​

function setup() {

  createCanvas(600, 600);

  ropes.push(new Rope(100, 100, 200));

}

​

function draw() {

  background(220);

  for (let r of ropes) {

    r.update();

  }

}

​

///// CLASS /////

​

let C_GRAVITY = 1;

let DISTANCE_BTW_BALLS = 30;

​

class Spring {

  constructor(a, b, restLength, stiffness) {

    this.bobA = a;

    this.bobB = b;

    this.len = restLength;

    this.k = stiffness; // spring constant

  }

  update() {

    let vector = p5.Vector.sub(this.bobB.pos, this.bobA.pos);

    let distance = vector.mag();

    let stretch = distance - this.len;

    let strength = -1 * stretch * this.k; // hooke's law

​

    // force to bobB

    let force = vector.copy();

    force.normalize();

    force.mult(strength);

    this.bobB.applyForce(force);

​

    // force to bobB

    let force1 = vector.copy();

    force1.normalize();

    force1.mult(strength * -1);

    this.bobA.applyForce(force1);

​

    //text(strength.toFixed(2), this.bobB.pos.x + 50, this.bobB.pos.y);

  }

  display() {

    push();

    stroke(255);

    strokeWeight(10);

    line(this.bobA.pos.x, this.bobA.pos.y, this.bobB.pos.x, this.bobB.pos.y);

    pop();

  }

}

​

class Ball {

  constructor(x, y, rad) {

    this.pos = createVector(x, y);

    this.vel = createVector(0, 0);

    this.acc = createVector(0, 0);

    this.rad = rad;

    this.mass = rad * 0.5; // MASS!

    //

    this.damping = 0.8;

  }

  update() {

    this.vel.add(this.acc);

    this.pos.add(this.vel);

    this.acc.mult(0);

​

    // let's apply damping here

    this.vel.mult(this.damping); // -5%;

  }

  applyForce(f) {

    if (this.mass > 0) {

      let force = p5.Vector.div(f, this.mass);

      this.acc.add(force);

    }

  }

  attractedTo(others) {

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

      let other = others[i];

      if (this != other) {

        let distance = this.pos.dist(other.pos);

        let magnitude =

          (C_GRAVITY * this.mass * other.mass) / (distance * distance);

        let force = p5.Vector.sub(other.pos, this.pos);

        force.normalize();

        force.mult(magnitude);

        this.applyForce(force);

      }

    }

  }

  repelledFrom(others) {

    // this method is duplicated from attractedTo()

    // then, the force vector is flipped.

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

      let other = others[i];

      if (this != other) {

        let distance = this.pos.dist(other.pos);

​

        if (distance < this.rad + DISTANCE_BTW_BALLS) {

          let magnitude =

            (C_GRAVITY * this.mass * other.mass) / (distance * distance);

          let force = p5.Vector.sub(other.pos, this.pos);

          force.normalize();

          force.mult(-1); // ***

          force.mult(magnitude);

          this.applyForce(force);

        }

      }

    }

  }

  reappear() {

    if (this.pos.x < 0) {

      this.pos.x = width;

    } else if (this.pos.x > width) {

      this.pos.x = 0;

    }

    if (this.pos.y < 0) {

      this.pos.y = height;

    } else if (this.pos.y > height) {

      this.pos.y = 0;

    }

  }

  bounce() {

    // x

    if (this.pos.x < 0) {

      this.pos.x = 0;

      this.vel.x = -this.vel.x;

    } else if (this.pos.x > width) {

      this.pos.x = width;

      this.vel.x = -this.vel.x;

    }

    // y

    if (this.pos.y < 0) {

      this.pos.y = 0;

      this.vel.y = -this.vel.y;

    } else if (this.pos.y > height) {

      this.pos.y = height;

      this.vel.y = -this.vel.y;

    }

  }

  drag() {

    if (mouseIsPressed) {

      let distance = dist(this.pos.x, this.pos.y, mouseX, mouseY);

      if (distance < this.rad) {

        // in

        this.pos.x = mouseX;

        this.pos.y = mouseY;

      }

    }

  }

  display() {

    push();

    translate(this.pos.x, this.pos.y);

    noStroke();

    fill(255, 200);

    //circle(0, 0, this.rad * 2);

    pop();

  }

}

​

class Rope {

  constructor(x, y, len) {

    this.balls = [];

    this.springs = [];

​

    let t;

    for (let i = 0; i <= len; i += 10) {

      let b = new Ball(x, y + i, 6);

      this.balls.push(b);

      if (t != null) {

        this.springs.push(new Spring(t, b, 5, 2));

      }

      t = b;

    }

    t = null;

  }

  update() {

    for (let s of this.springs) {

      s.update();

      s.display();

    }

​

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

      let b = this.balls[i];

      if (i == 0) {

        b.pos.x = lerp(b.pos.x, mouseX, 0.5);

        b.pos.y = lerp(b.pos.y, mouseY, 0.5);

      }

      b.drag();

      b.bounce();

      b.applyForce(createVector(0, 2));

​

      b.update();

​

      b.display();

    }

  }

}

​