[whatwg] I believe source rectangles for HTML5 Canvas drawImage are specified incorrectly

[Robert O'Callahan]

On Wed, Dec 19, 2012 at 4:17 AM, Kevin Gadd <kevin.gadd at gmail.com> wrote:

> Sorry, upon reading over the ImageBitmap part of the spec again I'm
> confused: Why is constructing an ImageBitmap asynchronous? I thought
> any decoding isn't supposed to happen until drawImage, so I don't
> really understand why this operation involves a callback and a delay.
> Making ImageBitmap creation async means that you *cannot* use this as
> a replacement for drawImage source rectangles unless you know all
> possible source rectangles in advance. This is not possible for many,
> many use cases (scrolling through a bitmap would be one trivial
> example).
>

I think this is a real problem.

It seems to me a synchronous constructor that creates an ImageBitmap for a
subimage of another ImageBitmap (but not other kind of source!) will be
needed.

Rob
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