78186 2012-02-08 17:26:20 -0800 Avoid compositing out-of-view fixed positioned elements 2012-12-17 12:10:33 -0800 1 1 1 Unclassified WebKit Layout and Rendering 528+ (Nightly build) Unspecified Unspecified RESOLVED FIXED P2 Normal --- 1 wangxianzhu wangxianzhu jamesr klobag simon.fraser vangelis webkit.review.bot oldest_to_newest 552669 0 wangxianzhu 2012-02-08 17:26:20 -0800 Like in http://techcrunch.com, a out-of-viewport fixed positioned element with negative z-index makes the whole page composited, even the element is never visible, causing unnecessary layer compositings. Should check if the fixed element is visible when determining if it should be composited. This avoids the problem of excessive repaints which still needs to be investigated and resolved. Experiments on chromium-linux showed that with the checking, the number of layers of http://techcrunch.com reduced from about 100 to 0. Experiments on chromium-android showed the number of layers reduced from 31 (including 3 fullscreen layers) to only 5~6. (http://techcrunch.com returns different pages for chromium-linux and chromium-android) 552677 1 126202 wangxianzhu 2012-02-08 17:34:12 -0800 Created attachment 126202 patch for preview (missing test) 552788 2 126202 jamesr 2012-02-08 20:05:07 -0800 Comment on attachment 126202 patch for preview (missing test) This is a nice find. For testing, I'd recommend use the layerTreeAsText() hook to make sure that we aren't making GraphicsLayers that we don't need to. 553677 3 126418 wangxianzhu 2012-02-09 18:09:01 -0800 Created attachment 126418 patch with layout test 553682 4 126418 jamesr 2012-02-09 18:12:02 -0800 Comment on attachment 126418 patch with layout test Great! R=me 553848 5 126418 webkit.review.bot 2012-02-09 22:35:10 -0800 Comment on attachment 126418 patch with layout test Clearing flags on attachment: 126418 Committed r107364: <http://trac.webkit.org/changeset/107364> 553849 6 webkit.review.bot 2012-02-09 22:35:14 -0800 All reviewed patches have been landed. Closing bug. 559599 7 wangxianzhu 2012-02-17 15:35:11 -0800 Changed title to be more accurate. 792383 8 simon.fraser 2012-12-16 15:04:31 -0800 There's a problem with this strategy, when combined with zooming;when zoomed in, we may consider a fixed element to be outside the viewport, and not composite it. However, zooming may bring that element back into the viewport, but if it doesn't have a layer yet, it won't be visible while zooming. 792912 9 wangxianzhu 2012-12-17 12:10:33 -0800 (In reply to comment #8) > There's a problem with this strategy, when combined with zooming;when zoomed in, we may consider a fixed element to be outside the viewport, and not composite it. However, zooming may bring that element back into the viewport, but if it doesn't have a layer yet, it won't be visible while zooming. Thanks for the finding. Filed bug 105202. 126202 2012-02-08 17:34:12 -0800 2012-02-09 18:09:01 -0800 patch for preview (missing test) 78186 text/plain 1492 wangxianzhu SW5kZXg6IFNvdXJjZS9XZWJDb3JlL0NoYW5nZUxvZwo9PT09PT09PT09PT09PT09PT09PT09PT09 PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09PT09Ci0tLSBTb3VyY2UvV2Vi Q29yZS9DaGFuZ2VMb2cJKHJldmlzaW9uIDEwNzE1NikKKysrIFNvdXJjZS9XZWJDb3JlL0NoYW5n ZUxvZwkod29ya2luZyBjb3B5KQpAQCAtMSwzICsxLDE1IEBACisyMDEyLTAyLTA4ICBYaWFuemh1 IFdhbmcgIDx3YW5neGlhbnpodUBjaHJvbWl1bS5vcmc+CisKKyAgICAgICAgQXZvaWQgY29tcG9z aXRpbmcgaW52aXNpYmxlIGZpeGVkIHBvc2l0aW9uZWQgZWxlbWVudHMKKyAgICAgICAgaHR0cHM6 Ly9idWdzLndlYmtpdC5vcmcvc2hvd19idWcuY2dpP2lkPTc4MTg2CisKKyAgICAgICAgUmV2aWV3 ZWQgYnkgTk9CT0RZIChPT1BTISkuCisKKyAgICAgICAgTm8gbmV3IHRlc3RzLiAoT09QUyEpCisK KyAgICAgICAgKiByZW5kZXJpbmcvUmVuZGVyTGF5ZXJDb21wb3NpdG9yLmNwcDoKKyAgICAgICAg KFdlYkNvcmU6OlJlbmRlckxheWVyQ29tcG9zaXRvcjo6cmVxdWlyZXNDb21wb3NpdGluZ0ZvclBv c2l0aW9uKToKKwogMjAxMi0wMi0wOCAgQWRhbSBLbGVpbiAgPGFkYW1rQGNocm9taXVtLm9yZz4K 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