Check out the sketch here
http://www.openprocessing.org/visuals/?visualID=34325

1. int w = 255;
   int h = 255;
   
   
   float xd;
   float yd;
   float xby;
   float yby;
   float xtot;
   float ytot;
   float dtot;
   int pass;
   PVector A;
   PVector B;
   PVector now;
   void setup(){
     size(w,h);
     A= new PVector (w/2,h/2);
     now = new PVector (w/2,h/2);
     B = new PVector(random(w),random(h));
     smooth();
     background(-1);
     ellipse(B.x,B.y,10,10);
   }
   
   void draw(){
     if(mouseX != pmouseX && mouseY !=pmouseY && mousePressed){
       B = new PVector (mouseX,mouseY);
       //ellipse(B.x,B.y,10,10);
     }
   
     xd = B.x-A.x;
     if (xd<0)xd=-xd;
     yd = B.y-A.y;
     if (yd<0)yd=-yd;
     float dtot = xd+yd;
     float xtot = A.x+B.x;
     float ytot = A.y+B.y;
   
     xby = xd/dtot;
     yby = yd/dtot;
   
     if (B.x>A.x && B.y > A.y){
       now.x+=xby;
       now.y+=yby;
     }
   
     if (B.x<A.x && B.y > A.y){
       now.x-=xby;
       now.y+=yby;
     }
     if (B.x<A.x && B.y < A.y){
       now.x-=xby;
       now.y-=yby;
     }
   
     if (B.x>A.x && B.y < A.y){
       now.x+=xby;
       now.y-=yby;
     }
   
   stroke(1,111);
     point(now.x,now.y);
     if(dist(now.x,now.y,B.x,B.y)<2){
       //if(now.x>B.x-xby || now.y>B.y-yby && sign ){
   if (mode==1)      A= new PVector(B.x,B.y);
   
         sign = true;
       B = new PVector(random(w),random(h));
        ecount ++;
      //if (ecount ==0)
      ellipse(B.x,B.y,10,10);
       now =  new PVector (A.x,A.y); 
     
   
     }
     ecount = 0;
   if (now.x<xby*2 || now.y<yby*2)sign = false;
   }
   int ecount;
   int mode = 1;
   
   void keyPressed(){
    if (key=='1')mode=1;
     if (key=='2')mode=2;
   }
   boolean sign = false;