app: add a proxy group which will keep sample point canvas items

app/display/gimpdisplayshell.c

@@ -53,7 +53,7 @@
 #include "tools/tool_manager.h"
 
 #include "gimpcanvas.h"
-#include "gimpcanvasgroup.h"
+#include "gimpcanvasproxygroup.h"
 #include "gimpdisplay.h"
 #include "gimpdisplayshell.h"
 #include "gimpdisplayshell-appearance.h"
@@ -293,6 +293,11 @@ gimp_display_shell_init (GimpDisplayShell *shell)
 
   shell->canvas_item = gimp_canvas_group_new ();
 
+  shell->sample_points = gimp_canvas_proxy_group_new ();
+  gimp_canvas_group_add_item (GIMP_CANVAS_GROUP (shell->canvas_item),
+                              shell->sample_points);
+  g_object_unref (shell->sample_points);
+
   shell->icon_size  = 32;
 
   shell->cursor_format   = GIMP_CURSOR_FORMAT_BITMAP;
@@ -800,6 +805,7 @@ gimp_display_shell_dispose (GObject *object)
     {
       g_object_unref (shell->canvas_item);
       shell->canvas_item = NULL;
+      shell->sample_points = NULL;
     }
 
   if (shell->event_history)

app/display/gimpdisplayshell.h

@@ -136,6 +136,7 @@ struct _GimpDisplayShell
   cairo_pattern_t   *checkerboard;     /*  checkerboard pattern               */
 
   GimpCanvasItem    *canvas_item;      /*  items drawn on the canvas          */
+  GimpCanvasItem    *sample_points;    /*  item proxies of sample points      */
 
   guint              title_idle_id;    /*  title update idle ID               */
   gchar             *title;            /*  current title                      */