ttf-parser

A high-level, safe, zero-allocation TrueType font parser.

Can be used as Rust and as C library.

Features

• A high-level API, for people who doesn't know how TrueType works internally. Basically, no direct access to font tables.
• A C API.
• Zero heap allocations.
• Zero unsafe.
• Zero dependencies.
• no_std/WASM compatible.
• Fast. See the Performance section.
• Stateless. No mutable parsing methods.
• Simple and maintainable code (no magic numbers).

Safety

• The library must not panic. Any panic considered as a critical bug and should be reported.
• The library forbids the unsafe code.
• No heap allocations, so crash due to OOM is not possible.
• All recursive methods have a depth limit.
• Technically, should use less than 64KiB of stack in the worst case scenario.
• Most of arithmetic operations are checked.
• Most of numeric casts are checked.

Alternatives

It's very hard to compare different libraries, so we are using table-based comparison. There are roughly three types of TrueType tables:

• A table with a list of properties (like head, OS/2, etc.).
  If a library tries to parse it at all then we mark it as supported.
• A table that contains a single type of data (glyf, CFF (kinda), hmtx, etc.).
  Can only be supported or not.
• A table that contains multiple subtables (cmap, kern, GPOS, etc.).
  Can be partially supported and we note which subtables are actually supported.

Legend:

• ✓ - supported
• ~ - partial
• nothing - not supported

Notes:

1. Matching points are not supported.
2. When using from Rust, the library binary overhead depends on used methods and can vary from 10KiB up to 100KiB.
   When using from C, we have to include the Rust's std too, which blows up the size.
3. Depends on build flags.

Performance

TrueType fonts designed for fast querying, so most of the methods are very fast. The main exception is glyph outlining. Glyphs can be stored using two different methods: using Glyph Data format and Compact Font Format (pdf). The first one is fairly simple which makes it faster to process. The second one is basically a tiny language with a stack-based VM, which makes it way harder to process.

The benchmark tests how long it takes to outline all glyphs in the font.

Note: FreeType is surprisingly slow, so I‘m worried that I’ve messed something up.

And here are some methods benchmarks:

test outline_glyph_276_from_cff2 ... bench:         778 ns/iter (+/- 15)
test from_data_otf_cff           ... bench:         760 ns/iter (+/- 13)
test from_data_otf_cff2          ... bench:         709 ns/iter (+/- 25)
test outline_glyph_276_from_cff  ... bench:         678 ns/iter (+/- 41)
test outline_glyph_276_from_glyf ... bench:         649 ns/iter (+/- 11)
test outline_glyph_8_from_cff2   ... bench:         476 ns/iter (+/- 14)
test from_data_ttf               ... bench:         352 ns/iter (+/- 11)
test glyph_name_post_276         ... bench:         223 ns/iter (+/- 5)
test outline_glyph_8_from_cff    ... bench:         261 ns/iter (+/- 13)
test outline_glyph_8_from_glyf   ... bench:         281 ns/iter (+/- 5)
test family_name                 ... bench:         183 ns/iter (+/- 102)
test glyph_name_cff_276          ... bench:         109 ns/iter (+/- 1)
test glyph_index_u41             ... bench:          16 ns/iter (+/- 0)
test glyph_name_cff_8            ... bench:           7 ns/iter (+/- 0)
test glyph_name_post_8           ... bench:           2 ns/iter (+/- 0)
test subscript_metrics           ... bench:           2 ns/iter (+/- 0)
test glyph_hor_advance           ... bench:           2 ns/iter (+/- 0)
test glyph_hor_side_bearing      ... bench:           2 ns/iter (+/- 0)
test glyph_name_8                ... bench:           1 ns/iter (+/- 0)
test ascender                    ... bench:           1 ns/iter (+/- 0)
test underline_metrics           ... bench:           1 ns/iter (+/- 0)
test strikeout_metrics           ... bench:           1 ns/iter (+/- 0)
test x_height                    ... bench:           1 ns/iter (+/- 0)
test units_per_em                ... bench:         0.5 ns/iter (+/- 0)
test width                       ... bench:         0.2 ns/iter (+/- 0)

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.