skera is a Rust library and binary for subsetting a font file according to provided input.

Use --keep-everything or the library's Plan::keep_everything to select all glyphs, Unicode mappings, names, layout items, and tables. The preset also preserves glyph names, legacy naming records, the .notdef outline, and Unicode range bits. CLI list operations then tailor those selections in command line order, while boolean flags and custom glyph mappings add to the preset. Tables are still subset and can be optimized or re-encoded.

CFF1 and CFF2 outlines support subsetting with retained subroutines, optional desubroutinization (--desubroutinize), hint removal (--no-hinting), and retained glyph IDs (--retain-gids). CFF1 subsetting includes CID fonts, custom and expert encodings, glyph names, and seac component closure. Retained-subroutine output requires each call's subroutine number to be an immediately preceding literal in the same program. Fonts using caller-supplied or computed targets require --desubroutinize; retained mode rejects them. Hint removal flattens individual glyphs when deleting their operands or changing caller-dependent mask boundaries would modify a shared program.

Use --text (or -t) to select Unicode characters directly from UTF-8 text. Text and Unicode selectors share the same selection set and support ordered replacement, addition (+=), and removal (-=) operations.

To use skera in your Rust project, add it via cargo:

cargo add skera

To install the skera command-line tool, use cargo install with the cli feature enabled:

cargo install skera --features cli

To subset a font using the command-line tool:

skera --path <INPUT_PATH> --unicodes <UNICODES> --output-file <OUTPUT_PATH>

For a full list of available options and flags, run:

skera --help

How-To: Profile a Skera Binary using Samply

Install samply using Cargo:

cargo install samply

Add the following configuration to your root Cargo.toml:

[profile.release]
debug = true

cargo build --release -p skera --features="cli"

Run the generated release executable using samply record. Replace with your compiled binary's name and <args...> with any execution arguments:

samply record target/release/skera <args...>

example:

samply record target/release/skera font-file --unicodes=* --output-file=out

Once your binary finishes execution, samply automatically starts a local web server and prints a URL to the console:

Server listening on http://127.0.0.1:3000
Press Ctrl+C to stop.

Open the provided link in your web browser. The browser will open the Firefox Profiler interface, populated with your recorded run's call tree, flame graph, and timeline views.

If samply is not suitable for your target environment, you may consider these alternative options:

cargo-flamegraph: A tool that utilizes perf (on Linux) or dtrace (on macOS) to generate a static vector-graphic .svg flame graph.

cargo install cargo-flamegraph
cargo flamegraph -p skera --features="cli"

perf (Linux-only): The standard system profiler on Linux, useful for command-line profiling and capturing kernel-level events.

perf record -g -- target/release/skera
perf report