From f9af0c03766d0570e3a6e32771d09258b7c0d41e Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <icculus@icculus.org>
Date: Tue, 5 Jan 2016 02:27:26 -0500
Subject: [PATCH] x11: Put a matching window_group wmhint on every window
 created.

This is useful to the Window Manager, so it can know to associate multiple SDL
windows with a single app.
---
 src/video/x11/SDL_x11video.c  | 3 +++
 src/video/x11/SDL_x11video.h  | 1 +
 src/video/x11/SDL_x11window.c | 3 ++-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/video/x11/SDL_x11video.c b/src/video/x11/SDL_x11video.c
index 13ddeb5db..a2ea05695 100644
--- a/src/video/x11/SDL_x11video.c
+++ b/src/video/x11/SDL_x11video.c
@@ -376,6 +376,9 @@ X11_VideoInit(_THIS)
     /* Get the process PID to be associated to the window */
     data->pid = getpid();
 
+    /* I have no idea how random this actually is, or has to be. */
+    data->window_group = (XID) (((size_t) data->pid) ^ ((size_t) _this));
+
     /* Open a connection to the X input manager */
 #ifdef X_HAVE_UTF8_STRING
     if (SDL_X11_HAVE_UTF8) {
diff --git a/src/video/x11/SDL_x11video.h b/src/video/x11/SDL_x11video.h
index 61cb58339..de991ca92 100644
--- a/src/video/x11/SDL_x11video.h
+++ b/src/video/x11/SDL_x11video.h
@@ -81,6 +81,7 @@ typedef struct SDL_VideoData
     int numwindows;
     SDL_WindowData **windowlist;
     int windowlistlength;
+    XID window_group;
 
     /* This is true for ICCCM2.0-compliant window managers */
     SDL_bool net_wm;
diff --git a/src/video/x11/SDL_x11window.c b/src/video/x11/SDL_x11window.c
index 7d0914e30..47731cd19 100644
--- a/src/video/x11/SDL_x11window.c
+++ b/src/video/x11/SDL_x11window.c
@@ -524,7 +524,8 @@ X11_CreateWindow(_THIS, SDL_Window * window)
     /* Setup the input hints so we get keyboard input */
     wmhints = X11_XAllocWMHints();
     wmhints->input = True;
-    wmhints->flags = InputHint;
+    wmhints->window_group = data->window_group;
+    wmhints->flags = InputHint | WindowGroupHint;
 
     /* Setup the class hints so we can get an icon (AfterStep) */
     classhints = X11_XAllocClassHint();