@jscad/modeling/src/operations/expansions/offsetGeom2.js

Constructive Solid Geometry (CSG) Library for JSCAD

const geom2 = require('../../geometries/geom2')
const poly2 = require('../../geometries/poly2')

const offsetFromPoints = require('./offsetFromPoints')

/*
 * Create a offset geometry from the given geom2 using the given options (if any).
 * @param {Object} options - options for offset
 * @param {Float} [options.delta=1] - delta of offset (+ to exterior, - from interior)
 * @param {String} [options.corners='edge'] - type corner to create during of expansion; edge, chamfer, round
 * @param {Integer} [options.segments=16] - number of segments when creating round corners
 * @param {geom2} geometry - geometry from which to create the offset
 * @returns {geom2} offset geometry, plus rounded corners
 */
const offsetGeom2 = (options, geometry) => {
  const defaults = {
    delta: 1,
    corners: 'edge',
    segments: 0
  }
  const { delta, corners, segments } = Object.assign({ }, defaults, options)

  if (!(corners === 'edge' || corners === 'chamfer' || corners === 'round')) {
    throw new Error('corners must be "edge", "chamfer", or "round"')
  }

  // convert the geometry to outlines, and generate offsets from each
  const outlines = geom2.toOutlines(geometry)
  const newoutlines = outlines.map((outline) => {
    const level = outlines.reduce((acc, polygon) => acc + poly2.arePointsInside(outline, poly2.create(polygon)), 0)
    const outside = (level % 2) === 0

    options = {
      delta: outside ? delta : -delta,
      corners,
      closed: true,
      segments
    }
    return offsetFromPoints(options, outline)
  })

  // create a composite geometry from the new outlines
  const allsides = newoutlines.reduce((sides, newoutline) => sides.concat(geom2.toSides(geom2.fromPoints(newoutline))), [])
  return geom2.create(allsides)
}

module.exports = offsetGeom2