[whatwg] Offscreen canvas (or canvas for web workers).

Oliver Hunt oliver at apple.com
Sat Mar 13 12:09:33 PST 2010

On Mar 13, 2010, at 9:10 AM, Jonas Sicking wrote:
> There is a use case, which I suspect is quite common, for using
> <canvas> to manipulate files on the users file system. For example
> when creating a photo uploader which does client side scaling before
> uploading the images, or for creating a web based GIMP like
> application.
> In this case we'll start out with a File object that needs to be read
> in to a <canvas>. One solution could be to read the File into memory
> in a ByteArray (or similar) and add a synchronous
> canvas2dcontext.fromByteArray function. This has the advantage of
> being more generic, but the downside of forcing both the encoded and
> decoded image to be read into memory.

Honestly i think  nice and consistent way for this work work would simply be to support
someImage.src = someFileObject

Which would be asynchronous, and support all the image formats the browser already supports.

> This is why I suggested adding a asynchronous fromBlob function.
> For extracting image data from a <canvas> I agree that a toBlob
> function has little advantage over a toByteArray function (with the
> possible exception that ByteArray so far is still vapor ware).
CanvasPixelArray is a ByteArray to all intents and purposes, and webkit and i _think_ opera implement it as such.  It would of course be good just to get all the native array types into ES, and then make WebLG + Canvas make use of those directly, and i doubt that is something we'll need to wait too long for.


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