X-Plane is marketed as the "most thorough, flexible, and realistic flight simulator available for personal computers" and ships not only for Windows and Macintosh platforms but also for Linux. Laminar Research produces X-Plane and while it's currently not part of our testing suite, we recently took X-Plane v9 Beta 18 for a test flight. Previously their community leader had classified using ATI Linux drivers with X-Plane as an "unusable disaster" with "insurmountable problems", but is that really the case? We explored the situation in this article.
Just be glad they offer an alternate mode other than framebuffer objects (FBOs) to provide programmatically generated textures- some won't do the PBuffer thing anymore or won't provide non-programmatic texture support without FBO's. It's an ARB extension that really makes things a lot easier to do for that sort of thing. Without them, you have to make an off-screen GUI rendering surface for the OS you are using, render into it, map into the UI pixel buffer (PBuffers- which may/may not work as well as it ought to depending on how well tied into the OS the driver actually is and how much resources the UI portions of the system have to make that surface for you...) and then copy from that mapping into a texture object.
Messy. Some modern code doesn't even GO there- either it's got proper FBO support, or it doesn't even run.
At least it works. I'll suspect they're missing something in their normals or like it for their shaders- NVidia will default some things to be the "expected" way, AMD with the ATI shader compiler won't. That's the usual reason for something looking like crap on the AMD stuff and not on NVidia when it comes to shader based stuff.