See this movie: http://www.2shared.com/video/RwpFidK...cylinder.html?
And this code:

---------------------
# glPush + some translation + rotation....

# Enable blending / transparancy
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

# Cylinder color (NB: ALPHA MUST BE < 1, DEFAULT IS 0.5)!
glColor4f(1.0, 1.0, 1.0, 0.2)

# Draw ends of cylinder:
cyl_obj = gluNewQuadric();

cylHgt = 0.2
glTranslate( 0.0, 0.0, -cylHgt/2 )

# Draw cylinder:
# gluDisk (GLUquadricObj, innerRadius, outerRadius, slices, rings)
gluDisk(cyl_obj, 0.0, 0.1, 12, 1);

# gluCylinder(gluNewQuadr, Radius_base, Radius_top,
# height, slices, stacks)
gluCylinder(cyl_obj, 0.1, 0.1, cylHgt, 12, 1);

glTranslate( 0.0, 0.0, cylHgt )
gluDisk(cyl_obj, 0.0, 0.1, 12, 1);

glPopMatrix() # -- POP PROJECTION MATRIX
---------------------

My question is: Why does the cylinder look like one side of it is different in terms of transparency, compared to the other side of the cylinder ?

http://www.2shared.com/video/RwpFidK...cylinder.html?

I mean: When the movie start, you can see that the whole cylinder has the same color everywhere... Then after a few seconds you see a dark spot moving along one of the rotating axes - is it due to lighting ? I don't understand this - I don't think it looks right and I don't think I want this behaviour...

Thank you for any ideas/comments/suggestions...!