Kerning groups and missing glyphs

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federicoparra
Posts: 3
Joined: 23 Apr 2021

Kerning groups and missing glyphs

Post by federicoparra »

I've been testing Kern On and see a lot of potential in this plugin. I know it might be a bit contradictory but I think it would be nice to retain control over the kerning groups prior to use Kern On (e.g. I would like to have the same kerning for different accentuated A's). I was also wondering how to include characters that Kern On seems to ignore, as the .case variations? I know that I could add "User-set autopairs" but I'd have to add each possible combination.
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Tim Ahrens
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Posts: 172
Joined: 11 Jul 2019

Re: Kerning groups and missing glyphs

Post by Tim Ahrens »

Regarding the missing kerning for the .case variations: They should be generated automatically. What are the pairs you would expect to be generated? Do you have the case feature defined? To determine which pairs are necessary, Kern On applies the OT features in the font, just like they would be applied when the font is used. It ignores the glyph names. Sorry, this information is not in the initial tutorial as I tried to keep it short. I’ll cover it in the next, more in-depth video. Hope this helps for now!

As for the kerning groups, sorry, Kern On doesn’t let you set them manually. One less thing to worry about! Before you push the Kern On button, all pairs are glyph-glyph pairs, and the classes are generated only as the very last step.

The reasoning when generating kerning classes is:
  • Ensure the given kerning data size is not exceeded, and
  • Optimize the kerning so that the important pairs are exported, and have a value close to the ideal value (the precise value determined by autokerning). So, the algorithm aims to minimize the sum of all errors (error means missing pairs or values that deviate from the ideal), considering the pairs’ frequencies.
The result sometimes looks a little unusual for human eyes but keep in mind that the aim is not to have pretty-looking kerning groups, but good results when the font is used.

In the final kerning, are there any pairs you are unhappy with? Anything missing? Any wrong values? Just let me know and I’ll investigate.
federicoparra
Posts: 3
Joined: 23 Apr 2021

Re: Kerning groups and missing glyphs

Post by federicoparra »

It works pretty well after updating the features, as you mentioned. As @Gini did, I also added some pairs with "dcaron" and "lcaron" (mainly accentuated letters) but probably there are no words with those occurrences. One thing that I feel could be useful is the kerning pairs of ".numr" and ".dnom" with "fraction", since this is how I generate fractions.
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Tim Ahrens
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Posts: 172
Joined: 11 Jul 2019

Re: Kerning groups and missing glyphs

Post by Tim Ahrens »

Agreed, the pairs necessary for the fractions would be helpful. Maybe this should be generalized to include all ligature-type composites in the font? I’ll put that on my list.
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