Java problem: bouncing balls - TranceAddict Forums


<?
import java.awt.*;



public class Bounce extends Animation {

    

    protected double X1, X2, Y1, Y2, Vx1, Vy1, Vx2, Vy2, dX, dY, vectorX, vectorY, Va1, Va2, Vb1, Vb2, VaP1, VaP2,

                        deltaT, deltaB, distance, metersPerPixel, gravity, elasticColl;

    protected int radius1, radius2, firstTime=1, pixelX1, pixelY1, pixelX2, pixelY2, mass1, mass2;

    protected Color color1 = Color.white;

    protected Color color2 = Color.red;

    

    protected void initAnimator() {

        deltaT = 0.0005;// simulation time interval in seconds

        setDelay((int)(1000*deltaT)); // needed for Animation superclass

        

        gravity = 20;

        

        elasticColl = 1.5;

        

        mass1 = 10;

        mass2 = 20;

        

        X1 = 1; // in meters

        Y1 = 2; // Y reference direction downwards!

        X2 = 4;

        Y2 = 5;

        Vx1 = 4; // in m/s

        Vy1 = -8;

        Vx2 = -5; // in m/s

        Vy2 = -1.3;

        

        metersPerPixel = 40;

        

        radius1 = 20; // in pixels!

        radius2 = 40;

        

        pixelX1 = (int) (metersPerPixel * X1); // screen position

        pixelY1 = (int) (metersPerPixel * Y1);

        pixelX2 = (int) (metersPerPixel * X2); // screen position

        pixelY2 = (int) (metersPerPixel * Y2);

    }

    

    protected void paintAnimator(Graphics g) {

        

        g.setColor(Color.black);

        if(firstTime==1) {

            g.fillRect(0,0,d.width,d.height); 

            firstTime=0;

        }

        

        g.fillOval(pixelX1 - radius1, pixelY1 - radius1, radius1 * 2, radius1 * 2);

        g.fillOval(pixelX2 - radius2, pixelY2 - radius2, radius2 * 2, radius2 * 2);



        //collision with walls

        if (pixelX1 < radius1 || pixelX1 > d.width - radius1) {

            Vx1 = -Vx1;

        }

        if (pixelY1 < radius1 || pixelY1 > d.height - radius1) {

            Vy1 = -Vy1;

        }

        if (pixelX2 < radius2 || pixelX2 > d.width - radius2) {

            Vx2 = -Vx2;

        }

        if (pixelY2 < radius2 || pixelY2 > d.height - radius2) {

            Vy2 = -Vy2;

        }

        

        //Apply the gravity on the balls

        Vy1 = Vy1+gravity*deltaT;

        Vy2 = Vy2+gravity*deltaT; 

        

        //calculate the distance between the center of the balls using pythagoras theorem

        //to check see if the balls collide

        dX = pixelX2-pixelX1; 

        dY = pixelY2-pixelY1;

        distance = Math.sqrt(dX*dX+dY*dY);     

        

        //collision check

        if (distance < radius1+radius2) {    

            

            //Calculate the vector towards the center of the ball (in the direction of the collision)

            vectorX = dX/distance;

            vectorY = dY/distance;

            

            //The new velocities in x- and y-axes of the collision

            Va1 = (Vx1*vectorX + Vy1*vectorY);

            Vb1 = (-Vx1*vectorY + Vy1*vectorX);

            Va2 = (Vx2*vectorX + Vy2*vectorY);

            Vb2 = (-Vx2*vectorY + Vy2*vectorX);

            

            //The new velocities after collision

            VaP1 = Va1 + elasticColl*(Va2-Va1)/(1+mass1/mass2);

            VaP2 = Va2 + elasticColl*(Va1-Va2)/(1+mass2/mass1);

            

            //Undo the projections

            Vx1 = VaP1*vectorX - Vb1*vectorY;

            Vy1 = VaP1*vectorY + Vb1*vectorX;

            Vx2 = VaP2*vectorX - Vb2*vectorY;

            Vy2 = VaP2*vectorY + Vb2*vectorX;        

        }    

            

        X1 += Vx1 * deltaT;

        Y1 += Vy1 * deltaT;

        X2 += Vx2 * deltaT;

        Y2 += Vy2 * deltaT;

        

        pixelX1 = (int) (metersPerPixel * X1);

        pixelY1 = (int) (metersPerPixel * Y1);

        pixelX2 = (int) (metersPerPixel * X2); 

        pixelY2 = (int) (metersPerPixel * Y2);

        

        //paint the balls

        g.setColor(color1);

        g.fillOval(pixelX1 - radius1, pixelY1 - radius1, radius1 * 2, radius1 * 2);

        g.setColor(color2);

        g.fillOval(pixelX2 - radius2, pixelY2 - radius2, radius2 * 2, radius2 * 2);

    }

}
?>

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-- Java problem: bouncing balls

Posted by Cloudburst on Feb-12-2006 18:37:

Java problem: bouncing balls

I dunno if there's any Java geeks in here (tell me where I could get help if you know). Anyway this might be more of a physics problem. I've gotten 2 balls bouncing good (assignment in a math course), but only when one balls weight is twice as big as the other one's. I want to preserve the energy in the collisions.

So:

if
mass1 = 2*mass2 or mass2 = 2*mass1 and elasticColl = 1.5
everything works fine. I'm not sure what's wrong.

CLICK HERE FOR APPLET

If anyone feels they could find the problem (I doubt it because it has to be done in a few hours), feel free to try.

PHP:

Posted by DjDeComp on Feb-12-2006 18:44:

yes

Posted by Cloudburst on Feb-12-2006 18:46:

Fucking hell...you can tell I'm desperate... I'M ASKING THE COR FOR HELP LOL.

Bah... waste of time I guess...

Posted by Coup on Feb-12-2006 18:47:

quote:
Originally posted by DjDeComp
yes

+1

Posted by stevieboy32808 on Feb-12-2006 18:52:

Collision and energy remind me a lot of these equations:

Momentum = mass*velocity <---Applies to collisions

kintetic energy(KE) = 1/2*(mass)(velocity)^2

You say you want to preserve the energy so somehow coming up with an equation relevant to the above you can set it equal to zero. Do you have a book outlining some sort of procedure and do you understand what I'm trying to say?

Posted by DjDeComp on Feb-12-2006 18:55:

quote:
Originally posted by Cloudburst
Fucking hell...you can tell I'm desperate... I'M ASKING THE COR FOR HELP LOL.

Bah... waste of time I guess...

desperate.. yes

wasting your time.. no

Posted by Sunsnail on Feb-12-2006 19:29:

you may want to check this site out

http://javahelp.com/mass