[whatwg] Synchronizing Canvas updates in a worker to DOM changes in the UI thread

Glenn Maynard glenn at zewt.org
Sun Oct 20 19:46:44 PDT 2013

(Whoops.  Why did Gmail send that as my work email?  It shouldn't have made
it through to the list, since it's not subscribed...)

On Sun, Oct 20, 2013 at 9:26 PM, Kyle Huey <me at kylehuey.com> wrote:

> On Sun, Oct 20, 2013 at 11:33 PM, Glenn Maynard <glenn at bluegoji.com>wrote:
>> It must not be possible for the UI thread to detect whether present() did
>> anything--if there's no frame in the ready buffer, nothing changes and the
>> UI thread can't detect this.  Similarly, it must not be possible for the
>> rendering thread to detect if the ready frame has been presented.  These
>> rules are to prevent exposing asynchronous behavior.
> Well you can readback from <canvas>es, so how is that going to work?

However it works today, since CanvasProxy needs the same thing.  If a
CanvasProxy/WorkerCanvas exists for a canvas, you should have to use a
toBlob method on that, and calls to that (and earlier calls in progress) on
the Canvas itself should fail.  (If CanvasProxy isn't doing that it seems
like a bug.)

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