fontcull

Crates.iofontcull
lib.rsfontcull
version2.0.1
created_at2025-11-30 21:58:46.080003+00
updated_at2026-01-23 13:10:14.759719+00
descriptionPure Rust font subsetting library
homepagehttps://github.com/bearcove/fontcull
repositoryhttps://github.com/bearcove/fontcull
max_upload_size
id1958898
size76,146
Amos Wenger (fasterthanlime)

documentation

README

fontcull

Font subsetting library. Subset fonts to only include glyphs that are actually used.

Features

  • No Python - No fonttools/pyftsubset dependency, just Rust + C++ for WOFF2
  • Multiple formats - Supports TTF, OTF, and WOFF2 input
  • WOFF2 output - Compress subsetted fonts to WOFF2 for web delivery
  • Static analysis (optional) - Parse HTML/CSS to detect font usage
  • Optional WOFF2 - Disable for pure Rust builds without C++ dependency

Feature flags

Feature Default Description
woff2 Yes WOFF2 compression/decompression (requires C++)
static-analysis No HTML/CSS parsing for font usage detection

For a pure Rust build without WOFF2 support:

[dependencies]
fontcull = { version = "2", default-features = false }

Usage

use fontcull::{subset_font_to_woff2, decompress_font};
use std::collections::HashSet;

// Load a font file
let font_data = std::fs::read("MyFont.ttf").unwrap();

// Define which characters to keep
let chars: HashSet<char> = "Hello World".chars().collect();

// Subset and compress to WOFF2
let woff2 = subset_font_to_woff2(&font_data, &chars).unwrap();
std::fs::write("MyFont-subset.woff2", woff2).unwrap();

With WOFF2 input

use fontcull::{decompress_font, subset_font_data, compress_to_woff2};
use std::collections::HashSet;

let woff2_input = std::fs::read("MyFont.woff2").unwrap();

// Decompress → Subset → Recompress
let decompressed = decompress_font(&woff2_input).unwrap();
let chars: HashSet<char> = "Hello".chars().collect();
let subsetted = subset_font_data(&decompressed, &chars).unwrap();
let woff2_output = compress_to_woff2(&subsetted).unwrap();

Static HTML/CSS analysis

Enable the static-analysis feature to parse HTML and CSS for font usage:

[dependencies]
fontcull = { version = "2", features = ["static-analysis"] }

use fontcull::{analyze_fonts, extract_css_from_html, subset_font_to_woff2};

let html = r#"<html>
  <head><style>body { font-family: "MyFont"; }</style></head>
  <body><p>Hello World</p></body>
</html>"#;

let css = extract_css_from_html(html);
let analysis = analyze_fonts(html, &css);

if let Some(chars) = analysis.chars_per_font.get("MyFont") {
    let font_data = std::fs::read("MyFont.ttf").unwrap();
    let woff2 = subset_font_to_woff2(&font_data, chars).unwrap();
    std::fs::write("MyFont-subset.woff2", woff2).unwrap();
}

API

Core functions

  • subset_font_data(font_data, chars) - Subset font to TTF bytes
  • subset_font_data_unicode(font_data, unicodes) - Subset using u32 codepoints

WOFF2 functions (requires woff2 feature)

  • subset_font_to_woff2(font_data, chars) - Subset and compress to WOFF2
  • subset_font_to_woff2_unicode(font_data, unicodes) - Subset to WOFF2 using codepoints
  • decompress_font(font_data) - Decompress WOFF2 to TTF/OTF
  • compress_to_woff2(font_data) - Compress TTF/OTF to WOFF2

Format detection

  • FontFormat::detect(data) - Detect font format from magic bytes

License

MIT

Commit count: 35

cargo fmt