/*
 * Copyright (c) 2003-2008 jMonkeyEngine
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 * * Neither the name of 'jMonkeyEngine' nor the names of its contributors 
 *   may be used to endorse or promote products derived from this software 
 *   without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.jme.util;

import com.jme.system.DisplaySystem;
import com.jme.system.JmeException;

/**
 * <code>Timer</code> is the base class for a high resolution timer. It is
 * created from getTimer("display system")
 *
 * @author Mark Powell
 * @version $Id: Timer.java,v 1.18 2007/03/09 10:19:34 rherlitz Exp $
 */
public abstract class Timer {
    protected static Timer instance;

    /**
     * Returns the current time in ticks. A tick is an arbitrary measure of time
     * defined by the timer implementation. The number of ticks per second is
     * given by <code>getResolution()</code>. The timer starts at 0 ticks.
     *
     * @return a long value representing the current time
     */
    public abstract long getTime();

    /**
     * Returns the time in seconds. The timer starts
     * at 0.0 seconds.
     *
     * @return the current time in seconds
     */
    public float getTimeInSeconds() {
        return getTime() / (float) getResolution();
    }

    /**
     * Returns the resolution of the timer.
     *
     * @return the number of timer ticks per second
     */
    public abstract long getResolution();

    /**
     * Returns the "calls per second". If this is called every frame, then it
     * will return the "frames per second".
     *
     * @return The "calls per second".
     */
    public abstract float getFrameRate();

    /**
     * Returns the time, in seconds, between the last call and the current one.
     *
     * @return Time between this call and the last one.
     */
    public abstract float getTimePerFrame();

    /**
     * <code>update</code> recalulates the frame rate based on the previous
     * call to update. It is assumed that update is called each frame.
     */
    public abstract void update();

    /**
     * Returns the high resolution timer. Timer is a singleton class so only one
     * instance of Timer is allowed.
     *
     * @return the timer defined by the SystemProvider
     */
    public static synchronized Timer getTimer() {
        if (instance == null) {
            if(DisplaySystem.getSystemProvider() == null) {
                throw new JmeException("Display System must be initialized before Timer.");
            }
            instance = DisplaySystem.getSystemProvider().getTimer();
        }
        
        return instance;
    }

	/**
	 * Set a user defined timer instance
	 * @param timer timer to use
	 */
	public static synchronized void setTimer(Timer timer) {
		instance = timer;
	}

	/**
     * Reset the timer to 0. Clear any tpf history.
     */
    public abstract void reset();
}

@@ -3186,16 +3186,17 @@
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Spelling error corrected.