[Webkit-unassigned] [Bug 90375] Parallel image decoders

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=90375





--- Comment #13 from Kwang Yul Seo <skyul at company100.net>  2012-07-11 00:13:31 PST ---
You can check out the updated test results in the following URL:

https://docs.google.com/spreadsheet/pub?key=0Ar2smwimcenMdGpnTEw2clZjSTNkbXNFNFM5dkYyRGc&output=html

A few notes:
- Adjust the threshold from 512x512 to 300x300
- Measure first painting time to make sure all the images are decoded.
- Add flickr.com: It is hard to measure page loading time (or first paint time) accurately because page loading time varies a lot due to dynamic resource requests of scripts. So we locally mirrored the site and removed scripts. 

As mentioned above, parallel image decoders can't improve page loading time (or first paint time) dramatically if images are not cached, because it takes a long time to fetch large images and image decoding can be performed in the meantime (interleaved with loading). If images are already cached, then parallel image decoders shine! 

However, there is still limitation. Even image heavy sites do not show all the images at once. To see all the images, we need to scroll down many pages. Because WebKit decodes images only when they need to be painted, not all the images are decoded in page loading.

Fortunately, parallel image decoders seem to increase scrolling responsiveness because images are decoded asynchronously in the background while the main thread repaints. I don't have a way to measure this in numbers, but we could feel this in image heavy sites such as http://kiru.kr/kiru/html/singlelongopst.htm

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