@jscad/modeling/src/operations/extrusions/slice/repair.js

Constructive Solid Geometry (CSG) Library for JSCAD

const vec3 = require('../../../maths/vec3')
const create = require('./create')

/*
 * Mend gaps in a 2D slice to make it a closed polygon
 */
const repair = (slice) => {
  if (!slice.edges) return slice
  let edges = slice.edges
  const vertexMap = new Map() // string key to vertex map
  const edgeCount = new Map() // count of (in - out) edges

  // Remove self-edges
  edges = edges.filter((e) => !vec3.equals(e[0], e[1]))

  // build vertex and edge count maps
  edges.forEach((edge) => {
    const inKey = edge[0].toString()
    const outKey = edge[1].toString()
    vertexMap.set(inKey, edge[0])
    vertexMap.set(outKey, edge[1])
    edgeCount.set(inKey, (edgeCount.get(inKey) || 0) + 1) // in
    edgeCount.set(outKey, (edgeCount.get(outKey) || 0) - 1) // out
  })

  // find vertices which are missing in or out edges
  const missingIn = []
  const missingOut = []
  edgeCount.forEach((count, vertex) => {
    if (count < 0) missingIn.push(vertex)
    if (count > 0) missingOut.push(vertex)
  })

  // pairwise distance of bad vertices
  missingIn.forEach((key1) => {
    const v1 = vertexMap.get(key1)

    // find the closest vertex that is missing an out edge
    let bestDistance = Infinity
    let bestReplacement
    missingOut.forEach((key2) => {
      const v2 = vertexMap.get(key2)
      const distance = vec3.distance(v1, v2)
      if (distance < bestDistance) {
        bestDistance = distance
        bestReplacement = v2
      }
    })
    console.warn(`slice.repair: repairing vertex gap ${v1} to ${bestReplacement} distance ${bestDistance}`)

    // merge broken vertices
    edges = edges.map((edge) => {
      if (edge[0].toString() === key1) return [bestReplacement, edge[1]]
      if (edge[1].toString() === key1) return [edge[0], bestReplacement]
      return edge
    })
  })

  return create(edges)
}

module.exports = repair