glewInit() crashing (segfault) after creating osme

Question

I'm trying to run an opengl application on a remote computing cluster. I'm using osmesa as I intend to execute off-screen software rendering (no x11 forwarding etc). I want to use glew (to make life dealing with shaders and other extension related calls easier), and I seem to have built and linked both mesa and glew fine.

When I call mesa-create-context, glewinit gives a OPENGL Version not available output, which probably means the context has not been created. When I call glGetString(GL_EXTENSIONS) i dont get any output, which confirms this. This also shows that glew is working fine on its own. (Other glew commands like glew version etc also work).

Now when I (as shown below), add the mesa-make-context-current function, glewinit crashes with a segfault. Running glGetString(GL_EXTENSIONS) gives me a list of extensions now however (which means context creation is successful!)

I've spent hours trying to figure this out, tried tinkering but nothing works. Would greatly appreciate any help on this. Maybe some of you has experienced something similar before?? Thanks again!

int Height = 1; int Width = 1;
OSMesaContext ctx; void *buffer; 
ctx = OSMesaCreateContext( OSMESA_RGBA, NULL );
buffer = malloc( Width * Height * 4 * sizeof(GLfloat) );

if (!OSMesaMakeCurrent( ctx, buffer, GL_UNSIGNED_BYTE, Width, Height )) {
printf("OSMesaMakeCurrent failed!\n");
return 0;
 }
-- glewinit() crashes after this.

Just to add, osmesa and glew actually did not compile initially. Because glew undefines GLAPI in it's last line and since osmesa will not include gl.h again, GLAPI remains undefined and causes an error in osmesa.h (119). I got around this by adding an extern to GLAPI, not sure if this is relevant though.

Answer 1

Looking at the source to glewInit in glew.c if glewContextInit succeeds it returns GLEW_OK, GLEW_OK is defined to 0, and so on Linux systems it will always call glxewContextInit which calls glX functions that in the case of OSMesa will likely not be ready for use. This will cause a segfault (as I see), and it seems that the glewInit function has no capability to handle this case unfortunately without patching the C source and recompiling the library.

If others have already solved this I would be interested, I have seen some patched versions of the glew.c sources that workaround this. It isn't clear if there is any energy in the GLEW community to merge changes in that address this use case.