[Webkit-unassigned] [Bug 160956] New: SVGs are sometimes offset by 0.5px on retina

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=160956

            Bug ID: 160956
           Summary: SVGs are sometimes offset by 0.5px on retina
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Macintosh
                OS: OS X 10.10
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: SVG
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jonasmunk at mac.com
                CC: zimmermann at kde.org

Created attachment 286365
  --> https://bugs.webkit.org/attachment.cgi?id=286365&action=review
Minimal test case

Sometimes SVGs are offset by .5 pixels when drawn on retina screen.

It looks like it happens randomly based on some vertical pixel-fitting.

I would expect the coordinate system for the SVG to start at a full pixel based on the container.

This is especially a problem when doing pixel-perfect/pixel-fitted icons for UI - not normally noticeable.

I have created a perfect 32x32 square SVG to test with (hopefully) + an example using xlink

In the attached test case:
1) The SVGs are drawn showing the problem where the top line in the rect is clipped
2) An image showing how Chrome draws it
3) An image showing how I see it on my machine with Webkit nightly
4) The same SVGs again - but now it draws correctly (probably because the content above makes it land on a full pixel or something)

Note it looks like Firefox has a problem with the first SVGs but only on low DPI screen.

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