My best solution is to use gif87a images with a white
background (black letters on white background) instead of gif89a
images (black letters on a transparent background), and to use the 'modulate'
mode.
I change the color of the object that the gif is texured with (from dark to
light)
to get the effect of 'back-lighting up' that letter of the alphabet. The
objects are the
lighted letters of the alphabet on a model of the Enigma Cipher Machine,
you press a key and a 'light' lights up under a letter behind the keyboard.
With all other settings the same, the transparent gif makes the object
'disappear',
just as J. Lee Dixon indicates below that it should (it did not disappear using
java3d1.2)
If I use a black and white gif, it works properly with java3d1.2.1b1 and
java3d1.2
Using the DECAL, BLEND, or REPLACE mode did not produce acceptable results,
although DECAL seems like it should.
Sorry for the bandwidth, but I wanted to have _a_ solution go into the archives
in case others have a similar problem.
Thanks for the help!
Tom Nelson
"J. Lee Dixon" wrote:
>
>
> Well, from reading some documentation about how the color (C) and the
> alpha (A) of a colored/textured polygon are computed:
>
> (where f=face(polygon) and t=texture)
>
> Modulate Mode:
> C = Cf*Ct
> A = Af*At
>
> In modulate mode, the alpha of the texture is *multiplied* by the alpha
> of the polygon. In other words, if you can see through the texture, the
> poly will be invisible as well.
>
> Decal Mode:
> C = Cf*(1-At) + Ct*At
> A = Af
>
> In decal mode, the texture will blend with the poly color, but the alpha
> will only be taken from the face. I think this may be the mode you
> want...
>
> (got this from the OpenGL red book...)
>
> -Lee
>
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