Movement of user causes AI to lag

[john price]

I started writing a game 2 days ago. It is a simple platform game. There are 3 platforms total : a "floor" and 2 "floating ramps". On the ground, between the "floating ramps", there is a "coin". On the second floating ramp, there is another "coin". You can pick up the coins. On the first floating ramp, there is a "gun". If you pick up the "gun", you can "shoot" "bullets". Only one "bullet" by the user is allowed to be shot at one time. The user can physically control the object (cube, box, etc) with the arrow buttons. Up physically moves the object up a certain distance. Moving to the right causes the world to move left. Moving to the left causes the world to move right. You may destroy 2 "targets" with the "bullets" if you have picked up the "gun". If the "targets" are "destroyed", an AI "character" (box, cube, etc) comes running at a constant speed to the left. It spits out a stream of "bullets". If the user destroys the AI "character", the character disappears along with its bullets. The only issue is when the character moves while the AI character is still "alive" and shooting "bullets". The character's location algorithm is composed of this :

enemy1 = new Ellipse2D.Double(screenX + 1250 - walked, 360, 30, 30);
//screenX = 0 - userInputToLeftAndRight
//1250 = offset of character's advance
//walked = amount of spaces walked already
//360 = irrelevant (it's on the ground)
//30 = irrelevant (it has 30 width)
//30 = irrelevant (it has 30 height)

When a user pushes the left or right arrow on their keyboard, a timer starts :

moveLeft = new Timer(20, new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	moving = true;
	screenX += 5;
	repaint();
	}
	});
	moveRight = new Timer(20, new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	moving = true;
	screenX -= 5;
	repaint();
	}
	});

These continue until the user stops holding down the key.

This is what happens when the AI "walks" (it walks if it is still "alive") :

enemyShoot = new Timer(40, new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	for (Point point : enemyBullets.keySet()) {
	int howFarTraveled = enemyBullets.get(point);
	if (howFarTraveled >= 50) {
			enemyBullets.remove(point);
			enemyBullets.put(new Point(enemy1.getBounds().x - 10, enemy1.getBounds().y + 10), new Integer(0)); //Problem code
		}
	else {
		enemyBullets.remove(point);
		enemyBullets.put(new Point((int)point.getX() - 10, (int)point.getY()), howFarTraveled + 10);
	}
	}
	repaint();
	}
	});
	enemyShoot.setRepeats(false);
	enemyWalk = new Timer(20, new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	walked += 3;
	enemyShoot.start();
	repaint();
	}
	});

I have marked what I believe to be the problem line above. I have tried changing the timer on the "enemyShoot" timer and it doesn't affect the problem. If a user is "running" full to the left, the "bullets" go out as far as they should. If a user is stopped, the "bullet's" path is shorter. If a user is "running" full to the right, the "bullets" start moving to the right at lower timer intervals (around 20 it is noticeably going to the left). I was wondering how to fix this problem. To me, it just seems like the lag of the repaint and the refreshing of the bullets. I would like the bullets to be consistently going to the right.

Here is the keyEvent info for left and right arrows :

case KeyEvent.VK_LEFT : 
	if (!moving) {
	moveLeft.start();
	repaint();
	}
	break;
	case KeyEvent.VK_RIGHT :
	if (!moving) {
	moveRight.start();
	repaint();
	}
	break;

Here is the release key code :

public void keyReleased(KeyEvent x) {
	switch (x.getKeyCode()) {
	case KeyEvent.VK_RIGHT : moveRight.stop(); moving = false; break;
	case KeyEvent.VK_LEFT : moveLeft.stop(); moving = false; break;
	}
	}
	});

The AI's bullet display system is the same as the character's bullet display system :

for (Point point : bulletTracker.keySet()) {
	bullet = new Rectangle2D.Double(point.x, point.y + 10, 10, 5); //user's "bullet"
	g2.fill(bullet);
	if (bullet.intersects(rec1)) { //rec1 = user
	life --;
	}
	}
	for (Point point : enemyBullets.keySet()) {
	Rectangle2D enemyBullet = new Rectangle2D.Double(point.x, point.y, 10, 5); //AI's "bullet"
	g2.fill(enemyBullet);
	if (enemyBullet.intersects(rec1)) {// rec1 = user
	life --;
	}
	}

Thanks,
John Price

EDIT : So, to restate my question... I would like a solution or help to finding a solution to fix the problem of the movement of the user causing the AI's "bullets" to not be consistent.

EDIT(2) : Please note that the AI movement isn't lagging. It is the "bullets" that the AI shoots.

[john price]

I found a solution. It was so simple. Instead of calculating it off of the previous point, which may be outdated, recalculate it based off of the AI character's position as you did in the first place, subtracting the amount of distance traveled :

enemyShoot = new Timer(40, new ActionListener() {
	public void actionPerformed(ActionEvent e) {
	for (Point point : enemyBullets.keySet()) {
	int howFarTraveled = enemyBullets.get(point);
	if (howFarTraveled >= 50) {
			enemyBullets.remove(point);
			enemyBullets.put(new Point(enemy1.getBounds().x - 10, enemy1.getBounds().y + 10), new Integer(0));
		}
	else {
		enemyBullets.remove(point);
		//enemyBullets.put(new Point((int)point.getX() - 10, (int)point.getY()), howFarTraveled + 10);
		enemyBullets.put(new Point((int)enemy1.getBounds().x - howFarTraveled - 10, (int)enemy1.getBounds().y + 10), howFarTraveled + 10);
	}
	}
	repaint();
	}
	});

Thanks,
John Price

EDIT : Although there is still some inconsistency when the user is running right or left (bullet stream is slower, but further when the user runs left and faster, but closer when the user runs right), it is much better than before. If anybody can give me a solution to how to make the algorithm better, that would be awesome.

[Akhilesh Trivedi]

john price wrote:...a solution to how to make the algorithm better, that would be awesome.

Will threading work?

[john price]

Could you show me what you are talking about (IE an example)?

Thanks,
John Price

[Randall Twede]

using threads is certainly something you should think about. i will post an old homework assignment that will demonstrate for you.

/*
 * Horserace.java
 * Program to simulate a horserace
 * Created on February 24, 2004, 11:02 AM
 */

/**
 *
 * Randall Twede
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Horserace extends JFrame implements ItemListener, ActionListener
{
    private JPanel topControls = new JPanel();
    private JPanel leftControls = new JPanel();
    private Box santaAnita = Box.createVerticalBox();
    private JTextArea results = new JTextArea(9, 40);
    private JButton start = new JButton("Start");
    private JButton reset = new JButton("Reset");
    private JRadioButton selected = new JRadioButton();
    private JRadioButton optionsArray[] = new JRadioButton[8];
    ButtonGroup optionsGroup = new ButtonGroup();
    private Horse[] horses = new Horse[8];
    private Thread[] threads = new Thread[8];
    private String finished[] = new String[8];
    private String chosenHorse = "";
    private int place = 0; // Incremented time a horse calls postResults()
    
    /** Creates a new instance of Horserace */
    public Horserace()
    {
        setTitle("Horserace");
        Container c = getContentPane();
        c.setLayout(new BorderLayout());
        initComponents();
        c.add(topControls, "North");
        c.add(leftControls, "West");
        c.add(santaAnita, "Center");
        c.add(results, "South");
    }
    
    // Improves readability of the constructor for this Class
    private void initComponents()
    {
        String labels[] = {"Seabiscuit", "Man O' War", "Native Dancer", "Secretariat", "Citation", "Seattle Slew", "Ruffian", "Cigar"};

        // Initialize the top Jpanel
        start.addActionListener(this);
        reset.addActionListener(this);
        topControls.add(start);
        topControls.add(reset);
 
        // Initialize the left Jpanel
        leftControls.setLayout(new GridLayout(8, 1));
        for(int i = 0; i < optionsArray.length; i++)
        {
            optionsArray[i] = new JRadioButton(labels[i]);
            leftControls.add(optionsArray[i]);
            optionsArray[i].addItemListener(this);
            optionsGroup.add(optionsArray[i]);
        }
        optionsArray[0].setSelected(true);
        selected = optionsArray[0]; // sets the default selection to Seabiscuit
        chosenHorse = selected.getLabel();
        
        // Initialized the center JPanel
        for (int i = 0; i < horses.length; i++)
        {
            horses[i] = new Horse(labels[i], this);
            santaAnita.add(horses[i]);
        }
    }    
    
    // Displays the results of the race
    public synchronized void postResults(String name)
    {
        finished[place] = name; // Add the horse's name to the array
        place++;    // Increment the array index
        if(place == 8)  // All the horses havea finished
        {
            String finish[] = {"first", "second", "third", "fourth", "fifth", "sixth", "seventh", "last"};
            if(finished[0].equals(chosenHorse))//The chosen horse finished first
            {
                results.setText("Your horse won!\n");
            }
            else
            {
                results.setText("Your horse did not win.\n");
            }
            for(int i = 0; i < horses.length; i++)
            {
                results.setText(results.getText() + finished[i] + " finshed " + finish[i] + ".\n");
            }
            place = 0;
        }
    }
    
    // A radio button was clicked
    public void itemStateChanged(ItemEvent e)
    {
        // Determine which horse was selected
       for(int i = 0; i < optionsArray.length; i++)
        {
            if(optionsArray[i].isSelected())
            {
                selected = optionsArray[i];
                chosenHorse = selected.getLabel();
            }
        }
    }
    
    // A button was clicked
    public void actionPerformed(ActionEvent e)
    {
        // It was the Start button
        if(e.getSource() == start)
        {
            results.setText(""); // Clear the text area
            for (int i = 0; i < horses.length; i++)
            { 
                threads[i] = new Thread(horses[i]);
                threads[i].start();
            }
            System.gc(); // Garbage collect old threads. no guarantee
        }
        // It was the reset button
        else
        {
            for (int i = 0; i < horses.length; i++)
            {
                horses[i].newRace();
            }
        }
    }
    
    public static void main(String args[])
    {
        Horserace race = new Horserace();
        race.setSize(600, 400);
        race.setLocation(100, 100);
        race.setVisible(true);
        race.setResizable(false);
        race.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

}

[code=java]
/*
 * Horse.java
 * Class to represent a Horse
 * Created on February 25, 2004, 3:21 PM
 */

/**
 *
 * Randall Twede
 */
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Horse extends JPanel implements Runnable
{
    private int x = 0;
    private final static int Y = 7;
    private final static int WIDTH = 20;
    private final static int HEIGHT = 10;
    private Horserace parent;
    private String name;
    
    /** Creates a new instance of Horse */
    public Horse(String n, Horserace hr)
    {
        name = n;
        parent = hr;
        setBackground(Color.GREEN);       
    }
    
    // Move the horse accross the screen
    public void run()
    {
        while( (x + WIDTH + WIDTH / 2) < 400)
        {
            x += (Math.random() * 20);
            try{Thread.sleep(50);} catch(Exception e){}
            repaint();
        }
        x = 400;
        repaint();
        parent.postResults(name);   // Tell the frame this horse finished
    }
    
    // Draw the horse
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor( new Color(202, 101, 0));
        g.fillOval(x, Y, WIDTH, HEIGHT);
        g.fillOval(x + WIDTH, Y, WIDTH / 2, HEIGHT);
    }
    
    // Move horse back to the starting line
    public void newRace()
    {
        x = 0;
        repaint();
    }
    
}

[/code]

[Phil Freihofner]

It's hard to know for sure, given the fragments of code that you show. But I am surprised to see an animated game with multiple Timers involved. Most of what I've seen is done via a single timed Game Loop (which might be triggered by a Timer, or might be managed via varying Sleep amounts, to keep the refresh rate constant).

You can learn a bit more about Game Loops at http://www.java-gaming.org/boards/java-game-tutorials/65/view.html if you are not already familiar with them.