[NTG-context] Inconsistent behavior: \addfontfeature and CLD local function

* [NTG-context] Inconsistent behavior: \addfontfeature and CLD local function
@ 2023-08-20 15:33 Hamid,Idris
  2023-08-20 15:45 ` [NTG-context] " Hans Hagen
  0 siblings, 1 reply; 3+ messages in thread
From: Hamid,Idris @ 2023-08-20 15:33 UTC (permalink / raw)
  To: ntg-context

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Dear gang,

For \addfeature and the like, a virtual font feature defined in terms of a CLD local function behaves differently from other font features. MWE:

==============
\startluacode
local function squeeze(tfmdata)
    for k, v in next, tfmdata.characters do
        v.width = 1.75 * (v.height or 0)
        v.depth  = 1.75 * (v.depth  or 0)
    end
end

local specification = {
    name        = "sqtfm",
    description = "test",
    manipulators = {
        base = squeeze,
        node = squeeze,
    }
}

fonts.handlers.otf.features.register(specification)
\stopluacode

\definefontfeature[forceno]
                  [mode=node,
                   script=latn]

\definefontfeature[forceyes]
                  [mode=node,
                   script=latn,
                   smcp=force,
                   sqtfm=force]
                   % smcp=yes,
                   % sqtfm=yes]

\showglyphs

\startTEXpage[offset=1em]
\definedfont[texgyretermes-regular*forceyes]
% \definedfont[texgyretermes-regular*forceno]
% \addfeature{forceyes}

abcdefg
\stopTEXpage
==============
 You may toggle these lines:

\definedfont[texgyretermes-regular*forceyes]
% \definedfont[texgyretermes-regular*forceno]
% \addfeature{forceyes}

With
\definedfont[texgyretermes-regular*forceyes]
active we get the expected result: small caps plus some negative squeeze (= spread in this case).

With
\definedfont[texgyretermes-regular*forceno]
\addfeature{forceyes}
active we get an *unexpected* result: small caps but no negative squeeze.

(Similar results occur if we toggle the "=force" lines with the "=yes" lines, but the larger project of which this is the MWE uses the force key.)

Clue: A CLD with a feature defined via fonts.handlers.otf.addfeature doesn't seem to have this problem:

==============

\startluacode
local function squeeze(tfmdata)
    for k, v in next, tfmdata.characters do
        v.width = 1.75 * (v.height or 0)
        v.depth  = 1.75 * (v.depth  or 0)
    end
end

local specification = {
    name        = "sqtfm",
    description = "test",
    manipulators = {
        base = squeeze,
        node = squeeze,
    }
}

fonts.handlers.otf.features.register(specification)

fonts.handlers.otf.addfeature {
    name = "stest",
    type = "substitution",
    data = {
        a = "X",
        b = "P",
    }
}
\stopluacode

\definefontfeature[forceno]
                  [mode=node,
                   script=latn]

\definefontfeature[forceyes]
                  [mode=node,
                   script=latn,
                   % % smcp=force,
                   sqtfm=force,
                   stest=force]
                   % % smcp=yes,
                   % sqtfm=yes,
                   % stest=yes]

\showglyphs

\startTEXpage[offset=1em]
\definedfont[texgyretermes-regular*forceyes]
% \definedfont[texgyretermes-regular*forceno]
% \addfeature{forceyes}

abcdefg
\stopTEXpage
==============

So only the local-function feature appears to exhibit this inconsistency.

What is the explanation for this inconsistent behavior?
Is there a way to get the expected result for \addfeature etc.?

Thank you in advance.

Best wishes
Idris

--
Professor Idris Samawi Hamid
Department of Philosophy
Colorado State University
Fort Collins, CO 80523

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