maptool/public/js/shadow.js

import { getPosition } from "/vendor/suncalc/suncalc.js";
import { elevationAt } from "/js/dem.js";
import { TERRAIN_SHADOW_ICON } from "/js/icons.js";

const MIN_ZOOM = 11; // below this, a screen is roughly the same scale as the 40km raymarch — "one screen, one shadow-casting neighborhood" stops holding
const GRID_COLS = 96;
const GRID_ROWS = 64;
const RAYMARCH_STEPS = 16;
const RAYMARCH_START_M = 150;
const RAYMARCH_MAX_M = 40000;
const RAYMARCH_RATIO = (RAYMARCH_MAX_M / RAYMARCH_START_M) ** (1 / (RAYMARCH_STEPS - 1)); // geometric spacing: dense near the point, coarse far out
const EARTH_RADIUS_M = 6371000;
const SHADOW_RGBA = [20, 20, 50, Math.round(0.45 * 255)];
const SLIDER_DEBOUNCE_MS = 300;

const IMAGE_SOURCE_ID = "terrain-shadow";

// An Overlays panel item (see overlays.js) shading the parts of the visible
// map currently blocked from the sun by surrounding terrain — offline
// equivalent of shademap.app, built on the same Terrarium DEM tiles
// HillshadeControl already renders (via dem.js) and the same sun-position
// math the toolbar readout uses (public/js/sun.js). No Web Worker: a
// recompute is dozens of small awaited fetches (mostly cache hits after the
// first pan), not sustained sync CPU work, so it already yields to the
// event loop on its own between grid rows without blocking a pan/zoom.
export class ShadowControl {
  constructor(map) {
    this._map = map;
    this._enabled = false;
    this._offlineAvailable = false;
    this._seq = 0; // bumped on every recompute/disable so a superseded in-flight one (a fast second pan, or turning the layer off mid-compute) discards its result instead of overwriting newer data
    this._moveHandler = null;
    this._sliderMinutes = currentMinutesOfDay();
    this._sliderTimer = null;

    // setStyle() (switching Online/Offline) tears down all custom sources/
    // layers — recompute puts the shadow layer back if it was on, same as
    // every other Overlays control.
    map.on("style.load", () => {
      if (this._enabled) this._recompute();
    });
  }

  mount(li) {
    li.innerHTML = `
      <div class="overlays-panel__row">
        <input type="checkbox" class="overlays-panel__toggle">
        <span class="overlays-panel__icon">${TERRAIN_SHADOW_ICON}</span>
        <button type="button" class="overlays-panel__name">Terrain shadow</button>
      </div>
      <div class="overlays-panel__details" hidden>
        <div class="shadow-control__time">
          <input type="range" class="shadow-control__slider" min="0" max="1439" step="5" value="${this._sliderMinutes}">
          <span class="shadow-control__clock">${formatMinutes(this._sliderMinutes)}</span>
        </div>
        <p class="shadow-control__hint" hidden>Zoom in further to compute terrain shadow.</p>
      </div>
    `;

    this._checkbox = li.querySelector(".overlays-panel__toggle");
    this._nameButton = li.querySelector(".overlays-panel__name");
    this._details = li.querySelector(".overlays-panel__details");
    this._slider = li.querySelector(".shadow-control__slider");
    this._clock = li.querySelector(".shadow-control__clock");
    this._hint = li.querySelector(".shadow-control__hint");

    this._checkbox.addEventListener("change", (event) => this._setEnabled(event.target.checked));
    this._nameButton.addEventListener("click", () => {
      const expanding = this._details.hidden;
      this._details.hidden = !expanding;
      this._nameButton.setAttribute("aria-expanded", String(expanding));
    });
    this._slider.addEventListener("input", () => {
      this._sliderMinutes = Number(this._slider.value);
      this._clock.textContent = formatMinutes(this._sliderMinutes);
      clearTimeout(this._sliderTimer);
      this._sliderTimer = setTimeout(() => this._recompute(), SLIDER_DEBOUNCE_MS);
    });
  }

  setOfflineAvailable(available) {
    this._offlineAvailable = available;
  }

  _setEnabled(enabled) {
    this._enabled = enabled;
    if (enabled) {
      this._moveHandler = () => this._recompute();
      this._map.on("moveend", this._moveHandler);
      this._recompute();
      return;
    }

    this._seq++;
    if (this._moveHandler) {
      this._map.off("moveend", this._moveHandler);
      this._moveHandler = null;
    }
    this._hint.hidden = true;
    this._removeLayer();
  }

  async _recompute() {
    const seq = ++this._seq;

    if (this._map.getZoom() < MIN_ZOOM) {
      this._hint.hidden = false;
      this._removeLayer();
      return;
    }
    this._hint.hidden = true;

    const bounds = this._map.getBounds();
    const center = this._map.getCenter();
    const date = this._selectedDate();
    // One sun position for the whole viewport — azimuth/altitude vary
    // negligibly across it next to the raymarch's own 150m-step coarseness.
    const sun = getPosition(date, center.lat, center.lng);

    const west = bounds.getWest();
    const east = bounds.getEast();
    const south = bounds.getSouth();
    const north = bounds.getNorth();

    const canvas = document.createElement("canvas");
    canvas.width = GRID_COLS;
    canvas.height = GRID_ROWS;
    const ctx = canvas.getContext("2d");
    const imageData = ctx.createImageData(GRID_COLS, GRID_ROWS);

    if (sun.altitude <= 0) {
      // Sun's below the horizon everywhere in view — no point raymarching.
      fillShadow(imageData);
    } else {
      for (let row = 0; row < GRID_ROWS; row++) {
        const lat = north - ((row + 0.5) / GRID_ROWS) * (north - south);
        const rowWork = [];
        for (let col = 0; col < GRID_COLS; col++) {
          const lng = west + ((col + 0.5) / GRID_COLS) * (east - west);
          rowWork.push(
            this._isShadowed(lng, lat, sun.azimuth, sun.altitude).then((shadowed) => setPixel(imageData, col, row, shadowed)),
          );
        }
        await Promise.all(rowWork); // yields once per row, so a fast pan/zoom's newer recompute can cut in
        if (seq !== this._seq) return;
      }
    }

    ctx.putImageData(imageData, 0, 0);
    if (seq !== this._seq) return;
    this._publish(canvas.toDataURL(), bounds);
  }

  async _isShadowed(lng, lat, sunAzimuth, sunAltitude) {
    const pointElev = await elevationAt(lng, lat, this._offlineAvailable);
    if (pointElev === null) return false; // no DEM data here — render sunlit rather than guess

    let dist = RAYMARCH_START_M;
    const samples = [];
    for (let i = 0; i < RAYMARCH_STEPS; i++) {
      samples.push(this._horizonSample(lng, lat, pointElev, sunAzimuth, dist));
      dist *= RAYMARCH_RATIO;
    }
    const angles = (await Promise.all(samples)).filter((a) => a !== null);
    const horizonMax = angles.length ? Math.max(...angles) : -90;
    return sunAltitude <= horizonMax;
  }

  async _horizonSample(lng, lat, pointElev, sunAzimuth, dist) {
    const sample = destinationPoint(lng, lat, sunAzimuth, dist);
    const sampleElev = await elevationAt(sample.lng, sample.lat, this._offlineAvailable);
    if (sampleElev === null) return null;
    const curvatureDrop = (dist * dist) / (2 * EARTH_RADIUS_M);
    return (Math.atan2(sampleElev - pointElev - curvatureDrop, dist) * 180) / Math.PI;
  }

  _selectedDate() {
    const date = new Date();
    date.setHours(0, this._sliderMinutes, 0, 0);
    return date;
  }

  // First image-source usage in this app — addSource/addLayer once, then
  // updateImage on every later recompute rather than remove+re-add.
  _publish(dataUrl, bounds) {
    const coordinates = [
      [bounds.getWest(), bounds.getNorth()],
      [bounds.getEast(), bounds.getNorth()],
      [bounds.getEast(), bounds.getSouth()],
      [bounds.getWest(), bounds.getSouth()],
    ];

    const source = this._map.getSource(IMAGE_SOURCE_ID);
    if (source) {
      source.updateImage({ url: dataUrl, coordinates });
    } else {
      this._map.addSource(IMAGE_SOURCE_ID, { type: "image", url: dataUrl, coordinates });
      this._map.addLayer({ id: IMAGE_SOURCE_ID, type: "raster", source: IMAGE_SOURCE_ID });
    }
  }

  _removeLayer() {
    if (this._map.getLayer(IMAGE_SOURCE_ID)) this._map.removeLayer(IMAGE_SOURCE_ID);
    if (this._map.getSource(IMAGE_SOURCE_ID)) this._map.removeSource(IMAGE_SOURCE_ID);
  }
}

// Flat-earth destination point (bearing/distance -> lng/lat) — fine under
// 40km, and nothing in this codebase already does lng/lat offset math.
function destinationPoint(lng, lat, bearingDeg, distanceM) {
  const bearing = (bearingDeg * Math.PI) / 180;
  const latRad = (lat * Math.PI) / 180;
  const dLat = (distanceM * Math.cos(bearing)) / EARTH_RADIUS_M;
  const dLng = (distanceM * Math.sin(bearing)) / (EARTH_RADIUS_M * Math.cos(latRad));
  return { lng: lng + (dLng * 180) / Math.PI, lat: lat + (dLat * 180) / Math.PI };
}

function setPixel(imageData, col, row, shadowed) {
  if (!shadowed) return; // ImageData starts fully transparent — nothing to do for a sunlit cell
  const i = (row * imageData.width + col) * 4;
  imageData.data.set(SHADOW_RGBA, i);
}

function fillShadow(imageData) {
  for (let i = 0; i < imageData.data.length; i += 4) imageData.data.set(SHADOW_RGBA, i);
}

function formatMinutes(minutes) {
  const h = Math.floor(minutes / 60);
  const m = minutes % 60;
  return `${String(h).padStart(2, "0")}:${String(m).padStart(2, "0")}`;
}

function currentMinutesOfDay() {
  const now = new Date();
  return now.getHours() * 60 + now.getMinutes();
}