[Webkit-unassigned] [Bug 36303] New: Inserting CSS rules one at a time via js causes slow synchronous style recalculation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=36303

           Summary: Inserting CSS rules one at a time via js causes slow
                    synchronous style recalculation
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh Intel
        OS/Version: Mac OS X 10.5
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: tstanis at google.com


Created an attachment (id=51049)
 --> (https://bugs.webkit.org/attachment.cgi?id=51049)
HTML page illustrating the bug

Using sheet.insertRule() causes webkit to re-evaluate all of the style rules
synchronously.  This means that if you have a bunch of rules that are added one
at a time, styles will be recalculated multiple times.  Instead, we should
start the relayout timer and evaluate all of these styles once.

Attached is an HTML page that clearly illustrates how slow this can be.  In my
tests this takes ~3000ms whereas firefox completes much quicker.

I have a fix in progress that brings this down to ~100ms.

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