//  Atoms

//  by Philip, January 16, 2021  

//

//  Basic framework for moving spheres with r, p, v, c.

//

//  And collisions

//  

​

let atoms = [];

​

let num = 100;

let v_initial = 100;

let r_min = 1;

let r_max = 10; 

​

let repeat = false; 

let collisions = true; 

​

function setup() {

  createCanvas(800, 600);

  noStroke();

  for (let i = 0; i < num; i++) {

    let r = random(r_min, r_max);

    let c = color(random(255), random(255), random(255));

    let v = createVector(random(-1.0, 1.0), random(-1.0, 1.0)).mult(v_initial); 

    let p = createVector(random(width), random(height));

    atoms[i] = new atom(p, v, r, c, atoms, i);                     

  }

}

​

function draw() {

  background(128);

  for (let i = 0; i < num; i++) {

    atoms[i].update();

    atoms[i].display();

  }

  noStroke();

  strokeWeight(1);

  fill(0);

}

​

// atom class

function atom(p, v, r, c, _others, _id) {

  this.p = p.copy();

  this.v = v.copy();

  this.r = r;

  this.c = c;

  this.others = _others;

  this.id = _id;

  this.dt = 1.0/60.0;

​

  this.update = function() {

    if (collisions) {

      // Check for collisions and add restoring forces

      let collisionForces = createVector(0,0,0);

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

        if (i != this.id) {

          let d = p5.Vector.sub(this.p, this.others[i].p);

          let penetration = ((this.r + this.others[i].r)) - d.mag();

          if (penetration > 0) {

            d.normalize();

            // Elastic component - restitution (note: does not conserve energy)

            collisionForces.add(d.mult(10 * penetration));

          }

        }

      }

      this.v.add(collisionForces.mult(1.0));

    }

    this.p.add(p5.Vector.mult(this.v, this.dt));

    //  Edge conditions

    if (repeat) {

      if (this.p.x > width) this.p.x -= width;

      if (this.p.x < 0) this.p.x += width;

      if (this.p.y > height) this.p.y -= height;

      if (this.p.y < 0) this.p.y += height;

    } else {

      if (this.p.x >= width) {

        this.v.x *= -1.0;

        this.p.x = width - 1;

      }

      if (this.p.x < 0) {

        this.v.x *= -1.0;

        this.p.x = 0.0;

      }

      if (this.p.y >= height) {

        this.v.y *= -1.0;

        this.p.y = height - 1;

      }

      if (this.p.y < 0) {

        this.v.y *= -1.0;

        this.p.y = 0.0;

      }

    }

  }

  this.display = function() {

    stroke(0);

    strokeWeight(1);

    fill(this.c);        

    ellipse(this.p.x, this.p.y, this.r * 2, this.r * 2);

  }

​

};

​