Discretionary Ligatures: more than only one lookup

mauro sacchetto

I noticed that in some fonts two different lookups are used for discretionary ligatures. In some ones, a distinction is made between "Discretionary Legatures" at all and "Discretionary Legatures in Latin". But is it possible to somehow select if you want to use both, or only one of the two? For example, in LaTeX, if the <+dlig> characteristic is inserted, the lookups are also applied. Is there a method to choose, or to "number" these lookups, for example how can you do for stylistic sets, which are numbered? Thank you!

Erwin Denissen

No, you can't activate lookups directly, only by feature.

mauro sacchetto

I solved it with a compromise. I have moved from dlig to liga the ligatures f_j and f_f_j, which seem to me more appropriate than optional. Secondly, I created a lookup for c_h and c_k only for German, in order to avoid breaking the two letters at the end of the line

John Hudson

in order to avoid breaking the two letters at the end of the line

Note that linebreaking behaviour is character-based, not glyph based, so simply making a combination of letters form a ligature when they are adjacent won't mean that they won't end up getting split across lines — and hence no longer be adjacent — if a linebreaking algorithm believes there is a linebreaking opportunity at that location. This is why correctly language tagging text is important, so e.g. a German dictionary can inform the decisions the algorithm makes.

mauro sacchetto

I generally use LaTeX for writing. It is clear that if I only activate the lookup, but I am writing in Italian, it can happen, as you rightly point out, that the two letters are still separate. However, if I set the language to "German", the two conditions you mention should be correctly fulfilled, so there is not only the binding, but within a German environment.