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

From: Justin Novosad <junov@chromium.org>
Date: Tue, 18 Dec 2012 10:39:27 -0500
Message-ID: <CABpaAqQnL24EcEQNAGaeo4fa6yG7c-VGbkfLh2mqfHXVW_xxGg@mail.gmail.com>
To: Kevin Gadd <kevin.gadd@gmail.com>
Cc: Vladimir Vukicevic <vladimir@pobox.com>, Rik Cabanier <cabanier@gmail.com>, whatwg@lists.whatwg.org, Jeff Muizelaar <jmuizelaar@mozilla.com>, Ian Hickson <ian@hixie.ch>, robert@ocallahan.org
On Tue, Dec 18, 2012 at 10:17 AM, Kevin Gadd <kevin.gadd@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.
>

The image may have to be downloaded, which is a good reason for being async.


> 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 am not sure I understand the problem. If you need synchronous behavior,
you can just make the app wait for the callback to be called.

    -Justin


> On Tue, Dec 18, 2012 at 7:12 AM, Kevin Gadd <kevin.gadd@gmail.com> wrote:
> > Is it possible to expose the width/height of an ImageBitmap, or even
> > expose all the rectangle coordinates? Exposing width/height would be
> > nice for parity with Image and Canvas when writing functions that
> > accept any drawable image source.
> >
> > Thanks for the prompt action here, this looks like a straightforward
> solution.
> >
> > -kg
> >
> > On Tue, Dec 18, 2012 at 7:03 AM, Justin Novosad <junov@chromium.org>
> wrote:
> >> Thanks Ian.
> >> http://html5.org/tools/web-apps-tracker?from=7588&to=7589
> >>
> >> On Tue, Dec 18, 2012 at 1:04 AM, Robert O'Callahan <
> robert@ocallahan.org>
> >> wrote:
> >>>
> >>> On Tue, Dec 18, 2012 at 6:57 PM, Rik Cabanier <cabanier@gmail.com>
> wrote:
> >>>>
> >>>> Does it matter that this solution is in the image world and not 2d
> >>>> canvas? It seems that this will have a bigger impact on the browser's
> >>>> codebase since it spans images and canvas.
> >>>
> >>>
> >>> I think that's a good thing --- it's more generally useful.
> >>>
> >>> Note that Ian has adopted this approach (via an ImageBitmap
> constructor).
> >>>
> >>>
> >>> Rob
> >>> --
> >>> Jesus called them together and said, “You know that the rulers of the
> >>> Gentiles lord it over them, and their high officials exercise
> authority over
> >>> them. Not so with you. Instead, whoever wants to become great among
> you must
> >>> be your servant, and whoever wants to be first must be your slave —
> just as
> >>> the Son of Man did not come to be served, but to serve, and to give
> his life
> >>> as a ransom for many.” [Matthew 20:25-28]
> >>>
> >>
> >
> >
> >
> > --
> > -kg
>
>
>
> --
> -kg
>
Received on Tuesday, 18 December 2012 15:39:54 UTC

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