which was left off of the NeXT pannel.  

It is in fact in the manual (in the OOGL File Formats Appearance and
Materials Panel sections), but it's pretty obscure.  Your suggestion
is indeed helpful, I'll clarify it.

Tamara