[whatwg] "offscreen canvas" /Access to canvas functionality from a worker
fbuchinger at gmail.com
Thu Dec 10 00:45:19 PST 2009
Does this mean that I have to implement my own image scaling method in
If so, I'd have to manually iterate over all pixels of the image, perform
some nearest-neighbour calculation and create a new ImageData Object with
This will be magnitudes sloooooooooower than scale() :(
I'd really appreciate if the "scale-images-before-upload" use case would be
considered better in the HTML5 spec. After all, images are the most
frequently uploaded file type and it has always been a hassle for users to
scale down their multi-megapixel photos manually before uploading them. Now
that we have the chance to solve this issue with pure-browser techniques, we
2009/12/7 Sigbjorn Finne <sigbjorn.finne at gmail.com>
> On 12/5/2009 13:24, Franz Buchinger wrote:
> > Gears introduced the concept of an "offscreen canvas" that doesn't draw
> > anything in the browser window, but can be used to manipulate images in a
> > web worker.
> > I used this functionality to implement a "resize-before-upload" feature
> > my photo gallery uploader. Now I'm trying to port my uploader to HTML5
> > there seems no way to delegate the scaling work to a HTML5 web worker.
> > Surely I could use the DOM canvas to scale down the photos in the main
> > "browser thread", but this means that the UI gets blocked during this
> > process.
> > If the user chooses more than a few multi-megapixel photos, the
> > CPU-intensive downscaling will likely freeze the browser and trigger a
> > script abortion warning.
> > Are there plans to introduce an "offscreen canvas" in html5? If not,
> > workarounds are possible?
> Hi Franz,
> ImageData is cloneable via postMessage(), so you could perform some
> forms of image processing that way.
> --sigbjorn <sof at opera.com>
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