tile-stencil/src/style-func.js

Load a MapLibre style document and parse it into Javascript functions

import { convertIfColor, buildInterpolator } from "./interpolate.js";

export function autoGetters(properties = {}, defaults) {
  return Object.entries(defaults).reduce((d, [key, val]) => {
    d[key] = buildStyleFunc(properties[key], val);
    return d;
  }, {});
}

function buildStyleFunc(style, defaultVal) {
  if (style === undefined) {
    return getConstFunc(defaultVal);

  } else if (typeof style !== "object" || Array.isArray(style)) {
    return getConstFunc(style);

  } else {
    return getStyleFunc(style);

  } // NOT IMPLEMENTED: zoom-and-property functions
}

function getConstFunc(rawVal) {
  const val = convertIfColor(rawVal);
  const func = () => val;
  return Object.assign(func, { type: "constant" });
}

function getStyleFunc(style) {
  const { type, property = "zoom", base = 1, stops } = style;

  const getArg = (property === "zoom")
    ? (zoom) => zoom
    : (zoom, feature) => feature.properties[property];

  const getVal = (type === "identity")
    ? convertIfColor
    : buildInterpolator(stops, base);

  if (!getVal) return console.log("style: " + JSON.stringify(style) +
    "\nERROR in tile-stencil: unsupported style!");

  const styleFunc = (zoom, feature) => getVal(getArg(zoom, feature));

  return Object.assign(styleFunc, {
    type: (property === "zoom") ? "zoom" : "property",
    property,
  });
}