Re: Antialiasing in GL contexts
the columns 'ns' and 'b' under 'ms' in glxinfo are the number of samples and buffers with multisample visuals. On Quadro FX 5500 cards I get ones like 16 1 and 8 1, for 'ms' and 'b' respectively. However, you point is right, even if you get a multisample visual with fbconfig, that's not enough like it was on the older SGI/IRIX system, you also need the environment variable set telling it which type of multisample you want to use (I prefer 7, 4x supersample, 4x multi).
So....there seem to be no way to toggle multi sample on/off programatically like on older systems that I've found. The OpenGL call, glEnable( GL_MULTISAMPLE ) also seems to have no effect, nor does glHint(GL_MULTISAMPLE_FILTER_HINT_NV, GL_NICEST) that I've detected. I found it an odd mechanism as well. And again, there's also a global override in the nvidia-settings control panel as well. I don't recall which of those two takes precedence. Seems like the method was created to cater to applications (especially games) which might not have considered multisample when they were created.
Hope that helps.