main: Don't use the compositor if not available

Bug: 16713

If one of the required X11 extension is not available, the composiutor
cannot be used.

Yet xfwm4 would still try to enable the compositor for each screen,
which would not work and prevent xfwm4 from starting.

If we can't use the compositor, well, we'd better not use it...

Signed-off-by: Olivier Fourdan <fourdan@xfce.org>

src/main.c

@@ -511,6 +511,70 @@ daemon_callback (const gchar  *name,
     return TRUE;
 }
 
+#ifdef HAVE_COMPOSITOR
+static gint
+init_compositor_display (DisplayInfo *display_info, gint compositor_mode)
+{
+    if (compositor_mode < COMPOSITOR_MODE_OFF)
+    {
+        compositor_mode = get_default_compositor (display_info);
+    }
+
+    /* Disabling compositor from command line */
+    if (!compositor_mode)
+    {
+        display_info->enable_compositor = FALSE;
+    }
+    compositorSetCompositeMode (display_info,
+                                (compositor_mode == COMPOSITOR_MODE_MANUAL));
+
+    return compositor_mode;
+}
+
+static void
+init_compositor_screen (ScreenInfo *screen_info, gint compositor_mode)
+{
+    DisplayInfo *display_info;
+
+    display_info = screen_info->display_info;
+    if (vblank_mode != VBLANK_AUTO)
+    {
+        compositorSetVblankMode (screen_info, vblank_mode);
+    }
+
+    if (compositor_mode == COMPOSITOR_MODE_AUTO)
+    {
+        compositorManageScreen (screen_info);
+    }
+    else if (compositor_mode == COMPOSITOR_MODE_MANUAL)
+    {
+        gboolean xfwm4_compositor;
+
+        xfwm4_compositor = TRUE;
+        if (screen_info->params->use_compositing)
+        {
+            /* Enable compositor if "use compositing" is enabled */
+            xfwm4_compositor = compositorManageScreen (screen_info);
+        }
+        /*
+           The user may want to use the manual compositing, but the installed
+           system may not support it, so we need to double check, to see if
+           initialization of the compositor was successful.
+          */
+        if (xfwm4_compositor)
+        {
+            /*
+               Acquire selection on XFWM4_COMPOSITING_MANAGER to advertise our own
+               compositing manager (used by WM tweaks to determine whether or not
+               show the "compositor" tab.
+             */
+            setAtomIdManagerOwner (display_info, XFWM4_COMPOSITING_MANAGER,
+                                   screen_info->xroot, screen_info->xfwm4_win);
+        }
+    }
+}
+#endif /* HAVE_COMPOSITOR */
+
 static int
 initialize (gint compositor_mode, gboolean replace_wm)
 {
@@ -527,17 +591,11 @@ initialize (gint compositor_mode, gboolean replace_wm)
     display_info = myDisplayInit (gdk_display_get_default ());
 
 #ifdef HAVE_COMPOSITOR
-    if (compositor_mode < COMPOSITOR_MODE_OFF)
+    if (display_info->enable_compositor)
     {
-        compositor_mode = get_default_compositor (display_info);
+        compositor_mode =
+            init_compositor_display (display_info, compositor_mode);
     }
-
-    /* Disabling compositor from command line */
-    if (!compositor_mode)
-    {
-        display_info->enable_compositor = FALSE;
-    }
-    compositorSetCompositeMode (display_info, (compositor_mode == COMPOSITOR_MODE_MANUAL));
 #else /* HAVE_COMPOSITOR */
     display_info->enable_compositor = FALSE;
 #endif /* HAVE_COMPOSITOR */
@@ -592,43 +650,12 @@ initialize (gint compositor_mode, gboolean replace_wm)
         {
             return -2;
         }
-
-        if (vblank_mode != VBLANK_AUTO)
-        {
-            compositorSetVblankMode (screen_info, vblank_mode);
-        }
-
-        if (compositor_mode == COMPOSITOR_MODE_AUTO)
+#ifdef HAVE_COMPOSITOR
+        if (display_info->enable_compositor)
         {
-            compositorManageScreen (screen_info);
+            init_compositor_screen (screen_info, compositor_mode);
         }
-        else if (compositor_mode == COMPOSITOR_MODE_MANUAL)
-        {
-            gboolean xfwm4_compositor;
-
-            xfwm4_compositor = TRUE;
-            if (screen_info->params->use_compositing)
-            {
-                /* Enable compositor if "use compositing" is enabled */
-                xfwm4_compositor = compositorManageScreen (screen_info);
-            }
-            /*
-               The user may want to use the manual compositing, but the installed
-               system may not support it, so we need to double check, to see if
-               initialization of the compositor was successful.
-             */
-            if (xfwm4_compositor)
-            {
-                /*
-                   Acquire selection on XFWM4_COMPOSITING_MANAGER to advertise our own
-                   compositing manager (used by WM tweaks to determine whether or not
-                   show the "compositor" tab.
-                 */
-                setAtomIdManagerOwner (display_info, XFWM4_COMPOSITING_MANAGER,
-                                       screen_info->xroot, screen_info->xfwm4_win);
-            }
-        }
-
+#endif /* HAVE_COMPOSITOR */
         sn_init_display (screen_info);
         myDisplayAddScreen (display_info, screen_info);
         screen_info->current_ws = getNetCurrentDesktop (display_info, screen_info->xroot);