[webkit-dev] Status of multithreaded image decoding

[Alpha Lam]

That's a good point. I'm not sure but a safe bet would be after RenderView
is layout'ed then iterate through images to start decoding.

The same thing would be needed for scrolling too, as page scrolls need to
iterate images in the viewport.

Alpha

2012/8/13 Alpha (Hin-Chung) Lam <hclam at google.com>

> That's a good point. I'm not sure but a safe bet would be after RenderView
> is layout'ed then iterate through images to start decoding.
>
> The same thing would be needed for scrolling too, as page scrolls need to
> iterate images in the viewport.
>
> Alpha
>
> 2012/8/13 Maciej Stachowiak <mjs at apple.com>
>
>>
>> The thing I'm not confident of is whether an image's position in absolute
>> coordinates can be changed by an ancestor after RenderImage::layout
>> completes. It would be helpful if a layout expert would weigh in.
>>
>>  - Maciej
>>
>> On Aug 13, 2012, at 3:20 AM, Dong Seong Hwang <luxtella at company100.net>
>> wrote:
>>
>> > https://bugs.webkit.org/show_bug.cgi?id=90375#c80
>> >
>> > In the above link, Hin-Chung shows how to determine whether an image
>> > is actually painted.
>> >
>> > 2012/8/13 Maciej Stachowiak <mjs at apple.com>:
>> >> I that case, starting async decoding at layout time makes sense if and
>> only
>> >> if at layout to e you can predict what you will paint. I don't know
>> enough
>> >> about our rendering to know of that is the case.
>> >>
>> >> - Maciej
>> >>
>> >>
>> >>
>> >> On Aug 12, 2012, at 5:34 PM, Peter Kasting <pkasting at chromium.org>
>> wrote:
>> >>
>> >> On Sun, Aug 12, 2012 at 1:24 PM, Maciej Stachowiak <mjs at apple.com>
>> wrote:
>> >>>
>> >>> Why not start asynchronous decoding immediately as the image is
>> loading,
>> >>> and synchronize at paint time? What is the benefit of waiting until
>> layout
>> >>> time to start decoding the image data?
>> >>
>> >>
>> >> Uninformed guess (since I haven't touched the decoders in a while), but
>> >> currently we don't decode unless the image is actually painted, which
>> helps
>> >> a ton on pages that are an enormous long string of images (common
>> cases:
>> >> Boston Big Picture blog, various porn sites), since most of the images
>> can
>> >> be decoded after initial layout, or not at all (if the user never
>> scrolls
>> >> down enough).  If we started decoding as images loaded I'd imagine
>> we'd do
>> >> (possibly a lot of) extra work compared to today.
>> >>
>> >> PK
>> >>
>> >>
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>> >>
>>
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