Add SDL_HINT_VIDEO_X11_NET_WM_PING to allow disabling

_NET_WM_PING protocol handling in CreateWindow if
desired.

include/SDL_hints.h

@@ -185,6 +185,20 @@ extern "C" {
  */
 #define SDL_HINT_VIDEO_X11_XRANDR           "SDL_VIDEO_X11_XRANDR"
 
+/**
+ *  \brief  A variable controlling whether the X11 _NET_WM_PING protocol should be supported.
+ *
+ *  This variable can be set to the following values:
+ *    "0"       - Disable _NET_WM_PING
+ *    "1"       - Enable _NET_WM_PING
+ *
+ *  By default SDL will use _NET_WM_PING, but for applications that know they
+ *  will not always be able to respond to ping requests in a timely manner they can
+ *  turn it off to avoid the window manager thinking the app is hung.
+ *  The hint is checked in CreateWindow.
+ */
+#define SDL_HINT_VIDEO_X11_NET_WM_PING      "SDL_VIDEO_X11_NET_WM_PING"
+
 /**
  *  \brief  A variable controlling whether the window frame and title bar are interactive when the cursor is hidden 
  *

src/video/x11/SDL_x11window.c

@@ -542,11 +542,23 @@ X11_CreateWindow(_THIS, SDL_Window * window)
                     (unsigned char *)&_NET_WM_BYPASS_COMPOSITOR_HINT_ON, 1);
 
     {
-        Atom protocols[] = {
-            data->WM_DELETE_WINDOW, /* Allow window to be deleted by the WM */
-            data->_NET_WM_PING, /* Respond so WM knows we're alive */
-        };
-        X11_XSetWMProtocols(display, w, protocols, sizeof (protocols) / sizeof (protocols[0]));
+        Atom protocols[2];
+        int proto_count = 0;
+        const char *ping_hint;
+
+        protocols[proto_count] = data->WM_DELETE_WINDOW; /* Allow window to be deleted by the WM */
+        proto_count++;
+        
+        ping_hint = SDL_GetHint(SDL_HINT_VIDEO_X11_NET_WM_PING);
+        /* Default to using ping if there is no hint */
+        if (!ping_hint || SDL_atoi(ping_hint)) {
+            protocols[proto_count] = data->_NET_WM_PING; /* Respond so WM knows we're alive */
+            proto_count++;
+        }
+
+        SDL_assert(proto_count <= sizeof(protocols) / sizeof(protocols[0]));
+
+        X11_XSetWMProtocols(display, w, protocols, proto_count);
     }
 
     if (SetupWindowData(_this, window, w, SDL_TRUE) < 0) {