README.md

earcut4j

This triangulation library is based on the javascript version located in @mapbox/earcut

The algorithm

The library implements a modified ear slicing algorithm, optimized by 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 by Martin Held and Triangulation by Ear Clipping by David Eberly.

Installation

Download the latest version:

Maven dependency:

<dependency>
  <groupId>io.github.earcut4j</groupId>
  <artifactId>earcut4j</artifactId>
  <version>2.2.2</version>
</dependency>

Or when using Gradle:

dependencies {
  compile "io.github.earcut4j:earcut4j:2.2.2"
}

Usage

List<Integer> triangles = Earcut.earcut(new double[] { 10,0, 0,50, 60,60, 70,10 }, null, 2);
// returns [1,0,3, 3,2,1]

Signature: earcut(double[] data, int[] holeIndices, int dim).

• data 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).
• dim 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.

// triangulating a polygon with a hole
List<Integer> triangles = Earcut.earcut(new double[] { 0, 0, 100, 0, 100, 100, 0, 100, 20, 20, 80, 20, 80, 80, 20, 80 }, new int[] { 4 }, 2);
// [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
List<Integer> triangles = Earcut.earcut(new double[] { 10, 0, 1, 0, 50, 2, 60, 60, 3, 70, 10, 4 }, null, 3);
// [1,0,3, 3,2,1]

If you pass a single vertice as a hole, Earcut treats it as a Steiner point.