tituli.features

OpenType features a style asks for, applied without a shaper where they can be (tituli#4).

A style may ask for features by tag (TextStyle(features=("tnum",)): tabular figures, so the digits of a changing number do not change width). Whether the font HAS a feature is a property of its bytes, so a face records which of the requested ones it applies (tituli.fonts.Face.applied_features); a feature the font lacks is not applied, and the caller can say so.

Pillow applies features only through libraqm, which is often absent, and its embedded face always lays out without it. So the features that are glyph SUBSTITUTIONS one for one (GSUB lookup type 1, also inside an extension lookup: tnum, lnum, onum, pnum, zero, smcp …) are applied here, from the font’s own tables: featured_glyphs() gives the substituted glyph names and featured_length() their advances. Measurement (length()) and outlines (tituli.run_outline()) read both, so they cannot disagree. A requested feature built from any other kind of lookup needs a shaper and is refused (FeatureError).

Needs fontTools (tituli[outlines]), like the outlines.

Functions

font_features(path[, index])	The GSUB feature tags a font declares.
applied_features(face)	The face's requested features that its font has, in request order.
featured_glyphs(face, text)	The glyph name each character of text draws with the face's applied features (None where the font has no glyph for it).
featured_length(face, text)	Advance width of text in pixels, from the substituted glyphs' own advances (the font's design metrics, scaled to the face's size).

Exceptions

FeatureError

A requested feature cannot be applied as asked; the message says what would.

exception tituli.features.FeatureError

Bases: ValueError

A requested feature cannot be applied as asked; the message says what would.

tituli.features.applied_features(face)

The face’s requested features that its font has, in request order.

Return type:

tuple[str, ...]

tituli.features.featured_glyphs(face, text)

The glyph name each character of text draws with the face’s applied features (None where the font has no glyph for it).

Return type:

list[str | None]

tituli.features.featured_length(face, text)

Advance width of text in pixels, from the substituted glyphs’ own advances (the font’s design metrics, scaled to the face’s size).

Return type:

float

tituli.features.font_features(path, index=0)

The GSUB feature tags a font declares.

Return type:

frozenset[str]

>>> from tituli import EMBEDDED, resolve_face
>>> "tnum" in font_features(resolve_face(EMBEDDED, size=12).path)
False