JSFiddle - React, Tailwind, and code Playground

by lostinplace

HTML

<!DOCTYPE html>
<html>
  <head>
    <title>Touch Tracker Marker</title>
    <meta name="viewport" content="width=device-width, user-scalable=no">
<style type="text/css">
body { margin: 0px; overflow: hidden; }
canvas { border: 1px solid black; }
</style>
<script type="text/javascript" src="magictouch.js"></script>
<script type="text/javascript">



</script>
</head>
<body onload="ol()">

<canvas id="canvas" width="300" height="300" style="top:0px; left:0px; width: 300px; height: 300px;"></canvas>


</body>
</html>

JavaScript

var canvas;
var ctx;
var w = 0;
var h = 0;

var timer;
var updateStarted = false;
var touches = [];


function update() {
    if (updateStarted) return;
    updateStarted = true;

    var nw = window.innerWidth;
    var nh = window.innerHeight;

    if ((w != nw) || (h != nh)) {
        w = nw;
        h = nh;
        canvas.style.width = w+'px';
        canvas.style.height = h+'px';
        canvas.width = w;
        canvas.height = h;
    }

    ctx.clearRect(0, 0, w, h);

    var i, len = touches.length;
    for (i=0; i<len; i++) {
        var touch = touches[i];
    var px = touch.pageX;
    var py = touch.pageY;

        ctx.beginPath();
        ctx.arc(px, py, 20, 0, 2*Math.PI, true);

        ctx.fillStyle = "rgba(0, 0, 200, 0.2)";
        ctx.fill();

        ctx.lineWidth = 2.0;
        ctx.strokeStyle = "rgba(0, 0, 200, 0.8)";
        ctx.stroke();
    console.log('drawn circle at ' + px +',' + py);
    }

    updateStarted = false;
}

function ol() {
    canvas = document.getElementById('canvas');
    ctx = canvas.getContext('2d');
    timer = setInterval(update, 15);

canvas.addEventListener('touchend', function() {
    ctx.clearRect(0, 0, w, h);
});

canvas.addEventListener('touchmove', function(event) {
  event.preventDefault();
  touches = event.touches;
});

canvas.addEventListener('touchstart', function(event) {
  console.log('start');
});
};