#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <assert.h>
#include <unistd.h>

#include <X11/Xlib.h>
#include <EGL/egl.h>
#include <GL/gl.h>

static XVisualInfo *
get_visual_info (Display *xdisplay, EGLDisplay *edisplay, EGLConfig egl_config)
{
  XVisualInfo visinfo_template;
  int template_mask = 0;
  XVisualInfo *visinfo = NULL;
  int visinfos_count;
  EGLint visualid;

  eglGetConfigAttrib(edisplay, egl_config,
                     EGL_NATIVE_VISUAL_ID, &visualid);
  assert(visualid != 0);

  visinfo_template.visualid = visualid;
  template_mask |= VisualIDMask;

  visinfo = XGetVisualInfo(xdisplay,
                           template_mask,
                           &visinfo_template,
                           &visinfos_count);

  return visinfo;
}

int main(int argc, char **argv)
{
  Display *xdisplay;
  EGLDisplay edisplay;
  EGLint ver_major, ver_minor;
  EGLint cfg_attributes[] = {
    EGL_RED_SIZE, 1,
    EGL_GREEN_SIZE, 1,
    EGL_BLUE_SIZE, 1,
    EGL_ALPHA_SIZE, EGL_DONT_CARE,
    EGL_DEPTH_SIZE, 1,
    EGL_BUFFER_SIZE, EGL_DONT_CARE,
    EGL_RENDERABLE_TYPE, EGL_OPENGL_BIT,
    EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
    EGL_NONE
  };
  EGLint context_attributes[] = {
    EGL_NONE
  };
  EGLConfig config;
  EGLContext context;
  EGLint n_configs;
  XVisualInfo *xvisual;
  Window win1, win2;
  EGLSurface surf1, surf2;
  XSetWindowAttributes attrs;
  XEvent xevent;
  Atom xdelete, xprotocols;

  xdisplay = XOpenDisplay(NULL);
  edisplay = eglGetDisplay(xdisplay);
  eglInitialize(edisplay, &ver_major, &ver_minor);

  eglBindAPI(EGL_OPENGL_API);

  n_configs = 0;
  eglChooseConfig(edisplay, cfg_attributes,
                  &config, 1, &n_configs);
  assert(n_configs == 1);

  context = eglCreateContext(edisplay, config, EGL_NO_CONTEXT,
                             context_attributes);
  assert(context != EGL_NO_CONTEXT);

  xvisual = get_visual_info(xdisplay, edisplay, config);

  attrs.override_redirect = True;
  attrs.colormap = XCreateColormap(xdisplay, DefaultRootWindow(xdisplay),
                                   xvisual->visual, AllocNone);
  attrs.border_pixel = 0;

  win1 = XCreateWindow(xdisplay, DefaultRootWindow(xdisplay),
                       -100, -100, 1, 1, 0,
                       xvisual->depth, InputOutput,
                       xvisual->visual,
                       CWOverrideRedirect|CWColormap|CWBorderPixel,
                       &attrs);

  surf1 = eglCreateWindowSurface(edisplay, config, (NativeWindowType)win1,
                                 NULL);

  eglMakeCurrent(edisplay, surf1, surf1, context);

  attrs.background_pixel = WhitePixel(xdisplay, DefaultScreen(xdisplay));
  attrs.border_pixel = 0;

  win2 = XCreateWindow(xdisplay, DefaultRootWindow(xdisplay),
                       0, 0, 640, 480, 0,
                       xvisual->depth, InputOutput,
                       xvisual->visual,
                       CWBorderPixel|CWColormap|CWBackPixel,
                       &attrs);
  surf2 = eglCreateWindowSurface(edisplay, config, (NativeWindowType)win2,
                                 NULL);

  XFree(xvisual);

  xdelete = XInternAtom(xdisplay, "WM_DELETE_WINDOW", False);
  xprotocols = XInternAtom(xdisplay, "WM_PROTOCOLS", False);
  XSetWMProtocols(xdisplay, win2, &xdelete, 1);

  XMapWindow(xdisplay, win2);

  eglMakeCurrent(edisplay, surf2, surf2, context);

  glViewport(0, 0, 640, 480);
  glClearColor(1, 0, 1, 1);
  glClear(GL_COLOR_BUFFER_BIT);

  eglSwapBuffers(edisplay, surf2);

  for (;;) {
    XNextEvent(xdisplay, &xevent);

    if (xevent.type == ClientMessage &&
        xevent.xclient.message_type == xprotocols &&
        xevent.xclient.format == 32 &&
        xevent.xclient.data.l[0] == xdelete)
      return 0;
  }
}