hello_world.c

/* x11 c interface hello world
 *
 * Expected outcome: shows a window with white background
 * and a black X drawn on it.
 *
 * Exit when either:
 *
 * - the X close button of the window is clicked
 * - a mouse on the window is released
 */

#include <stdlib.h>

#include "X11/Xlib.h"

int main(void) {
    Display *dsp = XOpenDisplay(NULL);
    if (!dsp) {
        return EXIT_FAILURE;
    }
    int screenNumber = DefaultScreen(dsp);
    unsigned long white = WhitePixel(dsp, screenNumber);
    unsigned long black = BlackPixel(dsp, screenNumber);
    Window win = XCreateSimpleWindow(
        dsp,
        DefaultRootWindow(dsp),
        50, 50,
        200, 200,
        0, black,
        white
    );
    XMapWindow(dsp, win);
    long eventMask = StructureNotifyMask;
    XSelectInput(dsp, win, eventMask);
    XEvent evt;
    do {
        XNextEvent(dsp, &evt);
    } while (evt.type != MapNotify);
    GC gc = XCreateGC(dsp, win, 0, NULL);
    XSetForeground(dsp, gc, black);
    XDrawLine(dsp, win, gc, 10,  10, 190, 190);
    XDrawLine(dsp, win, gc, 10, 190, 190,  10);
    eventMask = ButtonPressMask | ButtonReleaseMask;
    XSelectInput(dsp, win, eventMask);
    do {
        XNextEvent(dsp, &evt);
    } while (evt.type != ButtonRelease);
    XDestroyWindow(dsp, win);
    XCloseDisplay(dsp);
    return EXIT_SUCCESS;
}