æ has right side group ‘KO_ae’ instead of ‘KO_e’

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claegg
Posts: 18
Joined: 23 Apr 2021

æ has right side group ‘KO_ae’ instead of ‘KO_e’

Post by claegg »

I just noticed that æ has right side group ‘KO_ae’ instead of ‘KO_e’. Is that something that is hard-coded in Kern-On or can you say why that is the case?
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Tim Ahrens
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Re: æ has right side group ‘KO_ae’ instead of ‘KO_e’

Post by Tim Ahrens »

Hi Claus, are you using the latest version (1.18)?
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Tim Ahrens
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Joined: 11 Jul 2019

Re: æ has right side group ‘KO_ae’ instead of ‘KO_e’

Post by Tim Ahrens »

Okay, sorry, the algorithm is still not perfect. In November, I have spent a few weeks refining it but there is still some scope for improvement.

The kerning groups in Kern On are not hard-coded at all. To determine whether merging groups makes sense, Kern On looks the kerning values and determines how many additional glyph-glyph pairs (a.k.a. exceptions) will be necessary, and how many bytes will be saved because of the reduced class kerning table. If all values are identical then a merger won’t lead to any additional exceptions so that’s a a good candidate for a merger. However, Kern On is a bit sceptical if there are not many shared pairs between the two groups. I suspect that was the case here.

For all pairs that are defined only for one of the to-be-merged kerning groups, the members of the other groups will simply receive this value. This can lead to nonsensical kerning pairs, even if it only affects pairs that presumably never occur in the real world. Still, it is an issue. That was the old pre-November algorithm that was treating the task more like data-compression. I made the choices a bit more conservative, which means it is much safer from combining the wrong glyphs, but it may sometimes miss optimization opportunities.

I hope we can treat the ‘KO_ae’ vs ‘KO_e’ problem as a missed opportunity rather than a real bug? I imagine it doesn’t feel great to know this non-optimal configuration is in the font but, considering it’s fully automatic, maybe acceptable? Most importantly, the final rendering of the font will be fine.

Btw, if you want you can send me the .glyphs file, then I can have a closer look at why the e and ae are not merged.
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claegg
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Joined: 23 Apr 2021

Re: æ has right side group ‘KO_ae’ instead of ‘KO_e’

Post by claegg »

I can accept anything as long as the fonts are kerned in a visually pleasing way. How the hotdog is made … well, I’m okay with not asking and just eating it ;-)
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