Programs may fail to link to libGLEW

[jengelh]

Version: 2.2.0 (tar.gz)

Given this source file:

#include <GL/glxew.h>
int main()
{
        auto x = GLXEW_SGIX_fbconfig;
}

it will compile under standard GLEW,

22:15 a4:~ $ g++ -Wall -c x.cpp
x.cpp: In function ‘int main()’:
x.cpp:4:14: warning: unused variable ‘x’ [-Wunused-variable]
    4 |         auto x = GLXEW_SGIX_fbconfig;
      |              ^
22:15 a4:~ $ g++ x.cpp -lGLEW
22:15 a4:~ $ 

but if GLEW is built with EGL instead, the build fails at the link stage.

22:14 a4:~ $ g++ -Wall -c x.cpp
x.cpp: In function ‘int main()’:
x.cpp:4:14: warning: unused variable ‘x’ [-Wunused-variable]
    4 |         auto x = GLXEW_SGIX_fbconfig;
      |              ^
22:14 a4:~ $ g++ x.o -lGLEW
/usr/lib64/gcc/x86_64-suse-linux/15/../../../../x86_64-suse-linux/bin/ld: x.o: in function `main':
x.cpp:(.text+0x5): undefined reference to `__GLXEW_SGIX_fbconfig'
collect2: error: ld returned 1 exit status

What should ideally happen instead is that the compilation already fails. Possible options include: (1.) not offering OpenGL-specific symbol anmes in glxew.h when GLEW was built with EGL, (2.) not shipping glxew.h at all.

Or am I missing something and x.cpp should have tested for some macro to see whether OpenGL/EGL is in use in the first place?

[nigels-com]

#include <GL/glxew.h>

The code compiled for GLX GLEW, but would not link with EGL GLEW.
As expected and intended.

[jengelh]

But user code has no way to distinguish a GLX-based glew from a EGL-based glew (and e.g. aborting ./configure in the user code early on).

[nigels-com]

GLEW doesn't have an opinion about WGL, GLX or EGL.
The conundrum on Linux is that it is sometimes clearly GLX, sometimes clearly EGL, sometimes not clear at all.

[nigels-com]

Perhaps a problem for FindGLEW.
Looking at FindOpenGL what to do if both OpenGL::GLX and OpenGL::EGL are detected? Assume GLX?