layerforge

Deterministic preview compositor for layered product images. Give it a JSON manifest and receive AVIF and WebP files for cards, detail views, and zoom.

Features

• Composites up to 128 layers with masks, blend modes, offsets, scale, and rotation.
• Fills a masked layer with a material color, or tiles an uploaded material texture.
• Optional texture tiling and relief displacement through seamless-texture.
• Shape plugins reshape a layer before texturing. The package ships no product profiles.
• Resizes one lossless master into six artifacts: card (320), detail (800), and zoom (1600), each in AVIF and WebP.
• Runs as a library, a CLI, or an HTTP service with one serialized queue and a subprocess worker.

Install

npm install layerforge

Node.js 22 or later is required.

Library

import { renderLayerArtifactSet, renderLayerManifest } from "layerforge";

const master = await renderLayerManifest(manifest, { assetOrigin: "https://shop.example" });
const artifacts = await renderLayerArtifactSet(manifest, {
  assetOrigin: "https://shop.example",
  shapes,
  onTiming: (event) => console.log(event),
});

renderLayerManifest returns a lossless WebP master. renderLayerArtifactSet returns the six responsive files.

Manifest

{
  "version": 2,
  "kind": "layers_v2",
  "revision_id": "10000000-0000-4000-8000-000000000001",
  "output": { "width": 1200, "height": 900, "background": "#F7F2E8" },
  "layers": [
    {
      "id": "20000000-0000-4000-8000-000000000001",
      "layer_key": "base",
      "role": "base",
      "path": "/media/base.png",
      "content_hash": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
      "mask_path": null,
      "mask_content_hash": null,
      "material_texture_path": null,
      "material_texture_content_hash": null,
      "blend_mode": "normal",
      "opacity_basis_points": 10000,
      "offset_x_micropixels": 0,
      "offset_y_micropixels": 0,
      "scale_x_millionths": 1000000,
      "scale_y_millionths": 1000000,
      "rotation_millidegrees": 0,
      "z_order": 10
    }
  ]
}

Layer field	Meaning
id, layer_key, role	Identity. IDs and keys must be unique.
path, content_hash	Source image. The SHA-256 hash is a 64-character hex string.
blend_mode	normal, multiply, screen, overlay, or destination_in.
mask_path, mask_content_hash	Optional alpha mask, resized to the layer. Set both to null when absent.
material_color_hex	Optional solid fill through the source alpha.
material_texture_path, material_texture_content_hash	Optional tiled texture. Set both to null when absent.
material_texture_surface	Apply seamless tiling and relief displacement.
material_texture_scale_millionths	Texture scale, 100000 to 8000000.
shape_profile, shape_width_mm	Optional shape plugin and its width.
opacity_basis_points	0 to 10000, where 10000 is opaque.
offset_x_micropixels, offset_y_micropixels	Center offset in millionths of a pixel.
scale_x_millionths, scale_y_millionths	Layer scale in millionths.
rotation_millidegrees	Rotation in thousandths of a degree.
z_order	Draw order. Ties sort by layer_key, then id.

Asset paths must stay under the asset prefixes (/media/ and /cad/ by default) and must have no query, fragment, or .. segment. Set assetPrefixes to change the allowed prefixes.

Validation

validateLayerManifest checks a manifest without rendering and reports every problem. Each error has a JSON-pointer-style path and a message:

import { validateLayerManifest } from "layerforge";

const { valid, errors } = validateLayerManifest(manifest);
for (const { path, message } of errors) {
  console.error(`${path}: ${message}`);
}

normalizeLayerManifest applies the same checks and returns the normalized manifest with the layers sorted by z_order. It throws an error with one line per problem when the manifest is invalid. A render validates the manifest first, so an invalid manifest fails with the same errors before any asset is loaded.

The CLI checks a file without rendering:

layerforge --validate manifest.json

It prints one path: message line per error. The exit code is 0 for a valid manifest, 1 for an invalid manifest, and 2 for a usage error.

schema/layer-manifest.schema.json is a JSON Schema draft 2020-12 for the manifest. Editors pick it up through the $schema property:

{
  "$schema": "./node_modules/layerforge/schema/layer-manifest.schema.json",
  "version": 2,
  "kind": "layers_v2"
}

The published URL is https://raw.githubusercontent.com/M1chlCZ/layerforge/main/schema/layer-manifest.schema.json. The schema covers the default asset prefixes (/media/ and /cad/). validateLayerManifest also checks the rules JSON Schema cannot express: unique layer id and layer_key values, the output pixel budget, and custom assetPrefixes. Unknown properties are accepted at every level; the renderer ignores top-level extras and passes layer extras to shape plugins.

Shape plugins

A shape plugin reshapes or recolors one layer before texturing:

export const shapes = {
  rounded: async (source, { widthMm, layer }) => sharp(source)
    .resize({ width: widthMm * 10, fit: "fill" })
    .png()
    .toBuffer(),
};

Pass the module to the library through shapes, to the CLI through --shapes FILE, or to the service through SHAPES_MODULE. A layer with an unknown profile fails the render. A layer with a shape profile skips the material color fill, because the plugin owns the look of the layer.

CLI

layerforge render manifest.json --out preview --asset-origin https://shop.example --shapes shapes.mjs
layerforge --validate manifest.json
layerforge serve --port 3100 --asset-origin https://shop.example

The CLI reads ASSET_ORIGIN, SHAPES_MODULE, and PORT when the flag is absent.

Service

• POST /render with the manifest as JSON returns multipart/mixed with the six artifacts and X-Preview-Role, X-Preview-Width, and X-Preview-Height headers.
• GET /health returns {"status":"ok"}.
• One render runs at a time. Each render runs in a subprocess with a 65 second limit.
• The asset origin is trusted. Content hashes are format-checked, so configure an origin that you control.

docker build -t layerforge .
docker run --rm -p 3100:3100 -e ASSET_ORIGIN=https://shop.example layerforge

Limits

Item	Limit
Output	6000 per axis, 16 megapixels
Layers	128
Asset	16 MiB
Manifest	1 MiB

Third-party licenses

• sharp and its @img/sharp-* platform packages use Apache-2.0.
• The @img/sharp-libvips-* platform packages use LGPL-3.0-or-later. npm installs them for the target platform; they are not part of this package.
• Keep the license texts when you redistribute a built image or a bundled copy.

Development

npm ci
npm test
npm run benchmark

License

MIT. See LICENSE.