@deck.gl/experimental-layers/src/tile-layer/utils/viewport-util.js

Experimental layers for deck.gl

import {lngLatToWorld} from 'viewport-mercator-project';

const TILE_SIZE = 512;

function getBoundingBox(viewport) {
  const corners = [
    viewport.unproject([0, 0]),
    viewport.unproject([viewport.width, 0]),
    viewport.unproject([0, viewport.height]),
    viewport.unproject([viewport.width, viewport.height])
  ];

  return [
    corners.reduce((minLng, p) => (minLng < p[0] ? minLng : p[0]), 180),
    corners.reduce((minLat, p) => (minLat < p[1] ? minLat : p[1]), 90),
    corners.reduce((maxLng, p) => (maxLng > p[0] ? maxLng : p[0]), -180),
    corners.reduce((maxLat, p) => (maxLat > p[1] ? maxLat : p[1]), -90)
  ];
}

function pixelsToTileIndex(a) {
  return Math.floor(a / TILE_SIZE);
}

/**
 * Returns all tile indices in the current viewport. If the current zoom level is smaller
 * than minZoom, return an empty array. If the current zoom level is greater than maxZoom,
 * return tiles that are on maxZoom.
 */
export function getTileIndices(viewport, maxZoom, minZoom) {
  const z = Math.floor(viewport.zoom);
  if (minZoom && z < minZoom) {
    return [];
  }

  viewport = new viewport.constructor({
    ...viewport,
    zoom: z
  });

  const bbox = getBoundingBox(viewport);

  const [minX, minY] = lngLatToWorld([bbox[0], bbox[3]], viewport.scale).map(pixelsToTileIndex);
  const [maxX, maxY] = lngLatToWorld([bbox[2], bbox[1]], viewport.scale).map(pixelsToTileIndex);

  const indices = [];

  for (let x = minX; x <= maxX; x++) {
    for (let y = minY; y <= maxY; y++) {
      if (maxZoom && z > maxZoom) {
        indices.push(getAdjustedTileIndex({x, y, z}, maxZoom));
      } else {
        indices.push({x, y, z});
      }
    }
  }
  return indices;
}

/**
 * Calculates and returns a new tile index {x, y, z}, with z being the given adjustedZ.
 */
function getAdjustedTileIndex({x, y, z}, adjustedZ) {
  const m = Math.pow(2, z - adjustedZ);
  return {
    x: Math.floor(x / m),
    y: Math.floor(y / m),
    z: adjustedZ
  };
}