ArrayList particles;
ArrayList clearParticle;

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

  particles = new ArrayList();
  clearParticle = null;
}

void loop(){
  background(0);
  for( int i = 0; i < 30; i++ ){
    color c = color( 130, 70, 10 );
    float my = mouseY > height-4 ? height-4 : mouseY;
    particles.add( new Particle( mouseX, my, 0, 0, c ) );
  }
  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 );
    }
  }
}

class Particle{
  float x, y;
  float lastx, lasty;
  float dx, dy;
  color c;
  int count;
  static final float G = -0.5f;
  static final float E = 0.5f;
  Particle( float x, float y, float dx, float dy, color c ){
    this.x = x;
    this.y = y;
    this.lastx = x;
    this.lasty = y;
    this.dx = dx;
    this.dy = dy;
    this.c = c;
    this.count = 0;
  }
  void relax(){
    dx += 1.0f - random(2);
    dy += 1.0f - random(2);
    dy +=  Particle.G;
    x += dx;
    y += dy;
    dx *= 0.90;
    dy *= 0.90;

    //�ǂƂ̏Փ˔���
    if( x < 0 ){
      x = 0;
      dx *= -1 * Particle.E;
    }
    else if( x > width-1 ){
      x = width-1;
      dx *= -1 * Particle.E;
    }
    if( y < 0 ){
      if( dy <= 5 ){
        if( clearParticle == null ){
          clearParticle = new ArrayList();
        }
        clearParticle.add( this );
        y = 0;
        dy *= -1 * Particle.E;
        return;
      }
      else{
        y = 0;
        dy *= -1 * Particle.E;
      }
    }
    else if( y > height-4 ){
      y = height-4;
      dy *= -1 * Particle.E;
    }
    
    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;
  }
}