From c464b8bdcb2c02d7182727a463dd79a7aa6d08d3 Mon Sep 17 00:00:00 2001
From: Kim Woelders <kim@woelders.dk>
Date: Tue, 24 Aug 2021 10:17:47 +0200
Subject: [PATCH] Set _NET_WM_PID on WM check window

Shown by utilities like wmctrl and xrestop.
---
 src/xprop.c     | 4 ++++
 src/xpropdefs.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/xprop.c b/src/xprop.c
index 267f4967..97d5d844 100644
--- a/src/xprop.c
+++ b/src/xprop.c
@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <X11/Xatom.h>
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
@@ -725,9 +726,12 @@ ex_netwm_init(void)
 void
 ex_netwm_wm_identify(EX_Window root, EX_Window check, const char *wm_name)
 {
+   unsigned int        pid = getpid();
+
    ex_window_prop_window_set(root, ea_n._NET_SUPPORTING_WM_CHECK, &check, 1);
    ex_window_prop_window_set(check, ea_n._NET_SUPPORTING_WM_CHECK, &check, 1);
    _ex_window_prop_string_utf8_set(check, ea_n._NET_WM_NAME, wm_name);
+   ex_window_prop_card32_set(check, ea_n._NET_WM_PID, &pid, 1);
 }
 
 /*
diff --git a/src/xpropdefs.h b/src/xpropdefs.h
index f24c85d3..d27cceea 100644
--- a/src/xpropdefs.h
+++ b/src/xpropdefs.h
@@ -148,7 +148,7 @@
    notdef_ATOM_NETWM(_NET_WM_ICON_GEOMETRY)		/* Not used */
    DEFINE_ATOM_NETWM(_NET_WM_ICON)
 
-   notdef_ATOM_NETWM(_NET_WM_PID)			/* Not used */
+   DEFINE_ATOM_NETWM(_NET_WM_PID)
 
    notdef_ATOM_NETWM(_NET_WM_HANDLED_ICONS)		/* Not used */