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diff --git a/chalk/sdk/kis_canvas_observer.h b/chalk/sdk/kis_canvas_observer.h
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+++ b/chalk/sdk/kis_canvas_observer.h
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+/*
+ *  Copyright (c) 2003 Patrick Julien <freak@codepimps.org>
+ *
+ *  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.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#ifndef KIS_CANVAS_OBSERVER_H_
+#define KIS_CANVAS_OBSERVER_H_
+
+class KisCanvasSubject;
+
+/**
+ * This is the base interface plugins use to implement the Observer
+ * design pattern. Observer can register themselves with an implementation
+ * of KisCanvasSubject. The KisCanvasSubject will then call update()
+ * on all registered observers whenever something interesting has happened.
+ *
+ * (This is something my predecessor should have done with signals and slots,
+ * I think...)
+ */
+class KisCanvasObserver {
+public:
+    KisCanvasObserver() {};
+    virtual ~KisCanvasObserver() {};
+
+public:
+    /**
+     * Implement this function to query the KisCanvasSubject implementation
+     * about state that may be interesting, such as current paint color and
+     * so on.
+     *
+     * @param subject the KisCanvasSubject that may know something that's 
+     *                interesting for us.
+     */
+    virtual void update(KisCanvasSubject *subject) = 0;
+
+private:
+    KisCanvasObserver(const KisCanvasObserver&);
+    KisCanvasObserver& operator=(const KisCanvasObserver&);
+};
+
+#endif // KIS_CANVAS_OBSERVER_H_
+