[whatwg] WebWorkers and images

Berend-Jan Wever skylined at chromium.org
Thu Jan 13 02:08:10 PST 2011

I ended up creating a PageWorker object, which is constructed in the page
rather then in a WebWorker. It uses setInterval to repeatedly run a function
in the background to do the image processing directly on the canvas imageD
data. To reduce overhead, each interval runs the function in a small loop
for a certain number of ms. After each interval, the browser gets some time
to do UI updating. This seems to work well in my Mandelbrot fractal
renderer; the browser remains responsive:



Berend-Jan Wever (SkyLined at google.com) | Security Software Engineer
Google Netherlands B.V. | Reg: Claude Debussylaan 34, 15th floor 1082 MD
34198589 | NETHERLANDS | VAT / Tax ID:- 812788515 B01

On Sat, Jan 8, 2011 at 03:39, Glenn Maynard <glenn at zewt.org> wrote:

> On Fri, Jan 7, 2011 at 8:16 PM, Drew Wilson <atwilson at chromium.org> wrote:
> > I would recommend that people review this
> > thread:
> http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2010-February/025254.html
> > to understand the objections previously raised to this idea.
> To comment on one thing in particular:
> On Tue, Feb 23, 2010 at 12:05 AM, Jonas Sicking <jonas at sicking.cc>
> wrote:
> > I admit to not being a graphics expert, but I would imagine you have
> > to do quite a lot of drawing before
> > 1. Drawing on offscreen canvas
> > 2. Cloning the pixel data in order to ship it to a different thread
> > 3. Drawing the pixel data to the on-screen canvas
> > gets to be cheaper than
> > 1. Drawing to on-screen canvas.
> It's not about doing things more cheaply.  It's about not doing work
> in the UI thread, where it can hold up the whole tab or worse.  Even
> if it's somewhat more expensive in terms of CPU power used, doing this
> sort of work in a thread can be a huge win: keeping the UI
> consistently responsive.
> I've seen it in practice: select an image in an image box, start
> typing in another form field, and my typing freezes for half a second
> while an invisible canvas operation runs.
> --
> Glenn Maynard

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