[Plib-devel] ssg, transparent textures, and blending

[Curtis L. O. <cu...@in...>]

Ok, I literally want to cry. :-)

I've spent the last 4-5 days struggling with ssg, opengl states,
textures with alpha transparency, and blending ... nothing was working
right for me.  Everything was going screwy at every step of the way.
This has to have ranked right up there with the frustration level of
sorting out matrix tranformations.  You think you know how it works,
you've studied it in school, you got A's on your test, you've made
this stuff work before, but here's this proof laughing in your face,
this piece of non-working code that is saying you are obviously a
clueless idiot.

Ok, so I could get everything working correctly ... right up to the
point where I tried to enable either blending or alpha_test and blam,
my object would go away.  This morning I said to myself, "you know
Curt, it almost looks like opengl/ssg is honoring the alpha of the
underlying quad, and completely ignoring the alpha of your perfectly
good texture."

Hmmm ... interesting thought ... what is the alpha of my underlying
quad?  I suppose, if I'm GL_MODULATING my texture, the texture's alpha
would get modulated with the underlying quad's alpha, just like it is
with the RGB values.

Hmmm ... but if you build an ssgVtxTable ssgColourArray out of ssgVec3
there would be no way to specify an alpha component.  A huge obvious
oversite in the design of ssg.  If Steve wasn't on vacation I'd tear
him to shreds over this ... he just wasted the last week of my life.

Quick check the docs so I have some juicy proof for the public
lynching ... and sure enough there it is ... you are supposed to build
the ssgColourArray out of ssgVec__4__!  I'm a complete moron!  I've
been building my all my color lists out of ssgVec__3__ leaving the
alpha to default to 0.  Yikes!  Did I mention I'm a complete moron.

Specifying an alpha of 1.0 in my ssgColourArray makes all my problems
go away and suddenly everything works the way it's supposed to.  The
sun came out, the birds started to sing, yada, yada ...

Curt.
-- 
Curtis Olson   University of MN, ME Dept.       Flight Gear Project
Twin Cities    cu...@me...                  cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org