Realizing and Mapping

Canvas items are realized and mapped just as widgets are. These methods play the same role they do for widgets; realizing a canvas item allocates any GDK resources it plans to use, unrealizing it deallocates the same resources. Mapping a canvas item shows its GdkWindow, unmapping it hides the GdkWindow. Very few canvas items have a GdkWindow (GnomeCanvasWidget is the big exception), so most canvas items will not even implement map and unmap methods. GnomeCanvasRect does not. It does have realize and unrealize methods, however.

Here is its realize method:

static void
gnome_canvas_re_realize (GnomeCanvasItem *item)
{
  GnomeCanvasRE *re;

  re = GNOME_CANVAS_RE (item);

  if (re_parent_class->realize)
    (* re_parent_class->realize) (item);

  if (!item->canvas->aa) {
    re->fill_gc = gdk_gc_new (item->canvas->layout.bin_window);
    re->outline_gc = gdk_gc_new (item->canvas->layout.bin_window);
  }
}

      

And unrealize:

static void
gnome_canvas_re_unrealize (GnomeCanvasItem *item)
{
  GnomeCanvasRE *re;

  re = GNOME_CANVAS_RE (item);

  if (!item->canvas->aa) {
    gdk_gc_unref (re->fill_gc);
    gdk_gc_unref (re->outline_gc);
  }

  if (re_parent_class->unrealize)
    (* re_parent_class->unrealize) (item);
}
      

Note that your realize and unrealize methods are unlikely to have anything to do in antialiased mode, since there won't be any GDK resources to worry about.