Polymaps / Procedural Perlin

perlin-worker.js

onmessage = function(e) {
  var data = e.data.data = [],
      n = Math.pow(2, 7 - e.data.zoom),
      x0 = e.data.column * n,
      y0 = e.data.row * n,
      w = e.data.size.x,
      h = e.data.size.y;

  for (var y = 0, i = 0; y < h; y++) {
    for (var x = 0; x < w; x++) {
      data[i++] =
      data[i++] =
      data[i++] = 128 * (noise(x0 + x * n / w, y0 + y * n / h, 0) + 1);
      data[i++] = 255;
    }
  }

  postMessage(e.data);
}

// Derived from http://mrl.nyu.edu/~perlin/noise/
// Copyright (c) 2002 Ken Perlin

function noise(x, y, z) {
  var X = Math.floor(x) & 255,                       // FIND UNIT CUBE THAT
      Y = Math.floor(y) & 255,                       // CONTAINS POINT.
      Z = Math.floor(z) & 255;
  x -= Math.floor(x);                                // FIND RELATIVE X,Y,Z
  y -= Math.floor(y);                                // OF POINT IN CUBE.
  z -= Math.floor(z);
  var u = fade(x),                                   // COMPUTE FADE CURVES
      v = fade(y),                                   // FOR EACH OF X,Y,Z.
      w = fade(z);
  var A = p[X  ]+Y, AA = p[A]+Z, AB = p[A+1]+Z,      // HASH COORDINATES OF
      B = p[X+1]+Y, BA = p[B]+Z, BB = p[B+1]+Z;      // THE 8 CUBE CORNERS,

  return lerp(w, lerp(v, lerp(u, grad(p[AA  ], x  , y  , z   ),  // AND ADD
                                 grad(p[BA  ], x-1, y  , z   )), // BLENDED
                         lerp(u, grad(p[AB  ], x  , y-1, z   ),  // RESULTS
                                 grad(p[BB  ], x-1, y-1, z   ))),// FROM  8
                 lerp(v, lerp(u, grad(p[AA+1], x  , y  , z-1 ),  // CORNERS
                                 grad(p[BA+1], x-1, y  , z-1 )), // OF CUBE
                         lerp(u, grad(p[AB+1], x  , y-1, z-1 ),
                                 grad(p[BB+1], x-1, y-1, z-1 ))));
}

function fade(t) { return t * t * t * (t * (t * 6 - 15) + 10); }
function lerp(t, a, b) { return a + t * (b - a); }
function grad(hash, x, y, z) {
  var h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE
  var u = h<8 ? x : y,                    // INTO 12 GRADIENT DIRECTIONS.
      v = h<4 ? y : h==12||h==14 ? x : z;
  return ((h&1) == 0 ? u : -u) + ((h&2) == 0 ? v : -v);
}
var p = [], permutation = [151,160,137,91,90,15,
   131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
   190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
   88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
   77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
   102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
   135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
   5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
   223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
   129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
   251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
   49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
   138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
   ];
for (var i=0; i < 256 ; i++) p[256+i] = p[i] = permutation[i];

Maybe it should be wrapped in html to work in the example?