[gtk+] draw: call vfunc rather then emit signal for the common case

[Alexander Larsson <alexl src gnome org>]

commit cdd951e927ad37933eb12f62fc6eaafe542a7c29
Author: Alexander Larsson <alexl redhat com>
Date:   Mon Sep 14 11:36:43 2015 +0200

    draw: call vfunc rather then emit signal for the common case
    
    This avoids a lot of overhead in the common case where a signal
    is not connected and we're just using the class vfunc (which is true
    for all in-libgtk widgets). Additionally it makes backtraces in
    debuggers and profiles much much nicer to look at.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754986

 gtk/gtkwidget.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index ef279f4..4206c40 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -6834,9 +6834,18 @@ _gtk_widget_draw_internal (GtkWidget *widget,
 
       gdk_window_mark_paint_from_clip (window, cr);
 
-      g_signal_emit (widget, widget_signals[DRAW],
-                     0, cr,
-                     &result);
+      if (g_signal_has_handler_pending (widget, widget_signals[DRAW], 0, FALSE))
+        {
+          g_signal_emit (widget, widget_signals[DRAW],
+                         0, cr,
+                         &result);
+        }
+      else if (GTK_WIDGET_GET_CLASS (widget)->draw)
+        {
+          cairo_save (cr);
+          GTK_WIDGET_GET_CLASS (widget)->draw (widget, cr);
+          cairo_restore (cr);
+        }
 
 #ifdef G_ENABLE_DEBUG
       if (GTK_DEBUG_CHECK (BASELINES))