Umbrella, wireframe lines from Vec[]

gistfile1.txt

import {
  comp,
  juxtR,
  map,
  mapcat,
  partition,
  reducer,
  transduce,
  wrapSides,
} from '@thi.ng/transducers'
import { Vec } from '@thi.ng/vectors'
import { ModelSpec } from '@thi.ng/webgl'

/**
 * Reducer to collect unique points by ID.
 * Expects tuples of `[id, point]`
 */
const uniquePoints = () => {
  let ids = new Set()
  return reducer<number[], [number, Vec]>(
    () => [],
    (acc, x) => (ids.has(x[0]) ? acc : (ids.add(x[0]), acc.push(...x[1]), acc)),
  )
}

/**
 * Reducer to collect point IDs
 * Expects tuples of `[id, point]`
 */
const pushID = () =>
  reducer<number[], [number, Vec]>(
    () => [],
    (acc, x) => (acc.push(x[0]), acc),
  )

/**
 * Converts iterable of polygons (each a Vec[]) to a
 * single combined ModelSpec.
 *
 * @param polys
 * @param size - dimensionality
 */
const wireframePolys = (polys: Iterable<Vec[]>, size = 3): Partial<ModelSpec> => {
  let i = 0
  const [points, indices] = transduce(
    comp(
      mapcat(poly =>
        partition(
          2,
          1,
          wrapSides(
            map(p => [i++, p], poly),
            0,
            1,
          ),
        ),
      ),
      mapcat(x => <[number, Vec][]>x),
    ),
    // juxtaposed reducer
    juxtR(uniquePoints(), pushID()),
    polys,
  )
  return {
    attribs: {
      position: { data: new Float32Array(points), size },
    },
    indices: {
      data: new Uint16Array(indices),
    },
    uniforms: {},
    num: indices.length,
    mode: 1, // gl.LINES
  }
}

const polys = [
  [
    [0, 0, 0],
    [1, 0, 0],
    [1, 1, 0],
  ],
  [
    [0, 0, 1],
    [1, 0, 1],
    [1, 1, 1],
    [0, 1, 1],
  ],
  [
    [0, 0, 2],
    [1, 0, 2],
    [1, 2, 2],
  ],
]

console.log(wireframePolys(polys))
// {
//   attribs: {
//       position: {
//         data: Float32Array [
//             0, 0, 0, 1, 0, 0, 1, 1, 0,
//             0, 0, 1, 1, 0, 1, 1, 1, 1,
//             0, 1, 1, 0, 0, 2, 1, 0, 2,
//             1, 2, 2
//         ],
//         size: 3
//     }
//   },
//   indices: {
//     data: Uint16Array [
//       0, 1, 1, 2, 2, 0, 3,
//       4, 4, 5, 5, 6, 6, 3,
//       7, 8, 8, 9, 9, 7
//     ]
//   },
//   uniforms: {},
//   num: 20,
//   mode: 1
// }