vega-lite/src/compile/mark/encode/zindex.ts

Vega-Lite is a concise high-level language for interactive visualization.

import {isValueDef} from '../../../channeldef.js';
import {isPathMark} from '../../../mark.js';
import {signalOrValueRef} from '../../common.js';
import {UnitModel} from '../../unit.js';
import {wrapCondition} from './conditional.js';

export function zindex(model: UnitModel) {
  const {encoding, mark} = model;
  const order = encoding.order;

  if (!isPathMark(mark) && isValueDef(order)) {
    return wrapCondition({
      model,
      channelDef: order,
      vgChannel: 'zindex',
      mainRefFn: (cd) => signalOrValueRef(cd.value),
      invalidValueRef: undefined, // zindex encoding doesn't have continuous scales and thus can't have invalid values
    });
  }
  return {};
}