return ({

    pos: {x:pos.x, y:pos.y},

    velocity: {x:0, y:0} ,

    radius: 12,

    mass: 2

  })

}

​

let balls = [];

let num_balls = 80;

​

let G = 19.8;

​

let forceField = {

  pos: {x:0, y:0},

  velocity: {x:0, y:0} ,

  radius: 140

}

​

function setup() {

  createCanvas(800, 800);

  for (let i = 0; i < num_balls; i++) {

    balls.push(

      get_ball( { x: random(0, width), y:random(0, height)  } )

    )

  }

  forceField.pos = {x: width/2, y: height/2};

}

​

​

​

const solvePosition = (pos, vel, acc, dt) => {

  return pos + vel * dt + ((acc * (dt*dt)) / 2);

}

​

​

const verlet_gravity = (obj, dt) => {

  let acc_y = G;

  obj.pos.y += dt * (obj.velocity.y * acc_y /2);

  let new_acc_y = G;

  obj.velocity.y += dt * (acc_y + new_acc_y) /2;

  return obj;

}

​

​

function dist2 (v, w) {

  return ((v.x - w.x) * (v.x - w.x)) + ((v.y - w.y) * (v.y - w.y) )

}

​

​

function draw() {

  background(20);

  forceField.pos.y = mouseY;

  forceField.pos.x = mouseX;

  balls.map((ball) => {

    let d = dist2(ball.pos, forceField.pos);

    let real_d = Math.sqrt(d);

    let max_d = forceField.radius;

    let min_d = forceField.radius/4;

​

    let dt = deltaTime/1000;

​

​

    if (real_d < max_d) {

      let influence = map(real_d, max_d, min_d, 1, 0.1);

      influence = max(0.1, influence);

      dt *= influence;

    }

​

​

    ball = verlet_gravity(ball, dt);

​

​

    if(ball.pos.y > height*2)  {

      ball.pos.y = 20;

      ball.velocity.y = 0;

    }

     noStroke();

    fill(255);

    ellipse(ball.pos.x, ball.pos.y, ball.radius, ball.radius);

  })

  noFill();

  stroke(120);

  ellipse(forceField.pos.x, forceField.pos.y, forceField.radius, forceField.radius);

}