I have a texture mapped object that I am putting through a fragment shader. The original texture mapped to the object is anti-aliased, but I think that the fragment shader only works on the pixel level. So in my case, if I have an anti-aliased line, half the pixel might be black and half of it white. My fragment shader should act on black pixels, but I only want to apply it to the part of the pixel that is actually black. Is that possible?