kymostudio-core (Rust)

The pure-Rust core for kymostudio: an SVG → PNG/PDF rasterizer (built on resvg / svg2pdf) and the shared diagram engine. No browser, no headless Chrome, no C/Cairo/Skia system dependencies.

The engine half parses diagram-as-code into kymo's model, lays it out, and serializes to the .kymo.json interchange format the Python/JS front-ends consume — written once in Rust instead of duplicated per language. First subsystem: Mermaid flowchart import (mermaid_to_kymojson). See docs/specs/format-mermaid/.

One core crate, compiled to three targets from a single source via feature flags — so the Rust CLI, the Python package, and the JS/browser playground all share the exact same resvg engine (resvg is CSS-class-aware, the reason the project avoids cairosvg):

| Target | Feature | Build tool | Consumer | |--------|---------|-----------|----------| | Native lib | system-fonts (default) | cargo | kymostudio CLI crate | | Python extension (abi3) | python | maturin → wheel | packages/python | | wasm (browser + Node) | wasm | wasm-pack → pkg | packages/js, website playground |

Core functions: svg_to_png(svg: &[u8], scale: f32) and svg_to_pdf(svg: &[u8]) (rasterizer), plus mermaid_to_kymojson(src: &str) (engine). Each binding (src/python.rs, src/wasm.rs) is a thin façade.

CLI — kymo

The kymo command-line tool lives in the sibling kymostudio crate (a thin front-end over this core). Install it with cargo install kymostudio.

Build each target

# Native lib + tests
cargo test

# The `kymo` CLI (sibling crate)
cargo build --release --manifest-path ../kymostudio/Cargo.toml   # -> ../kymostudio/target/release/kymo

# Python wheel (abi3, one wheel for CPython ≥ 3.10)
maturin build --release --out dist        # -> dist/kymostudio_core-*-abi3-*.whl
#   import _kymostudio_core; _kymostudio_core.svg_to_png(svg_bytes, scale)

# wasm (browser + Node) — system-fonts OFF (no fs/mmap on wasm).
# Plain `wasm` is the LEAN module (no svgToPng/svgToPdf — 0.9 MB vs 6.1 MB raw);
# add `pdf` for the full surface the npm/vscode artifacts ship.
wasm-pack build --target web --out-dir pkg --out-name kymostudio_core \
  -- --no-default-features --features wasm,pdf
#   import { svgToPng } from './pkg/kymostudio_core.js'

CI builds and smoke-tests all of the above across Linux/macOS/Windows — see .github/workflows/rust.yml.

Library use (Rust)

let svg = std::fs::read("in.svg")?;
let png: Vec<u8> = kymostudio_core::svg_to_png(&svg, 1.0)?;
std::fs::write("out.png", png)?;

The version is kept in lockstep with the rest of the monorepo (Cargo.toml → version).