Question

Is there a quick test to determine if a browser supports CORS-enabled images not tainting a canvas when drawn on them. I know Chrome 15 supports this, Firefox 9Beta but not Firefox 8, Safari doesn’t, IE9 doesn’t. But there must be a pretty simple test to determine this, is basically drawing on a canvas with an image and seeing if you get an exception when you try to get image data, or is there any other easy way to determine this.

Answer 1

Here is how I tested for CORS tained canvas support. If someone has a way without having to load an image, please post it here:

function CanvasFunctions() {
    var _initialized = false, _corsNotSupported = false;


    function DrawImage(image, src) {
        jQuery.when(initialized()).then(function () { 
            if (_corsNotSupported) {
               image.src = GetProxyImage(src);
            } else {
               image.src = src;
            } 
        }
    }

    function initialized() {
        if (_initialized) {
            return true;
        }

        var dfd = $.Deferred();

        var src = 'http://example.com/corsImage.jpg',
            image.onload = function () {
                var canvas = document.createElement('canvas');
                canvas.width = 250;
                canvas.height = 250;
                var ctx = canvas.getContext('2d');
                ctx.drawImage(image, 0, 0, 200, 200);
                try {
                    var hit = ctx.getImageData(0, 0, 1, 1).data[3] > 1;
                    console.log('Canvas was not tainted by CORS image, hit: ' + hit);
                } catch (e)  {
                    console.log('Canvas was tainted by CORS image, reverting to passthru for images');
                    _corsNotSupported = true;
                }
                _initialized = true;
                dfd.resolve(true);
            });

        image.src = src;


        return dfd.promise();
    }
}