On Half-Life 2 AA
Drivers aren't likely to fix the problem, with the exception of the ATI 9500-9800. There's hope there for being able to use FSAA properly. You are out of luck on NVidia unless either NVidia or us come up with some clever way of solving this problem.
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The problem is specifically with multisample antialiasing on any card that uses multisample antialiasing. If you use supersampling you should be fine. Actually, this problem has existed for any game that uses light maps that are packed into a subrect (like Quake 3, etc). You will be able to turn FSAA if you like (in the control panel for your video card), but it's likely to have artifacts on triangle boundaries. We don't recommend turning multisample antialiasing on for cards that don't have centroid sampling. . .your mileage may vary.
Shout outs to XBit , Tiscali, Blues (for the quote), and this forum thread