#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>
#include <X11/Xlib.h>
#include <X11/keysym.h>

#define ARRAY_LENGTH(a) (sizeof (a) / sizeof ((a)[0]))
static const int width = 400;
static const int height = 300;

static void
draw (Display *dpy, Drawable drawable, GC gc)
{
    XPoint points0[] = {
        { -10,  20 },
        {  20, -10 },
        {  40,  20 },
        {  60, -20 },
    };

    XPoint points1[] = {
        { -2, 40 },
        {  0, 42 },
        {  2, 40 },
        {  4, 42 },
        {  6, 40 },
    };

    XPoint points2[] = {
        { -2, 50 },
        {  0, 52 },
        {  2, 50 },
        {  4, 52 },
        {  6, 50 },
    };

    XDrawLines (dpy, drawable, gc,
                points0, ARRAY_LENGTH (points0), CoordModeOrigin);
    XDrawLines (dpy, drawable, gc,
                points1, ARRAY_LENGTH (points1), CoordModeOrigin);
    XDrawLines (dpy, drawable, gc,
                points2, ARRAY_LENGTH (points2), CoordModeOrigin);
}

int 
main (int argc, char **argv)
{
    Display *display;
    Window win;
    unsigned long event_mask;
    GC gc;
    Visual *visual;
    Colormap cmap;
    XEvent xev;
    XGCValues gcv;
    XSetWindowAttributes attributes;
    int scr, depth;
    const char *display_name;

    display_name = getenv ("DISPLAY");
    display = XOpenDisplay (display_name);
    if (display == NULL) {
        fprintf (stderr, "Failed to open display: %s\n", display_name);
        return 1;
    }

    scr = DefaultScreen (display);
    cmap = DefaultColormap (display, scr);
    visual = DefaultVisual (display, scr);
    depth = DefaultDepth (display, scr);

    attributes.background_pixel = WhitePixel(display, scr);
    win = XCreateWindow (display, RootWindow (display, scr),
                         0, 0, width, height, 0, depth,
                         InputOutput, visual,
                         CWBackPixel, &attributes);

    gcv.foreground = BlackPixel(display, scr);
    gc = XCreateGC(display, win, GCForeground, &gcv);

    event_mask = (KeyPressMask | StructureNotifyMask | ExposureMask);
    XSelectInput (display, win, event_mask);

    XMapWindow (display, win);

    while (1) {
        XNextEvent (display, &xev);

        switch (xev.xany.type) {
        case KeyPress:
            if (XKeycodeToKeysym (display, xev.xkey.keycode, 0) == XK_q)
                goto out;
            break;

        case ConfigureNotify:
        case Expose:
            draw (display, win, gc);
            break;
        }
    }

 out:
    XFreeGC (display, gc);
    XDestroyWindow (display, win);
    XCloseDisplay (display);

    return 0;
}