How can I draw an image from the HTML5 File API on Canvas?

Question

You have a File instance which is not an image.

To get an image, use new Image(). The src needs to be an URL referencing to the selected File. You can use URL.createObjectURL to get an URL referencing to a Blob (a File is also a Blob): http://jsfiddle.net/t7mv6/86/.

var ctx = document.getElementById('canvas').getContext('2d');
var img = new Image;
img.onload = function() {
    ctx.drawImage(img, 20,20);
    alert('the image is drawn');
}
img.src = URL.createObjectURL(e.target.files[0]);

Note: be sure to revoke the object url when you are done with it otherwise you’ll leak memory. If you’re not doing anything too crazy, you can just stick a URL.revokeObjectURL(img.src) in the img.onload function.

References:

https://developer.mozilla.org/en/DOM/File
http://html5demos.com/file-api

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