User:JDrewniak (WMF)/notes/System font stack

System font stack proposal
In T175877, a proposal was made to change the fonts used on mobile Wikimedia websites. The proposal suggests using fonts that were designed specifically for popular operating systems (Android, Windows, iOS, Mac, Linux). This font stack is commonly known as the "system" font stack. The rationale behind this change is that, because these fonts were designed specifically for the screen a person is looking at, they offer a better reading experience than the default fonts, which in some cases (e.g.Helvetica) predate the operating system (and personal computing in general) by decades.

The proposed font stack (CSS)
body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", Helvetica, Arial, sans-serif; } This font stack correlates to the following operating systems.

[[File:System_font-stack_by_OS.png|none|thumb|444x444px|To see this table in a more visual spreadsheet

see this font-stack breakdown by OS

]]

Testing methodology
This report serves to test whether these new fonts actually do provide a better reading experience across the ~300 languages used by Wikimedians today. The proposed fonts should have equal or better language support than the current font, and provide a visually improved reading experience (i.e. are they "more legible" or do they look "better"?).

To test this hypothesis, screenshots of the home pages of Wikipedia in every available language were taken and analyzed for differences and potential errors. These screenshots were taken on all popular operating systems and browsers.

See the font stack screenshot table



On mobile
Users of iOS 9 & up, and Windows Phone would see a font change. Android, however, would largely be unaffected. This is because stock Android comes packaged with precious few fonts. On versions 3 & down, stock Android only comes with the "Droid" font family. On versions 4 & up, stock Android comes with the "Roboto" font family as the only sans-serif option. Third-party Android vendors however, sometimes package their own fonts on Android, like "Samsung Sans" and override the default sans-serif font. In this scenario, specifying "Roboto" in the font-stack might gives users a more consistent experience across Android devices.

Users of iOS 8 & down would be unaffected by this change since Apples’ system font "San Francisco" was only introduced in iOS version 9. Previously, the default font was "Helvetica Neue".

On desktop
Although this change is targeted at mobile devices, if implemented on desktop, this change would be significant. Windows users would see the biggest upgrade. The Segoe UI font is significantly more readable than Arial across a wide array of languages, and is being vigorously improved by Microsoft. See Highlights by OS, Windows for more details.

In testing, the only noticeable degradation on desktop was seen on Safari on MacOS (however, these bugs were not reproducible on a stock installation). When testing locally, the San Francisco font was missing a few diacritic characters that resulted in missing characters (squares with question marks) on Safari. On chrome and Firefox however, these missing diacritics fell back to "Helvetica Neue" and remained legible.

Technical Implications
On the web, fonts play a role not only in text, but sometime in layout. When using the ‘inline-block’ display type for example, the white-space properties of a font can effect the spacing as well as the width of HTML elements. The line-height of fonts can also effect layout. This means that text-inputs can get wider and elements can be misplaced if a font changes. No major changes of this nature were observed in testing, but if implemented on desktop, changes to Visual Editor and other rich applications would have to be examined across a wide range of browser and operating systems.

iOS
San Francisco - Rounder, lighter, wider.

In general the San Francisco font is wider in all directions. It has wider character spacing, larger line-heigh and slightly bigger x-heigh than helvetica. Language support is on-par with Helvetica.

Windows
Segoe UI - shorter, wider, bolder.

Segoe UI has a smaller x height and larger line-height than Arial. It has better anti-aliasing, making it seem blacker than other fonts on Windows, and the bold version is slightly bolder than Arial. Compared to Arial, Segoe UI has better support for Cyrillic, Greek, additional support for a multitude of south-asian fonts, and a much improved Arabic design.

See Unicode blocks supported by the Arial font vs Unicode blocks supported by the Segoe UI font.

Ubuntu
Certain flavours of Ubuntu, like "Kubuntu" ship with a wide range of freely-licensed fonts, among them is "Lato", the font preferred by the Wikimedia foundation design team. Lato supports 100+ Latin-​​based lan­guages, 50+ Cyrillic-​​based lan­guages as well as Greek and IPA pho­net­ics. It offers better legibility in Cyrillic scripts than the default Ubuntu font.

Mac OS
Testing on Mac OS revealed a potential issue with the proposed font stack change. This issue presented itself on Safari, and only on one personal computer. Testing on SauceLabs and Browserstack did not surface this issue, but it is worth further inquiry to determine if this is in fact an isolated incident. On certain language Wikipedias, like Southern Min, missing characters were displayed instead of the fallback font. The missing characters appeared because the system font, San Francisco, is missing a few unicode combining characters. These missing character might affect users of the Taiwanese Pe̍h-ōe-jī script. However, this bug was only spotted on Safari on Mac, and only on one computer (so far). Other browsers on Mac used the fallback fonts as expected.

This bug appears to be an isolated event, since it was un-reproducible on stock Mac OS installations on SuaceLabs and Browserstack.