polygon-tools

Polygon tools.

install

npm i polygon-tools

browser

The minified code is availabe through S3:

https://fpcdn.s3.amazonaws.com/apps/polygon-tools/0.4.6/polygon-tools.min.js

build

Build minified javascript for use in browser:

npm run build

The library is exposed as PolygonTools.

varpolygon=[[0,0],[100,0],[100,100],[0,100]];vararea=PolygonTools.polygon.area(polygon);

documentation

Documentation is available here.

examples

• Union
• Subtract
• Intersection
• Triangulate
• Tesselator
• Polygon Winding

polygon

Summary of polygon methods:

• area(pts)
• normal(pts)
• centroid(pts)
• winding(pts)
• is_cw(pts)
• is_ccw(pts)

import{polygon}from'polygon-tools';constPOLYGON=[[0,0],[100,0],[100,100],[0,100]];// Signed area - 2D onlyletarea=polygon.area(POLYGON);// Polygon normal - both 2D and 3D polygonsletnormal=polygon.normal(POLYGON);// Polygon centroid - 2D onlyletcentroid=polygon.centroid(POLYGON);// Polygon winding - 2D onlyletwinding=polygon.winding(POLYGON);// result is one of:const{WINDING_CW,WINDING_CCW,WINDING_UNKNOWN}=polygon;// test for WINDING_CWpolygon.is_cw(POLYGON);// test for WINDING_CCWpolygon.is_ccw(POLYGON);

boolean operations

• union (...polygons)
• subtract (...polygons)
• intersection (a, b)

import{polygon}from'polygon-tools';constPOLY_A=[[0,0],[100,0],[100,100],[0,100]];constPOLY_B=[[50,50],[150,50],[150,150],[50,150]];// union(polyA, polyB, polyN, ...)letunion=polygon.union(POLY_A,POLY_B);// subtract(polyA, polyB, polyN, ...)// NOTE: poly B..N are subtracted from Aletsubtract=polygon.subtract(POLY_A,POLY_B);// intersection(polyA, polyB)letintersection=polygon.intersection(POLY_A,POLY_B);

triangulation

• triangulate(polygon, holes)

import{polygon}from'polygon-tools';constPOLYGON=[[0,0],[100,0],[100,100],[0,100]];constHOLE=[[30,30],[30,70],[70,70],[70,30]];// returns an array of triangleslettriangles=polygon.triangulate(POLYGON,[HOLE]);

using the tesselator

Instead of the convenience methods above, the tesselator can also be used directly. Different vertex sizes can be used so vertex attributes like UVs and normals are correctly interpolated.

import{tesselator}from'polygon-tools';constPOLYGON=[[0,0],[100,0],[100,100],[0,100]];constHOLE=[[30,30],[30,70],[70,70],[70,30]];letoptions={polygons: [POLYGON],holes: [HOLE],vertexSize: 2,windingRule: tesselator.GLU_TESS_WINDING_POSITIVE,boundaryOnly: false,normal: null,autoWinding: true};lettriangles=tesselator.run(options);

use with PIXI

Suppose we want a textured polygon with holes. In such cases we cannot use polygon.subtract because any interior hole is returned as another polygon. To create polygons with holes we need use triangulation.

Assuming we have the triangles (see above) and some texture:

letsprite=newPIXI.Sprite(texture);letmask=newPIXI.Graphics();// create pathsletpaths=triangles.map(tri=>{returntri.reduce((p,v)=>{returnp.push(v[0],v[1]);},[]);});paths.forEach(path=>{mask.beginFill(0xff0000);mask.drawPolygon(path);});sprite.mask=mask;sprite.addChild(mask);