[Webkit-unassigned] [Bug 79389] New: Excessive style when starting CSS3 animations

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=79389

           Summary: Excessive style when starting CSS3 animations
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: CSS
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: robarnold at fb.com
                CC: jmkaldor at fb.com


Created an attachment (id=128532)
 --> (https://bugs.webkit.org/attachment.cgi?id=128532&action=review)
Testcase

See the attached testcase for an example. In it, we begin animating a div smoothly using JS to modify the transform property but when we switch to using the CSS3 animation, there is a noticeable visual hitch. We've observed this on the latest versions of Safari, Mobile Safari and Chrome (which most clearly shows the problem). The inspector seems to attribute this hitch to a style recalc.

On mobile safari, NUMBER_OF_LAYERS can be set lower (say, 256). You may need to tune this number depending on your machine to observe the problem.

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