weighted-straight-skeleton

This is a TypeScript library that wraps the basic functionality of CGAL's weighted straight skeleton implementation using Wasm (WebAssembly). You can use this library to generate weighted straight skeletons of polygons with or without holes.

Installation

npm i weighted-straight-skeleton

Usage

This library supports both arrays of points (SkeletonBuilder.buildFromPolygon) and GeoJSON polygons (SkeletonBuilder.buildFromGeoJSON).

Input requirements

• Input polygon must have at least one ring.
• The first ring is always the outer ring, and the rest are inner rings.
• Outer rings must be counter-clockwise oriented and inner rings must be clockwise oriented.
• All rings must be weakly simple.
• Each ring must have a duplicate of the first vertex at the end.
• If weights or angles are provided, the number of weights or angles must match the number of vertices in the polygon.

Example

add to your package.json

	"weighted-straight-skeleton": "github:pcace/weighted-straight-skeleton#main"

then run npm install

Using Weights

import { SkeletonBuilder, Skeleton } from 'weighted-straight-skeleton'

// Contains two rings: outer and inner.
const polygon = [
	[
		[-1, -1],
		[0, -12],
		[1, -1],
		[12, 0],
		[1, 1],
		[0, 12],
		[-1, 1],
		[-12, 0],
		[-1, -1]
	], [
		[-1, 0],
		[0, 1],
		[1, 0],
		[0, -1],
		[-1, 0]
	]
];

// optionally send weights for each polygon vertex
const weights = [
	[1.5, 1.0, 1.5, 1.8, 1.5, 1.8, 1.5, 1.8, 1.5],
	[1.5, 1.8, 1.5, 1.5, 1.5]
];

// Initialize the Wasm module by calling init() once.
SkeletonBuilder.init().then(() => {
	const result = SkeletonBuilder.buildFromPolygonWithWeights(polygon, weights);
	
	// Check if the skeleton was successfully constructed
	if (result !== null) {
		for (const vertex of result.vertices) {
			// Do something with vertices
		}

		for (const polygon of result.polygons) {
			// Do something with polygons
		}
	}
});

Using Angles

import { SkeletonBuilder, Skeleton } from 'weighted-straight-skeleton'

// Contains two rings: outer and inner.
const polygon = [
	[
		[-1, -1],
		[0, -12],
		[1, -1],
		[12, 0],
		[1, 1],
		[0, 12],
		[-1, 1],
		[-12, 0],
		[-1, -1]
	], [
		[-1, 0],
		[0, 1],
		[1, 0],
		[0, -1],
		[-1, 0]
	]
];

// optionally send angles for each polygon vertex
const angles = [
	[45, 90, 45, 60, 45, 60, 45, 60, 45],
	[45, 60, 45, 45, 45]
];

// Initialize the Wasm module by calling init() once.
SkeletonBuilder.init().then(() => {
	const result = SkeletonBuilder.buildFromPolygonWithAngles(polygon, angles);
	
	// Check if the skeleton was successfully constructed
	if (result !== null) {
		for (const vertex of result.vertices) {
			// Do something with vertices
		}

		for (const polygon of result.polygons) {
			// Do something with polygons
		}
	}
});

Development

Note: Tested with emscripten version 3.1.16

1. Clone this repository.
2. Run npm i to install dependencies.
3. Optionally, rebuild the Wasm module:
   1. Install Emscripten and make sure that it's in your PATH.
   2. cd src/core, then sh ./install_libraries.sh to download and unpack all dependencies.
   3. mkdir build && cd build to create a build directory.
   4. emcmake cmake .. to generate the build files.
   5. emmake make to build the Wasm module. Rerun this whenever your .cpp files change.
4. Run npm run build to build the library or npm run dev to start a development server that watches for changes.

References

• CGAL straight skeleton user manual