SpectrWM XTerm Background Color Change on Focus

bashrc

finish() {
  rm ${HOME}/.xterm-bash/$PPID
}

trap finish EXIT

echo -en $$ > ${HOME}/.xterm-bash/$PPID

spectrwm.c.patch

diff --git a/spectrwm.c b/spectrwm.c
index 9b0ad2c..f76a828 100644
--- a/spectrwm.c
+++ b/spectrwm.c
@@ -1055,6 +1055,7 @@ void	 focus(struct binding *, struct swm_region *, union arg *);
 void	 focus_flush(void);
 void	 focus_pointer(struct binding *, struct swm_region *, union arg *);
 void	 focus_region(struct swm_region *);
+void	 send_xterm_command(struct ws_win *, int, char *);
 void	 focus_win(struct ws_win *);
 void	 focusin(xcb_focus_in_event_t *);
 #ifdef SWM_DEBUG
@@ -3960,6 +3961,63 @@ unfocus_win(struct ws_win *win)
 	    ewmh[_NET_ACTIVE_WINDOW].atom, XCB_ATOM_WINDOW, 32, 1, &none);
 
 	DNPRINTF(SWM_D_FOCUS, "unfocus_win: done.\n");
+
+	send_xterm_command(win, 11, "GRAY");
+}
+
+void send_xterm_command(struct ws_win *win, int command, char *data) {
+
+	xcb_atom_t			apid;
+	xcb_get_property_cookie_t	pc;
+	xcb_get_property_reply_t	*pr;
+	pid_t				xterm_pid = 0;
+	char filename[256];
+	char bash_stdin[32];
+	int bash_pid = 0;
+	FILE *f = NULL;
+	char xterm_command[64];
+
+	if (!win || !win->id) {
+		return;
+	}
+
+	if (0 != strncmp("XTerm", win->ch.class_name, 6)) {
+		return;
+	}
+
+	// 1. Get PID of XTerm
+	apid = get_atom_from_string("_NET_WM_PID");
+	if (apid != XCB_ATOM_NONE) {
+		pc = xcb_get_property(conn, 0, win->id, apid, XCB_ATOM_CARDINAL, 0, 1);
+		pr = xcb_get_property_reply(conn, pc, NULL);
+		if (pr) {
+			if (pr->format == 32) {
+				xterm_pid = *((pid_t *)xcb_get_property_value(pr));
+				// 2. Get PID of child process (bash)
+				sprintf(filename, "%s/.xterm-bash/%d", getenv("HOME"), xterm_pid);
+				f = fopen(filename, "rb");
+				if (f) {
+					fscanf(f, "%d", &bash_pid);
+					fclose(f);
+				} else {
+					printf("\n%s file wasn't created!\n", filename);
+				}
+			}
+
+			free(pr);
+		}
+	}
+
+	if (bash_pid) {
+		// 3. Send escape sequence directly to that process
+		sprintf(bash_stdin, "/proc/%d/fd/0", bash_pid);
+		f = fopen(bash_stdin, "w");
+		if (f) {
+			sprintf(xterm_command, "\e]%d;%s\a", command, data);
+			fwrite(xterm_command, strlen(xterm_command), 1, f);
+			fclose(f);
+		}
+	}
 }
 
 void
@@ -4106,6 +4164,8 @@ focus_win(struct ws_win *win)
 	}
 
 out:
+	send_xterm_command(win, 11, "WHITE");
+
 	free(gifr);
 	free(war);
 	DNPRINTF(SWM_D_FOCUS, "focus_win: done.\n");