#include <stdio.h>
#include <X11/Xlib.h>
#include <GL/glx.h>

/* build: gcc -Wall simple.c -o simple $(pkg-config --cflags --libs gl x11)
   run: for i in {0..300}; do (./simple &); done
*/

int main(int argc, char *argv[])
{
   int width = 128;
   int height = 128;
   int glAttribs[] = {
      GLX_RGBA,
      GLX_DEPTH_SIZE, 1,
      None
   };
   Display *dpy;
   XVisualInfo *visInfo;
   int scrn;
   Window root;
   Window win;
   XSetWindowAttributes winAttribs;
   unsigned long winAttribsMask;
   GLXContext glCtx;

   dpy = XOpenDisplay(NULL);
   if (!dpy) {
      fprintf(stderr, "Couldn't open default display\n");
      return 1;
   }

   scrn = DefaultScreen(dpy);

   root = RootWindow(dpy, scrn);

   visInfo = glXChooseVisual(dpy, scrn, glAttribs);
   if (!visInfo) {
      fprintf(stderr, "Failed to select visual\n");
      return 1;
   }

   glCtx = glXCreateContext(dpy, visInfo, 0, True);
   if (!glCtx) {
      fprintf(stderr, "Couldn't create GL context\n");
      return 1;
   }

   winAttribs.border_pixel = 0;
   winAttribs.colormap = XCreateColormap(dpy, root, visInfo->visual, AllocNone);
   winAttribs.event_mask = StructureNotifyMask | ExposureMask | KeyPressMask;
   winAttribsMask = CWBorderPixel | CWColormap | CWEventMask;
   win = XCreateWindow(dpy, root, 0, 0, width, height, 0,
                       visInfo->depth, InputOutput,
                       visInfo->visual,
                       winAttribsMask, &winAttribs);

   XMapWindow(dpy, win);

   glXMakeCurrent(dpy, win, glCtx);

   printf("GL_RENDERER = %s\n", (char *) glGetString(GL_RENDERER));

   glViewport(0, 0, width, height);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();

   while (1) {
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   
      glColor3f(1.0, 1.0, 1.0);
      glBegin(GL_LINE);
      glVertex2f(-1.0, -1.0);
      glVertex2f( 1.0, -1.0);
      glVertex2f(1.0, 1.0);
      glVertex2f(-1.0, 1.0);
      glEnd();
   
      glFlush();
      //same result with glXSwapBuffers(dpy, win);
   }

   return 0;
}