document.title = '回転する渦巻き';

var style = document.createElement('style');
style.innerText = 'html,body{overflow:hidden;cursor:none;}';
document.getElementsByTagName('head').item(0).appendChild(style);

var canvas = document.createElement('canvas');
var w = document.body.clientWidth;
var h = document.body.clientHeight;
var min = Math.min(w,h);
canvas.setAttribute('width',w);
canvas.setAttribute('height',h);
let demo = document.getElementById('demo');
demo.appendChild(canvas);

var ctx = canvas.getContext('2d');
var cx = w/2;
var cy = h/2;
var t = 0;
var bgcolor = '#fff';
var color = '#000';
var lw = 2;


function getRandomColor(){
  var ch = Math.floor(Math.random()*360);
  //var r = Math.floor(Math.random()*128)+128;
  //var g = Math.floor(Math.random()*128)+128;
  //var b = Math.floor(Math.random()*128)+128;
  var color = 'hsl('+ch+',100%,50%)';
  return color;
}

function setRandom(){
  bgcolor = getRandomColor();
  color = getRandomColor();
  lw = Math.random()*8+1;
}

function draw() {
  ctx.clearRect(0, 0, w, h);
  ctx.fillStyle = bgcolor;
  ctx.strokeStyle = color;
  ctx.fillRect(0, 0, w, h);
  ctx.lineWidth = lw;
  ctx.beginPath();
  ctx.moveTo(cx, cy);
  for(i=0;i<9999;i++){
    var rad = i * Math.PI/60 + t;
    var r = min/9000 * i;
    ctx.lineTo(cx+Math.cos(rad)*r, cy+Math.sin(rad)*r);
  }
  ctx.stroke();
}
draw();
setInterval(function(){
  t++;
  draw()
},99);






document.oncontextmenu = function () {return false;}
function resize() {
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;
  console.table({w:canvas.width, h:canvas.height});
  w = document.body.clientWidth;
  h = document.body.clientHeight;
  cx = w/2;
  cy = h/2;
}

window.onresize = resize;
window.addEventListener('click', function() {
  resize();
  document.body.requestFullscreen();
}, false );

window.addEventListener('dblclick', function() {
  setRandom();
}, false );

document.addEventListener('fullscreenchange',function(e){
  resize();
});

ページのソースを表示 : Ctrl+U , DevTools : F12

view-source:https://hi0a.com/demo/-js/js-canvas-vortex/