/* === S Y N F I G ========================================================= */
/*! \file layer_pastecanvas.h
-** \brief Template Header
+** \brief Header file for implementation of the "Paste Canvas" layer
**
** $Id$
**
** \legal
** Copyright (c) 2002-2005 Robert B. Quattlebaum Jr., Adrian Bentley
-** Copyright (c) 2007 Chris Moore
+** Copyright (c) 2007, 2008 Chris Moore
**
** This package is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public License as
mutable Rect bounds;
sigc::connection child_changed_connection;
+
+ // Nasty hack: Remember whether we called an extra ref() when
+ // setting the canvas, so we know whether to call an extra unref()
+ // when finished with the canvas.
+ //
+ // Here's the story:
+ //
+ // The root canvas is destructed first. That sets the
+ // Layer::canvas_ (the parent canvas) of any PasteCanvas layer it
+ // contains to nil, due to a call to Layer::set_canvas(0),
+ // triggered by the connection made when Layer::set_canvas
+ // originally set its canvas_ member to point to the root canvas.
+ // ~Canvas does begin_delete() which triggers that connection.
+ //
+ // After ~Canvas has run, the members of the root canvas are
+ // freed, including its children_ list. If this was the last
+ // reference to the child canvas that the pastecanvas uses, that
+ // child canvas will Layer_PasteCanvas::set_sub_canvas(0) on the
+ // PasteCanvas layer to set its canvas (the child, pasted canvas)
+ // not to refer to the soon-to-be destroys child canvas. But
+ // set_sub_canvas() originally looked at the value of
+ // Layer::canvas_ (the parent canvas, obtained via
+ // Layer::get_canvas()) to decide whether to do an extra ref() on
+ // canvas (the child canvas). We need to unref() it now if we
+ // did, but we've forgotten whether we did. So we use this
+ // 'extra_reference' member to store that decision.
+ bool extra_reference;
public:
virtual void on_canvas_set();