[webkit-dev] Status of multithreaded image decoding

Maciej Stachowiak mjs at apple.com
Mon Aug 13 10:33:41 PDT 2012

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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