cover.js

export default function(x, y, z) {
  if (isNaN(x = +x) || isNaN(y = +y) || isNaN(z = +z)) return this; // ignore invalid points

  var x0 = this._x0,
      y0 = this._y0,
      z0 = this._z0,
      x1 = this._x1,
      y1 = this._y1,
      z1 = this._z1;

  // If the octree has no extent, initialize them.
  // Integer extent are necessary so that if we later double the extent,
  // the existing octant boundaries don’t change due to floating point error!
  if (isNaN(x0)) {
    x1 = (x0 = Math.floor(x)) + 1;
    y1 = (y0 = Math.floor(y)) + 1;
    z1 = (z0 = Math.floor(z)) + 1;
  }

  // Otherwise, double repeatedly to cover.
  else {
    var t = x1 - x0 || 1,
        node = this._root,
        parent,
        i;

    while (x0 > x || x >= x1 || y0 > y || y >= y1 || z0 > z || z >= z1) {
      i = (z < z0) << 2 | (y < y0) << 1 | (x < x0);
      parent = new Array(8), parent[i] = node, node = parent, t *= 2;
      switch (i) {
        case 0: x1 = x0 + t, y1 = y0 + t, z1 = z0 + t; break;
        case 1: x0 = x1 - t, y1 = y0 + t, z1 = z0 + t; break;
        case 2: x1 = x0 + t, y0 = y1 - t, z1 = z0 + t; break;
        case 3: x0 = x1 - t, y0 = y1 - t, z1 = z0 + t; break;
        case 4: x1 = x0 + t, y1 = y0 + t, z0 = z1 - t; break;
        case 5: x0 = x1 - t, y1 = y0 + t, z0 = z1 - t; break;
        case 6: x1 = x0 + t, y0 = y1 - t, z0 = z1 - t; break;
        case 7: x0 = x1 - t, y0 = y1 - t, z0 = z1 - t; break;
      }
    }

    if (this._root && this._root.length) this._root = node;
  }

  this._x0 = x0;
  this._y0 = y0;
  this._z0 = z0;
  this._x1 = x1;
  this._y1 = y1;
  this._z1 = z1;
  return this;
}