demo: Utility for animating values

repos/demo/include/util/lazy_value.h

@@ -0,0 +1,85 @@
+/*
+ * \brief  Animated value
+ * \author Norman Feske
+ * \date   2010-10-29
+ */
+
+/*
+ * Copyright (C) 2010-2013 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__UTIL__LAZY_VALUE_H_
+#define _INCLUDE__UTIL__LAZY_VALUE_H_
+
+template <typename T>
+class Lazy_value
+{
+	private:
+
+		T _speed;
+		T _curr;
+		T _dst;
+		T _accel;
+
+	public:
+
+		Lazy_value()
+		: _speed(0), _curr(0), _dst(0), _accel(1)
+		{ }
+
+		Lazy_value(T value)
+		: _speed(0), _curr(value), _dst(value), _accel(1)
+		{ }
+
+		void dst(T dst, unsigned steps)
+		{
+			_dst = dst;
+			T delta = (_curr > _dst) ? _curr - _dst : _dst - _curr;
+			if (steps == 0)
+				steps = 1;
+			_accel = (4*delta) / (steps*steps);
+			_speed = 0;
+			if (_accel < 1)
+				_accel = 1;
+		}
+
+		T dst() { return _dst; }
+
+		void assign(T value) { _curr = value; }
+
+		void animate()
+		{
+			/* destination value reached? */
+			if (_curr == _dst) {
+				_speed = 0;
+				return;
+			}
+
+			/* change value with current speed */
+			if (_curr > _dst) {
+				_curr -= _speed;
+				if (_curr < _dst) _curr = _dst;
+			} else {
+				_curr += _speed;
+				if (_curr > _dst) _curr = _dst;
+			}
+
+			/* adapt speed */
+			T delta = _curr - _dst;
+			if (delta < 0) delta = -delta;
+
+			if (_speed*_speed < delta*_accel)
+				_speed += _accel;
+			else
+				_speed -= _accel;
+
+			if (_speed < 1) _speed = 1;
+		}
+
+		operator T () const { return _curr; }
+};
+
+#endif /* _INCLUDE__UTIL__LAZY_VALUE_H_ */