ArrayList particles;
ArrayList clearParticle;

int focusx, focusy;

void setup(){
  size( 500, 500 );
  background( 0 );

  focusx = (int)random( width );
  focusy = (int)random( height );

  particles = new ArrayList();
  clearParticle = null;
  for( int i = 0; i < 10; i++ ){
    color c = color( random( 50 ), random( 50 ), random( 100 ) );
    particles.add( new Particle( focusx + 80 - random( 160 ), focusy + 80 - random( 160 ), 2-random(4), 2-random(4), c, 0 ) );
  }
}

void loop(){

  clearParticle = null;
  Iterator it = particles.iterator();
  while( it.hasNext() ){
    Particle p = ( Particle )it.next();
    p.relax();
    p.drawSelf();
  }
  if( clearParticle != null ){
    it = clearParticle.iterator();
    while( it.hasNext() ){
      Particle p = ( Particle )it.next();
      particles.remove( p );
      if( p.depth < 4 ){
        for( int i = 0; i < 3; i++ ){
          color c = color( random( 50 ), random( 50 ), random( 100 ) );
          particles.add( new Particle( p.x, p.y, 2-random(4), 2-random(4), c, p.depth ) );
        }
      }
    }
  }

  if( particles.size() == 0 ){
    focusx = (int)random( width );
    focusy = (int)random( height );
    for( int i = 0; i < 10; i++ ){
      color c = color( random( 50 ), random( 50 ), random( 100 ) );
      particles.add( new Particle( focusx + 80 - random( 160 ), focusy + 80 - random( 160 ), 2-random(4), 2-random(4), c, 0 ) );
    }
  }
  if( mousePressed ){
    background( 0 );
  }
}

class Particle{
  float x, y;
  float lastx, lasty;
  float dx, dy;
  color c;
  int count;
  int depth;
  Particle( float x, float y, float dx, float dy, color c, int depth ){
    this.x = x;
    this.y = y;
    this.lastx = x;
    this.lasty = y;
    this.dx = dx;
    this.dy = dy;
    this.c = c;
    this.count = 0;
    this.depth = depth+1;
  }
  void relax(){
    dx += ( focusx - x ) * 0.01;
    dy += ( focusy - y ) * 0.01;
    x += dx;
    y += dy;

    //•Ç‚Æ‚Ì�Õ“Ë”»’è
    if( x < 0 ){
      x = 0;
      dx *= -1;
    }
    else if( x > width-1 ){
      x = width-1;
      dx *= -1;
    }
    if( y < 0 ){
      y = 0;
      dy *= -1;
    }
    else if( y > height-4 ){
      y = height-4;
      dy *= -1;
    }

    c = subtract( c, color( 3, 3, 3 ) );
    count++;
    if( count > 30 ){
      if( clearParticle == null ){
        clearParticle = new ArrayList();
      }
      clearParticle.add( this );
    }
  }
  void drawSelf(){
    int addx, addy = 0;
    int pos;

    pos = width * (int)y + (int)x;
    pixels[pos] = add( pixels[pos], subtract( c, color( 40, 40, 40 ) ) );
    pos = width * (int)y + (int)(x+1);
    pixels[pos] = add( pixels[pos], subtract( c, color( 20, 20, 20 ) ) );
    pos = width * (int)y + (int)(x+2);
    pixels[pos] = add( pixels[pos], subtract( c, color( 40, 40, 40 ) ) );

    pos = width * (int)(y+1) + (int)x;
    pixels[pos] = add( pixels[pos], subtract( c, color( 20, 20, 20 ) ) );
    pos = width * (int)(y+1) + (int)(x+1);
    pixels[pos] = add( pixels[pos], c );
    pos = width * (int)(y+1) + (int)(x+2);
    pixels[pos] = add( pixels[pos], subtract( c, color( 20, 20, 20 ) ) );

    pos = width * (int)(y+2) + (int)x;
    pixels[pos] = add( pixels[pos], subtract( c, color( 40, 40, 40 ) ) );
    pos = width * (int)(y+2) + (int)(x+1);
    pixels[pos] = add( pixels[pos], subtract( c, color( 20, 20, 20 ) ) );
    pos = width * (int)(y+2) + (int)(x+2);
    pixels[pos] = add( pixels[pos], subtract( c, color( 40, 40, 40 ) ) );

    lastx = x;
    lasty = y;
  }
}

color subtract( color c1, color c2 ){
  float c1R = c1 >> 16 & 0xff;
  float c1G = c1 >> 8 & 0xff;
  float c1B = c1 & 0xff;
  float c2R = c2 >> 16 & 0xff;
  float c2G = c2 >> 8 & 0xff;
  float c2B = c2 & 0xff;
  color resultc = color( c1R-c2R, c1G-c2G, c1B-c2B );
  return resultc;
}
color add( color c1, color c2 ){
  float c1R = c1 >> 16 & 0xff;
  float c1G = c1 >> 8 & 0xff;
  float c1B = c1 & 0xff;
  float c2R = c2 >> 16 & 0xff;
  float c2G = c2 >> 8 & 0xff;
  float c2B = c2 & 0xff;
  color resultc = color( c1R+c2R, c1G+c2G, c1B+c2B );
  return resultc;
}