let acceleration;

let oldX, oldY;

let draw_line = false;

let diameter_slider;

let random_color;

​

function setup() {

  frameRate(60);

  var theCanvas = createCanvas(600, 400);

  diameter_slider = createSlider(10, 50, 20, 5);

  diameter_slider.position(0, 0);

  acceleration = createVector(0, 4);

}

​

function draw() {

  background(240);

  fill(0);

  text("Diameter: " + diameter_slider.value(), diameter_slider.x + diameter_slider.width + 5, diameter_slider.y + 15);

  line(0, 20, 240, 20);

  line(240, 0, 240, 20);

  if (draw_line) {

    dashed_line(oldX, oldY, mouseX, mouseY, 50);

    fill(random_color);

    ellipse(oldX, oldY, diameter_slider.value());

  }

  for (bouncer of bouncers) {

    bouncer.update_vel(deltaTime);

    bouncer.update_pos(deltaTime / 1000);

    bouncer.wall_collision()

  }

  for (collision of find_colliders()) {

    update_colliders(bouncers[collision[0]], bouncers[collision[1]]);

  }

  for (bouncer of bouncers) {

    bouncer.draw();

  }

}

​

function mousePressed() {

  oldX = mouseX;

  oldY = mouseY;

  if (!mouse_in_box(0, 0, 240, 20)) {

    draw_line = true;

    random_color = color(random(100, 255), random(100, 255), random(100, 255));

  }

}

​

function mouseReleased() {

  if (draw_line) {

    let vx = (oldX - mouseX) / 1;

    let vy = (oldY - mouseY) / 1;

    bouncers.push(new Bouncer(oldX, oldY, vx, vy, diameter_slider.value(), random_color));

    draw_line = false;

  }

}

​

function mouse_in_box(x1, y1, x2, y2) {

  if (mouseX > x1 && mouseX < x2 &&

    mouseY > y1 && mouseY < y2) {

    return true;

  }

  return false;

}

​

function dashed_line(x1, y1, x2, y2, small_length) {

  fill(0);

  let distance = Math.sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2);

  let num_lines = distance / small_length * 2;

  num_lines = 2 * Math.floor(num_lines / 2) + 1;

  let xfrac = (x2 - x1) / num_lines;

  let yfrac = (y2 - y1) / num_lines;

  for (let i = 0; i < num_lines; i += 2) {

    line(x1 + xfrac * i, y1 + yfrac * i,

      x1 + xfrac * (i + 1), y1 + yfrac * (i + 1));

  }

}

​

function find_colliders() {

  let colliders = [];

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

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

      if (circle_collision(bouncers[i], bouncers[j])) {

        colliders.push([i, j]);

      }

    }

  }

  return colliders;

}

​

function update_colliders(c1, c2) {

  let vCollision = p5.Vector.sub(c2.pos, c1.pos);

  let vRelativeVelocity = p5.Vector.sub(c1.vel, c2.vel);

  let speed = p5.Vector.dot(vRelativeVelocity, vCollision);

  if (speed < 0) {

    return;

  }

​

  let impulse = 2 * speed / (c1.mass + c2.mass) / vCollision.magSq();

  impulse *= Math.min(c1.restitution, c2.restitution);

​

  c1.vel = p5.Vector.sub(c1.vel, p5.Vector.mult(vCollision, impulse * c2.mass));

  c2.vel = p5.Vector.add(c2.vel, p5.Vector.mult(vCollision, impulse * c1.mass));

​

}

​

function circle_collision(c1, c2) {

  let threshold = (c1.radius + c2.radius) ** 2;

  let sep_vec = p5.Vector.sub(c1.pos, c2.pos);

  let dist_sq = sep_vec.magSq();

  if (dist_sq < threshold) {

    return true;

  }

  return false;

}

​

class Bouncer {

  constructor(initX, initY, initVX, initVY, diameter, color) {

    this.pos = createVector(initX, initY);

    this.vel = createVector(initVX, initVY);

    this.diameter = diameter;

    this.radius = this.diameter / 2;

    this.color = color;

    this.mass = this.diameter ** 3;

    this.restitution = 0.90;

    this.friction = 0.98;

  }

  draw() {

    fill(this.color);

    ellipse(this.pos.x, this.pos.y, this.diameter);

  }

  update_pos(dt) {

    this.pos.add(p5.Vector.mult(this.vel, dt));

  }

  update_vel(dt) {

    this.vel.add(p5.Vector.mult(acceleration, dt));

  }

  wall_collision() {

    if (this.pos.x < this.radius) {

      this.pos.x = this.radius;

      this.vel.x = Math.abs(this.vel.x) * this.restitution;

      this.vel.y *= this.friction;

    } else if (this.pos.x > width - this.radius) {

      this.pos.x = width - this.radius;

      this.vel.x = -Math.abs(this.vel.x) * this.restitution;

      this.vel.y *= this.friction;

    }

    if (this.pos.y < this.radius) {

      this.pos.y = this.radius;

      this.vel.y = Math.abs(this.vel.y) * this.restitution;

      this.vel.x *= this.friction;

    } else if (this.pos.y > height - this.radius) {

      this.pos.y = height - this.radius;

      this.vel.y = -Math.abs(this.vel.y) * this.restitution;

      this.vel.x *= this.friction;

    }

  }

}