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

Robert O'Callahan robert at ocallahan.org
Wed Dec 19 01:29:23 PST 2012

On Wed, Dec 19, 2012 at 5:39 PM, Rik Cabanier <cabanier at gmail.com> wrote:

> On Tue, Dec 18, 2012 at 1:14 PM, Robert O'Callahan <robert at ocallahan.org>wrote:
>> It seems to me a synchronous constructor that creates an ImageBitmap for
>> a subimage of another ImageBitmap (but not other kind of source!) will be
>> needed.
> Did you mean to say a synchronous constructor?

Yes. That's what I said.

> Reading the new spec (
> http://www.whatwg.org/specs/web-apps/current-work/#imagebitmap), I still
> fail to see how this is better than a drawimage with dx=dy=0 and
> dw/dy=canvas width/height

You mean, how is using createImageBitmap better than drawing the input
ImageBitmap into a temporary canvas and then using that canvas instead of
the result of createImageBitmap?

Basically, createImageBitmap is a more direct approach that's easier to
optimize to avoid copying the image data.

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]

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