OpenGL Quirks in Linux

November 5, 2005 5:36 PM
I had trouble linking to the Irrlicht library. It always complained that linking to glXGetProcAddress() failed. As always, google didn't fail me and I found out the cause of the problem. Typically, GLX implementation of the NVIDIA driver does not have glXGetProcAddress. The patch for this in Irrlicht is simple, you have to modify COpenGLDriver.cpp by adding the following line after #ifdef _IRR_COMPILE_WITH_OPENGL_:

#define glXGetProcAddress glXGetProcAddressARB

Once you do this, compile Irrlicht.

What this means to developers using OpenGL

To recap, linking issues with glXGetProcAddress() probably mean an Nvidia driver is installed in Linux. Just change all glXGetProcAddress() calls using the above #define to glXGetProcAddressARB() calls. This fix only works for me if the define is placed before including glx.h.

So how do you handle this portably? Obviously, there are people out there with Nvidia drivers installed and there are others with a perfectly working glXGetProcAddress. This is where autoconf comes to one's rescue. If you're not familiar with autoconf/automake, then this would be the time to get familiar with it.

This simple autoconf test will check exactly for such a situation and defines a special variable in case it is encountered when the user runs ./configure:

#after checking for opengl

have_glx=no

AC_CHECK_HEADER([GL/glx.h], have_glx=yes,
			    AC_MSG_ERROR([Required file glx.h
			    missing!]))

if test "$have_glx" = yes; then

have_procaddr=no

AC_CHECK_FUNCS([glXGetProcAddress], have_procaddr=yes,
	AC_MSG_WARN([glXGetProcAddress is not linkable. Enabling fix for such a situation...]))

 if test "$have_procaddr" = no; then
    AC_CHECK_FUNCS([glXGetProcAddressARB],AC_DEFINE(HAVE_GLX_BUT_NO_GLXGETPROCADDR),
      AC_MSG_ERROR([You don't have glXGetProcAddressARB as well. Bailing!]))
 fi

fi

Once you put this in configure.in, and include config.h (generated by autoheader), the following code in your C or C++ source file will automatically enable this fix.

/* add config.h */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#ifdef HAVE_GLX_BUT_NO_GLXGETPROCADDR
/* This has to come before glx.h is included. */
#define glXGetProcAddress glXGetProcAddressARB
#endif

#include <GL/glx.h>
#endif

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