How to use the vega-scenegraph.Gradient function in vega-scenegraph

function q_legend_def(scale) {
    // setup legend marks
    var titles = dl.extend(m.titles, legendTitle(config)),
        gradient = dl.extend(m.gradient, legendGradient(config)),
        labels = dl.extend(m.labels, hLegendLabels(config)),
        grad = new Gradient();

    // setup color gradient
    var dom = scale.domain(),
        min = dom[0],
        max = dom[dom.length-1],
        f = scale.copy().domain([min, max]).range([0,1]);

    var stops = (scale.type !== 'linear' && scale.ticks) ?
      scale.ticks.call(scale, 15) : dom;
    if (min !== stops[0]) stops.unshift(min);
    if (max !== stops[stops.length-1]) stops.push(max);

    for (var i=0, n=stops.length; i

export default function(scale, p0, p1, count, group) {
  scale = getScale(scale, (group || this).context);

  const gradient = Gradient(p0, p1);

  let stops = scale.domain(),
      min = stops[0],
      max = peek(stops),
      fraction = identity

  if (!(max - min)) {
    // expand scale if domain has zero span, fix #1479
    scale = (scale.interpolator
      ? get('sequential')().interpolator(scale.interpolator())
      : get('linear')().interpolate(scale.interpolate()).range(scale.range())
    ).domain([min=0, max=1]);
  } else {
    fraction = scaleFraction(scale, min, max);
  }