This isn't the right place to discuss iOS behaviors. Your best bet is to file a 
bug at http://bugreporter.apple.com describing the behavior you see. Be sure to 
include a test case.

Simon

On Oct 13, 2011, at 10:16 AM, Stephen Mattison wrote:

> Thanks for the reply Zoltan. What I am seeing on iOS is that sometimes the 
> decoding task runs in the main thread sometimes in the web thread. Is this 
> something that Apple is doing?
> 
> Cheers,
> Stephen
> 
> On Wed, Oct 12, 2011 at 11:25 PM, Zoltan Horvath <[email protected]> wrote:
> On Wed, 12 Oct 2011 22:53:25 +0200, Stephen Mattison 
> <[email protected]> wrote:
> 
> Hey Zoltan thanks for the input! Is there anything I can do to make sure
> that the decoding always happens in the WebThread? Ie not adding to the DOM
> or creating a dom fragment or something?
> 
> Currently, there is no WebThread in WebKit. If you are using WebKit2 then 
> there will be separated process for UI things and for Web things, what 
> increases UI's responsiveness, but with the current implementation 
> imagedecoding can block the loading a bit.
> 
> Zoltan
> 
> On Wed, Oct 12, 2011 at 3:01 AM, Zoltan Horvath <[email protected]> wrote:
> 
> On Wed, 12 Oct 2011 03:39:19 +0200, Stephen Mattison <
> [email protected]> wrote:
> 
>  The problem I'm having is that it does not appear that PNGs are decoded in
> the background in Webkit on iOS. Right now what I have is essentially a
> ScrollView. I have a div the size of the viewport with another div that
> scales with the content. I am scrolling the content div using a transition
> and translate3d to achieve GPU acceleration. The scrolling looks great.
> However the content is composed of images and they cannot all fit in
> memory
> at once so I am loading them on demand. The problem arises when I set the
> background-image css property to a locally stored PNG image and then
> attempt
> to scroll. I get a noticeable delay/jerkiness/hiccup as the image is
> decoded. Is there something I should be doing differently?
> 
> 
> Hey!
> 
> WebKit is decoding images in the mainthread when there is new chunk of
> image and it hasn't decoded yet, thus it is imaginable that it blocks your
> main thread for 'longer' time.
> 
> I have a sketchy implementation for Qt to support imagedecoding in a
> (currently 1) separate thread.
> If you are interested check: https://bugs.webkit.org/show_**
> bug.cgi?id=69515 <https://bugs.webkit.org/show_bug.cgi?id=69515>
> 
> Regards,
> Zoltan
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> 
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