Thursday, December 20, 2007

"Driver Bugs"

I have spent perhaps the last two weeks tracking down driver-related problems. But the term "driver bug" is heavily overused (blog around and you'll see that many OpenGL developers get frustrated...) A few examples of the gray areas:
  • Sometimes there will be a bug in application code that shows up only on certain hardware. Drivers are concerned with making video cards go fast, not spanking programmers who don't know what they're doing. This is exactly what happened to me in beta 2 with the crash-on-nVidia-with-C172 bug. This was just plain broken code in X-Plane, but for some reason the ATI drivers didn't have a problem with it (probably because they were performing an optimization which let them ignore the bogus call I made). NVidia specific, but not NVidia's fault!
  • On OS X with the Radeon 9600XT, runway lights don't show up. Adding an extra line to the pixel shaders "fixes" the problem. I believe the problem is in the driver (or the shader compiler more specifically) but by changing the code to the shader we work around the problem. A change in X-Plane addresses the problem, but not X-Plane's fault!
  • The "36061" errors that some users have been seeing turn out to be because (through a very convoluted chain of events) X-Plane was asking the video card to operate in a mode that it could not operate in. Turns out this can be fixed by changing X-Plane's code (fix will be in beta 12) or by getting new drivers. This one wasn't really a driver bug - more that the drivers were limited in a way X-Plane did not expect. (Our fault for being picky!)
The situation is fundamentally tricky - games are integrators of other people's technology - as such, we get blamed by the end user for a fault anywhere in the system. At the same time, it's way too easy to turn around and blame the part supplier, and unfair when the source of the bug hasn't been identified.

I am looking now at problems on Windows with dual core machines and nVidia cards. The problem goes away both by changing a registry setting that affects the driver and by changing X-Plane's code. So I think it's too soon to tell on this one.

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