Crate cosmic::iced_widget::renderer::graphics::text::cosmic_text::fontdb

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fontdb is a simple, in-memory font database with CSS-like queries.

§Features

  • The database can load fonts from files, directories and raw data (Vec<u8>).
  • The database can match a font using CSS-like queries. See Database::query.
  • The database can try to load system fonts. Currently, this is implemented by scanning predefined directories. The library does not interact with the system API.
  • Provides a unique ID for each font face.

§Non-goals

  • Advanced font properties querying.
    The database provides only storage and matching capabilities. For font properties querying you can use ttf-parser.

  • A font fallback mechanism.
    This library can be used to implement a font fallback mechanism, but it doesn’t implement one.

  • Application’s global database.
    The database doesn’t use static, therefore it’s up to the caller where it should be stored.

  • Font types support other than TrueType.

§Font vs Face

A font is a collection of font faces. Therefore, a font face is a subset of a font. A simple font (*.ttf/*.otf) usually contains a single font face, but a font collection (*.ttc) can contain multiple font faces.

fontdb stores and matches font faces, not fonts. Therefore, after loading a font collection with 5 faces (for example), the database will be populated with 5 FaceInfo objects, all of which will be pointing to the same file or binary data.

§Performance

The database performance is largely limited by the storage itself. We are using ttf-parser, so the parsing should not be a bottleneck.

On my machine with Samsung SSD 860 and Gentoo Linux, it takes ~20ms to load 1906 font faces (most of them are from Google Noto collection) with a hot disk cache and ~860ms with a cold one.

On Mac Mini M1 it takes just 9ms to load 898 fonts.

§Safety

The library relies on memory-mapped files, which is inherently unsafe. But since we do not keep the files open it should be perfectly safe.

If you would like to use a persistent memory mapping of the font files, then you can use the unsafe Database::make_shared_face_data function.

Structs§

  • Database
    A font database.
  • FaceInfo
    A single font face info.
  • ID
    A unique per database face ID.
  • Query
    A database query.
  • Weight
    Specifies the weight of glyphs in the font, their degree of blackness or stroke thickness.

Enums§