//The collision function here is not pure, and does some weird things when
//balls do not collide "nicely"

Ball[] balls = new Ball[100];

void setup() {
  size(300,300);
  smooth();
  noStroke();
  
  for(int i=0; i< balls.length; i=i+1)
  {
    balls[i] = new Ball(random(0,width),random(0,height),random(-.5,.5),random(-.5,.5), 100);
  }

}

void draw() {
  background(0);
  
  for(int i=0; i< balls.length; i=i+1)
  {
    balls[i].render();
    balls[i].update();
    collision();
  }

}


void collision()
{
float distx, disty;

  for(int i=0; i< balls.length; i=i+1)
  {
     for(int j=i; j< balls.length; j=j+1)
     {
       
      if(j != i)
      {
        distx=balls[i].getX() - balls[j].getX();
        disty=balls[i].getY() - balls[j].getY();
        
       if( (abs(distx)<10) && (abs(disty)<10) )
         { 
         balls[i].setVX( -1*balls[i].getVX() );
         balls[i].setVY( -1*balls[i].getVY() );
         balls[j].setVX( -1*balls[j].getVX() );
         balls[j].setVY( -1*balls[j].getVY() );

         balls[j].setC(255);
         balls[i].setC(255);
         }
      
      }
   }
             
  }
}


class Ball {
  float x,y,vx,vy;
  float s;
  color c;
  
  Ball(float x_, float y_, float vx_, float vy_, color c_) {
     x=x_;
     y=y_;
     vx=vx_;
     vy=vy_;
     c=c_;
     s=10;
  }
  
         
         void setC(color c_) {c=c_;}
         
         float getX() {return x;}
	 float getY() {return y;}
	 void setX(float x_) {x = x_;}
	 void setY(float y_) {y = y_;}
         void setXY(float x_, float y_) {x = x_;y = y_;}
         
         float getVX() {return vx;}
	 float getVY() {return vy;}
	 void setVX(float vx_) {vx = vx_;}
	 void setVY(float vy_) {vy = vy_;}
         void setVXY(float vx_, float vy_) {vx = vx_;vy = vy_;}
  
  
  void update() {
      
       if (x+vx > width )
        {x=width; vx=-1*vx;}
       else if (x+vx <0)
        {x=0; vx=-1*vx;}
       else
        {x=x+vx;}
        
       if (y+vy > height )
        {y=height; vy=-1*vy;}
       else if (y+vy <0)
        {y=0; vy=-1*vy;}
       else
        {y=y+vy;}
      
    }
  
  
  void render() {
      fill(c);
      ellipse(x,y,s,s);
      //reset c
      c=100;
  }
  
}