//g++ little.C -lGL -lX11
#include "GL/glx.h"	///usr/include/GL
#include "GL/gl.h"

#include <iostream>
#include <cstdlib>
using namespace std;

int main()
{
	Display *const display = XOpenDisplay(0);
	if (display == 0) {
		cerr << "Could not open a display.\n";
		return EXIT_FAILURE;
	}

	cout << "Opened a display whose connection number is "
		<< XConnectionNumber(display) << ".\n";

        if (!glXQueryExtension(display, 0, 0)) {
                cerr << "X server has no OpenGL GLX extension.\n";
                return EXIT_FAILURE;
        }

	cout << "The display has an OpenGL GLX extension.\n";

	if (const GLubyte *const p = glGetString(GL_EXTENSIONS)) {
		cout << "GL extensions: \"" << p << "\"\n";
	} else {
		cout << "No GL extensions.\n";
	}

        int attributeList[] = {
                //GLX_RGBA,
                GLX_DOUBLEBUFFER,
                GLX_DEPTH_SIZE, 24,
                None
        };

        XVisualInfo *const visual =
                glXChooseVisual(display, DefaultScreen(display), attributeList);
        if (visual == 0) {
                cerr << "Couldn't get a Visual\n";
                return EXIT_FAILURE;
        }

	/*
	Before i5.nyu.edu had /dev/winlock,
	glXCreateContext caused Xvfb to Segmentation Fault(coredump).
	Now that we have /devwinlock,
	glXCreateContext causes Xvfb say fstat: Bad file number.
	*/
        const GLXContext context =
		glXCreateContext(display, visual, 0, GL_TRUE);

        if (context == 0) {
                cerr << "Couldn't get a GLXContext\n";
                return EXIT_FAILURE;
        }

	XCloseDisplay(display);
	cout << "The display is closed.\n";
	return EXIT_SUCCESS;
}