randy
c9561a5489
Shades the visible map by whether each point is currently blocked from the sun by surrounding terrain (shademap.app-style), computed fully offline via the same Terrarium DEM tiles the Terrain shading layer already renders, plus this session's sun-position math and Radar's checkbox+expandable UI shape. dem.js pulls elevation-at-a-point out on its own since TODO.adoc's slope readout and solar calculator will need the same lookup.
73 lines
2.9 KiB
JavaScript
73 lines
2.9 KiB
JavaScript
// Elevation lookups against the same Terrarium-encoded terrain tiles
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// overlays.js's HillshadeControl already renders — pulled into its own file
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// since TODO.adoc lists two more near-future features (slope readout, solar
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// calculator) that will need the same "elevation at a point" primitive,
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// shadow.js's raymarch being the first real consumer.
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import { ONLINE_TERRAIN_TILES } from "/js/overlays.js";
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const DEM_ZOOM = 10; // fixed lookup zoom, independent of the map's own display zoom
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const TILE_SIZE = 256;
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const tileCache = new Map(); // "z/x/y" -> Promise<Int16Array|null>, so concurrent lookups on the same not-yet-fetched tile share one fetch
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let offlinePmtiles = null;
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function lngLatToTile(lng, lat, zoom) {
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const n = 2 ** zoom;
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const x = ((lng + 180) / 360) * n;
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const latRad = (lat * Math.PI) / 180;
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const y = ((1 - Math.log(Math.tan(latRad) + 1 / Math.cos(latRad)) / Math.PI) / 2) * n;
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const tileX = Math.floor(x);
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const tileY = Math.floor(y);
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return {
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tileX,
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tileY,
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px: Math.min(TILE_SIZE - 1, Math.floor((x - tileX) * TILE_SIZE)),
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py: Math.min(TILE_SIZE - 1, Math.floor((y - tileY) * TILE_SIZE)),
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};
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}
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async function decodeTerrarium(pngBytes) {
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const bitmap = await createImageBitmap(new Blob([pngBytes], { type: "image/png" }));
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const canvas = new OffscreenCanvas(bitmap.width, bitmap.height);
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const ctx = canvas.getContext("2d");
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ctx.drawImage(bitmap, 0, 0);
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const { data } = ctx.getImageData(0, 0, bitmap.width, bitmap.height);
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const elevations = new Int16Array(bitmap.width * bitmap.height);
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for (let i = 0; i < elevations.length; i++) {
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elevations[i] = data[i * 4] * 256 + data[i * 4 + 1] + data[i * 4 + 2] / 256 - 32768;
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}
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return elevations;
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}
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async function fetchTileBytes(z, x, y, offlineAvailable) {
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if (offlineAvailable) {
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if (!offlinePmtiles) offlinePmtiles = new window.pmtiles.PMTiles(`${window.location.origin}/tiles/terrain.pmtiles`);
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const result = await offlinePmtiles.getZxy(z, x, y);
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return result ? new Uint8Array(result.data) : null;
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}
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const url = ONLINE_TERRAIN_TILES[0].replace("{z}", z).replace("{x}", x).replace("{y}", y);
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const response = await fetch(url);
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return response.ok ? new Uint8Array(await response.arrayBuffer()) : null;
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}
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function fetchTile(z, x, y, offlineAvailable) {
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const key = `${z}/${x}/${y}`;
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let cached = tileCache.get(key);
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if (cached) return cached;
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const promise = fetchTileBytes(z, x, y, offlineAvailable)
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.then((bytes) => (bytes ? decodeTerrarium(bytes) : null))
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.catch(() => null);
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tileCache.set(key, promise);
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return promise;
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}
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// -> Promise<number|null> — null on a fetch/decode failure, or a point
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// falling outside a partial offline extract's zoom range.
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export async function elevationAt(lng, lat, offlineAvailable) {
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const { tileX, tileY, px, py } = lngLatToTile(lng, lat, DEM_ZOOM);
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const elevations = await fetchTile(DEM_ZOOM, tileX, tileY, offlineAvailable);
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return elevations ? elevations[py * TILE_SIZE + px] : null;
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}
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