@nowline/export-png

@nowline/export-png

Rasterizes a Nowline-rendered SVG to PNG using @resvg/resvg-js (a Rust→WASM SVG rasterizer). Bundled into the nowline CLI.

License: Apache 2.0 Part of: lolay/nowline monorepo Spec: specs/handoffs/m2c.md § 3

Install

pnpm add @nowline/export-png @nowline/export-core @nowline/renderer

Usage

import { layoutRoadmap } from '@nowline/layout';
import { renderSvg } from '@nowline/renderer';
import { resolveFonts } from '@nowline/export-core';
import { exportPng } from '@nowline/export-png';

const svg = await renderSvg(layoutRoadmap(file, resolved, { theme }));
const fonts = (await resolveFonts({ headless: true })).pair();
const png = await exportPng({ ast, resolved, model, sourcePath, today }, svg, {
    scale: 2,
    fonts,
});

// `png` is a Uint8Array of PNG bytes.

Options

Option	Default	Notes
scale	2	Pixel-density multiplier. Scales the root <svg width/height> before rasterization. Common values: 1, 1.5, 2, 3.
background	model	Override the background color (CSS color or transparent).
fonts	resolveFonts()	Pre-resolved sans/mono pair. If omitted, the exporter calls @nowline/export-core's resolver itself.
resvgOptions	(none)	Escape hatch for resvg-js options. Use sparingly.

The scale factor is applied by rewriting the root SVG element's width/height attributes — resvg-js 2.6.x ignores fitTo when fontBuffers is set, so this is the workaround the package uses to keep custom-font rendering deterministic.

Determinism

• WASM module: lazy-loaded on first call; cached process-globally. The _resetResvgModule() test seam clears the cache.
• loadSystemFonts: false — only fonts passed via fontBuffers are visible to resvg, so identical input produces identical bytes regardless of host machine.
• Font bytes come from @nowline/export-core's 5-step resolver. With --headless (or the equivalent option here), the bundled DejaVu pair is used and the output is byte-stable across macOS / Linux / Windows.
• The PNG header bytes are \x89PNG\r\n\x1a\n followed by an IHDR chunk whose dimensions equal scale × <svg width> × scale × <svg height>.

Snapshot tests

Snapshots live in test/__snapshots__/. Regenerate with vitest -u. Hash tests in test/export-png.test.ts confirm byte-stability across re-renders.

License

Apache-2.0.