[gnome-builder] graph: keep surface around if width/height did not change

[Christian Hergert <chergert src gnome org>]

commit ecbfc94397744bf6f9a56533b0000eaf97c2943e
Author: Christian Hergert <christian hergert me>
Date:   Wed Jun 17 16:46:06 2015 -0700

    graph: keep surface around if width/height did not change
    
    If only the X and Y coordinates changed, we can avoid redrawing the
    graph surface.
    
    We don't actually hit this today in Builder, because the GbWorkspace
    works hard to not change the width/height when animating. Also, the
    X/Y stays at 0,0 relative to its GdkWindow.
    
    But good to add nonetheless.

 contrib/rg/rg-graph.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/contrib/rg/rg-graph.c b/contrib/rg/rg-graph.c
index 90dac51..16ae525 100644
--- a/contrib/rg/rg-graph.c
+++ b/contrib/rg/rg-graph.c
@@ -259,11 +259,15 @@ rg_graph_size_allocate (GtkWidget     *widget,
 {
   RgGraph *self = (RgGraph *)widget;
   RgGraphPrivate *priv = rg_graph_get_instance_private (self);
+  GtkAllocation old_alloc;
 
   g_assert (RG_IS_GRAPH (self));
   g_assert (alloc != NULL);
 
-  g_clear_pointer (&priv->surface, cairo_surface_destroy);
+  gtk_widget_get_allocation (widget, &old_alloc);
+
+  if ((old_alloc.width != alloc->width) || (old_alloc.height != alloc->height))
+    g_clear_pointer (&priv->surface, cairo_surface_destroy);
 
   GTK_WIDGET_CLASS (rg_graph_parent_class)->size_allocate (widget, alloc);
 }