Pure-Rust rewrite of the Linux fontconfig library (no system
dependencies) - using allsorts as a font parser in order to
parse .woff, .woff2, .ttc, .otf and .ttf
NOTE: Also works on Windows and macOS - without external dependencies!
There are a number of reasons why I want to have a pure-Rust version of fontconfig:
- fontconfig with all dependencies (expat and freetype) is ~190.000 lines of C (extremely bloated for what it does)
- fontconfig, freetype, expat and basically any kind of parsing in C is a common attack vector (via maliciously crafted fonts). The Rust version (allsorts) checks the boundaries before accessing memory, so attacks via font files should be less common.
- it gets rid of the cmake / cc dependencies necessary to build azul on Linux
- fontconfig isn't really a "hard" library to rewrite, it just parses fonts and selects fonts by name
- Rust has existing xml parsers and font parsers, just use those
- It allows fontconfig libraries to be purely statically linked
- Font parsing / loading can be easily multithreaded (parsing font files in parallel)
- It reduces the number of necessary non-Rust dependencies on Linux for azul to 0
- fontconfig (or at least the Rust bindings) do not allow you to store an in-memory cache, only an on-disk cache, requiring disk access on every query (= slow)
- Potential
no_stdsupport for minimal binaries?
Now for the more practical reasons:
- libfontconfig 0.12.x sometimes hangs and crashes (see issue)
- libfontconfig introduces build issues with cmake / cc (see issue)
- To support font fallback in CSS selectors and text runs based on Unicode ranges, you have to do several calls into C, since fontconfig doesn't handle that
- The rust rewrite uses multithreading and memory mapping, since that is faster than reading each file individually
- The rust rewrite only parses the font tables necessary to select the name, not the entire font
- The rust rewrite uses very few allocations (some are necessary because of UTF-16 / UTF-8 conversions and multithreading lifetime issues)
use rust_fontconfig::{FcFontCache, FcPattern};
fn main() {
let cache = FcFontCache::build(); let result =
cache.query(&FcPattern {
name: Some(String::from("Arial")),
.. Default::default()
});
println!("font path: {:?}", result);
}- cache building: ~90ms for ~530 fonts
- cache query: ~4µs
MIT