Friday, July 18, 2014

"Invalid parameter" debug messages when using wxGLCanvas

While debugging a problem with wxGLCanvas today, I noticed that every run of the OpenGL cube sample resulted in several copies of the following message in the MSVS debug output window:

Invalid parameter passed to C runtime function.

Now this is an error message just as I love them: it's worrisome enough to make you feel like you ought to do something about it, but without any information allowing you to find out what, actually, should be done. Luckily, there are not that many ways to write to the debug output under Windows and putting a breakpoint on OutputDebugStringA() (surprisingly used instead of OutputDebugStringW() that I tried first) discovered that the debug message was given from deep inside GDI ChoosePixelFormat() function which ends up calling wglChoosePixelFormat() in opengl32.dll which, in turn, calls into ATI driver DLL (atioglxx.dll) which ends up calling _wcscpy_s() with a NULL parameter which is clearly a bug, but it's not our bug.

So, finally the problem is not related to wxWidgets, even if you will see it every time you use wxGLCanvas with (this, buggy, version of) ATI OpenGL drivers. But at the very least I now know that if I see this message again, I can set a breakpoint on {,,msvcrt.dll}__invoke_watson function, using MSVS debugger idiosyncratic syntax, and directly see where does the problem occur. Hopefully this can be useful to someone else too and maybe it will save you some time chasing bugs in ATI code.

Ah, and the original problem which started all this? It turned out to be bogus. Today hasn't been very productive so far...

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