[whatwg] Fwd: Why can't ImageBitmap objects have width and height attributes? (and other e-mails)

Justin Novosad junov at google.com
Thu Jul 18 09:27:18 PDT 2013

On Thu, Jul 18, 2013 at 3:18 AM, K. Gadd <kg at luminance.org> wrote:

> >
> > > 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).
> >
> > Yeah, it's not supposed to be a replacement for drawImage().
> >
> This is why I was confused then, since I was told on this list that
> ImageBitmap was a solution for the problem of drawing subrectangles of
> images via drawImage (since the current specified behavior makes it
> impossible to precisely draw a subrectangle). :(
This is a really good point and case.  I was under the impression that the
color bleeding prevention was to be solved with ImageBitmaps, but as you
point out, it breaks down for cutting rectangles on the fly. Furthermore, I
think there is also no good solution for synchronously cutting rectangles
out of animated image sources like an animated canvas or a playing video.
Two possible solutions that were brought up so far on this list:

a) have synchronous versions of createImageBitmap
b) have a rendering option to modify drawImage's edge filtering behavior
(either an argument to drawImage or a rendering context attribute)

I took note of this concern here:

>  -kg

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