fixedframerategame.java

java 3d game jme 工程开发源代码

/*
 * Copyright (c) 2003-2009 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
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 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
// $Id: FixedFramerateGame.java 4091 2009-01-21 19:01:20Z joshua.j.ellen $
package com.jme.app;

import java.util.logging.Level;
import java.util.logging.Logger;

import com.jme.input.InputSystem;
import com.jme.util.Timer;

/**
 * A game that attempts to run at a fixed frame rate.
 * <p>
 * The main loop makes every effort to render at the specified rate, however
 * this is not guaranteed and the frame rate may dip below the desired value.
 * The game logic is updated at the same rate as the rendering; for example,
 * if the rendering is running at 60 frames per second, the logic will also
 * be updated 60 times per second.
 * <p>
 * Limiting the frame rate of the game is useful for playing nice with the
 * underlying operating system. That is, if the game loop is left unchecked,
 * it tends to use up 100% of the CPU cycles; while this may be fine for
 * fullscreen applications (as it will yield to important processes) it can
 * cause issues with applications running in a normal window.
 * <p>
 * If no frame rate is specified, the game will run at 60 frames per second.
 * <p>
 * Note that {@link #setFrameRate(int)} cannot be called prior to calling
 * {@link #start()} or a {@code NullPointerException} will be thrown.
 * 
 * @author Eric Woroshow
 * @version $Revision: 4091 $, $Date: 2009-01-22 03:01:20 +0800 (星期四, 22 一月 2009) $
 */
public abstract class FixedFramerateGame extends AbstractGame {
    private static final Logger logger = Logger
            .getLogger(FixedFramerateGame.class.getName());

    //Frame-rate managing stuff
    private Timer timer;

    private int frames = 0;

    private long startTime;

    private long preferredTicksPerFrame;

    private long frameStartTick;

    private long frameDurationTicks;

    /**
     * Set preferred frame rate. The main loop will make every attempt to
     * maintain the given frame rate. This should not be called prior to the
     * application being <code>start()</code> -ed.
     * 
     * @param fps
     *            the desired frame rate in frames per second
     */
    public void setFrameRate(int fps) {
        if (fps <= 0) {
                throw new IllegalArgumentException(
                        "Frames per second cannot be less than one.");
        }

        logger.info("Attempting to run at " + fps + " fps.");
        preferredTicksPerFrame = timer.getResolution() / fps;
    }

    /**
     * Gets the current frame rate.
     * 
     * @return the current number of frames rendering per second
     */
    public float getFramesPerSecond() {
        float time = (timer.getTime() - startTime)
                / (float) timer.getResolution();
        float fps = frames / time;

        startTime = timer.getTime();
        frames = 0;

        return fps;
    }

    /**
     * <code>startFrame</code> begin monitoring the current frame. This method
     * should be called every frame before update and drawing code.
     */
    private void startFrame() {
        frameStartTick = timer.getTime();
    }

    /**
     * <code>endFrame</code> ends the current frame. Pads any excess time in
     * the frame by sleep()-ing the thread in order to maintain the desired
     * frame rate. No attempt is made to rectify frames which have taken too
     * much time.
     */
    private void endFrame() {
        frames++;

        frameDurationTicks = timer.getTime() - frameStartTick;

        while (frameDurationTicks < preferredTicksPerFrame) {
            long sleepTime = ((preferredTicksPerFrame - frameDurationTicks) * 1000)
                    / timer.getResolution();

            try {
                Thread.sleep(sleepTime);
            } catch (InterruptedException e) {
                logger.warning("Error sleeping during main loop.");
            }

            frameDurationTicks = timer.getTime() - frameStartTick;
        }
    }

    /**
     * Render and update logic at a specified fixed rate.
     */
    public final void start() {
        logger.info("Application started.");
        try {
            getAttributes();

            initSystem();

            assertDisplayCreated();

            timer = Timer.getTimer();
            setFrameRate(60); //default to 60 fps

            initGame();

            //main loop
            while (!finished && !display.isClosing()) {
                startFrame();

                //handle input events prior to updating the scene
                // - some applications may want to put this into update of the game state
                InputSystem.update();

                //update game state, do not use interpolation parameter
                update(-1.0f);

                //render, do not use interpolation parameter
                render(-1.0f);

                //swap buffers
                display.getRenderer().displayBackBuffer();

                endFrame();

                Thread.yield();
            }

        } catch (Throwable t) {
            logger.logp(Level.SEVERE, this.getClass().toString(), "start()", "Exception in game loop", t);
        } finally {
            cleanup();
        }
        logger.info("Application ending.");

        display.reset();
        quit();
    }

    /**
     * Quits the program abruptly using <code>System.exit</code>.
     * 
     * @see AbstractGame#quit()
     */
    protected void quit() {
        if (display != null) {
            display.close();
        }
        System.exit(0);
    }

    /**
     * @param interpolation
     *            unused in this implementation
     * @see AbstractGame#update(float interpolation)
     */
    protected abstract void update(float interpolation);

    /**
     * @param interpolation
     *            unused in this implementation
     * @see AbstractGame#render(float interpolation)
     */
    protected abstract void render(float interpolation);

    /**
     * @see AbstractGame#initSystem()
     */
    protected abstract void initSystem();

    /**
     * @see AbstractGame#initGame()
     */
    protected abstract void initGame();

    /**
     * @see AbstractGame#reinit()
     */
    protected abstract void reinit();

    /**
     * @see AbstractGame#cleanup()
     */
    protected abstract void cleanup();
}