[whatwg] Offscreen canvas (or canvas for web workers).

Philip Taylor excors+whatwg at gmail.com
Mon Mar 15 03:46:51 PDT 2010

On Mon, Mar 15, 2010 at 7:05 AM, Maciej Stachowiak <mjs at apple.com> wrote:
> Copying from one canvas to another is much faster than copying to/from
> ImageData. To make copying to a Worker worthwhile as a responsiveness
> improvement for rotations or downscales, in addition to the OffscreenCanvas
> proposal we would need a faster way to copy image data to a Worker. One
> possibility is to allow an OffscreenCanvas to be copied to and from a
> background thread. It seems this would be much much faster than copying via
> ImageData.

Maybe this indicates that implementations of getImageData/putImageData
ought to be optimised? e.g. do the expensive multiplications and
divisions in the premultiplication code with SIMD. (A seemingly
similar thing at http://bugzilla.openedhand.com/show_bug.cgi?id=1939
suggests SSE2 makes things 3x as fast). That would avoid the need to
invent new API, and would also benefit anyone who wants to use
ImageData for other purposes.

Philip Taylor
excors at gmail.com

More information about the whatwg mailing list