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Facilities for making networked multiplayer games.
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//
// Nenya library - tools for developing networked games
// Copyright (C) 2002-2012 Three Rings Design, Inc., All Rights Reserved
// https://github.com/threerings/nenya
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published
// by the Free Software Foundation; either version 2.1 of the License, or
// (at your option) any later version.
//
// This library 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
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

package com.threerings.media.util;

/**
 * Used to control animation timing when displaying a {@link MultiFrameImage}. This interface
 * allows for constant framerates, or more sophisticated animation timing.
 */
public interface FrameSequencer
{
    /**
     * Called prior to the execution of an animation sequence (not necessarily immediately, so
     * time stamps should be obtained in the first call to tick).
     *
     * @param source the multi-frame image that is providing the animation frames.
     * @return initial frame index
     */
    public int init (MultiFrameImage source);

    /**
     * Called every display frame, the frame sequencer should return the index of the animation
     * frame that should be displayed during this tick. If the sequencer returns -1, it is taken
     * as an indication that the animation is finished and should be stopped.
     */
    public int tick (long tickStamp);

    /**
     * Called if the display is paused for some length of time and then unpaused. Sequencers
     * should adjust any time stamps they are maintaining internally by the delta so that time
     * maintains the illusion of flowing smoothly forward.
     */
    public void fastForward (long timeDelta);

    /**
     * A frame sequencer that delivers a constant frame rate in either one shot or looping mode.
     */
    public static class ConstantRate implements FrameSequencer
    {
        /**
         * Creates a constant rate frame sequencer with the desired target frames per second.
         *
         * @param framesPerSecond the target frames per second.
         * @param loop if false, the sequencer will report the end of the animation after
         * progressing through all of the frames once, otherwise it will loop indefinitely.
         */
        public ConstantRate (double framesPerSecond, boolean loop) {
            _millisPerFrame = (long)(1000d / framesPerSecond);
            _loop = loop;
        }

        // documentation inherited from interface
        public int init (MultiFrameImage source) {
            _frameCount = source.getFrameCount();
            _startStamp = 0l;

            return 0;
        }

        // documentation inherited from interface
        public int tick (long tickStamp) {
            // obtain our starting timestamp if we don't already have one
            if (_startStamp == 0) {
                _startStamp = tickStamp;
            }

            // compute our current frame index
            int frameIdx = (int)((tickStamp - _startStamp) / _millisPerFrame);

            // if we're not looping and we've exhausted our frames, we
            // return -1 to indicate that the animation should stop
            return (_loop || frameIdx < _frameCount) ? (frameIdx % _frameCount) : -1;
        }

        // documentation inherited from interface
        public void fastForward (long timeDelta) {
            _startStamp += timeDelta;
        }

        protected long _millisPerFrame;
        protected boolean _loop;
        protected int _frameCount;
        protected long _startStamp;
    }
}