Particle[] particles;

void setup(){
  background( 0 );
  size( 200, 200 );
  framerate(30);
  particles = new Particle[2];
  for( int i = 0; i < particles.length; i++ ){
    particles[i] = new Particle( random(width), random(height), random(2)+2, random(2)+2, random(0.9)+0.1, random(0.9)+0.1, random(0.9)+0.1 );
  }
}

void loop(){
  int i, x, y, pos;
  float xlen, ylen, len, a, fr, fg, fb;
  for( i = 0; i < particles.length; i++ ){
    particles[i].relax();
  }
  for( x = 0; x < width; x++ ){
    for( y = 0; y < height; y++ ){
      pos = y*width+x;
      fr = ( pixels[pos] >> 16 & 0xff ) -50;
      fg = ( pixels[pos] >> 8 & 0xff ) -50;
      fb = ( pixels[pos] & 0xff ) -50;
      for( i = 0; i < particles.length; i++ ){
        xlen = x - particles[i].x;
        ylen = y - particles[i].y;
        len = ( float )Math.sqrt( xlen*xlen + ylen*ylen );
        a = 2000/len;
        fr += a*particles[i].r;
        fg += a*particles[i].g;
        fb += a*particles[i].b;
      }
      pixels[pos] = ( (int)fr << 16 ) & ( (int)fg << 8 ) & (int)fb;
    }
  }
}

class Particle{
  float x, y, dx, dy;
  float r, g, b;
  Particle( float x, float y, float dx, float dy, float r, float g, float b ){
    this.x = x;
    this.y = y;
    this.dx = dx;
    this.dy = dy;
    this.r = r;
    this.g = g;
    this.b = b;
  }
  void relax(){
    this.x += this.dx;
    this.y += this.dy;
    if( this.x < 0 || this.x >= width ){
      this.dx *= -1;
    }
    if( this.y < 0 || this.y >= height ){
      this.dy *= -1;
    }
  }
}