Headless rendering

@oh-just-another/headless renders scene documents to SVG/PNG in plain Node.js — no DOM, no browser, no canvas shim. (Server-side by definition, so no live demo on this page.)

pnpm add @oh-just-another/headless
pnpm add @resvg/resvg-js   # optional peer dep — only needed for renderToPng

Scene JSON → SVG + PNG

Both functions accept an in-memory Scene or the JSON string that @oh-just-another/serialization emits (parsed and validated for you):

// render.mjs — run with: node render.mjs
import { readFile, writeFile } from "node:fs/promises";
import { renderToSvg, renderToPng } from "@oh-just-another/headless";

const sceneJson = await readFile("scene.json", "utf8");

// SVG — synchronous, pure JS, no optional deps.
await writeFile("out.svg", renderToSvg(sceneJson));

// PNG — async, rasterized via @resvg/resvg-js (Rust → WASM).
await writeFile("out.png", await renderToPng(sceneJson, { scale: 2 }));

Options

Option	Applies to	Effect
width / height	both	Output size in CSS px; defaults to the scene viewport's size
measureText	both	Custom text measurer (defaults to a built-in approximation)
skipInstall	both	Skip the implicit installBuiltinRenderers() when you registered your own shape renderers
scale	PNG	Device-pixel factor; 2 = retina. Default 1
background	PNG	Colour behind the scene. Default white
fitToWidth / fitToHeight	PNG	Fit output to N device px (aspect preserved); overrides scale

Notes

• renderToSvg(scene, options?) returns a string; renderToPng(scene, options?) returns a Promise<Uint8Array> and throws with an install hint if @resvg/resvg-js is missing. SVG-only consumers never pay for the ~3 MB WASM payload.
• Typical uses: rendering diagrams in CI, OG images, thumbnails for a document list, server-side export endpoints. Combine with data conversion to turn Mermaid/dot/drawio input into images.