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+/*
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+ * Copyright (c) 2002-2012 LWJGL Project
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+ * All rights reserved.
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+ *
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+ * Redistribution and use in source and binary forms, with or without
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+ * modification, are permitted provided that the following conditions are
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+ * met:
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+ *
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+ * * Redistributions of source code must retain the above copyright
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+ * notice, this list of conditions and the following disclaimer.
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+ *
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+ * * Redistributions in binary form must reproduce the above copyright
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+ * notice, this list of conditions and the following disclaimer in the
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+ * documentation and/or other materials provided with the distribution.
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+ *
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+ * * Neither the name of 'LWJGL' nor the names of
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+ * its contributors may be used to endorse or promote products derived
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+ * from this software without specific prior written permission.
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+ *
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+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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+ */
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+package com.jme3.system.lwjgl;
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+
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+
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+/**
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+* A highly accurate sync method that continually adapts to the system
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+* it runs on to provide reliable results.
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+*
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+* @author Riven
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+* @author kappaOne
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+*/
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+class Sync {
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+
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+
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+
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+ /** number of nano seconds in a second */
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+ private static final long NANOS_IN_SECOND = 1000L * 1000L * 1000L;
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+
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+ /** The time to sleep/yield until the next frame */
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+ private static long nextFrame = 0;
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+
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+ /** whether the initialisation code has run */
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+ private static boolean initialised = false;
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+
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+ /** for calculating the averages the previous sleep/yield times are stored */
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+ private static RunningAvg sleepDurations = new RunningAvg(10);
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+ private static RunningAvg yieldDurations = new RunningAvg(10);
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+
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+
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+ /**
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+ * An accurate sync method that will attempt to run at a constant frame rate.
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+ * It should be called once every frame.
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+ *
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+ * @param fps - the desired frame rate, in frames per second
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+ */
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+ public static void sync(int fps) {
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+ if (fps <= 0) return;
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+ if (!initialised) initialise();
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+
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+ try {
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+ // sleep until the average sleep time is greater than the time remaining till nextFrame
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+ for (long t0 = getTime(), t1; (nextFrame - t0) > sleepDurations.avg(); t0 = t1) {
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+ Thread.sleep(1);
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+ sleepDurations.add((t1 = getTime()) - t0); // update average sleep time
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+ }
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+
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+ // slowly dampen sleep average if too high to avoid yielding too much
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+ sleepDurations.dampenForLowResTicker();
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+
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+ // yield until the average yield time is greater than the time remaining till nextFrame
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+ for (long t0 = getTime(), t1; (nextFrame - t0) > yieldDurations.avg(); t0 = t1) {
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+ Thread.yield();
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+ yieldDurations.add((t1 = getTime()) - t0); // update average yield time
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+ }
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+ } catch (InterruptedException e) {
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+
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+ }
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+
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+ // schedule next frame, drop frame(s) if already too late for next frame
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+ nextFrame = Math.max(nextFrame + NANOS_IN_SECOND / fps, getTime());
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+ }
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+
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+ /**
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+ * This method will initialise the sync method by setting initial
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+ * values for sleepDurations/yieldDurations and nextFrame.
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+ *
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+ * If running on windows it will start the sleep timer fix.
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+ */
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+ private static void initialise() {
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+ initialised = true;
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+
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+ sleepDurations.init(1000 * 1000);
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+ yieldDurations.init((int) (-(getTime() - getTime()) * 1.333));
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+
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+ nextFrame = getTime();
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+
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+
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+ // On windows the sleep functions can be highly inaccurate by
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+ // over 10ms making in unusable. However it can be forced to
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+ // be a bit more accurate by running a separate sleeping daemon
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+ // thread.
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+ Thread timerAccuracyThread = new Thread(new Runnable() {
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+ public void run() {
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+ try {
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+ while(true)Thread.sleep(Long.MAX_VALUE);
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+ } catch (Exception e) {}
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+ }
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+ });
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+
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+ timerAccuracyThread.setName("LWJGL Timer");
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+ timerAccuracyThread.setDaemon(true);
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+ timerAccuracyThread.start();
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+ }
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+
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+
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+ /**
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+ * Get the system time in nano seconds
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+ *
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+ * @return will return the current time in nano's
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+ */
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+ private static long getTime() {
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+ long time= System.currentTimeMillis()& 0x7FFFFFFFFFFFFFFFL;
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+ long res= 1000;
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+ return (time * NANOS_IN_SECOND) / res;
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+ }
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+
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+ private static class RunningAvg {
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+ private final long[] slots;
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+ private int offset;
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+
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+ private static final long DAMPEN_THRESHOLD = 10 * 1000L * 1000L; // 10ms
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+ private static final float DAMPEN_FACTOR = 0.9f; // don't change: 0.9f is exactly right!
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+
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+ public RunningAvg(int slotCount) {
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+ this.slots = new long[slotCount];
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+ this.offset = 0;
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+ }
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+
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+ public void init(long value) {
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+ while (this.offset < this.slots.length) {
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+ this.slots[this.offset++] = value;
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+ }
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+ }
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+
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+ public void add(long value) {
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+ this.slots[this.offset++ % this.slots.length] = value;
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+ this.offset %= this.slots.length;
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+ }
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+
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+ public long avg() {
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+ long sum = 0;
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+ for (int i = 0; i < this.slots.length; i++) {
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+ sum += this.slots[i];
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+ }
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+ return sum / this.slots.length;
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+ }
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+
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+ public void dampenForLowResTicker() {
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+ if (this.avg() > DAMPEN_THRESHOLD) {
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+ for (int i = 0; i < this.slots.length; i++) {
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+ this.slots[i] *= DAMPEN_FACTOR;
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+ }
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+ }
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+ }
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+ }
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+}
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