return ((a % b) + b) % b;

}

​

let rows = 35, cols = 35, rw, cw;

​

function updateCRW(){

  cw = width/cols;

  rw = height/rows;

}

​

let particles = [];

​

function randomize(n = parseInt(input_randomizeN.value) || 15){

  for(let i = 0; i < n; i++){

    particles.push(new Particle(floor(random(-2,3)), floor(random(cols)), floor(random(rows)), floor(random(-1,2)), floor(random(-1,2))));

  }

}

​

function setup() {

  createCanvas(660, 660);

  updateCRW();

  randomize();

}

​

function draw() {

  background(220);

  translate(cw/2, rw/2);

  if(draggingVelocity){

    noFill();

    stroke(200,0,200);

    line(selectedParticle.x * cw, selectedParticle.y * rw, mouseX - cw/2, mouseY - rw/2);

  }

  fill(100,100,100);

  noStroke();

  for(let i = 0; i < cols; i++){

    for(let j = 0; j < rows; j++){

      circle(i * cw, j * rw, 1);

    }

  }

  particles.forEach(p => p.render());

}

​

let draggingVelocity = false, selectedParticle = null;

​

function mousePressed(){

  const mx = floor(mouseX / cw), my = floor(mouseY / rw);

  if(mx < 0 || my < 0 || mx >= cols || my >= rows) return;

  const mass = [RIGHT, CENTER, LEFT].indexOf(mouseButton) - 1;

  let newParticle = true;

  for(let i = 0; i < particles.length; i++){

    if(particles[i].x === mx && particles[i].y === my){

      newParticle = false;

      if(mass === 0){

        draggingVelocity = true;

        selectedParticle = particles[i];

        break;

      }

      particles[i].mass += mass;

      if(particles[i].mass === 0 && particles[i].velX === 0 && particles[i].velY === 0) particles.splice(i, 1);

      break;

    }

  }

  if(newParticle) particles.push(new Particle(mass, mx, my));

  return false;

}

​

function mouseReleased(){

  if(mouseButton !== CENTER || !draggingVelocity) return;

  const mx = max(0, min(floor(mouseX / cw), cols - 1)), my = max(0, min(floor(mouseY / rw), rows - 1));

  selectedParticle.velX = (mx - selectedParticle.x) % cols;

  selectedParticle.velY = (my - selectedParticle.y) % rows;

  selectedParticle.cropVelocity();

  draggingVelocity = false;

}

​

function step(){

  if(particles.length === 0) return;

  for(let i = 0; i < particles.length; i++){

    for(let j = i + 1; j < particles.length; j++){

      if(particles[i].x === particles[j].x && particles[i].y === particles[j].y) continue; //failsafe

      particles[i].pullTowards(particles[j]);

      particles[j].pullTowards(particles[i]);

    }

    particles[i].applyGravity();

  }

  for(let i = particles.length - 1; i >= 0; i--){

    //console.log(particles[i].display());

    particles[i].applyVelocity();

    if(particles[i].mass === 0 && particles[i].velX === 0 && particles[i].velY === 0) particles.splice(i, 1);

  }

  //console.log("-".repeat(25));

  for(let i = 0; i < particles.length; i++){

    for(let j = i + 1; j < particles.length; j++){

      if(particles[i].x === particles[j].x && particles[i].y === particles[j].y){

        particles[i].mass += particles[j].mass;

        particles[i].velX += particles[j].velX; //speed++++++++++++++++++++++++++++=

        particles[i].velY += particles[j].velY;

        particles.splice(j, 1);

        j--;

      }

    }

  }

}

​

​

let intv = null;

​

function clock(){

  if(intv === null){

    intv = setInterval(step, 1000/floor(parseInt(input_fps.value) || 60));

    button_clock.innerHTML = "Stop";

    button_step.disabled = "disabled";

    return;

  }clearInterval(intv);

  intv = null;

  button_step.disabled = "";

  button_clock.innerHTML = "Start";

}