On Tue, Apr 7, 2015 at 6:42 PM, Robert O'Callahan <rob...@ocallahan.org> wrote:
> On Wed, Apr 8, 2015 at 11:41 AM, Kenneth Russell <k...@google.com> wrote:
>> I apologize for taking so long to update this proposal, but it's now
>> in a reasonable state:
>> https://wiki.whatwg.org/wiki/OffscreenCanvas
>> (Renamed per feedback from Anne -- thanks.)
>> Please offer your feedback. Multiple browser implementers agreed on
>> this form of the API at a recent face-to-face meeting of the WebGL
>> working group, and the proposal should be able to address multiple use
>> cases. I'm very interested in prototyping it to see if it can offer
>> better parallelism.
> It seems fine.


> As far as I can tell, the only significant difference between
> this and WorkerCanvas is using an HTMLCanvasElement "bitmaprenderer" as a
> zero-copy way to render an ImageBitmap, instead of HTMLImageElement.

That's the main difference. Another is that OffscreenCanvas can be
directly instantiated from both the main thread and workers.

>Can you explain what the problem was with using HTMLImageElement?

One browser implementer pointed out that HTMLImageElement has several
complex internal states related to loading, and they do not want to
conflate that with the display of ImageBitmaps. I've documented this
in the OffscreenCanvas proposal. (I originally thought Canvas had more
complex internal state, but now think that it can be easier to define
new behavior against a new canvas context than <img>.)


> Rob
> --
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