ttf-parser 0.3.0

ttf-parser

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

Features

• A high-level API.
• Zero allocations.
• Zero dependencies.
• no_std compatible.
• Fast.
• Stateless.
• Simple and maintainable code (no magic numbers).

Supported TrueType features

• (cmap) Character to glyph index mapping using glyph_index() method. All subtable formats except Mixed Coverage (8) are supported.
• (cmap) Character variation to glyph index mapping using glyph_variation_index() method.
• (glyf) Glyph outlining using outline_glyph() method.
• (hmtx) Retrieving a glyph's horizontal metrics using glyph_hor_metrics() method.
• (vmtx) Retrieving a glyph's vertical metrics using glyph_ver_metrics() method.
• (kern) Retrieving a glyphs pair kerning using glyphs_kerning() method.
• (maxp) Retrieving a total number of glyphs using number_of_glyphs() method.
• (name) Listing all name records using names() method.
• (name) Retrieving a font's family name using family_name() method.
• (name) Retrieving a font's PostScript name using post_script_name() method.
• (post) Retrieving a font's underline metrics name using underline_metrics() method.
• (head) Retrieving a font's units per EM value using units_per_em() method.
• (hhea) Retrieving a generic font info using: ascender(), descender(), height() and line_gap() methods.

Supported OpenType features

• (CFF ) Glyph outlining using outline_glyph() method.
• (OS/2) Retrieving a font kind using is_regular(), is_italic(), is_bold() and is_oblique() methods.
• (OS/2) Retrieving a font's weight using weight() method.
• (OS/2) Retrieving a font's width using width() method.
• (OS/2) Retrieving a font's X height using x_height() method.
• (OS/2) Retrieving a font's strikeout metrics using strikeout_metrics() method.
• (OS/2) Retrieving a font's subscript metrics using subscript_metrics() method.
• (OS/2) Retrieving a font's superscript metrics using superscript_metrics() method.

Methods' computational complexity

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. Currently, it takes 60% more time to outline all glyphs in SourceSansPro-Regular.otf (which uses CFF) rather than in SourceSansPro-Regular.ttf.

test outline_cff  ... bench:   1,617,138 ns/iter (+/- 1,261)
test outline_glyf ... bench:     995,771 ns/iter (+/- 2,801)

Here is some methods benchmarks:

test outline_glyph_276_from_cff  ... bench:       1,203 ns/iter (+/- 4)
test outline_glyph_276_from_glyf ... bench:         796 ns/iter (+/- 3)
test outline_glyph_8_from_cff    ... bench:         497 ns/iter (+/- 3)
test from_data_otf               ... bench:         372 ns/iter (+/- 5)
test outline_glyph_8_from_glyf   ... bench:         347 ns/iter (+/- 1)
test family_name                 ... bench:         269 ns/iter (+/- 3)
test from_data_ttf               ... bench:          72 ns/iter (+/- 3)
test glyph_index_u41             ... bench:          24 ns/iter (+/- 0)
test glyph_2_hor_metrics         ... bench:           8 ns/iter (+/- 0)

family_name is expensive, because it allocates a String and the original data is stored as UTF-16 BE.

Some methods are too fast, so we execute them 1000 times to get better measurements.

test x_height            ... bench:         847 ns/iter (+/- 0)
test units_per_em        ... bench:         564 ns/iter (+/- 2)
test strikeout_metrics   ... bench:         564 ns/iter (+/- 0)
test width               ... bench:         287 ns/iter (+/- 0)
test ascender            ... bench:         279 ns/iter (+/- 1)
test subscript_metrics   ... bench:         279 ns/iter (+/- 0)

Safety

• The library must not panic. Any panic considered as a critical bug and should be reported.
• The library has a single unsafe block for array casting.

Alternatives

• font-rs - Mainly a glyph outline extractor. No documentation. Has less features. Doesn't support CFF. Has a lot of magic numbers.
• stb_truetype - Mainly a glyph outline extractor. Isn't allocation free. Has less features. Doesn't support CFF. Has a lot of magic numbers. Uses panic a lot.
• truetype - Simply maps TrueType data to the Rust structures. Doesn't actually parses the data. Isn't allocation free. Has some unsafe. Unmaintained.
• font - Very similar to ttf-parser, but supports less features. Still an alpha. Isn't allocation free.
• fontdue - Parser and rasterizer. In alpha state. Allocates all the required data. Doesn't support CFF.

(revised on 2019-09-24)

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.