vega-util/src/transform.js

JavaScript utilities for Vega.

import {identity} from './accessors.js';
import peek from './peek.js';
import toNumber from './toNumber.js';

const exp = sign =>
  x => sign * Math.exp(x);

const log = sign =>
  x => Math.log(sign * x);

const symlog = c =>
  x => Math.sign(x) * Math.log1p(Math.abs(x / c));

const symexp = c =>
  x => Math.sign(x) * Math.expm1(Math.abs(x)) * c;

const pow = exponent =>
  x => x < 0 ? -Math.pow(-x, exponent) : Math.pow(x, exponent);

function pan(domain, delta, lift, ground) {
  const d0 = lift(domain[0]),
        d1 = lift(peek(domain)),
        dd = (d1 - d0) * delta;

  return [
    ground(d0 - dd),
    ground(d1 - dd)
  ];
}

export function panLinear(domain, delta) {
  return pan(domain, delta, toNumber, identity);
}

export function panLog(domain, delta) {
  var sign = Math.sign(domain[0]);
  return pan(domain, delta, log(sign), exp(sign));
}

export function panPow(domain, delta, exponent) {
  return pan(domain, delta, pow(exponent), pow(1/exponent));
}

export function panSymlog(domain, delta, constant) {
  return pan(domain, delta, symlog(constant), symexp(constant));
}

function zoom(domain, anchor, scale, lift, ground) {
  const d0 = lift(domain[0]),
        d1 = lift(peek(domain)),
        da = anchor != null ? lift(anchor) : (d0 + d1) / 2;

  return [
    ground(da + (d0 - da) * scale),
    ground(da + (d1 - da) * scale)
  ];
}

export function zoomLinear(domain, anchor, scale) {
  return zoom(domain, anchor, scale, toNumber, identity);
}

export function zoomLog(domain, anchor, scale) {
  const sign = Math.sign(domain[0]);
  return zoom(domain, anchor, scale, log(sign), exp(sign));
}

export function zoomPow(domain, anchor, scale, exponent) {
  return zoom(domain, anchor, scale, pow(exponent), pow(1/exponent));
}

export function zoomSymlog(domain, anchor, scale, constant) {
  return zoom(domain, anchor, scale, symlog(constant), symexp(constant));
}