Expand description
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 usestatic, 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.