[Webkit-unassigned] [Bug 39884] New: Full Page Zoom: rounding errors with element metrics

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=39884

           Summary: Full Page Zoom: rounding errors with element metrics
           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: ojan at chromium.org
                CC: hyatt at apple.com


Google Spreadsheets has some bugs with rounding errors during full page zoom. The cause is the rounding to an int in adjustForLocalZoom in Element.cpp. It used to be unusable during full page zoom because the rounding errors would add up to quite a bit. They've thrown a bunch of JS code at it that detects the zoom level and guesses at what the rounding error will be. It mostly works now, but it's unfortunate, it's fragile and this surely affects other sites.

Firefox doesn't have this problem because use decimal values both interally and exposed to JS. Should we do the same? That's a super scary change, but it's the only way I can think of making full-page zoom actually work.

Test case attached.

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