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  1. Hello, Mr. Lottes. I apologize for rudely hijacking this blog post with an (at least partly) unrelated comment, but I was unable to find an email address to use instead.

    I'm having problems with FXAA 3.11. For some reason, the OpenGL FXAA shader is not working properly on my GTX 770. I have managed to reproduce the problem on a GTX 780 but not on my GTX 460M. The problem occurred suddenly after a driver update without any changes at all to the shader.

    FXAA Off: http://i.imgur.com/FkfrazB.jpg
    FXAA On: http://i.imgur.com/TMmvE8T.jpg
    FXAA On with gather4 enabled: http://i.imgur.com/aLQk8gD.jpg

    With FXAA enabled and gather4 disabled, FXAA is not working correctly and fails to handle lines that are almost vertical or horizontal. Enabling gather4 magically solves the problem.

    Here's the shader I am using: http://pastebin.com/Preu7Y3c I have only modified the top part and added the main() method. All input value are correct.

    I understand that you're no longer affiliated with Nvidia, but I just wanted to inform you since you are the creator of this shader. I've had very bad experience with reporting driver bugs to Nvidia (read: not knowing where to report them), so if you're not interested perhaps you could at least point me in the right direction?


    1. I'd try posting on the OpenGL forum at,


      With the title "OpenGL shader compiler bug with FXAA, regression in driver ???.?? isolated to Kepler GPUs only", filling in the ???.?? with the driver you have problems with. Then in the body fill in as much info as you have. For instance what driver did you have before the update. This will help them narrow down the change list range for when the regression happened. The GTX 460M is a Fermi GPU, the GTX 770 and GTX 780 are Kepler based GPUs, this will help them isolate it. BTW, for FXAA you really do want gather4 enabled, it should be the faster path from what I remember. Chances are that if FXAA is in their QA tests, they have gather4 enabled (the driver FXAA would have this enabled), so maybe they wouldn't catch any problem when gather4 is disabled. However compiler bugs are important regardless, so I'd still file the bug.

      If you don't get progress on the dev forum, then drop another message here. In theory they'd respond to the dev forum, but I haven't been there for a while so I don't know exactly any more.

      Hope that helps.

    2. Thank you for your help! I have posted a thread on the DevTalk forum:


      Let's hope this will be fixed soon. ^^