int screen_width = 340;
int screen_height = 280;
int num_particles = 2000;
float[] particles = new float[num_particles*2];
float[] vel = new float[num_particles*2];
float flicker;

void setup() {
  size(340, 280, JAVA2D);
  strokeWeight(2);
  smooth();
  background(104);
  fill(100, 100, 100);
  noStroke();

  frameRate(30);

  flicker = 1;

  for (int i = 0; i < num_particles*2; i+=2) {
    particles[i] = random(2, screen_width-2);
    particles[i+1] = random(2, screen_height-2);
  }

  for (int i = 0; i < num_particles*2; i+=2) {
    vel[i] = random(-1,1)*0.25;
    vel[i+1] = random(-1,1)*0.25;
  }
}


void draw() {

  background(255);

  // update velocities
  for (int i = 0; i < num_particles*2; i+=2) {
    if (particles[i] + vel[i] > screen_width-2) {
      vel[i] *= -1;// + random(-10,10)/10;
    }
    else if (particles[i] + vel[i] < 2) {
      vel[i] *= -1;// + random(-10,10)/10;
    }

    if (particles[i+1] + vel[i+1] > screen_height-2) {
      vel[i+1] *= -1;// + random(-10,10)/10;
    }
    else if (particles[i+1] + vel[i+1] < 2) {
      vel[i+1] *= -1;// + random(-10,10)/10; 
    }

    // gravity
    //float dz_x = cos(particles[i]/25);
    //float dz_y = cos(particles[i+1]/25);
    //vel[i] += dz_x*0.1;
    //vel[i+1] += dz_y;

    // friction
    //vel[i] *= 0.99;
    //vel[i+1] *= 0.99;

    if (vel[i] > 4) vel[i] = 4;
    else if (vel[i] < -4) vel[i] = -4;
    if (vel[i+1] > 4) vel[i+1] = 4;
    else if (vel[i+1] < -4) vel[i+1] = -4;
  }

  // update positions
  for (int i = 0; i < num_particles*2; i+=2) {
    particles[i] += vel[i];
    particles[i+1] += vel[i+1];
  }

  // draw
  for (int i = 0; i < num_particles*2; i+=2) {
    float z = sin(particles[i]/25) + sin(particles[i+1]/25);
    float disparity = z*2 + 1;
    //fill(255,0,0,127);
    if (flicker > 0) {
      //fill(255,0,0,127);
      ellipse(particles[i], particles[i+1], 2, 2);
    }
    //fill(47,255,255,127);
    else {
      //fill(47,255,255,127);
      ellipse(particles[i]+disparity, particles[i+1], 2, 2);
    }
    //ellipse(random(0,screen_width), random(0,screen_height), 200, 150);
    //rect(random(0,screen_width),random(0,screen_height),random(0,screen_width),random(0,screen_height));
  }

  if (flicker == 2) {
    flicker = -2;
  }
  flicker++;
}