[Webkit-unassigned] [Bug 48570] New: iframes forced into slow scrolling mode by containing RenderLayer sometimes

Thu Oct 28 15:37:43 PDT 2010

https://bugs.webkit.org/show_bug.cgi?id=48570

           Summary: iframes forced into slow scrolling mode by containing
                    RenderLayer sometimes
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Mac OS X 10.5
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: jamesr at chromium.org
                CC: hyatt at apple.com, fishd at chromium.org,
                    simon.fraser at apple.com

With this HTML the interior iframe blits while scrolling:

<!DOCTYPE html>
<html style='overflow:hidden'>
<body style=''>
<iframe src="http://webkit.org">

however with this HTML the interior frame is forced into the slow scrolling path:

<!DOCTYPE html>
<html style='overflow:hidden'>
<body style='overflow:hidden'>
<iframe src="http://webkit.org">

I believe the body's RenderLayer is setting the isOverlapped flag on the iframe's FrameView.

This issue has been affecting GMail, causing all scrolling to require a full repaint.  The GMail team is adjusting their CSS to avoid this issue, but it's likely this is affecting more websites.

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