Source: grid/hexbin.js

import { createSteppedArray } from "../helpers/createSteppedArray.js";
/**
 * @function hexbin
 * @summary Compute a hexbin grid.
 * @description The `hexbin()` function allows to create a hexbin grid in SVG coordinates.
 * @param {number} [step = 50] - Step of the grid.
 * @param {array} [start = [0,0]] - Positioning coordinates [x,y].
 * @param {number} [width = 1000] - Width of the grid
 * @param {number} [height = 500] - Height of the grid
 * @param {boolean} [overflow = true] - Depending on the step you choose, the grid may be smaller than the bounding box defined by with and height. With overflow = true, the grid is allowed to exceed the bounding box.
 * @returns {object} - A GeoJSON FeatureCollection
 * @example
 * geogrid.hexbin({step:30})
 */
export function hexbin({
  step = 50,
  width = 1000,
  height = 500,
  start = [0, 0],
  overflow = true,
} = {}) {
  const w = step;
  const size = w / Math.sqrt(3);
  const h = size * 1.5;

  const x0 = overflow ? start[0] - w / 2 : start[0];
  //const x0 = start[0];
  const y0 = overflow ? start[1] - size : start[1];

  const yEnd = overflow ? height + y0 + size * 2 : height + y0 - size;
  const y = createSteppedArray(y0 + size, yEnd, h);

  const grid = [];

  // Pour chaque ligne Y
  y.forEach((yy, row) => {
    const offset = (row % 2) * (w / 2);
    let xEnd = overflow ? width + x0 : width + x0 - w - w / 2;

    const x = createSteppedArray(x0 + offset + w / 2, xEnd, w);

    x.forEach((xx) => {
      if (xx <= width + x0) {
        grid.push([xx, yy]);
      }
    });

    if (x[x.length - 1] < width + x0) {
      grid.push([x[x.length - 1] + w, yy]);
    }
  });

  const features = grid.map(([cx, cy], i) => {
    const hex = [];
    for (let a = 0; a < 6; a++) {
      const angle = (Math.PI / 180) * (60 * a - 30);
      hex.push([cx + size * Math.cos(angle), cy + size * Math.sin(angle)]);
    }
    hex.push(hex[0]);

    return {
      type: "Feature",
      geometry: {
        type: "Polygon",
        coordinates: [hex],
      },
      properties: {
        index: i,
      },
    };
  });

  return {
    type: "FeatureCollection",
    grid: "hexbin",
    geo: false,
    features: features,
  };
}