tetris-prng/chart.js

A Fibonacci linear feedback shift register used as a PRNG (Pseudo-random Number Generator), as in NES Tetris.

var tprng = require('./');

init(tprng, 900, 1, 'Tetris seed, 16 bits, (range 0-65535)', 65000);
init(tprng.lfsr(0x8988, [1, 9], 31), 900, 1, 'Tetris seed, 32 bits');
//init(tprng.seeded(0x0, 1, 9, 31), 600, 1, '0 seed, 32 bits');
init(tprng.lfsr(0xFFFFFFFF, [1, 9], 31), 900, 1, '0xFFFFFFFF seed, 32 bits');
init(tprng.lfsr(0x8988, [16,15,13,4], 31), 900, 1, 'Tetris seed, 4 taps, 32 bits');
init(tprng.lfsr(0xFFFFFFFF, [16,15,13,4], 31), 900, 1, '0xFFFFFFFF seed, 4 taps, 32 bits');
init(tprng.lfsr(0x11, [16,15,13,4], 31), 900, 1, '0x11 seed, 4 taps, 32 bits');

function init(gen, renderWidth, renderHeight, label, scale) {
  scale = scale || 1;

  var cvs = document.createElement('canvas');
  var ctx = cvs.getContext('2d');
  cvs.width = renderWidth;
  cvs.height = renderHeight;
  var p = document.createElement('p');
  p.textContent = label;
  var container = document.createElement('div');
  container.appendChild(cvs);
  container.appendChild(p);
  document.body.appendChild(container);

  var style = document.createElement('style');
  style.textContent = ''
    + 'p { margin-top: 0; font-size: 120%; }'
    + 'canvas { -webkit-transform: scaleY(10); transform: scaleY(10); }';
  document.head.appendChild(style);

  var lastNumbers = Array(1000).join(0).split('').map(function() { return -1 });

  (function render() {
    lastNumbers.shift();
    lastNumbers.push(gen());

    ctx.clearRect(0, 0, renderWidth, renderHeight);
    var imgdata = ctx.getImageData(0, 0, renderWidth, renderHeight);

    for (var i = 0; i < lastNumbers.length; i++) {
      var alpha = Math.floor(i / (lastNumbers.length - 1) * 255);
      var value = lastNumbers[i];
      var x = Math.floor((value / 0xFFFFFFFF) * renderWidth * scale);
      var y = renderHeight / 2;

      if (x < 0) continue;

      imgdata.data[x*4+3] = alpha;
    }

    ctx.putImageData(imgdata, 0, 0);

    requestAnimationFrame(render);
  }())
}