[gtk+] window: Check if we can use CSD before enabling them

[Emmanuele Bassi <ebassi src gnome org>]

commit c5e5ee67490e7e7af56052d8f8beb75db002c2f1
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Jun 3 14:07:29 2015 +0100

    window: Check if we can use CSD before enabling them
    
    The change in 03213b9509fc1df16c66194ea168aed6c15110e9 changed the rules
    as to when CSD can be enabled, but it also unconditionally enables CSD
    with the implicit assumption that client-side shadows were the real
    issue, and that we could work around that by drawing our own borders.
    This also means that setting a titlebar for a GtkWindow will enable CSD
    unconditionally.
    
    In reality, some window managers (like Matchbox) *only* support
    server-side decorations, and will ignore all hints to the contrary, to
    the point of drawing decorations at random locations on top of the
    window.
    
    Since CSD are enabled unconditionally, the GTK_CSD environment variable
    is also not a suitable escape hatch.
    
    In the grand tradition of asking ourselves if we should do something
    just because we can, we should split the environment checks from the
    checks on what the user requested; by doing that, we can also check
    when enabling client-side decorations, and ideally bail out if needed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=750343

 gtk/gtkwindow.c |   50 +++++++++++++++++++++++++++++++-------------------
 1 files changed, 31 insertions(+), 19 deletions(-)
---
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 423c6bd..9fe882f 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -4056,6 +4056,32 @@ gtk_window_supports_client_shadow (GtkWindow *window)
   return TRUE;
 }
 
+static gboolean
+gtk_window_can_use_csd (GtkWindow *window)
+{
+  const gchar *csd_env;
+
+#ifdef GDK_WINDOWING_BROADWAY
+  if (GDK_IS_BROADWAY_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
+    return TRUE;
+#endif
+
+#ifdef GDK_WINDOWING_WAYLAND
+  if (GDK_IS_WAYLAND_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
+    return TRUE;
+#endif
+
+#ifdef GDK_WINDOWING_MIR
+  if (GDK_IS_MIR_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
+    return TRUE;
+#endif
+
+  csd_env = g_getenv ("GTK_CSD");
+
+  /* If GTK_CSD is unset we default to CSD support */
+  return csd_env == NULL || (strcmp (csd_env, "1") == 0);
+}
+
 static void
 gtk_window_enable_csd (GtkWindow *window)
 {
@@ -4063,6 +4089,10 @@ gtk_window_enable_csd (GtkWindow *window)
   GtkWidget *widget = GTK_WIDGET (window);
   GdkVisual *visual;
 
+  /* If the environment does not support CSD, then there's no point in enabling them */
+  if (!gtk_window_can_use_csd (window))
+    return;
+
   /* We need a visual with alpha for client shadows */
   if (priv->use_client_shadow)
     {
@@ -5839,7 +5869,6 @@ static gboolean
 gtk_window_should_use_csd (GtkWindow *window)
 {
   GtkWindowPrivate *priv = window->priv;
-  const gchar *csd_env;
 
   if (priv->csd_requested)
     return TRUE;
@@ -5850,24 +5879,7 @@ gtk_window_should_use_csd (GtkWindow *window)
   if (priv->type == GTK_WINDOW_POPUP)
     return FALSE;
 
-#ifdef GDK_WINDOWING_BROADWAY
-  if (GDK_IS_BROADWAY_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
-    return TRUE;
-#endif
-
-#ifdef GDK_WINDOWING_WAYLAND
-  if (GDK_IS_WAYLAND_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
-    return TRUE;
-#endif
-
-#ifdef GDK_WINDOWING_MIR
-  if (GDK_IS_MIR_DISPLAY (gtk_widget_get_display (GTK_WIDGET (window))))
-    return TRUE;
-#endif
-
-  csd_env = g_getenv ("GTK_CSD");
-
-  return (g_strcmp0 (csd_env, "1") == 0);
+  return gtk_window_can_use_csd (window);
 }
 
 static void