GF update : vertical metrics

[RosaWagner]

I am almost done with reviewing the changes to update the font on Google Fonts, although few things doesn't match Google specs anymore. Biggest issue is the vertical metrics, I think a decision should be made before I submit to you a PR with the modifications.

Version 1.051 (Source repo) typoAscender = 750; typoDescender = "-250"; typoLineGap = 200; winAscent = 1100; winDescent = 395; use_typo_metrics = disabled

Version 1.002 (GF repo) typoAscender = 750; typoDescender = "-250"; typoLineGap = 200; winAscent = 1100; winDescent = 395; hheaAscender = 1100; hheaDescender = "-395"; use_typo_metrics = disabled

What’s wrong with it ?

• Source version misses HHEA metrics to give instructions to applications in Mac environment
• Both versions have USE_TYPO_METRICS disabled, which mean that Windows applications are using the WIN metrics to calculate linespacing.
• TYPO and WIN metrics are not equivalent, which means that softwares which use TYPO metrics over WIN metrics (when Use_Typo_metrics is disabled) don’t display linespacing the same way within the same OS environment.
• LineGap is not 0. This metric is not consistently used by softwares, ie some softwares within the same OS environment may display it and other not.
• WIN metrics don’t cover the highest glyph of the font, it may be cut off when rendered on Windows text machines. (Highest: nikhahit_maiTri-thai (top y: 1174.0), Lowest: saraUu-thai.small (bottom y: -391.0))

What is recommended ?

• Since Windows softwares support ‘use_typo_metrics’ since 2006, it is recommended to enable this option so WIN metrics are used only to set the size of the rendering box, TYPO metrics for the linespacing.
• It is good practice to round up Y-Max and Y-Min for WIN metrics to make sure glyphs are entirely displayed even at small ppm sizes.
• To optimise cross-platforms consistency, it is then recommended to synchronise HHEA and TYPO metrics, and set LineGap values to 0.
• Ascenders metrics should cover an accentuated capital to allow primitive text editors to display accents in first line of texts (highest single accentuated caps is A with hook above y=935)
• For optimal user experience it is also recommended to centred capitals in the text-frame (caps-height=644) and provide an average baseline to baseline distance of 120%-130% of the font size. But doing so, in this case, will greatly modify layout of existing documents.

Suggested vertical metrics for next update (version 2.000) 1) We give former WIN metrics to TYPO and HHEA metrics for a minimal impact on web and office applications (but existing indesign documents will be impacted, and linespacing is a bit loose). TypoAscender = HheaAscender = 1100 TypoDescender = HheaDescender = -395 TypoLineGap = HheaLineGap = 0 winAscent = 1180 (y-max rounded up) winDescent = 400 (y-min rounded up) use_typo_metrics = enabled

2) Another solution for good user experience would be these values (linespacing 125% of UPM, caps centred), although it would modify deeply existing documents on every platforms and applications: TypoAscender = HheaAscender = 946 TypoDescender = HheaDescender = -302 TypoLineGap = HheaLineGap = 0 winAscent = 1180 winDescent = 400 use_typo_metrics = enabled

@davelab6 : I used Marc script to have about 125% of linespacing and I then recalculated to center capitals (GF script suggest 975 and -242). Which solution would you recommend ?

[RosaWagner]

Maybe there were a lot of informations in this post. Let's rephrase this way: vertical metrics doesn't match Google Spec, the update of this font is a good opportunity to correct the vertical metrics as well :) To avoid regression we suggest solution 1) above. The important thing here is to preserve current paragraph set up on web pages using the font. Do you agree ?

[suppakit-]

I think it is good if it adapts to Google Spec. What we care about is people who have used previous versions. If there is no effect on the original layout.

[RosaWagner]

On the web pages there will be no changes.

[suppakit-]

OK. I agree with you. Thank you very much for the advice.