[NTG-context] If a Font Has Ligature Glyphs But No Feature?

[Bruce Horrocks]

> On 20 Jul 2022, at 05:31, Michael Urban via ntg-context <ntg-context at ntg.nl> wrote:
> 
> Aside from purchasing a real font product from Linotype at enormous expense and hoping it is better equipped, is there a way to coerce ConTeXt into using the ligature glyphs for fi and fl?

Yes - I had to do the same for a font called Venetian 301 for which I found these 4 files:

Filename			Name as it appears to MacOS
--------			--------------------------
Venetian301BT-Roman.otf		Venetian 301 Regular
Venetian301BT-Italic.otf	Venetian 301 Italic
Venetian301BT-Bold.otf		Venetian 301 Bold
venetian-301-demi-bt.ttf	Venetian Dm BT Demi

They each had the fi and fl ligatures, but at different character positions depending on which file, and they weren't recognised by default. So I used the following code to add them (and add en and em dash substitution as well).

%% ---- start
\startluacode
    fonts.handlers.otf.addfeature {
        name = "v1",	-- these character substitutions will be applied to venetian-301-demi-bt
        type = "ligature",
        data = {
            [0xF001] = { "f", "i" },
            [0xF002] = { "f", "l" },
        }
    }
    fonts.handlers.otf.addfeature {
        name = "v2",	-- these character substitutions will be applied to Venetian301BT
        type = "ligature",
        data = {
            [0xFB01] = { "f", "i" },
            [0xFB02] = { "f", "l" },
        }
    }
    fonts.handlers.otf.addfeature {
        name = "v3",	-- these character substitutions will be applied to both
        type = "ligature",
        data = {
            [0x2013] = { "-", "-" },      -- en dash
            [0x2014] = { "-", "-", "-" }, -- em dash
        }
    }
\stopluacode
\definefontfeature [venetian-301-demi-ligatures] [v1=yes,v3=yes]
\definefontfeature [venetian-301-BT-ligatures]   [v2=yes,v3=yes]

\starttypescript [serif] [myBookFont]
  \definefontsynonym [Serif]       [file:venetian-301-demi-bt] [features=venetian-301-demi-ligatures]
  \definefontsynonym [SerifBold]   [file:Venetian301BT-Bold]   [features=venetian-301-BT-ligatures]
  \definefontsynonym [SerifItalic] [file:Venetian301BT-Italic] [features=venetian-301-BT-ligatures]
\stoptypescript
%% ---- end

Note that the names v1, v2 and v3 are entirely arbitrary. Also, the \starttypescript section sets the font features to be just those I've defined - potentially losing whatever 'default' would provide. But since the font doesn't seem to have a lot of features in the first place I've so far not noticed any problems. I'm sure a real expert could tell you how to retain 'default' and add the ligatures, if needed.

Regards,
—
Bruce Horrocks
Hampshire, UK