earcut/README.md

## Earcut

The fastest and smallest JavaScript polygon triangulation library. 2.5KB gzipped.

[![Build Status](https://travis-ci.org/mapbox/earcut.svg?branch=master)](https://travis-ci.org/mapbox/earcut)
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#### The algorithm

The library implements a modified ear slicing algorithm,
optimized by [z-order curve](http://en.wikipedia.org/wiki/Z-order_curve) hashing
and extended to handle holes, twisted polygons, degeneracies and self-intersections
in a way that doesn't _guarantee_ correctness of triangulation,
but attempts to always produce acceptable results for practical data.

It's based on ideas from
[FIST: Fast Industrial-Strength Triangulation of Polygons](http://www.cosy.sbg.ac.at/~held/projects/triang/triang.html) by Martin Held
and [Triangulation by Ear Clipping](http://www.geometrictools.com/Documentation/TriangulationByEarClipping.pdf) by David Eberly.

#### Why another triangulation library?

The aim of this project is to create a JS triangulation library
that is **fast enough for real-time triangulation in the browser**,
sacrificing triangulation quality for raw speed and simplicity,
while being robust enough to handle most practical datasets without crashing or producing garbage.
Some benchmarks using Node 0.12:

(ops/sec)         | pts  | earcut    | libtess  | poly2tri | pnltri
------------------| ---- | --------- | -------- | -------- | ---------
OSM building      | 15   | _648,935_ | _50,640_ | _61,501_ | _122,966_
dude shape        | 94   | _34,379_  | _10,339_ | _8,784_  | _11,172_
holed dude shape  | 104  | _26,849_  | _8,883_  | _7,494_  | _2,130_
complex OSM water | 2523 | _564_     | _77.54_  | failure  | failure
huge OSM water    | 5667 | _116_     | _29.30_  | failure  | failure

The original use case it was created for is [Mapbox GL](https://www.mapbox.com/mapbox-gl), WebGL-based interactive maps.

If you want to get correct triangulation even on very bad data with lots of self-intersections
and earcut is not precise enough, take a look at [libtess.js](https://github.com/brendankenny/libtess.js).

#### Usage

```js
var triangles = earcut([10,0, 0,50, 60,60, 70,10]); // returns [1,0,3, 3,2,1]
```

Signature: `earcut(coords[, holeIndices, numDimensions = 2])`.

* `coords` is a flat array of vertice coordinates like `[x0,y0, x1,y1, x2,y2, ...]`.
* `holeIndices` is an array of hole indices if any
  (e.g. `[5, 8]` for a 12-vertice input would mean one hole with vertices 5–7 and another with 8–11).
* `numDimensions` is the number of coordinates per vertice in the input array (`2` by default).

Each group of three vertice indices in the resulting array forms a triangle.

```js
// triangulating a polygon with a hole
earcut([0,0, 100,0, 100,100, 0,100,  20,20, 80,20, 80,80, 20,80], [4]);
// [3,0,4, 5,4,0, 3,4,7, 5,0,1, 2,3,7, 6,5,1, 2,7,6, 6,1,2]

// triangulating a polygon with 3d coords
earcut([10,0,1, 0,50,2, 60,60,3, 70,10,4], null, 3);
// [1,0,3, 3,2,1]
```

If your input is a multi-dimensional array (e.g. [GeoJSON Polygon](http://geojson.org/geojson-spec.html#polygon)),
you can convert it to the format expected by Earcut with [a couple lines of codes](viz/viz.js#L99-L115).

#### Install

NPM and Browserify:

```bash
npm install earcut
```

Browser builds:

```bash
npm install
npm run build-dev # builds dist/earcut.dev.js, a dev version with a source map
npm run build-min # builds dist/earcut.min.js, a minified production build
```

Running tests:

```bash
npm test
```

![](https://cloud.githubusercontent.com/assets/25395/5778431/e8ec0c10-9da3-11e4-8d4e-a2ced6a7d2b7.png)

#### Ports to other languages

- [mapbox/earcut.hpp](https://github.com/mapbox/earcut.hpp) (C++11)
- [Cawfree/earcut-j](https://github.com/Cawfree/earcut-j) (Java)

#### Changelog

##### 2.0.0 (Apr 30, 2015)

- **Breaking**: changed the API to accept a flat input array of vertices with hole indices and return triangle indices.
  It makes the indexed output much faster than it was before (up to 30%) and improves memory footprint.

##### 1.4.2 (Mar 18, 2015)

- Fixed another rare edge case with a tiny hole in a huge polygon.

##### 1.4.1 (Mar 17, 2015)

- Fixed a rare edge case that led to incomplete triangulation.

##### 1.4.0 (Mar 9, 2015)

- Fixed indexed output to produce indices not multiplied by dimension and work with any number of dimensions.

##### 1.3.0 (Feb 24, 2015)

- Added a second argument to `earcut` that switches output format to flat vertex and index arrays if set to `true`.

##### 1.2.3 (Feb 10, 2015)

- Improved performance (especially on recent v8) by avoiding `Array` `push` with multiple arguments.

##### 1.2.2 (Jan 27, 2015)

- Significantly improved performance for polygons with self-intersections
  (e.g. big OSM water polygons are now handled 2-3x faster)

##### 1.2.1 (Jan 26, 2015)

- Significantly improved performance on polygons with high number of vertices
  by using z-order curve hashing for vertice lookup.
- Slightly improved overall performance with better point filtering.

##### 1.1.0 (Jan 21, 2015)

- Improved performance on polygons with holes by switching from Held to Eberly hole elimination algorithm
- More robustness fixes and tests

##### 1.0.1 — 1.0.6 (Jan 20, 2015)

- Various robustness improvements and fixes.

##### 1.0.0 (Jan 18, 2015)

- Initial release.