D3 Examples - Square Circle Spiral Illusion II

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<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
    <style type="text/css">
​
body {
  background: #888;
}
​
rect {
  stroke-width: 2.5px;
}
​
/*
.square:nth-child(2n + 1) rect {
}
*/
​
    </style>
  </head>
  <body>
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@2.6.0/d3.js"></script>
    <script type="text/javascript" src="jwerty.js"></script>
    <script type="text/javascript">
​
var w = 960,
    h = 500,
    start = Date.now();
​
var rings = [ ];
​
var n = 6;
for (i in d3.range(n))
{
    if(i < 3)
        var speed = (i-3) * 1e-2;
    else
        var speed = (i-2) * 1e-2;
    rings.push({ 
        radius: 65*i, 
        width: 16, 
        speed: speed,
        phase: i
    })
}
​
var svg = d3.select("body").append("svg:svg")
    .attr("width", w)
    .attr("height", h)
  .append("svg:g")
    .attr("transform", "translate(" + w / 2 + "," + h / 2 + ")scale(.6)");
​
var ring = svg.selectAll("g")
    .data(rings)
  .enter().append("svg:g")
    .attr("class", "ring")
    .each(ringEnter);
​
var a = 1.
​
//jwerty.key('↑', function () { 
jwerty.key(',←', function () { 
    a -= .1;
});
//jwerty.key('↓', function () { 
jwerty.key('→', function () { 
    a += .1;
});
​
​
var color = d3.scale.linear()
    .domain([-1, 1])
    .interpolate(d3.interpolateRgb)
    .range(['#fff', '#000'])
​
var opacity = d3.scale.linear()
    .domain([-1, 1])
    .range([.3, 1])
​
b = 1;
d3.timer(function() {
  var elapsed = Date.now() - start,
  rotate = function(d,i) { 
    return "rotate(" + (a * d.speed * elapsed) + ")"; 
  };
​
  var damp = .3
  var rings = svg.selectAll("g.ring")
      .attr("transform", rotate)
    .selectAll("rect")
      .attr("transform", rotate)
      .attr("fill", function(d,i) {
          var eo = -1
          if(i % 2 == 0) eo = 1;
          var theta = damp * a * d.speed * elapsed * eo;
          var sin = Math.sin(theta) 
          return color( sin );
      })
      .attr("fill-opacity", function(d) {
          var eo = -1
          if(i % 2 == 0) eo = 1;
          var theta = Math.sin(damp * a * d.speed * elapsed * eo) 
          return opacity( theta );
      })
      .attr("stroke", function(d) {
          var eo = -1
          if(i % 2 == 0) eo = 1;
          var theta = Math.cos(damp * a * d.speed * elapsed * eo) 
          return color( theta );
      })
​
​
});
​
function ringEnter(d, i) {
  var n = Math.floor(2 * Math.PI * d.radius / d.width * Math.SQRT1_2),
      k = 360 / n;
​
  d3.select(this).selectAll("g")
      .data(d3.range(n).map(function() { return d; }))
    .enter().append("svg:g")
      .attr("class", "square")
      .attr("transform", function(_, i) { return "rotate(" + i * k + ")translate(" + d.radius + ")"; })
    .append("svg:rect")
      .attr("x", -d.width / 2)
      .attr("y", -d.width / 2)
      .attr("width", d.width)
      .attr("height", d.width);
}
​
    </script>
<p> Use the left and right arrow keys to control the speed </p>
  </body>
</html>
​
    