Render Queue by syntagmatic

index.html

<!DOCTYPE html>
<title>Render Queue</title>
<style type="text/css">
html, body { background: #f7f7f7; height: 100%; margin: 0; padding: 0; color: #b6b6b6; font-family: Ubuntu, Helvetica, sans-serif; font-size: 15px; line-height: 1.35em;}
a { color: #6be; text-decoration: none; }
#canvas { position: fixed; }
#center { position: absolute; top: 0; left: 0; margin: 40px; width: 520px; padding: 20px; background: #444; background: rgba(0,0,0,0.9); border-radius: 8px;}
h1 { margin-top:0; padding: 3px 0; font-size: 1.4em; }
h1, h3 { color: #f9f9f9; border-bottom: 1px solid #333; }
h3 { font-size: 1em; }
.yellow { color: #ea3; }
</style>
<body>
  <canvas id="canvas" width=600 height=600></canvas>
  <div id="center">
    <h1>Render Queue</h1>
    <p>
    Progressive rendering for too much data.
    </p>
    <p>
    This page has 600,000 randomly placed points with <a href="//bl.ocks.org/3289530">HCL color space</a> interpolation. By putting the data in a queue and rendering 1,000 dots per frame, the page slowly builds up the final image. Using <a href="//paulirish.com/2011/requestanimationframe-for-smart-animating/">requestAnimationFrame</a>, the page remains responsive during rendering.
    </p>
    <p>
    There is a pause on page load as the data is generated. This could be improved by processing the data in a queue, and running both the processing and rendering queues concurrently.
    </p>
    <p>
    Another good improvement would be a logging pattern for performance benchmarks.
    </p>
    <p>
    This pattern based on the <a href="//bl.ocks.org/1297383">performance</a> <a href="//bl.ocks.org/1296930">tests</a> of <a href="https://groups.google.com/forum/?fromgroups#!topic/d3-js/ZJ6pznVU5LQ">Steven Bannasch and Ger Hobbelt</a> and polyline rendering from <a href="//bl.ocks.org/d/3290392/">Nutrient parallel coordinates</a>.
    </p>
    <p>
    <em>Think you can do better?</em>
    </p>
    <p>
    Render Queue is <a href="render-queue.js">only 70 lines long</a> and licensed under the WTFPL.<br/>
    So do it.
    </p>
    <h1>API Reference</h1>
    <h3></em>renderQueue(function)</h3>
    <p>
      Return a renderQueue by passing in a <em>function which renders one data point</em>.
    </p>
    <h3>queue(data)</h3>
    <p>
      Populate the queue with an array of data and begin rendering.
    </p>
    <h3>queue.clear(function)</h3>
    <p>
      Provide a function which clears the canvas. This is called when new data is passed in.
    </p>
    <h3>queue.add(data)</h3>
    <p>
      Add an array of data to the queue and render it.
    </p>
    <h3>queue.invalidate()</h3>
    <p>
      Invalidate the queue and stop rendering.
    </p>
    <h3>queue.rate(<em>num</em>)</h3>
    <p>
      Get or set the number of data entries to be rendered each frame.
    </p>
    <h3>queue.remaining()</h3>
    <p>
      Get the length of the queue. This decreases as rendering occurs.
    </p>
    <!--
    <pre>
      var draw_dot = function(p) {
        ctx.fillRect(p.x, p.y, 1,1);
      };

      var clear_canvas = function() {
        ctx.clearCanvas(0,0,w,h);
      };

      var render = renderQueue(draw_dot).clear(clear_canvas);

      var data = d3.range(50000)
        .map(function(i) {
          return {
            x: Math.random(),
            y: Math.random()
          }
        });

      render(data);
    </pre>
    -->
  <h1>License</h1>
    <small><pre>
DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
Version 2, December 2004 

Copyright (C) 2012 Kai Chang <kai.s.chang@@gmail.com> 

Everyone is permitted to copy and distribute verbatim or modified 
copies of this license document, and changing it is allowed as long 
as the name is changed. 

DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE 
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 

0. You just DO WHAT THE FUCK YOU WANT TO. 
    </pre></small>
  </div>
</body>
<script src="//d3js.org/d3.v2.js"></script>
<script src="render-queue.js"></script>
<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

canvas.width = document.body.clientWidth;
canvas.height = document.body.clientHeight;
ctx.globalCompositeOperation = "destination-over";

var color = d3.scale.linear()
   .domain([0, 0.5, 1])
      .range(["#ef2212", "#e7c767", "#2799df"])
      .interpolate(d3.interpolateHcl);

// set up a render queue
var render = renderQueue(dot)
  .clear(clear_canvas);

// queue up some generated data
render(generate(600000));

function generate(n) {
  return d3.range(n).map(function(i) {
    return [
      canvas.width*Math.random(),              // x
      canvas.height*Math.random(),             // y
      color(Math.random())
    ];
  });
};

function dot(pos) {
  ctx.fillStyle = pos[2];
  ctx.beginPath();
  ctx.fillRect(pos[0]-1,pos[1]-1,2,2);
  ctx.stroke();
  ctx.fill();
};

function clear_canvas() {
  ctx.clearRect(0,0,canvas.width,canvas.height);
};

</script>

render-queue.js

var renderQueue = (function(func) {
  var _queue = [],                  // data to be rendered
      _rate = 1000,                 // number of calls per frame
      _invalidate = function() {},  // invalidate last render queue
      _clear = function() {};       // clearing function

  var rq = function(data) {
    if (data) rq.data(data);
    _invalidate();
    _clear();
    rq.render();
  };

  rq.render = function() {
    var valid = true;
    _invalidate = rq.invalidate = function() {
      valid = false;
    };

    function doFrame() {
      if (!valid) return true;
      var chunk = _queue.splice(0,_rate);
      chunk.map(func);
      timer_frame(doFrame);
    }

    doFrame();
  };

  rq.data = function(data) {
    _invalidate();
    _queue = data.slice(0);   // creates a copy of the data
    return rq;
  };

  rq.add = function(data) {
    _queue = _queue.concat(data);
  };

  rq.rate = function(value) {
    if (!arguments.length) return _rate;
    _rate = value;
    return rq;
  };

  rq.remaining = function() {
    return _queue.length;
  };

  // clear the canvas
  rq.clear = function(func) {
    if (!arguments.length) {
      _clear();
      return rq;
    }
    _clear = func;
    return rq;
  };

  rq.invalidate = _invalidate;

  var timer_frame = window.requestAnimationFrame
    || window.webkitRequestAnimationFrame
    || window.mozRequestAnimationFrame
    || window.oRequestAnimationFrame
    || window.msRequestAnimationFrame
    || function(callback) { setTimeout(callback, 17); };

  return rq;
});