rust-fontconfig

Pure-Rust rewrite of the Linux fontconfig library (no system dependencies) - using ttf-parser and allsorts

NOTE: Also works on Windows and macOS - without external dependencies!

Motivation

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 versions (ttf-parser, allsorts) all check 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 their 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
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_std support 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)

```rust 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);

} ```

MIT