Drawing text to <canvas> with @font-face does not work at the first time
When I draw a text in a canvas with a typeface that is loaded via @font-face, the text doesn't show correctly. It doesn't show at all (in Chrome 13 and Firefox 5), or the typeface is wrong (Opera 11). This type of unexpected behavior occurs only at the first drawing with the typeface. After then everything works fine.
Is it the standard behavior or something?
Thank you.
PS: Following is the source code of the test case
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>@font-face and <canvas></title>
<style id="css">
@font-face {
font-family: 'Press Start 2P';
src: url('fonts/PressStart2P.ttf');
}
</style>
<style>
canvas, pre {
border: 1px solid black;
padding: 0 1em;
}
</style>
</head>
<body>
<h1>@font-face and <canvas></h1>
<p>
Description: click the button several times, and you will see the problem.
The first line won't show at all, or with a wrong typeface even if it does.
<strong>If you have visited this page before, you may have to refresh (or reload) it.</strong>
</p>
<p>
<button id="draw">#draw</button>
</p>
<p>
<canvas width="250" height="250">
Your browser does not support the CANVAS element.
Try the latest Firefox, Google Chrome, Safari or Opera.
</canvas>
</p>
<h2>@font-face</h2>
<pre id="view-css"></pre>
<h2>Script</h2>
<pre id="view-script"></pre>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script id="script">
var x = 30,
y = 10;
$('#draw').click(function () {
var canvas = $('canvas')[0],
ctx = canvas.getContext('2d');
ctx.font = '12px "Press Start 2P"';
ctx.fillStyle = '#000';
ctx.fillText('Hello, world!', x, y += 20);
ctx.fillRect(x - 20, y - 10, 10, 10);
});
</script>
<script>
$('#view-css').text($('#css').text());
$('#view-script').text($('#script').text());
</script>
</body>
</html>
Solution 1:
Drawing on canvas has to happen and return immediately when you call the fillText method. However, the browser has not yet loaded the font from the network, which is a background task. So it has to fall back to the font it does have available.
If you want to make sure the font is available, have some other element on the page preload it, eg.:
<div style="font-family: PressStart;">.</div>
Solution 2:
Use this trick and bind an onerror event to an Image element.
Demo here: works on the latest Chrome.
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var link = document.createElement('link');
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = 'http://fonts.googleapis.com/css?family=Vast+Shadow';
document.getElementsByTagName('head')[0].appendChild(link);
// Trick from https://stackoverflow.com/questions/2635814/
var image = new Image();
image.src = link.href;
image.onerror = function() {
ctx.font = '50px "Vast Shadow"';
ctx.textBaseline = 'top';
ctx.fillText('Hello!', 20, 10);
};
Solution 3:
You can load fonts with the FontFace API before using it in the canvas:
const myFont = new FontFace('My Font', 'url(https://myfont.woff2)');
myFont.load().then((font) => {
document.fonts.add(font);
console.log('Font loaded');
});
The font resource myfont.woff2 is first downloaded. Once the download completes, the font is added to the document's FontFaceSet.
The specification of the FontFace API is a working draft at the time of this writing. See browser compatibility table here.
Solution 4:
The nub of the problem is that you are trying to use the font but the browser has not loaded it yet and possibly has not even requested it. What you need is something that will load the font and give you a callback once it is loaded; once you get the callback, you know it is okay to use the font.
Look at Google's WebFont Loader; it seems like a "custom" provider and an active callback after the load would make it work.
I've never used it before, but from a quick scan of the docs you need to make a css file fonts/pressstart2p.css, like this:
@font-face {
font-family: 'Press Start 2P';
font-style: normal;
font-weight: normal;
src: local('Press Start 2P'), url('http://lemon-factory.net/reproduce/fonts/Press Start 2P.ttf') format('ttf');
}
Then add the following JS:
WebFontConfig = {
custom: { families: ['Press Start 2P'],
urls: [ 'http://lemon-factory.net/reproduce/fonts/pressstart2p.css']},
active: function() {
/* code to execute once all font families are loaded */
console.log(" I sure hope my font is loaded now. ");
}
};
(function() {
var wf = document.createElement('script');
wf.src = ('https:' == document.location.protocol ? 'https' : 'http') +
'://ajax.googleapis.com/ajax/libs/webfont/1/webfont.js';
wf.type = 'text/javascript';
wf.async = 'true';
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(wf, s);
})();
Solution 5:
What about using simple CSS to hide a div using the font like this:
CSS:
#preloadfont {
font-family: YourFont;
opacity:0;
height:0;
width:0;
display:inline-block;
}
HTML:
<body>
<div id="preloadfont">.</div>
<canvas id="yourcanvas"></canvas>
...
</body>