[Webkit-unassigned] [Bug 76137] New: Borders and box masks behave incorrectly with overlapping offsets

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=76137

           Summary: Borders and box masks behave incorrectly with
                    overlapping offsets
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: WebCore Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: ianh at apple.com


Created an attachment (id=122147)
 --> (https://bugs.webkit.org/attachment.cgi?id=122147&action=review)
test case

See attached test case.  An 8x8 image is used as a box mask and a border image.  The test case includes three offsets to divide the image into nine parts -- 3, 4, and 5.  The rendering is incorrect in the 4 and 5 cases (though it may not appear so in the box mask case -- the untouched areas are left unclipped unless we fall into the transparency layer path by e.g. pinch zooming).

It seems like we should do what it says at <http://www.w3.org/TR/css3-background/#border-image-width>:
If two opposite ‘border-image-width’ offsets are large enough that they overlap, then the used values of all ‘border-image-width’ offsets are proportionally reduced until they no longer overlap. In mathematical notation: Given Lwidth as the width of the border image area, Lheight as its height, and Wside as the border image width offset for the side side, let f = min(Lwidth/(Wleft+Wright), Lheight/(Wtop+Wbottom)). If f < 1, then all W are reduced by multiplying them by f.

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