orbis-core/src/index.ts

import * as d3geo from 'd3-geo';
import * as d3geoProjection from 'd3-geo-projection';
import * as d3geoPolygon from 'd3-geo-polygon';
import { PNG } from 'pngjs';
import { readFile } from 'fs/promises';

type Coords = [number, number]
type Bounds = [Coords, Coords]

type ProjectionFunction = (...args: unknown[]) => (
  d3geo.GeoProjection | d3geoProjection.GeoProjection
)

const referenceWidth = 960 as const;
const referenceHeight = 480 as const;

type ProjectOptions = {
  inputDimensions?: { width: number, height: number },
  bounds?: Bounds,
}

type Projection = [string, ...unknown[]]

const isValidLongitude = (lng: number) => lng >= -180 && lng <= 180;
const isValidLatitude = (lat: number) => lat >= -90 && lat <= 90;
const getCenter = (bounds: Bounds): Coords => {
  const [nw, se] = bounds;
  const [nwLng, nwLat] = nw;
  const [seLng, seLat] = se;
  return [
    // TODO: better center checking that wraps longitudes
    (nwLng + seLng) / 2,
    (nwLat + seLat) / 2,
  ];
};

export const projectPoint = (
  point: [number, number],
  projection: Projection,
  options: ProjectOptions = {},
): [number, number] | null => {
  const [lng, lat] = point;
  if (!(isValidLongitude(lng) && isValidLatitude(lat))) {
    throw new RangeError('Invalid value for point. Only values from [-180, -90] to [180, 90] are allowed');
  }

  const [projectionName, ...projectionArgs] = projection;
  if (projectionName === 'Equirectangular') {
    return point;
  }

  const projectionFunctionName = `geo${projectionName}`;
  let geoProjectionSource: Record<string, unknown> | undefined;
  if (projectionFunctionName in d3geoPolygon) {
    geoProjectionSource = d3geoPolygon as Record<string, unknown>;
  } else if (projectionFunctionName in d3geoProjection) {
    geoProjectionSource = d3geoProjection;
  } else if (projectionFunctionName in d3geo) {
    geoProjectionSource = d3geo;
  }

  if (!geoProjectionSource) {
    throw new Error(`Unknown projection: ${projectionName}`);
  }

  const projectionFn = geoProjectionSource[projectionFunctionName] as ProjectionFunction;
  const baseProjection = projectionFn(...projectionArgs);
  const {
    bounds = [[-180, 90], [180, -90]],
    inputDimensions = { width: referenceWidth, height: referenceHeight },
  } = options;

  const { invert } = baseProjection.center(getCenter(bounds));
  if (!invert) {
    return null;
  }

  const { width: sx, height: sy } = inputDimensions;
  return invert([
    (lng / sx) * referenceWidth,
    (lat / sy) * referenceHeight,
  ]) as [number, number];
};

const retrievePngData = async (pngInput: string | Buffer | PNG) => {
  if (typeof pngInput === 'string') {
    const pngFile = await readFile(pngInput);
    return PNG.sync.read(pngFile);
  }

  if (typeof pngInput === 'object') {
    return pngInput instanceof PNG ? pngInput : PNG.sync.read(pngInput);
  }

  throw new TypeError('Invalid input argument.');
};

const prepareOutputData = (
  _projection: Projection,
  sourceWidth: number,
  sourceHeight: number,
): PNG => {
  const [tx, ty] = [sourceWidth, sourceHeight];
  return new PNG({
    width: tx,
    height: ty,
  });
};

export const project = async (
  pngInput: string | Buffer | PNG,
  projection: Projection,
  options?: ProjectOptions,
) => {
  const sourcePngData = await retrievePngData(pngInput);
  const { width: sx, height: sy, data: sourceData } = sourcePngData;
  // const [tx, ty] = currentProjectionData.bounds(bounds)([sx, sy]);
  // TODO correctly compute result bounds
  const outputPngData = prepareOutputData(projection, sx, sy);
  const { width: tx, height: ty, data: targetData } = outputPngData;

  let i = 0;
  for (let y = (sy - ty) / 2; y < (ty + ((sy - ty) / 2)); y += 1) {
    for (let x = 0; x < (tx + ((sx - tx) / 2)); x += 1) {
      const projected = projectPoint([x, y], projection, {
        bounds: options?.bounds,
      });
      if (projected) {
        const [lambda, phi] = projected;
        if (!(lambda > 180 || lambda < -180 || phi > 90 || phi < -90)) {
          // eslint-disable-next-line no-bitwise
          const q = (((90 - phi) / 180) * sy | 0) * sx + (((180 + lambda) / 360) * sx | 0) << 2;
          targetData[i] = sourceData[q];
          targetData[i + 1] = sourceData[q + 1];
          targetData[i + 2] = sourceData[q + 2];
          targetData[i + 3] = sourceData[q + 3];
        }
      }
      i += 4;
    }
  }

  return outputPngData;
};