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+
+/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
+
+/*
+    Rosegarden
+    A MIDI and audio sequencer and musical notation editor.
+
+    This program is Copyright 2000-2008
+        Guillaume Laurent   <[email protected]>,
+        Chris Cannam        <[email protected]>,
+        Richard Bown        <[email protected]>
+
+    The moral rights of Guillaume Laurent, Chris Cannam, and Richard
+    Bown to claim authorship of this work have been asserted.
+
+    Other copyrights also apply to some parts of this work.  Please
+    see the AUTHORS file and individual file headers for details.
+
+    This program is free software; you can redistribute it and/or
+    modify it under the terms of the GNU General Public License as
+    published by the Free Software Foundation; either version 2 of the
+    License, or (at your option) any later version.  See the file
+    COPYING included with this distribution for more information.
+*/
+
+#ifndef _RG_CANVASITEMGC_H_
+#define _RG_CANVASITEMGC_H_
+
+#include <vector>
+
+
+class QCanvasItem;
+
+
+namespace Rosegarden
+{
+
+
+
+/**
+ * A pseudo GC in which CanvasItems whose ownership isn't clear cut
+ * can be put for periodical removal.
+ *
+ * This is especially for SegmentItems which can put their repeat
+ * rectangles when they're being deleted.
+ *
+ * The problem this solves is a classic ownership/double deletion
+ * case. The SegmentCanvas deletes all its items on destruction. But
+ * the SegmentItems have an auxiliary "repeat rectangle" which is a
+ * QCanvasRectangle, that needs to be deleted when the SegmentItem is
+ * itself deleted.
+ *
+ * However, if the SegmentItem deletes its repeat rectangle, then when
+ * the SegmentCanvas destruction occurs, the SegmentCanvas dtor will
+ * get a list of all its children (QCanvas::allItems()), containing
+ * both SegmentItems and their repeat rectangles. Deleting a
+ * SegmentItem will delete its repeat rectangle, which will still be
+ * present in the all children list which the SegmentCanvas dtor is
+ * iterating over.
+ * 
+ * So a solution is simply to push to-be-deleted repeat rectangles on
+ * this GC, which should be processed on canvas updates, for instance.
+ *
+ */
+class CanvasItemGC
+{
+public:
+    /// mark the given item for GC
+    static void mark(QCanvasItem*);
+
+    /// GC all marked items
+    static void gc();
+
+    /// Forget all marked items - don't delete them
+    static void flush();
+
+protected:
+    static std::vector<QCanvasItem*> m_garbage;
+};
+
+
+
+}
+
+#endif