[Plib-devel] ssgSimpleState Question (bug?)

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

Steve,

For my flight gear application I had been noticing some strange
lighting effects where the entire scene would jump to a noticably (and
erroneously) brighter state depending on view direction, pitching the
nose of the plane up, pitching down, etc.  Strange.

Today I was looking a bit closer at what was going on, and it turns
out that this effect happens whenever my moon is visible in the view
frustum.  (i.e. not being culled.)  In otherwords, whenever the moon
gets drawn, my scene gets erroneously brighter.

Looking a bit closer, it appears to be related to how I've set up the
ssgSimpleState for my moon.  Here is the code:

    orb_state = new ssgSimpleState();
    orb_state->setTexture( (char *)path.c_str() );
    orb_state->setShadeModel( GL_SMOOTH );
    orb_state->enable( GL_LIGHTING );
    orb_state->enable( GL_CULL_FACE );
    orb_state->enable( GL_TEXTURE_2D );
    orb_state->enable( GL_COLOR_MATERIAL );
    orb_state->setColourMaterial( GL_DIFFUSE );
    orb_state->setMaterial( GL_AMBIENT, 0.0, 0.0, 0.0, 1.0 );
    orb_state->setMaterial( GL_SPECULAR, 0.0, 0.0, 0.0, 1.0 );
    orb_state->enable( GL_BLEND );
    orb_state->enable( GL_ALPHA_TEST );
    orb_state->setAlphaClamp( 0.01 );

Now if I have the following setMaterial() line commented out, this
weird/erroneous effect goes away (but then my moon isn't drawn
correctly)

    // orb_state->setMaterial( GL_AMBIENT, 0.0, 0.0, 0.0, 1.0 );

Notice that I enable(GL_COLOR_MATERIAL), and then
setColourMaterial(GL_DIFFUSE).  I want the ambient component locked to
black so I can make my dark side of the moon blending work correctly.

Am I making sense?  I realize there is undefined weirdness in the
opengl spec when you mix setColorMaterial() and setMaterial()
... we've been through that enough times.

plib doesn't seem to like it when some of my simple states use
enable(GL_COLOR_MATERIAL) and some don't so I had been standardizing
on using GL_COLOR_MATERIAL.  But, in plib I can't seem to correctly
enable(GL_COLOR_MATERIAL) just for the DIFFUSE component, and set the
ambient component to something else.

Am I missing something here as to proper usage of plib simple states?
Is there some standard way to accomplish what I want to do in plib?

Thanks,

Curt.
-- 
Curtis Olson   Human Factors Research Lab       Flight Gear Project
Twin Cities    cu...@hf...                cu...@fl...
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org