// AnimationThread.java
// This file provides the class AnimationThread which is needed by
// the applet whose main class is in Animate.java.
// S. Tanimoto, 10 April 1999.

// An animation thread is responsible for updating the location
// of one animation object according to the points in its trajectory.
// It does one update approximately every SLEEP_PERIOD milliseconds.
// If it is the "repainting thread" then it also calls repaint,
// so that the screen will get updated.
// Each thread is told when it is created whether it is the repainting
// thread or not.  The boolean parameter repaintingThread controls this.

// This class provides a static method animationInProgress() which returns
// true if any animation threads are still running.

import java.util.*;
import java.awt.*;

public class AnimationThread extends Thread {
    AnimationObject theObj; // The anim. obj. whose location needs updating.
    Canvas theAC;
    boolean repaintingThread = false;
    static int numActiveThreads = 0;
    static final int SLEEP_PERIOD = 150; // milliseconds.

    public AnimationThread(AnimationObject theObj, Canvas theAC,
                           boolean repaintingThread) {
        this.theObj = theObj;
        this.theAC  = theAC;
        this.repaintingThread = repaintingThread;
    }
    public void run() {
        if (theObj == null) return;
        if (theObj.trajectory == null) return;
        oneMore(); // Add one to the number of running anim. threads.
        for (Enumeration locations = theObj.trajectory.elements();
             locations.hasMoreElements();) {
            theObj.currentLocation = (Point) locations.nextElement();
            try { Thread.sleep(SLEEP_PERIOD); }
            catch (InterruptedException e) {}
            if (repaintingThread) theAC.repaint();
        }
        oneLess(); // Reduce num. of running threads by one.
    }

    // Prevent concurrent writes to this shared variable when
    // incrementing and decrementing the number of active anim. threads.
    synchronized void oneMore() {
        numActiveThreads++;
    }
    synchronized void oneLess() {
        numActiveThreads--;
    }

    public static boolean animationInProgress() {
        if (numActiveThreads > 0) return true;
        return false;
    }
}