[whatwg] [canvas] request for {create, get, put}ImageDataHD and ctx.backingStorePixelRatio

Glenn Maynard glenn at zewt.org
Tue Mar 20 15:36:05 PDT 2012

On Tue, Mar 20, 2012 at 2:08 PM, Boris Zbarsky <bzbarsky at mit.edu> wrote:

> That would indeed be very nice.  The question is what happens if drawing
> happens after the getImageData call...  Or for that matter after the
> putImageData call (though I suspect there's less need for putImageData to
> be async).

The drawing calls that happen after would need to be buffered (or otherwise
flush the queue, akin to calling glFinish), so the operations still happen
in order.

putImageData being async makes sense, too, for the same reason: it avoids
having to flush drawing commands earlier in the queue, which helps keep
putImageData from blocking.  It's a bit trickier, though: what happens if
the argument passed to putImageData is modified before it's written?  You'd
either need a mechanism to detect changes, so you can make a copy (eg. a
copy-on-write mechanism for ArrayBuffer--though that sort of sounds useful
in its own right), or to just say that any changes to made to the buffer
before the async operation completes will be reflected in the copy.

Glenn Maynard

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