Kern table overflow

Post Reply
Eben Sorkin
Posts: 15
Joined: 27 Apr 2021

Kern table overflow

Post by Eben Sorkin »

Can you avoid kern table overflow with Kern On by using the "Use Extension Kerning" feature in glyphs?
Eben Sorkin
Posts: 15
Joined: 27 Apr 2021

Re: Kern table overflow

Post by Eben Sorkin »

I'm asking this because of the warning about the 36kb limit in the video here https://kern-on.com/getting-started @ 6:42 ( near the end ).
User avatar
Tim Ahrens
Site Admin
Posts: 164
Joined: 11 Jul 2019

Re: Kern table overflow

Post by Tim Ahrens »

The limit for the old-fashioned kerning (i.e. without extension kerning and written by Glyphs 2) is 64 kB.

You can probably set the value to more than 64 kB and then use extension kerning when you export the fonts. Have you tried that out? Extension kerning is not supported by all applications, though.

Currently, Kern On internally simulates quite exactly (within about 2%) the way the kerning ends up in a font if it is generated by Glyphs 2 (which uses makeOTF for that).

In Glyphs 3, kerning is or will be written differently, and the aim is to use the techniques Behdad Esfahbod explained in his Robothon 2018 talk. That way it would be possible to get more than 64 kB into a font without using extension kerning. I might work together with the Glyphs team on that, let’s see. At least it would affect how Kern On generates (optimizes) the kerning classes.
Eben Sorkin
Posts: 15
Joined: 27 Apr 2021

Re: Kern table overflow

Post by Eben Sorkin »

I'd love it if the kerning in Glyphs 2 when generated by KO could make use of the extension kerning feature. I'm curious about what apps don't make use of the extension kerning. I'll have to look at that.
User avatar
Tim Ahrens
Site Admin
Posts: 164
Joined: 11 Jul 2019

Re: Kern table overflow

Post by Tim Ahrens »

You can use extension kerning if you are using Kern On. Just add the custom parameter in you font info. You are right, not all apps seem to be using it (and I’d also have to do research to say which ones).
Eben Sorkin
Posts: 15
Joined: 27 Apr 2021

Re: Kern table overflow

Post by Eben Sorkin »

I was chatting to Rainer by email and he said everything except for MS office circa 2000 supports extension kerning.
User avatar
Tim Ahrens
Site Admin
Posts: 164
Joined: 11 Jul 2019

Re: Kern table overflow

Post by Tim Ahrens »

Excellent! So you can simply enter a number > 64kB and then use Extension Kerning.
Post Reply