Thread: Simple Game Physics & Animation (Air Hockey)

Why are you using a JLabel instead of simply drawing the puck to a JPanel directly?

While I could use the experience, I need to put in images in place of pucks and labels appear to be the only option.

A continuous loop seems like a bad idea. It should only check collision once per frame.

I did mean every frame.

I can't really tell without seeing your code, and I can't really look at anything except an SSCCE- something simple, just a few lines, without anything extra.

Well, what I posted up there in the first post was pretty much stripped of anything else. All the pertinent code was up there too. What I need is some implementable way to check for collisions, and I just need some ideas, but my code is up there. I've snipped the calculations too (check first post), so those are just 10 lines each (and the first one has 5 almost repeated anyway).

80 fps is huge...

I guess you're right. I did realize that it didn't matter much, and I set it to 40 FPS.

...But really, you should consider not doing it at all...

I agree, it might seem to be an annoyance, but I want to leave paddle control to the mouse - so you can see why I wouldn't want them to be able to access all the parts of the screen. I'm leaning towards dealing with it internally now, i.e. just disable paddle movement when it leaves the area. That should work well.


Thanks a lot for your help and interest by the way. I'd appreciate it if you'd look at the coding above again now, I've stripped it to bare minimum.

I don't get it - what would you do with a compilable version? My code doesn't need debugging, I just need a suggestion of how to do it. I don't see how running the actual program might help your case, but here is something you can copy and paste:

Main:

import java.awt.Cursor;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.Timer;
 
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
 
 
public class NewJFrame extends javax.swing.JFrame {
 
    /** Creates new form NewJFrame */
    public NewJFrame() {
        initComponents();
        myinit();
        getContentPane().setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
        //myinit();
 
    }
 
 
    double speed = 1;
    double globalFPS = 60;
 
    boolean magnetism = false;
 
 
    Timer t = new Timer((int)(1000/(speed*globalFPS)), new ActionListener() {public void actionPerformed(ActionEvent e) {timerfunc3();}});
    void timerfunc3()
    {
        ch.update();
 
        puck1.update();
        //puck2.update();
        puck3.update();
        puck4.update();
 
 
        if (magnetism)
        {
            double dist = ch.distance(puck1, puck4);
            puck1.velx += 200/globalFPS * (puck4.posx - puck1.posx)/dist;
            puck1.vely += 200/globalFPS * (puck4.posy - puck1.posy)/dist;
        }
    }
 
 
 
 
    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
    private void initComponents() {
 
        l1 = new javax.swing.JLabel();
        l2 = new javax.swing.JLabel();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jButton3 = new javax.swing.JButton();
        l3 = new javax.swing.JLabel();
        l4 = new javax.swing.JLabel();
 
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setMinimumSize(new java.awt.Dimension(400, 500));
        setResizable(false);
        addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                formMouseClicked(evt);
            }
            public void mouseEntered(java.awt.event.MouseEvent evt) {
                formMouseEntered(evt);
            }
            public void mousePressed(java.awt.event.MouseEvent evt) {
                formMousePressed(evt);
            }
            public void mouseReleased(java.awt.event.MouseEvent evt) {
                formMouseReleased(evt);
            }
        });
        addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
            public void mouseMoved(java.awt.event.MouseEvent evt) {
                formMouseMoved(evt);
            }
        });
        addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyPressed(java.awt.event.KeyEvent evt) {
                formKeyPressed(evt);
            }
            public void keyReleased(java.awt.event.KeyEvent evt) {
                formKeyReleased(evt);
            }
        });
        getContentPane().setLayout(null);
 
        l1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/transp.png"))); // NOI18N
        l1.setText("jLabel1");
        getContentPane().add(l1);
        l1.setBounds(160, 130, 40, 40);
 
        l2.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/transp.png"))); // NOI18N
        l2.setText("jLabel1");
        getContentPane().add(l2);
        l2.setBounds(340, 10, 40, 40);
 
        jButton1.setText("Start Tmer");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
        getContentPane().add(jButton1);
        jButton1.setBounds(40, 20, 83, 23);
 
        jButton2.setText("Stop Timer");
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });
        getContentPane().add(jButton2);
        jButton2.setBounds(130, 20, 90, 23);
 
        jButton3.setText("Debug");
        jButton3.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton3ActionPerformed(evt);
            }
        });
        getContentPane().add(jButton3);
        jButton3.setBounds(240, 20, 63, 23);
 
        l3.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/30ps.png"))); // NOI18N
        l3.setText("jLabel1");
        getContentPane().add(l3);
        l3.setBounds(60, 260, 30, 30);
 
        l4.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/transp.png"))); // NOI18N
        l4.setText("jLabel1");
        getContentPane().add(l4);
        l4.setBounds(160, 250, 40, 40);
 
        pack();
    }// </editor-fold>//GEN-END:initComponents
 
 
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton1ActionPerformed
        // TODO add your handling code here:
        t.start();
 
    }//GEN-LAST:event_jButton1ActionPerformed
 
    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton2ActionPerformed
        // TODO add your handling code here:
        t.stop();
    }//GEN-LAST:event_jButton2ActionPerformed
 
    private void jButton3ActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_jButton3ActionPerformed
        // TODO add your handling code here:
    }//GEN-LAST:event_jButton3ActionPerformed
 
 
 
 
 
    private void formMousePressed(java.awt.event.MouseEvent evt) {//GEN-FIRST:event_formMousePressed
        magnetism = true;
    }//GEN-LAST:event_formMousePressed
 
 
 
    private void formMouseReleased(java.awt.event.MouseEvent evt) {//GEN-FIRST:event_formMouseReleased
        // TODO add your handling code here:
        magnetism = false;
    }//GEN-LAST:event_formMouseReleased
 
    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }
 
    void myinit()
    {
        puck1 = new Puck(l1, 100, 0, globalFPS);
        puck2 = new Puck(l2, 120, 80, globalFPS);
        puck3 = new Puck(l3, -120, 0, globalFPS);
        puck4 = new Puck(l4, 0, 0, globalFPS);
 
        puck1.frictionEnabled = false;
        puck2.frictionEnabled = false;
        puck3.frictionEnabled = false;
        puck4.frictionEnabled = false;
 
        ch = new CollisionHandler(0, 0, 400, 470);
 
        ch.add(puck1);
        //ch.add(puck2);
        ch.add(puck3);
        ch.add(puck4);    }
 
    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton3;
    private javax.swing.JLabel l1;
    private javax.swing.JLabel l2;
    private javax.swing.JLabel l3;
    private javax.swing.JLabel l4;
    // End of variables declaration//GEN-END:variables
 
    Puck puck1;
    Puck puck2;
    Puck puck3;
    Puck puck4;
    CollisionHandler ch;
}

The CH class:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
 
public class CollisionHandler {
 
    int minx;
    int miny;
 
    int maxx;
    int maxy;
    int plimit = 10;
 
    //double velrest = 0.7;
    //double ebound = 0.8;
    double epuck = 0.9;
 
    private Puck[] plist = new Puck[10];
    private int counter = 0;
 
    public CollisionHandler(int lx, int ly, int ux, int uy)
    {
        minx = lx;
        miny = ly;
        maxx = ux;
        maxy = uy;
    }
 
    public boolean add(Puck p)
    {
        if (counter > plimit) return false;
 
        for (int i = 0; i < counter; i++)
        {
            if (plist[i] == p)
                return false;
        }
 
        plist[counter] = p;
        counter++;
        return true;
    }
 
    public double distance(Puck a, Puck b)
    {
        return Math.sqrt( (a.getCentreX()- b.getCentreX()) * (a.getCentreX()- b.getCentreX()) + (a.getCentreY()- b.getCentreY()) * (a.getCentreY()- b.getCentreY()) );
    }
 
    //If colls get jittery with top and left, change to: posx = minx + some_offset
 
    public void update()
    {
        for(int i = 0; i < counter; i++)
        {
            Puck t = plist[i];
 
            if (Math.abs(t.velx) > t.velrest)
            {
                if(t.posx > maxx - t.width)
                {
                    t.posx = maxx - t.width;
                    t.velx *= -t.ebound;
                }
 
                if (t.posx < minx)
                {
                    t.posx = minx;
                    t.velx *= -t.ebound;
                }
            }
 
            if (Math.abs(t.vely) > t.velrest)
            {
                if(t.posy > maxy - t.height)
                {
                    t.posy = maxy - t.height;
                    t.vely *= -t.ebound;
                }
 
                if (t.posy < miny)
                {
                    t.posy = miny;
                    t.vely *= -t.ebound;
                }
            }
 
            /*inter-puck collisions: TODO*/
            if (counter <= 1) return; //No collisions for less than 1
 
            for (int j = i + 1; j < counter; j++)
            {
                Puck t2 = plist[j];
                int coll = (int)distance(t, t2) - (t.width + t2.width) / 2;
 
 
                if (coll < 0) //&& !(t.velx < t.velrest && t2.velx < t2.velrest && t.vely < t.velrest && t2.vely < t2.velrest))
                {
                    double cos = Math.abs(t.getCentreX() - t2.getCentreX())/((t.width + t2.width) / 2);
                    double sin = Math.abs(t.getCentreY() - t2.getCentreY())/((t.width + t2.width) / 2);
 
                    double u1 = t.velx*cos + t.vely*sin;
                    double u2 = t2.velx*cos + t2.vely*sin;
 
                    double v1 = (t.mass*u1 + t2.mass*u2 + epuck * t2.mass * (u2 - u1) ) / (t.mass + t2.mass);
                    double v2 = (t.mass*u1 + t2.mass*u2 + epuck * t.mass * (u1 - u2) ) / (t.mass + t2.mass);
 
                    t.velx = v1*cos + t.velx*sin*sin - t.vely*cos*sin;
                    t.vely = v1*sin + t.vely*cos*cos - t.velx*sin*cos;
 
                    t2.velx = v2*cos + t2.velx*sin*sin - t2.vely*cos*sin;
                    t2.vely = v2*sin + t2.vely*cos*cos - t2.velx*sin*cos;
 
                    System.out.println("Bam! " + i + j);// + distance(t, t2) + ", And width- " + (t.width + t2.width) / 2);
 
                }
            }
 
            //End outer for*/
        }
 
    }
}

And the Puck class:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
 
public class Puck {
 
    double mass = 1;
 
    double posx = 0;
    double posy = 0;
 
    double velx;
    double vely;
    double velrest = 0.7;
 
    double ebound = 0.9;
    double mu = 3; //Actually, mu*g
    boolean frictionEnabled = true;
 
    double FPS;
 
    javax.swing.JLabel label;
    int width = 40;
    int height = 40;
 
 
    /*public Puck(javax.swing.JLabel a)
    {
 
    }*/
 
    public Puck(javax.swing.JLabel lbl, double vx, double vy, double f)
    {
        label = lbl;
 
        posx = label.getX();
        posy = label.getY();
 
        width = label.getWidth();
        height = label.getHeight();
 
        velx = vx;
        vely = vy;
 
        FPS = f;
 
    }
 
    public double getCentreX()
    {
        return posx + width/2;
    }
 
    public double getCentreY()
    {
        return posy + width/2;
    }
 
    public void update()
    {
        if (Math.abs(velx) > velrest)
        {
            posx += velx/FPS;
            if (frictionEnabled) velx -= Math.signum(velx) * mu / FPS;
            label.setBounds((int)posx, (int)posy, width, height);
        }
 
        if (Math.abs(vely) > velrest)
        {
            posy += vely/FPS;
            if (frictionEnabled) vely -= Math.signum(vely) * mu / FPS;
            label.setBounds((int)posx, (int)posy, width, height);
        }
 
    }
 
    public void setpos(int x, int y)
    {
        posx = x;
        posy = y;
        label.setBounds((int)posx, (int)posy, width, height);
    }
}

Note - You will have to change the image stuff in initComponents() in the main NewJFrame class, add some random image if you want.

Also, you can set initial velocities in the myInit() function towards the end in the main NewJFrame class. (The second and third arguments while defining Pucks).