Bug 158441 – Misaligned inline-block due to fractional padding/margin/other vertical spacing

• Status: NEW
• Component: Layout and Rendering

[Han]

Tested on WebKit Nightly r201711

UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/602.1.36+ (KHTML, like Gecko) Version/9.1.1 Safari/601.6.17

# Example URL:
http://output.jsbin.com/tivuvov

# Steps to reproduce the problem:
1. Open http://output.jsbin.com/tivuvov
2. See misaligned x and 2

# What is the expected behavior?
x and 2 should always line up, because according to the CSS 2.1 spec:

    The baseline of an 'inline-block' is the baseline of its last line box in the normal flow

https://www.w3.org/TR/CSS21/visudet.html#propdef-vertical-align

Firefox 46 displays the correct behavior.

# What went wrong?
At certain fractional values of padding or margin, the x and 2 are misaligned, for example .3em.

# Notes

Safari 9.1.1 and Chrome 50 have the same problem, at I think all the same fractional values, but the misalignment is much more severe.

[Han]

Cross-ref: https://bugs.chromium.org/p/chromium/issues/detail?id=617763

[Han]

Before reporting this bug I did find an existing bug that appears similar, [Subpixel layout: Inline-block is offset from dominant baseline with em based padding](136332), but unlike this bug, 136332 has been fixed in Chrome, whereas this bug is *worse* in Chrome.


[136332]: https://bugs.webkit.org/show_bug.cgi?id=136332

[Ahmad Saleem]

Took reduced test case from Chrome bug: https://jsfiddle.net/vu71job4/show

^ I am able to reproduce using above in WebKit TOT (265630@main). Both Chrome Canary 117 and Firefox Nightly 116 have both 'x' (xx) with proper baseline and no issue in alignment.

[Radar WebKit Bug Importer]

<rdar://problem/122587250>