This may be q question for Harfbuzz, so forgive me if this is the wrong place.
OTF/TTF font support is pretty good in Writer. Optional features can be enabled with
:<feature_id> appended to font name in styles. Other features are enabled by default. However the list of accepted features is not readily accessible.
Where can it be found?
What is the impact of enabling Asian or complex text layout on features? Are some of them considered script dependent in Writer?
My question is motivated by modifications I am applying on a TTF font (cursive style) to manage glyph shape variations in a user-friendly manner, i.e. the glyph is automatically selected without user action. The font targets a narrow subset of the Latin script. Since glyphs are connected, fine adjustments cannot be made with kerning tables. This is solved with ‘liga’ (mandatory ligatures) and not ‘dlig’ (discretionary ligatures) which would require user adding
:dlig in font selection.
Contextual shapes are handled with contextual replacement but rules are difficult to get them right and require exhaustive definition of character sets, making the rule vulnerable to incomplete or incorrect set definition.
A simplified, more reliable approach, would be possible if feature ‘fina’ is always taken into account. ‘fina’ and the like are primarily used in West Asian scripts like Arabic to select the proper shape (here, final variant). ‘curs’ would also be of great help.