let N = 2000;

let G = 1;

let dt = 0.2;

let grid;

​

let particles_pos = new Float32Array(2*N);

let particles_vel = new Float32Array(2*N);

​

let forces = new Float32Array(2*N)

​

function setup() {

  createCanvas(400, 400);

  grid = new Grid(width, height, r, 10);

  for(let i = 0; i < 2*N; ++i) {

    particles_pos[i] = random()*400;

  }

  particles_vel.fill(0);

  forces.fill(0);

  noStroke();

  fill("purple");

  stroke("red");

}

​

function show_particles() {

  strokeWeight(2)

  beginShape(POINTS);

   for(let p = 0; p < N; p += 1 ) {

    stroke(particles_vel[2*p]*10, particles_vel[2*p+1]*10, (particles_vel[2*p] + particles_vel[2*p+1])*8)

    vertex(particles_pos[2*p],particles_pos[2*p+1]);

  }

  endShape();

}

function update_particles() {

   for(let i = 0; i < 2*N; i += 1 ) {

     particles_vel[i] += forces[i] * dt;

     particles_vel[i] *= 0.99

     particles_pos[i] += particles_vel[i] * dt;

     if(particles_pos[i] < 0) {

       particles_pos[i] = random();

       particles_vel[i] *= -0.99;

     }

     if(particles_pos[i] > 400) {

       particles_pos[i] = 400 - random();

       particles_vel[i] *= -0.99;

     }

  }

}

function draw() {

  background(220);

  forces.fill(0);

  for(let p = 0; p < N; p += 1 ) {

    forces[2*p + 1] = G;

  }

  grid.update(particles_pos)

  grid.compute_interactions(particles_pos, forces);

  // console.log(forces)

  update_particles();

  show_particles();

}