1 /*
    2   gcc -lX11 xtopmost.c
    3  */
    4 #include <X11/X.h>
    5 #include <X11/Xlib.h>
    6 #include <X11/Xutil.h>
    7 
    8 #include <stdlib.h>
    9 #include <string.h>
   10 #include <stdio.h>
   11 
   12 #define _NET_WM_STATE_REMOVE        0
   13 #define _NET_WM_STATE_ADD           1
   14 #define _NET_WM_STATE_TOGGLE        2
   15 
   16 Bool set_always_on_top(Display *dpy, Window wnd)
   17 {
   18         Atom wmStateAbove, wmNetWmState;
   19         XClientMessageEvent xclient;
   20 
   21         wmStateAbove = XInternAtom(dpy, "_NET_WM_STATE_ABOVE", 1);
   22         if (wmStateAbove == None)
   23                 goto fail_above;
   24 
   25         wmNetWmState = XInternAtom(dpy, "_NET_WM_STATE", 1);
   26         if (wmNetWmState == None)
   27                 goto fail_state;
   28 
   29         memset(&xclient, 0, sizeof(xclient));
   30         xclient.type = ClientMessage;
   31         xclient.window = wnd;
   32         xclient.message_type = wmNetWmState;
   33         xclient.format = 32;
   34         xclient.data.l[0] = _NET_WM_STATE_ADD;
   35         xclient.data.l[1] = wmStateAbove;
   36 
   37         XSendEvent(dpy, DefaultRootWindow(dpy), False,
   38                    SubstructureRedirectMask | SubstructureNotifyMask,
   39                    (XEvent *)&xclient);
   40 
   41         XFlush(dpy);
   42         return True;
   43 fail_above:
   44         fputs("cannot find _NET_WM_STATE_ABOVE atom\n", stderr);
   45         return False;
   46 fail_state:
   47         fputs("cannot find _NET_WM_STATE atom\n", stderr);
   48         return False;
   49 }
   50 
   51 int main(void)
   52 {
   53         int run = 1, status = EXIT_FAILURE;
   54         Atom atom_wm_delete;
   55         Display* dpy;
   56         Window wnd;
   57         XEvent e;
   58 
   59         /* open a conenction to the display server */
   60         dpy = XOpenDisplay(NULL);
   61         if (!dpy) {
   62                 fputs("cannot open display!\n", stderr);
   63                 return EXIT_FAILURE;
   64         }
   65 
   66         atom_wm_delete = XInternAtom(dpy, "WM_DELETE_WINDOW", True);
   67         if (atom_wm_delete == None) {
   68                 fputs("cannot find WM_DELETE_WINDOW atom\n", stderr);
   69                 return EXIT_FAILURE;
   70         }
   71 
   72         /* create window */
   73         wnd = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy),
   74                                   0, 0, 200, 100, 0, 0, 0);
   75         if (!wnd) {
   76                 fputs("cannot create window!\n", stderr);
   77                 goto outdpy;
   78         }
   79 
   80         XSelectInput(dpy, wnd, ExposureMask | StructureNotifyMask);
   81         XSetWMProtocols(dpy, wnd, &atom_wm_delete, 1);
   82         XFlush(dpy);
   83 
   84         XStoreName(dpy, wnd, "Always on top!");
   85         XMapWindow(dpy, wnd);
   86 
   87         /* in this function, we set the window manager hint */
   88         set_always_on_top(dpy, wnd);
   89 
   90         /* event loop */
   91         while (run) {
   92                 XNextEvent(dpy, &e);
   93 
   94                 switch (e.type) {
   95                 case Expose:
   96                         XClearWindow(dpy, e.xany.window);
   97                         XFlush(dpy);
   98                         break;
   99                 case ClientMessage:
  100                         if (e.xclient.data.l[0] == (long)atom_wm_delete) {
  101                                 XUnmapWindow(dpy, wnd);
  102                                 run = 0;
  103                         }
  104                         break;
  105                 }
  106         }
  107 
  108         /* cleanup */
  109         status = EXIT_SUCCESS;
  110         XDestroyWindow(dpy, wnd);
  111 outdpy:
  112         XCloseDisplay(dpy);
  113         return status;
  114 }