Particle tentacles

This got a little weird.

forked from veltman's block: Particle tentacles

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8" />
</head>
<body>
  <canvas width="960" height="500"></canvas>
  <canvas width="960" height="500" class="offscreen" style="display: none;"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>

var width = 960,
    height = 500;

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    offscreen = document.querySelector(".offscreen"),
    offscreenContext = offscreen.getContext("2d");

offscreenContext.globalAlpha = 0.8;

var numDots = 1200;

var points = d3.range(numDots).map(function(d, i){
  return {
    position: new Vec2(Math.random() * width, Math.random() * height),
    velocity: new Vec2(Math.random() * 3, Math.random() * 3)
  };
});

d3.shuffle(points);

points.forEach(function(p, i){
  p.target = points[i + 1] || points[0];
  p.color = d3.interpolateRainbow(i / numDots);
});

var maxVelocity = 3,
    maxForce = 0.4;

d3.timer(function(t){

points.forEach(function(p){
    var destination = p.target.position.clone(),
        desiredVelocity = destination.subtract(p.position).normalize().scale(maxVelocity),
        steering = desiredVelocity.subtract(p.velocity).truncate(maxForce);

p.velocity.add(steering).truncate(maxVelocity);

});

offscreenContext.clearRect(0, 0, width, height);
  offscreenContext.drawImage(canvas, 0, 0, width, height);
  context.clearRect(0, 0, width, height);
  context.drawImage(offscreen, 0, 0, width, height);

points.forEach(function(p, i){

// Wall bounces
    if (p.position.x + p.velocity.x < 0 || p.position.x + p.velocity.x >= width) {
      p.velocity.x = -p.velocity.x;
    }

if (p.position.y + p.velocity.y < 0 || p.position.y + p.velocity.y >= height) {
      p.velocity.y = -p.velocity.y;
    }

p.position.add(p.velocity);

context.beginPath();
    context.fillStyle = p.color;
    context.arc(p.position.x, p.position.y, 2, 0, 2 * Math.PI);
    context.fill();

});

function Vec2(x, y) {
  this.x = x || 0;
  this.y = y || 0;
  return this;
};

Vec2.prototype.add = function(v) {
  this.x += v.x;
  this.y += v.y;
  return this;
};

Vec2.prototype.clone = function() {
  return new Vec2(this.x, this.y);
};

Vec2.prototype.subtract = function(v) {
  this.x -= v.x;
  this.y -= v.y;
  return this;
};

Vec2.prototype.scale = function(s) {
  this.x = this.x * s;
  this.y = this.y * s;
  return this;
};

Vec2.prototype.normalize = function() {
  var length = this.length();
  this.x = this.x / length;
  this.y = this.y / length;
  return this;
};

Vec2.prototype.length = function() {
  return Math.sqrt(this.x * this.x + this.y * this.y);
};

Vec2.prototype.truncate = function(max) {
  var length = this.length();
  if (length > max) {
    this.x = this.x * max / length;
    this.y = this.y * max / length;
  }
  return this;
};

Vec2.prototype.dot = function(v) {
  return this.x * v.x + this.y * v.y;
};

</script>

https://d3js.org/d3.v4.min.js