HTML 5 Canvas – Writing Random Characters

November 22, 2013 6:43 am Published by Leave your thoughts

Here’s a little tutorial of HTML5’s Canvas + JavaScript to generate random fours.

Check out the demo!

First we’ll need a Canvas element.

<canvas id="myCanvas"></canvas>

In the head section of the document add

<script src=""></script>
<script type="text/javascript">
        //in here we set the width and height of canvas to whatever the available screen resolution is
        //using innerHeight and innerWidth
	$('#myCanvas').attr("height", window.innerHeight);
	$('#myCanvas').attr("width", window.innerWidth);
	w = $('#myCanvas').width();
	h = $('#myCanvas').height();

var context;
var w = 0;
var h = 0;
var x=0;
var y=0;
var col =0;
function init(){
        //init sets the canvas and starts an interval to be called every 10 milliseconds
	context= myCanvas.getContext('2d');
function random_hex_color()
	/* get random red, green, and blue from 0 to 255 */
	var randomred = 00;
	var randomgreen = 00;
	var randomblue = 00;
        //blue is not randomized here because i only wanted shades or red and green to add blue shades, simply add a third case statement.
		case 1:	
			randomred = Math.floor(Math.random() * 255);
		case 2: 
			randomgreen = Math.floor(Math.random() * 255);
	/* convert each decimal number to hexadecimal */
	var hred = new String(randomred.toString(16));
	var hgreen = new String(randomgreen.toString(16));
	var hblue = new String(randomblue.toString(16));
	/* pad with 0 if necessary
	(e.g. make sure to output 05 instead of just 5) */
	hred = String('00'+hred).slice(-2);
	hgreen = String('00'+hgreen).slice(-2);
	hblue = String('00'+hblue).slice(-2);
	return '#'+hred+hgreen+hblue;

function drawFour(){
        //this is the function that gets called on interval.
        //here x, y, fontsize, alpha, and color are randomized then drawn on the canvas with fillText()
	x = (Math.random()*w);
	y = (Math.random()*h);
	var fontsize = (Math.random()*75);
	var randomalpha = Math.random()*1;
	context.font = fontsize + "px Arial";
	context.globalAlpha = randomalpha;
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