Class Kerning errors

Stephen Rapp's picture

I have used class kerning before, but just ran into a problem I had not encountered before.

All my previous classes were simple with both sides being the same. I watched a video on class kerning this evening and he explained also how to do class kerning on one side only.

In this family of typefaces that I'm working on I had a handful of alternate letters and some ligatures that I had under the dlig feature. Previous to this I had not generated a kern feature since I knew I would be adding more classes.

Anyway… when I generated the kern feature on the first font with the new one-side-only kerning classes and then compiled it in the OT panel I got a whole list of warnings.

[WARNING] Start of new pair positioning subtable; some pairs may never be accessed: [A Adieresis Aring Agrave Atilde Acircumflex Aacute A.alt Amacron Abreve Aogonek] [T T_H T_H_E T_T T_T_Y T_U T_V T_W T_Y]

It still compiles and the kerning seems to work as it should in the metrics window. When I deleted the new classes, deleted the kern feature and regenerated it without the new classes it was fine. Anybody know what's going on with that?

Here is a sample of a left-side only kerning class:
_Tleftside: T' T_H T_H_E T_T T_T_Y T_U T_V T_W T_Y
I then checked the box to the right side.


k.l.'s picture

Please could anyone dig for the (how-to?) page that contains a bunch of discussions related to class kerning? All has been said there, but I cannot find it any more ...

blank's picture

When this happens to me it’s because a glyph appears in the same side of multiple classes. On a related note, you might want to just switch to kerning in Metrics Machine. Its group creation tool includes an error checker that shows where conflicts have occurred.

Stephen Rapp's picture

James, can you give me a simple example of what you mean by «a glyph appears in the same side of multiple classes». It seems like that might be a natural thing, but maybe I'm just not getting it. For instance, I have a class for T that includes all the accented T's. Then I have 2 classes for T that each have glyphs (ligatures} that have T on either end. Does that cause what you're referring to?

k.l.'s picture

This was a good discussion, and in one of my posts there are more links:

Two more:

Stephen Rapp's picture

Thanks Karsten. I had tried a search, but sometimes the search feature here doesn't seem to function.

blank's picture

Does that cause what you’re referring to?

That could be the problem if there is a conflict between your ligature and duplicate T classes, or if you accidentally put a T into another class entirely. It might be worth copy/pasting those classes into text edit and looking at them blown up. I sometimes miss syntax problems in my classes because I have a hard time reading the tiny text in the class window.

paragraph's picture

I would run the auto diagnostic in Tools/Kerning Assistance first (the yang/yin button).
Also, it happened to me when I had different glyph names defined in the classes and the font.

Stephen Rapp's picture

Thanks so much for all the help.
I reworked the classes so that I didn't have glyphs doubled and it worked perfectly. I always love it when I can learn something new like this. Typophile is such a great resource.

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