double letterspaced ligatures

[schlcht]

Using the letterspace font feature, letterspacing within ligatures will be doubled (this does not happen with the typesetters function):

\input luaotfload.sty
\tracingoutput 1
\showboxdepth  10
\showboxbreadth100
\font\x = "EB Garamond:mode=node;+liga;+dlig" at 10pt
{\x\directlua{typesetters.kerns.set(0.2)}
Thefoofi}

\font\x = "EB Garamond:mode=node;-liga;letterspace=0.2" at 10pt
\x Thefoofi

\font\x = "EB Garamond:mode=node;+liga;letterspace=0.2" at 10pt
\x Thefoofi

\font\x = "EB Garamond:mode=node;+liga;+dlig;letterspace=0.2" at 10pt
\x Thefoofi
\bye

(BTW: Is there a possibility to selectively disable the breaking of ligatures? I reckon it could somehow be done with the keeptogether and/or keepligatures functions, but I don't really understand their intended use.)

[phi-gamma]

Thanks for reporting, I’ll look into it. Regarding your other question:

(BTW: Is there a possibility to selectively disable the breaking of ligatures? I reckon it could somehow be done with the keeptogether and/or keepligatures functions, but I don't really understand their intended use.)

keeptogether() and keepligatures() are predicates: they receive a pair of glyph nodes or a ligature node respectively and depending on whether they return true or false the node processor will insert a kern or leave them untouched. I’ve put together a demo:

• pln-letterspace-5.tex
• pln-letterspace-5.lua

It’s very underoptimized to keep it simple (unnecessary string building etc.), but it shows one approach.

[schlcht]

Thank you very much for the demo, this should get me started.

[phi-gamma]

As of today (2013-08-31) this should no longer occur.
@schlcht please verify.

[phi-gamma]

Closing this. @schlcht please reopen if you disagree.