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

Oliver Hunt oliver at apple.com
Mon Apr 16 14:06:53 PDT 2012

On Apr 16, 2012, at 2:00 PM, Darin Fisher <darin at chromium.org> wrote:
> I have learned that it is not commonly accepted that reading ImageData can be slow.  I had assumed otherwise.

Yes, it's possible to make reading image data slow, but i can make _anything_ slow.  I could make postMessage slow even though it's ostensibly asynchronous simply by triggering a copy of a large enough object.

The problem I have is that there has been any demonstration that making the data read asynchronous will save substantial time vs. a) the typical operations that will subsequently be performed on the retrieved data or b) that it would generally take longer than a runloop cycle.

Knowingly adding complexity without any good metrics that show getImageData{HD} is sufficiently expensive to warrant that complexity seems like the wrong path to take.

> -Darin

More information about the whatwg mailing list