#include <X11/Xlib.h>
#include <stdlib.h>
#include <stdio.h>

#include <unistd.h>

const int SIZE = 128;

int main()
{
    //Open connection to the X server
    Display* dpy = XOpenDisplay(NULL);

    //Get the pointer position.. Have to go through all the screens
    bool found       = false;
    int  foundScreen = -1;
    int  x, y; //location of the cursor
    for (int screenNum = 0; screenNum < XScreenCount(dpy); ++screenNum)
    {
        Window tmp1, tmp2;    //Don't care about the windows
        int    tmpx, tmpy;    //Don't care about the local X, Y
        unsigned int tmpMask; //Don't care about the mask

        if (XQueryPointer(dpy, RootWindow(dpy, screenNum), &tmp1, &tmp2, &x, &y, &tmpx, &tmpy, &tmpMask))
        {
            found       = true;
            foundScreen = screenNum;
            break;
        }
    }

    if (!found) //Don't do something unexepected
        return -1;

    //Now, create the indicator window.

    Window ourWindow = XCreateSimpleWindow(dpy, RootWindow(dpy, foundScreen),
                                           x - SIZE/2, y - SIZE/2,
                                           SIZE,       SIZE,
                                           0,  0, BlackPixel(dpy, foundScreen));

    //Don't deal with the WM
    XSetWindowAttributes attrs;
    attrs.override_redirect = True;
    XChangeWindowAttributes(dpy, ourWindow, CWOverrideRedirect, &attrs);
    XSelectInput(dpy, ourWindow, ButtonPressMask | ExposureMask);
    XMapWindow(dpy, ourWindow);

    bool quit = false;

    //We also grab the mouse so any click closes it.
    //(perhaps it would be better if left-click recentered, right-click closed or such?)
    XGrabPointer(dpy, RootWindow(dpy, foundScreen), False, ButtonPressMask, GrabModeAsync, GrabModeAsync,
                 None, None, CurrentTime);

    while (!quit)
    {
        XEvent ev;
        XNextEvent(dpy, &ev);

        switch (ev.type)
        {
            case Expose:
            case GraphicsExpose:
            {
                //Paint the target thingy. Really simple: 4 bands, using black and white, alternating.
                GC gc = XCreateGC(dpy, ourWindow, 0, 0);
                XSetFillStyle(dpy, gc, FillSolid);

                //Outter band is already black, so we paint w/white 1/8th way in
                XSetForeground(dpy, gc, WhitePixel(dpy, foundScreen));
                XFillRectangle(dpy, ourWindow, gc, SIZE/8, SIZE/8, SIZE - SIZE/4, SIZE - SIZE/4);

                //Now another black band
                XSetForeground(dpy, gc, BlackPixel(dpy, foundScreen));
                XFillRectangle(dpy, ourWindow, gc, SIZE/4, SIZE/4, SIZE - SIZE/2, SIZE - SIZE/2);

                //And the inner white one
                XSetForeground(dpy, gc, WhitePixel(dpy, foundScreen));
                XFillRectangle(dpy, ourWindow, gc, 3*SIZE/8, 3*SIZE/8, SIZE/4, SIZE/4);

                XFreeGC(dpy, gc);
                break;
            }
            case ButtonPress:
                quit = true;
                break;
            default:
                break;
        }

    }


    XUngrabPointer(dpy, CurrentTime);
}