Hilbert paths

Hilbert curve formula from https://github.com/ryan-williams/hilbert/blob/master/hilbert2d.js (see also https://github.com/ryan-williams/hilbert-js).

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
    // Feel free to change or delete any of the code you see in this editor!
    var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 530)
    .append('g')
    .attr('transform', 'translate(10,10)')

var scale = 8,
        max = Math.pow(2, Math.floor(Math.log2(512/scale)));
    
    var color = d3.scaleOrdinal(d3.schemeCategory20b);
    
    var n=0, m=0, segments = [];
    while (n < max*max){
      m = 3 + Math.floor(100 * Math.random() * Math.random());
      segments.push([n, n += m]);
    }
    segments[segments.length-1][1] = max*max;
    svg.append('g')
    .selectAll('path')
    .data(segments)
    .enter()
    .append('path')
    .attr('fill', 'transparent')
    .attr('stroke', (d,i) => color(i))
    .attr('stroke-width', '8')
    .attr('stroke-linecap',"square")

.attr('d', d =>
      'M'
      + d3.range(d[0], d[1])
            .map(e => [(xy = d2xy(e), scale * xy.x), scale * xy.y])
            .join('L')
     );
    
    svg.append('path')
    .attr('fill', 'transparent')
    .attr('stroke', '#fff')
    .attr('stroke-width', '1')
    .attr('d', 'M' + d3.range(max*max).map(d2xy).map(d => [scale * d.x, scale * d.y]).join('L'))

t = svg.append('text')
      .attr("y", 100)
      .attr("x", 512)
      .attr("font-size", 36)
      .style("font-family", "monospace");
 
    var c = d3.range(7)
    .map(i =>
         svg.append('circle')
         .attr("r", 5)
         .attr('fill', 'white')
        );
    
    d3.interval(e => {
      var xy = d2xy((e/10) % (max*max));
      c[Math.floor(Math.random()*c.length)]
      .transition()
      .duration(10)
        .attr('cx', scale * xy.x)
        .attr('cy', scale * xy.y)
      t.text(JSON.stringify(xy));

},10);

// https://github.com/ryan-williams/hilbert/blob/master/hilbert2d.js
var horseshoe2d = [0, 1, 3, 2];

function d2xy(d) {
  d = Math.floor(d);
  var curPos = {
    x: 0,
    y: 0
  };
  var s = 1;
  var iter = 0;
  while (d > 0) {
    var ry = 1 & (d/2);
    var rx = 1 & (ry ^ d);

// Rotate, if need be
    if (rx == 0) {
      if (ry == 1) {
        curPos = {
          x: s - 1 - curPos.x,
          y: s - 1 - curPos.y
        };
      }
      curPos = {
        x: curPos.y,
        y: curPos.x
      };
    }

curPos = {
      x: curPos.x + s*rx,
      y: curPos.y + s*ry
    };

s *= 2;
    d = Math.floor(d/4);
    iter = (iter + 1) % 2;
  }
  if (iter == 0) {
    curPos = {
      x: curPos.y,
      y: curPos.x
    };
  }
  return curPos;
};

xy2d = function(x, y) {
  x = Math.floor(x);
  y = Math.floor(y);
  var s = 1;
  var max = Math.max(x,y);
  var level = 0;
  for (; 2*s <= max; s*=2) {
    level = (level + 1) % 2;
  }
  if (level % 2 == 1) {
    var t = x;
    x = y;
    y = t;
  }

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