[Webkit-unassigned] [Bug 139956] New: Vertical % or viewport sized units render a bit too small

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=139956

            Bug ID: 139956
           Summary: Vertical % or viewport sized units render a bit too
                    small
    Classification: Unclassified
           Product: WebKit
           Version: 525.x (Safari 3.2)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: davideads at gmail.com

Hopefully I can describe this effectively:

For a recent project I made a stacked bar chart using pure CSS and percentage units. Each section of the bar has a percentage based height. All the sections heights add up to 100%. However, unless the container height is such that the percentage based heights map to an exact integer pixel size (e.g. 9% of 500px is 45px, but 9% of 380px is 34.199px), the total height of the boxes is consistently less than the total height of the container. I made a demo:

http://apps.npr.org/lookatthis/posts/publichousing-webkit-bug-demo/ (actual in-the-wild project here: http://apps.npr.org/lookatthis/posts/publichousing)

The percent heights add up to 100%, but the boxes themselves occupy a few pixels less than 100%.

The same behavior can be seen using viewport-relative units like vh.

I was able to replicate in Safari (OS X, iOS) and Chrome (on OS X, Android, iOS). It doesn't show up in Firefox.

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