glXSwapIntervalSGI segfault

Question

I'm trying to disable vertical sync on Linux in a program built around SDL and openGL. I am running an old integrated ATI card with Gallium 0.4 as the driver.

I attempt to disable vsync by calling glXSwapInterval(0) in my code, but when I do this, although the program compiles fine, I get a segfault when I try to run it.

gdb gives me the rather unhelpful message:

Program received signal SIGSEGV, Segmentation fault.
0x00000000 in ?? ()

Does anyone have any idea as to what might be going on?

Answer 1

glXSwapIntervalEXT and glXSwapIntervalSGI are extension functions; You normally access extensions' function addresses through glXGetProcAddress, though some libGL.so may export them directly.

Most easy solution: Get a OpenGL extension loader library, like GLEW (it's in all major Linux distribution's package repositories). Replace all occurances of #include <GL/gl.h> with #include <GL/glew.h> and #include <GL/glx.h> with #include <GL/glxew.h>, add libGLEW.so to your list of linked libraries, and call glewInit() right after creating and binding a OpenGL context. Then test if the extension is actually available!