jscad-projection.js

const projection = function (params, ...csgs) {
  const defaults = {
    plane: [0, 0, 1, 1],// x, y, z, w : as an array, magically simple !! 
    cut: false
  }
  const {plane, cut} = Object.assign({}, defaults, params)

  const [x, y, z, w] = plane
  // for now we still have to convert arrays to something way more complicated internally , sigh
  const orthobasis = new CSG.OrthoNormalBasis(new CSG.Plane(new CSG.Vector3D([x, y, z]), w)) 

  const results = csgs.map(function (csg) {
    if (cut) {
      return csg.sectionCut(orthobasis)
    } else {
      let cags = []
      csg.polygons
        .map(function (polygon) {
          let cag = polygon.projectToOrthoNormalBasis(orthobasis)
          if (cag.sides.length > 0) {
            cags.push(cag)
          }
        })
      let result = new CAG().union(cags)
      return result
    }
  })

  return results.length > 1 ? results : results[0]
}