Reactive RXJS drawing example

app.js

var canvas = document.getElementById("container");
var ctx = canvas.getContext("2d");

// The line settings
ctx.lineWidth = 4;
ctx.lineJoin = ctx.lineCap = "round";

var intervalSource = Rx.Observable.interval(2 * 1000, Rx.Scheduler.requestAnimationFrame);
var pauser = new Rx.Subject();

var mouseMove = Rx.Observable.fromEvent(canvas, "mousemove");
var mouseDown = Rx.Observable.fromEvent(canvas, "mousedown");
var mouseUp   = Rx.Observable.fromEvent(canvas, "mouseup");

var windowResize = Rx.Observable.fromEvent(window, "resize")
  .throttleFirst(250 /* ms */);

var mousePath = mouseDown
  .first()
  .concat(mouseMove.takeUntil(mouseUp))
  .repeat();

var snapToGrid = mousePath
  .map(function (e) {

    var gridWidth = 15;
    var x = Math.round(e.x / gridWidth) * gridWidth;
    var y = Math.round(e.y / gridWidth) * gridWidth;

    return {
      x: x,
      y: y,
    };
  })
  .distinctUntilChanged();

snapToGrid
  .bufferWithCount(2, 1)
  .subscribe(function (e) {

  // console.log("N", e.x, e.y);
  // newTick(e.y);
  // var drawLine = function (p) {

  //   ctx.lineTo(p.x, p.y);
  //   ctx.stroke();
  // };

  // drawLine(e);
  // drawCircle(e.x, e.y, 2, "#aaa");
});

mouseDown.subscribe(function (first) {

  console.log("First Event", first);

  ctx.beginPath();
  ctx.moveTo(first.x, first.y);

  // mouseMove.resume();
});

mouseUp.subscribe(function (last) {

  console.log("Last event");
  ctx.closePath();

  // mouseMove.pause();
});

mousePath
  .map(roundEventValues)
  .distinctUntilChanged()
  // .debounce(5)
  // .bufferWithCount(2)
  .subscribe(function (point) {

  var drawEvent = function (e) {

    var x = e.x;
    var y = e.y;

    drawCircle(x, y, 4);
  };

  var drawLine = function (p) {

    ctx.lineTo(p.x, p.y);
    ctx.stroke();
  };

  var drawQuadLine = function (a, b)
  {
    var midPoint = midPointBtw(a, b);
    ctx.quadraticCurveTo(a.x, a.y, midPoint.x, midPoint.y);
    ctx.stroke();
  };

  console.log("D", point);
  // drawQuadLine(points[0], points[1]);
  drawLine(point);
  // drawLine(points[1]);
});

intervalSource.subscribe(function (e) {
   console.log("Interval");
});

windowResize.subscribeOnNext(function (e) {
  var size = getWindowSize();
  console.log("Resize window", size);

  canvas.setAttribute("height", size.height);
  canvas.setAttribute("width", size.width);
});

function roundEventValues (e)
{
  return {
    x: ~~e.x,
    y: ~~e.y,
  };
}

function drawCircle(x, y, radius, defaultColor)
{
  var hr    = Math.floor(radius / 2);
  var color = defaultColor || "#fff";

  ctx.fillStyle = color;

  ctx.beginPath();
  ctx.arc(x - hr, y - hr, radius, radius, Math.PI * 2, true);
  ctx.closePath();
  ctx.fill();
}

function midPointBtw (p1, p2)
{
  return {
    x: p1.x + (p2.x - p1.x) / 2,
    y: p1.y + (p2.y - p1.y) / 2
  };
}

function getWindowSize ()
{
  return {
    width:  window.innerWidth,
    height: window.innerHeight,
  };
}

function onLoad ()
{
  var size = getWindowSize();
  console.log("Window loaded", getWindowSize());

  canvas.setAttribute("height", size.height);
  canvas.setAttribute("width", size.width);
}

function main ()
{

  console.log("Called main");
  window.addEventListener("load", onLoad);
}

main();



// Drawing chart for the mouse movements

// var n = 40,
//     random = d3.random.normal(0, 200),
//     data = d3.range(n).map(random);
// var margin = {top: 20, right: 20, bottom: 20, left: 40},
//     width = 400 - margin.left - margin.right,
//     height = 200 - margin.top - margin.bottom;

// var x = d3.scale.linear()
//     .domain([0, n - 1])
//     .range([0, width]);
// var y = d3.scale.linear()
//     .domain([0, 1000])
//     .range([height, 0]);
// var line = d3.svg.line()
//     .x(function(d, i) { return x(i); })
//     .y(function(d, i) { return y(d); });
// var svg = d3.select(".x-axis").append("svg")
//     .attr("width", width + margin.left + margin.right)
//     .attr("height", height + margin.top + margin.bottom)
//   .append("g")
//     .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
// svg.append("defs").append("clipPath")
//     .attr("id", "clip")
//   .append("rect")
//     .attr("width", width)
//     .attr("height", height);
// svg.append("g")
//     .attr("class", "x axis")
//     .attr("transform", "translate(0," + y(0) + ")")
//     .call(d3.svg.axis().scale(x).orient("bottom"));
// svg.append("g")
//     .attr("class", "y axis")
//     .call(d3.svg.axis().scale(y).orient("left"));
// var path = svg.append("g")
//     .attr("clip-path", "url(#clip)")
//   .append("path")
//     .datum(data)
//     .attr("class", "line")
//     .attr("d", line);
// // tick();

// function newTick (y) {
//   // push a new data point onto the back
//   data.push(y);
//   // redraw the line, and slide it to the left
//   path
//       .attr("d", line)
//       .attr("transform", "")
//     .transition()
//       .duration(500)
//       .ease("linear")
//       .attr("transform", "translate(" + x(-1) + ",0)");
//       // .each("end", tick);
//   // pop the old data point off the front
//   data.shift();
// }


// function tick() {
//   // push a new data point onto the back
//   data.push(random());
//   // redraw the line, and slide it to the left
//   path
//       .attr("d", line)
//       .attr("transform", "")
//     .transition()
//       .duration(500)
//       .ease("linear")
//       .attr("transform", "translate(" + x(-1) + ",0)")
//       .each("end", tick);
//   // pop the old data point off the front
//   data.shift();
// }

index.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Drawing</title>
  <link rel="stylesheet" type="text/css" href="./style.css">
</head>
<body>
    <div>
        <canvas id="container" width="600" height="600"></canvas>
    </div>
    <div class="x-axis"></div>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/3.1.1/rx.all.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.6/d3.min.js"></script>
    <script src="./app.js"></script>
</body>
</html>

style.css

body {
  margin: 0;
  padding: 0;
  overflow: hidden;
}

#container {
/*  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  bottom: 0;
*/

  background-color: #adf;
  /*width: 900px;*/
  /*height: 900px;*/
}

canvas {
  pointer: crosshair;

  background: rgba(147,206,222,1);
  background: linear-gradient(to right, rgba(147,206,222,1) 0%, rgba(117,189,209,1) 41%, rgba(73,165,191,1) 100%);
}

svg {
  font: 10px sans-serif;
}
.line {
  fill: none;
  stroke: #000;
  stroke-width: 1.5px;
}
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}