jtBaseApp/node_modules/topojson-client/src/transform.js

import identity from "./identity.js";

export default function(transform) {
  if (transform == null) return identity;
  var x0,
      y0,
      kx = transform.scale[0],
      ky = transform.scale[1],
      dx = transform.translate[0],
      dy = transform.translate[1];
  return function(input, i) {
    if (!i) x0 = y0 = 0;
    var j = 2, n = input.length, output = new Array(n);
    output[0] = (x0 += input[0]) * kx + dx;
    output[1] = (y0 += input[1]) * ky + dy;
    while (j < n) output[j] = input[j], ++j;
    return output;
  };
}