[Webkit-unassigned] [Bug 74003] New: Ugly text rendering (kerning) on zoom transform within SVG

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Wed Dec 7 08:51:33 PST 2011


           Summary: Ugly text rendering (kerning) on zoom transform within
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: All
               URL: http://www.mysparebrain.com/svgbug.html
        OS/Version: All
            Status: UNCONFIRMED
          Severity: Normal
          Priority: P2
         Component: SVG
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: tim_webkit at schmerg.com
                CC: zimmermann at kde.org

Created an attachment (id=118216)
 --> (https://bugs.webkit.org/attachment.cgi?id=118216&action=review)
Screenshot showing ugly kerning after text rendered when transformed to be zoomed out is then zoomed in

When a transform is applied to text elements within SVG, it seems the kerning details (gaps between individual characters) are simply scaled up or down according to the (pixel/sub-pixel) rounded values determined when the text was first rendered - this leads to very ugly results at times, and can only be fixed by resetting the text content of the spans which forces a re-calculation of the character spacing.

To see a particularly ugly case, see test case number 2 at the test page above and use the button to zoom out seven or eight times (or more), then use the 'recreate spans' button to re-render the (illegibly small) text, and then reset zoom and you'll see the now legible text is badly laid out until you recreate spans again - see screenshot attachment.

Some other browsers suffer slightly from this (Firefox 4,5 and 6) but nowhere near as badly - they'll typically have just one or two character gaps out by just one pixel.
Bug report also post to chrome as http://code.google.com/p/chromium/issues/detail?id=98392 but advised to post here instead (ie underlying webkit issue) as it occurs in both Chrome and Safari.

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