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Information about this web site => Request for physics Simulations => Topic started by: slayer 64 on September 02, 2009, 05:42:48 am



Title: Ball line collision and response. multiple collisions at once
Post by: slayer 64 on September 02, 2009, 05:42:48 am
i use a program called game maker. (http://www.yoyogames.com/make) i read 2D collision (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=4.msg15#msg15) and created that simulation in game maker. you can find it here. (http://gmc.yoyogames.com/index.php?showtopic=446075) i've used what i found and made a ball collide with a line. but when the ball collides with more than 1 line, it cuts through one of the lines every time. when the ball collides with more than 1 ball it jumps back a little too far, leaving a gap when the 2 balls should be touching perfectly.

can you make an example like 2D collision but will handle multiple balls and lines?
here is my code, its game maker code but i think you can understand it.
thank you.

var denominator,position,x1,y1,x2,y2,i;

//collide with lines
for(i=0;i<ds_list_size(obj_lines.lines)-2;i+=2)
{
    x1=ds_list_find_value(obj_lines.lines,i);
    y1=ds_list_find_value(obj_lines.lines,i+1);
    x2=ds_list_find_value(obj_lines.lines,i+2);
    y2=ds_list_find_value(obj_lines.lines,i+3);

    dx=x2-x1;
    dy=y2-y1;

    denominator=sqr(dx)+sqr(dy);

    if denominator>0
    {
        position=median(0,1,((x-x1)*dx+(y-y1)*dy)/denominator);
       
        //find tangent point on line
        px=x1+position*dx;
        py=y1+position*dy;
       
        //get distance from ball to tanget point
        dx=px-x;
        dy=py-y;
        dis=sqrt(sqr(dx)+sqr(dy));
       
        if dis<=radius+obj_lines.radius
        {
            //normalize
            dx/=dis;
            dy/=dis;
           
            //calculate the component of velocity in the direction
            vp1=hspeed*dx+vspeed*dy;
           
            if vp1!=0
            {
                dt=(radius+obj_lines.radius-dis)/vp1;
               
                //move the ball back so they just touch
                x-=hspeed*dt;
                y-=vspeed*dt;
               
                //projection of the velocities in these axes
                va1=(hspeed*dx+vspeed*dy);
                vb1=(-hspeed*dy+vspeed*dx);
               
                //bounce. 1 would keep be a perfect slide against the line
                b=1;
               
                //new velocities in these axes
                vaP1=va1+b*(0-va1);
               
                hspeed=vaP1*dx-vb1*dy; 
                vspeed=vaP1*dy+vb1*dx;
               
                //we move the balls back in time so we need to move them forward
                x+=hspeed*dt;
                y+=vspeed*dt;
            }
        }
    }
}


Title: Re: Ball line collision and response. multiple collisions at once
Post by: lookang on September 02, 2009, 09:44:55 am
http://www.um.es/fem/EjsWiki/Main/ExamplesMultipleCollisions by Francisco Esquembre is possibly a suitable example for u to study and discuss on.


Title: Re: Ball line collision and response. multiple collisions at once
Post by: book reviews on September 13, 2009, 08:03:46 am
Hem.... i think i can use that technique to complete my game project. Thanks for that usefull information


Title: Re: Ball line collision and response. multiple collisions at once
Post by: Clotaire on November 10, 2010, 05:58:01 pm
http://www.um.es/fem/EjsWiki/Main/ExamplesMultipleCollisions by Francisco Esquembre is possibly a suitable example for u to study and discuss on.

I check your code when there are some overlap, you ask the program to give the ball a new random velocity. it is right?


Title: Re: Ball line collision and response. multiple collisions at once
Post by: lookang on November 10, 2010, 08:55:50 pm
http://www.um.es/fem/EjsWiki/Main/ExamplesMultipleCollisions by Francisco Esquembre is possibly a suitable example for u to study and discuss on.

I check your code when there are some overlap, you ask the program to give the ball a new random velocity. it is right?
no. it is not random at all.
Code:
//System.out.println ("Collision between "+collision1 +" and "+collision2);
//System.out.println ("at x[1]= "+x[collision1] +" and x[2] = "+x[collision2]);
double deltax = x[collision2]-x[collision1];
double deltay = y[collision2]-y[collision1];
double distance = Math.sqrt(deltax*deltax+deltay*deltay);

double rx=deltax/distance, ry=deltay/distance; // Unit vector joining centers
double sx=-ry, sy=rx; // Vector ortogonal to the previous one

double vr1=(vx[collision1]*rx+vy[collision1]*ry), vs1=(vx[collision1]*sx+vy[collision1]*sy); // Projections for disk 1
double vr2=(vx[collision2]*rx+vy[collision2]*ry), vs2=(vx[collision2]*sx+vy[collision2]*sy); // Projections for disk 2

double vr1d=( 2*mass[collision2]*vr2 + (mass[collision1]-mass[collision2])*vr1 )/(mass[collision1]+mass[collision2]); // New velocity for disk 1
double vr2d=( 2*mass[collision1]*vr1 + (mass[collision2]-mass[collision1])*vr2 )/(mass[collision1]+mass[collision2]); // New velocity for disk 2
// Undo the projections
vx[collision1]=vr1d*rx+vs1*sx; vy[collision1]=vr1d*ry+vs1*sy;
vx[collision2]=vr2d*rx+vs2*sx; vy[collision2]=vr2d*ry+vs2*sy;