Bug 159617 – font-size measured in ex or ch scales quadratically with page zoom

• Component: Layout and Rendering
• Status: NEW

[Peter Krautzberger]

WebKit's behavior seems identical to https://bugs.chromium.org/p/chromium/issues/detail?id=408777. 

Copied from there:

> Example URL:
> http://web.mit.edu/andersk/Public/font-size-css-units.html
> 
> Steps to reproduce the problem:
> 1. Visit http://web.mit.edu/andersk/Public/font-size-css-units.html
> 2. At 100% page zoom, observe that all the lines are roughly the same size.
> 3. Zoom in.
> 
> What is the expected behavior?
> All lines should get bigger by the same ratio.
> 
> What went wrong?
> The lines where font-size is measured in ex or ch get bigger much faster than the other lines.  At 500% page zoom, they are shown at 25 times their original size.
> 
> Does it occur on multiple sites: Yes
> 
> Does this work in other browsers? Yes

While Blink is also affected, Firefox and IE/Edge are not.

Thanks in advance for looking into it!

[Peter Krautzberger]

The Blink bug has been fixed now, cf. https://bugs.chromium.org/p/chromium/issues/detail?id=408777.

Using WebKitGTK+ 2.24.2, it appears the problem has been partially fixed in WebKit as well, i.e., it seems ex units are ok but ch units are still scaling up too much.

[Ahmad Saleem]

I am able to reproduce this bug in Safari Technology Preview 152 on macOS 12.5.1 and while zooming into test case from Comment 0, both "ch" and "ex" font-size grow faster than others while in all other browsers (Chrome Canary 107 and Firefox Nightly 106), it is not the case. Just wanted to share updated testing results. Thanks!

[Radar WebKit Bug Importer]

<rdar://problem/99295934>