[Plib-devel] A COLOR_MATERIAL test case.

[Steve B. <sjb...@ai...>]

OK - I've spent some time to write a nice, simple test case to
allow us to better discuss the color material problem in a
clear manner.  The program is derived from a logo competition
entry at work - and I've applied nice simple textures and
deliberately screwed with the polygon ordering to make for
LOTS of state switching.  It's also timed to run no faster
than 60Hz with a nasty hack - try to ignore that - I was in
a hurry.

So - Compile 'logo.cxx' using the attached Makefile.
Run it in the same directory as the two texture maps I provide.

You should see a little animation of some origami - with spots
on one side of the paper and stripes on the other.  Admire it
for a while...fun isn't it!

OK - so now you can play around by editing logo.cxx and rebuilding
it.

* Go to line 446 - notice that the vertex colours are alternating
  between white and magenta (see the 'i & 1' part?).
  You don't see that in the animation because glColorMaterial is *not*
  enabled and White is the default glMaterial colour.

* At line 497 you can see where I set up two material properties
  - one for the spotted side of the paper, the other for the
  stripes.  Try changing *one* of the 'disable(GL_COLOR_MATERIAL)'
  calls to an 'enable'.  Running the program again will show
  that one side of the paper is now covered with purple splotches.

  This is good.  It's working just fine.

* Now try enabling GL_COLOR_MATERIAL for *both* sides of the
  paper - and change the 'setMaterial(GL_EMISSION...)' calls to
  make one side of the paper emit (say) Blue light and the other
  side (say) Red.  You might want to change the vertex colours
  to darker values to make this more obvious (because White+Anything
  is still White) - but even without doing that it's obvious in
  the shadowed areas.

  According to Curt's theory, this test should fail because we'd
  be making glMaterial calls while GL_COLOR_MATERIAL is enabled.

  But guess what?  It works OK!

Now, that's on a GeForce card with the nVidia Linux drivers. YMMV.

In fact, I tried a dozen things - and SSG performed flawlessly in
all situations....which suprised me quite a bit because other
programs that I've written HAVE shown problems that appear to be
GL_COLOR_MATERIAL related.

  8-P

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjb...@ai... (home)  http://www.woodsoup.org/~sbaker
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