fake_glvendor.c

/*
 * clang -O2 -s -lGL -ldl -shared fake_glvendor.c -fPIC -o fake_glvendor.so
 */

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

#include <GL/gl.h>

static const GLubyte* (*real_glGetString)(GLenum name) = NULL;
static char *vendor = NULL;
static char *renderer = NULL;

void __attribute__ ((constructor)) ctor(void) {
    real_glGetString = dlsym(RTLD_NEXT, "glGetString");
    if(real_glGetString == NULL) {
        fprintf(stderr, "[fake_glvendor] Failed to dlsym 'glGetString': %s\n", dlerror());
        abort();
    }

    vendor = getenv("FAKE_VENDOR");
    renderer = getenv("FAKE_RENDERER");
}

const GLubyte* glGetString(GLenum name) {
    if(name == GL_VENDOR) {
        return (GLubyte*) vendor;
    }

    if(name == GL_RENDERER) {
        return (GLubyte*) renderer;
    }

    return real_glGetString(name);
}