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detect ClearType using javascript
/*
* TypeHelpers version 1.0
* Zoltan Hawryluk, Nov 24 2009.
* @see http://www.useragentman.com/blog/2009/11/29/how-to-detect-font-smoothing-using-javascript/
*
* Released under the MIT License. http://www.opensource.org/licenses/mit-license.php
*
* Works for
* - IE6+ (Windows),
* - Firefox 3.5+ (Windows, Mac, Linux),
* - Safari 4+ (Windows, Mac OS X),
* - Chrome 3.0+ (Windows).
* Opera 10.10 and under reports unknown support for font-smoothing.
*
* Modified by Christian Beier (www.beier-christian.eu) to detect the ClearType technology.
*
* Required: jQuery 1.3.x
*
*
* METHODS
* -------
*
* hasSmoothing() returns:
* true if font smoothing is enabled
* false if font smoothing isn't enabled
* null if it cannot detect if it's on or not.
*
* addClasses() adds the following classes to the html tag:
* "hasFontSmoothing-true" if font smoothing is enabled
* "hasFontSmoothing-false" if it isn't
* "hasFontSmoothing-unknown" if it cannot detect it.
*
*/
var TypeHelpers = new function(){
var me = this;
me.hasSmoothing = function(){
// IE has screen.fontSmoothingEnabled - sweet!
if (typeof(screen.fontSmoothingEnabled) != "undefined") {
return screen.fontSmoothingEnabled;
} else {
try {
// Create a 35x35 Canvas block.
var canvasNode = document.createElement("canvas");
canvasNode.width = "35";
canvasNode.height = "35"
// We must put this node into the body, otherwise
// Safari Windows does not report correctly.
canvasNode.style.display = "none";
document.body.appendChild(canvasNode);
var ctx = canvasNode.getContext("2d");
// draw a black letter "O", 32px Arial.
ctx.textBaseline = "top";
ctx.font = "32px Arial";
ctx.fillStyle = "black";
ctx.strokeStyle = "black";
ctx.fillText("O", 0, 0);
// start at (8,1) and search the canvas from left to right,
// top to bottom to see if we can find a non-black pixel. If
// so we return true.
for (var j = 8; j <= 32; j++) {
for (var i = 1; i <= 32; i++) {
var imageData = ctx.getImageData(i, j, 1, 1).data
var alpha = imageData[3];
if (alpha != 255 && alpha != 0 && alpha > 180) {
return true; // font-smoothing must be on.
}
}
}
// didn't find any non-black pixels - return false.
return false;
}
catch (ex) {
// Something went wrong (for example, Opera cannot use the
// canvas fillText() method. Return null (unknown).
return null;
}
}
}
$(document).ready(function() {
var result = me.hasSmoothing();
if (result == true) {
$('html').addClass('hasFontSmoothing-true');
} else if (result == false) {
$('html').addClass('hasFontSmoothing-false');
} else { // result == null
$('html').addClass('hasFontSmoothing-unknown');
}
});
}
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@blebedev blebedev commented Jun 11, 2013

This code returns a false positive on Firefox 21.0 on Windows 7.

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@blebedev blebedev commented Jun 11, 2013

This code also returns a false positive on IE9 (win7) when users force ClearType off using this method: http://stackoverflow.com/questions/5427315/disable-cleartype-text-anti-aliasing-in-ie9#tab-top

Removing the screen.fontSmoothingEnabled if statement fixes this problem.

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