Improve ttfautohint hinting

[BladeMF]

I know it's not your job, but please can you guys help me identify what is missing in the patched NerdFonts since 2008 onwards so that the height changes so significantly - ryanoasis/nerd-fonts#519?

I really like to use the new versions and I really like oh-my-zsh, but I am stuck at the 2005 version.

I'm attaching patched fonts from the latest version (where the result is the same). static.zip

Edit: added version
Windows Terminal Preview
Version: 1.4.2652.0

[DHowett]

Hmm.. could it be the “use typographic metrics” flag?

[BladeMF]

Wow you're fast! Thank you very much for responding. If I can add the flag using, say, font forge, I would be so grateful! Especially if someone pointed me at some directions how.

[BladeMF]

Does this mean it is not?

[BladeMF]

Some more info (sorry for the spam):

Found 2 differences and changed them and re-exported the font, had no difference.

Also, Word does not render the fonts differently:

[aaronbell]

Forgive me if I say that the NerdFonts patcher is something like taking a sledgehammer to a nail. It does the job but does so without consideration for preserving the integrity of the original font. At least, that was my experience in looking at the resultant font file last year.

OK, so looking at the version you provided versus our latest version, I see some modifications that could result in spacing changes. For example, modification of the xMax and yMax values in the head table and an increase in ascender in the hhea table, but the changes that you're talking about seem to be inconsistent across OTF and TTF, and generally with glyphs appearing bigger than they should. Is that accurate?

That would lead me to think that the hinting may be responsible. If the hinting is different between the two fonts (and I'm not sure if Nerd Fonts is changing anything on that front), then x-heights can change, and glyphs may appear bigger.

Unfortunately, it isn't anything we can help you with because, as I said, it has a lot to do with how the patcher works. I'm hoping to release a (mostly) complete NF version here at some point which would solve the issue for you, but that's still in the works.

[aaronbell]

Something else to keep in mind. Once we started shipping the variable font, we no longer manually hinted the static instances. So there would be a change in the rendering between the pre-variable static version of Cascadia and the post-variable static version.

If you’re comparing with the older version then that might be a root cause too.

[BladeMF]

Aaron (@aaronbell), I totally agree with you on your point, but I have to check if something could be done. My faith stems from several the fact that the 2005 version worked - so it didn't get as "destroyed". Also Word doesn't seem to see the difference and I was hoping it would be something small.

...seem to be inconsistent across OTF and TTF, and generally with glyphs appearing bigger than they should. Is that accurate?

Yes and the OTF appears even more distorted (look for the small letter "i" - the stem nearly touches the dot). Try alt-tabbing between the 2008 OTF version and the 2005 version and it becomes obvious.

Once we started shipping the variable font, we no longer manually hinted the static instances.

That came to my mind as well. That is why I installed the static TTF regular version to see how that looks and it didn't look distorted.

So my very humble request is this - if this is something that is fixable or things I could try, I'd be very grateful to be pointed in that direction as I know next to nothing about fonts. So, is there something like this?

[aaronbell]

Yikes, that is definitely a significant change. TBH, I'm not even sure where to point you to get started. I'll give it a think.

Could you do me a favor and package up the pre-modded, and modded versions for the 2005 / 2008 fonts that you're using? Thanks!

[BladeMF]

The change is totally in the "what the..." range. Thank you so much for looking into this!

This is everything that I've tried - CascadiaCode.zip. Only the 2005 patched version looks like the original font. 2008 and 2009 look practically the same. Also, the 2005 was the last variable width font that patched normally. 2008 and 2009 variable width fonts crash the patcher. 2008 I tried both TTF and OTF and the OTF looks worse.

I'd be happy to help further!

[BladeMF]

The command I use is this, but I've tried all the parameters and nothing, including --careful and --preserve-line-height (or something simalar sounding):

cd /mnt/d/Downloads/CascadiaCode-2008.25/ttf/static
fontforge -script ~/font-patcher -c CascadiaCode-Regular.ttf

[aaronbell]

OK, I've had a chance to take a look through these and to be honest, I don't see any differences between the NerdFont version and the official version that would be responsible for the differences that you're observing (I do see other significant changes between the two fonts, but they wouldn't result in the x-height modification).

As I read through your concerns, though, something became more clear. The 2005 version was the last version of the TTF that worked OK. That was also the last release before we switched to the variable font version, which means it was the last version to have manual hints.

The 2008 and 2009 releases were variable font releases and contain manual hints. Static instances were then provided as a 'backup' option for users for whom the variable fonts don't work, and therefore are just autohinted with ttfautohint.

I believe that the reason why the fonts look different than the 2005 version is because ttfautohint is choosing to set the hints differently than my manual hints (used in 2005, and on the variable font versions of 2008 / 2009). In running ttfautohint, I didn't do any manual adjustment to how it interprets the font—modifying this would likely cause improved results, but given they're provided purely as backup, improving ttfautohint is a low priority. On the plus side, if you want to do so (and figure out some good settings for us to use), the documentation is pretty extensive.

As for the OTFs, these are all autohinted with psautohint and have had the same settings throughout. OTFs on Windows tend to be a mixed bag and TBH I'm not as knowledgeable about the rasterizer interprets (or ignores) included ps hints. So can't comment on that.

[BladeMF]

Again, I appreciate you looking into it! I wonder why my test with installing the actual backup TTF didn't show distortions. Probably I didn't test it right. But if you are correct, the static TTF, if installed, will show the same distorted result, right?

So you are saying that I need to play with ttfautohint's settings and produce static fonts that look better, right? If so, I would appreciate a head start, maybe the settings you used? Maybe some hints? I am unsure if my knowledge will suffice for a useful test, but I am always willing to try stuff :)

[aaronbell]

Yes, the static instances that we provide should show the same effects on your device as the modified version. If you want to try that, I'd suggest uninstalling all of the versions, and installing one of the PL ones (to avoid overlap with one of the Windows Terminal fonts).

I used the standard setting with pretty much no modifications. Here's the current way we call it:
ttfautohint --stem-width nsn --reference "CascadiaCode-Regular.ttf" "CascadiaCode-Regular-hinted.ttf"

Looking at the documentation, I see something related to x-height which might do it.

[BladeMF]

Thank you, sound like fun!

Should I use the variable width font for base or the current TTF one and change its hints?