Michael Bayne
b6f5317ad2
git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@158 ed5b42cb-e716-0410-a449-f6a68f950b19
102 lines
3.2 KiB
Java
102 lines
3.2 KiB
Java
//
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// $Id$
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//
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// Nenya library - tools for developing networked games
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// Copyright (C) 2002-2007 Three Rings Design, Inc., All Rights Reserved
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// http://www.threerings.net/code/nenya/
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//
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// This library is free software; you can redistribute it and/or modify it
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// under the terms of the GNU Lesser General Public License as published
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// by the Free Software Foundation; either version 2.1 of the License, or
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// (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License along with this library; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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package com.threerings.media.util;
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/**
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* Used to vary a value over time where time is provided at discrete
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* increments (on the frame tick) and the value is computed appropriately.
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*/
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public abstract class TimeFunction
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{
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/**
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* Every time function varies a value from some starting value to some
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* ending value over some duration. The way in which it varies
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* (linearly, for example) is up to the derived class.
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*
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* <p><em>Note:</em> it is assumed that we will operate with
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* relatively short durations such that integer arithmetic may be used
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* rather than long arithmetic.
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*/
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public TimeFunction (int start, int end, int duration)
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{
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_start = start;
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_end = end;
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_duration = duration;
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}
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/**
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* Configures this function with a starting time. This method need not
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* be called, and instead the first vall to {@link #getValue} will be
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* used to obtain a starting time stamp.
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*/
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public void init (long tickStamp)
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{
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_startStamp = tickStamp;
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}
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/**
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* Called to fast forward our time stamps if we are ever paused and
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* need to resume where we left off.
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*/
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public void fastForward (long timeDelta)
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{
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_startStamp += timeDelta;
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}
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/**
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* Returns the current value given the supplied time stamp. The value
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* will be bounded to the originally supplied starting and ending
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* values at times 0 (and below) and {@link #_duration} (and above)
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* respectively.
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*/
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public int getValue (long tickStamp)
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{
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if (_startStamp == 0L) {
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_startStamp = tickStamp;
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}
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int dt = (int)(tickStamp - _startStamp);
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if (dt <= 0) {
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return _start;
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} else if (dt >= _duration) {
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return _end;
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} else {
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return computeValue(dt);
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}
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}
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/**
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* This must be implemented by our derived class to compute our value
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* given the specified elapsed time (in millis).
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*/
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protected abstract int computeValue (int dt);
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/** Our starting and ending values. */
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protected int _start, _end;
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/** The number of milliseconds over which we vary our value. */
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protected int _duration;
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/** The timestamp at which we began varying our value. */
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protected long _startStamp;
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}
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