@chartdown/render-svg

Deterministic, seeded SVG renderer for Chartdown — plain-text TTRPG maps. Same input, same seed, byte-identical SVG. Zero runtime dependencies beyond @chartdown/core.

import { renderSource } from "@chartdown/render-svg";

const { svg, diagnostics } = renderSource(source, { mode: "gm" });
// options: mode ("player" | "gm"), theme (Chartdown theme source), level

Player mode strips GM secrets fail-closed. Themes are themselves Chartdown documents. Try the playground or see the spec.

The resolved scene

render resolves a whole scene per call — positions, outlines, half-planes, organic finishing — and discards it. resolveScene returns it instead, for a host that draws with its own primitives rather than consuming the SVG (ADR 0051).

import { resolveScene } from "@chartdown/render-svg";

const scene = resolveScene(doc, { mode: "gm" });
// { schemaVersion, mapType, mode, unit, extent, levels?, features, walls?, diagnostics }

scene.schema.json sits beside this README and is the normative shape; examples/gumdrop-vale/gumdrop-vale.scene.json is a worked one. The schema versions with this package, not with SPEC_VERSION — a renderer output is not language.

Geometry is in the map's own units. A region's extent: units, cells on a battlemap, hexes on a hexcrawl — never canvas pixels, because a canvas number moves with detail: and ADR 0037 forbids a rendering choice from moving geometry. A grid map's geometry is a cell union rather than an outline: a structure occupies cells, and spec 06 §3 derives the outline from them, so the derived perimeter rides along.

Geometry is what is drawn, after organic finishing — the outline the coast has, not the one the document declared. Your coast therefore agrees with this renderer's coast on the same document, which is the point.

There is no ink in it. No stroke widths, no font sizes, no legibility floor, no zone insets, no glyph scatter. Each feature carries its derivation chain, so you apply your own theme through the same fallback this renderer uses; a theme document is already the interchange format for the rest.

Two exclusions worth knowing before you build on it:

• Placed labels are not in v1. A feature carries where its label wants to go, not where arbitration put it, so two implementations will put the same things in the same places and label them differently. Arbitration is interleaved with emission and the placer is stateful; hoisting it is its own change.
• detail: is an input to determinism on a region. A scene is a pure function of (document, seed, renderer version, mode, detail:). Organic finishing runs in canvas space, so a larger canvas grows texture and the dependence propagates through relational placement — examples/vessany's coast has 400 vertices at overview and 665 at reference. Resolve at the detail: you intend to draw, and do not mix scenes from two. Grid maps have no such knob and are unaffected.