// build with:
// $ gcc -std=gnu99 `pkg-config --cflags --libs gl ` q.c

#define _XOPEN_SOURCE   500
#define GL_GLEXT_PROTOTYPES
#include <GL/glx.h>
#include <stdio.h>
#include <X11/Xlib.h>
#include <unistd.h>

int main(void)
{
    Display *dpy = XOpenDisplay(NULL);
    Window root = DefaultRootWindow(dpy);
    Window wnd1 = XCreateSimpleWindow(dpy, root, 0, 0, 10, 10, 0, 0, 0);
    Window wnd2 = XCreateSimpleWindow(dpy, root, 0, 0, 10, 10, 0, 0, 0);

    GLint att[] = { GLX_RGBA, GLX_DEPTH_SIZE, 24, GLX_DOUBLEBUFFER, None };
    XVisualInfo *vi;
    vi = glXChooseVisual(dpy, 0, att);
    if (NULL == vi) {
        fprintf(stderr, "failed to choose visual\n");
        return 1;
    }

    GLXContext glc = glXCreateContext(dpy, vi, NULL, GL_TRUE);

    printf("playing with context\n");
    for (int k = 0; k < 1000; k ++) {
        printf(".");
        fflush(stdout);
        for (int j = 0; j < 100; j ++) {
            glXMakeCurrent(dpy, wnd1, glc);
            glXMakeCurrent(dpy, wnd2, glc);
            glXSwapBuffers(dpy, wnd2);
        }
    }
    printf("done\n");
    return 0;
}