>>1
きわめて簡易

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

main()
{
Display *disp;
Window win;

disp = XOpenDisplay(NULL);
win = XCreateSimpleWindow(disp, RootWindow(disp, 0),
0, 0, 400, 300, 1, BlackPixel(disp, 0), WhitePixel(disp, 0));
XMapWindow(disp, win);
XFlush(disp);
while(True);
}