FlappyTurtle/LinearColorAnimator.java

import java.awt.Color;

class LinearColorAnimator
{
    private Color _start, _end;
    private final AnimationListener _listener;
    private int _duration;
    private double _elapsed;
    private boolean _started;
    private boolean _finished;

    /*
     * @param duration Duration in seconds
     */
    public LinearColorAnimator(Color start, Color end, int duration, AnimationListener listener)
    {
        _start = start;
        _end = end;
        _duration = duration;
        _listener = listener;
    }

    /*
     * @param elapsed Elapsed time since last call in ms
     */
    public void update(double elapsed)
    {
        if (_started)
        {
            _elapsed += elapsed * 1e-3;

            if (_elapsed > _duration)
            {
                _started = false;
                _finished = true;
                if (_listener != null)
                {
                    _listener.onAnimationFinished();
                }
            }
        }
    }

    public void start()
    {
        _started = true;
        _finished = false;
        _elapsed = 0;
    }

    public void reset()
    {
        _started = _finished = false;
        _elapsed = 0;
    }

    public void setStart(Color c)
    {
        _start = c;
    }

    public void setEnd(Color c)
    {
        _end = c;
    }

    public void setDuration(int duration)
    {
        _duration = duration;
    }

    public boolean hasStarted()
    {
        return _started;
    }

    public boolean hasFinished()
    {
        return _finished;
    }

    public Color getStart()
    {
        return _start;
    }

    public Color getEnd()
    {
        return _end;
    }

    public Color getCurrentColor()
    {
        if (_finished)
        {
            return _end;
        }
        if (!_started)
        {
            return _start;
        }
        int diffR = _end.getRed() - _start.getRed();
        int diffG = _end.getGreen() - _start.getGreen();
        int diffB = _end.getBlue() - _start.getBlue();
        double elapsedRatio = _elapsed / _duration;
        return new Color((int)(_start.getRed() + diffR * elapsedRatio),
                         (int)(_start.getGreen() + diffG * elapsedRatio),
                         (int)(_start.getBlue() + diffB * elapsedRatio));
    }

    interface AnimationListener
    {
        public abstract void onAnimationFinished();
    }
}