fix(street-level): read the older {zoom, kind} zoomFor shape (#1288)

Restore legacy provider zoomFor compatibility and document supported return values.

Contribution by @asturksever.

changelog.d/1288-zoomfor-legacy-shape.md

@@ -0,0 +1,4 @@
+- A Street Level provider whose `zoomFor` still answers `{zoom, kind}`, the
+  shape before the core went slim, draws its lines again instead of a silent
+  blank; an overview level or any answer that is not a whole zoom shows the
+  zoom-in hint (asturksever, #1288).

docs/CURRENT-STATE.md

@@ -3753,6 +3753,10 @@ disabled. With it, coverage draws as z11–14 sequence lines below 60 km; the pr
 tiles (12 MB → ~80 KB) and shares one upstream fetch between concurrent
 requests for a tile.
 
+Line coverage accepts a provider’s numeric `zoomFor` result or its legacy
+`{zoom, kind}` shape. Overview levels and invalid zooms show the zoom-in hint
+instead of silently requesting no tiles.
+
 Coverage is z11–14 sequence lines below 60 km; above that nothing is drawn and
 the panel says to zoom in. Tiles come from the visible ground within range of
 the camera, nearest first, at most 9 (the halves of a view across

src/layers/streetLevel/lineCoverage.js

@@ -105,6 +105,25 @@ function pointsOf(sequence) {
  * @property {boolean} [keepOrder]        Cap a tile's lines in the order decoded (default: newest first).
  */
 
+/**
+ * The tile zoom a provider's `zoomFor` answered, or null. Providers written
+ * before the core went slim return `{zoom, kind}`: its zoom is read, and an
+ * `'overview'` level draws nothing, since nothing is drawn from orbit. Any
+ * other answer that is not a whole zoom draws nothing too, rather than
+ * asking for no tiles without a hint.
+ * @param {unknown} level
+ * @returns {number|null}
+ */
+export function coverageZoom(level) {
+  const zoom =
+    level && typeof level === 'object'
+      ? level.kind === 'overview'
+        ? null
+        : level.zoom
+      : level;
+  return Number.isInteger(zoom) && zoom >= 0 ? zoom : null;
+}
+
 /**
  * Camera-driven sequence lines from any XYZ line-tile source, near the
  * ground only, draped on terrain and 3D tiles alike. Nothing is drawn from
@@ -115,8 +134,9 @@ function pointsOf(sequence) {
  * @param {(tile: {x: number, y: number, z: number}, init: {signal: AbortSignal}) => Promise<{sequences: Array<object>}>} options.fetchTile
  *   A decoded tile; sequences are `{id, parts, capturedAt, isPano}`. A
  *   rejection may carry `keyRequired`, `keyRejected` or `retryAfterSec`.
- * @param {(heightM: number|null) => number|null} options.zoomFor
- *   Tile zoom for a camera height above ground; null draws nothing.
+ * @param {(heightM: number|null) => number|{zoom: number, kind?: string}|null} options.zoomFor
+ *   Tile zoom for a camera height above ground; null draws nothing. The
+ *   older `{zoom, kind}` shape is still read (see `coverageZoom`).
  * @param {{coverage: string, selected: string}} options.colors
  * @param {string} options.pickPrefix   Pick-id prefix of the lines.
  * @param {string} options.renderKey    Render-governor reason.
@@ -380,7 +400,7 @@ export function createLineCoverage({
     const height = Number.isFinite(cameraHeight)
       ? cameraHeight - (ground ?? 0)
       : null;
-    const zoom = zoomFor(height);
+    const zoom = coverageZoom(zoomFor(height));
     if (zoom == null) return { hint: messages.tooHigh || ZOOM_IN_HINT };
     // Rays meet the ground where it really is (1,600 m up in Denver) and stop
     // short of the horizon, which would stretch the box to the world.

src/layers/streetLevel/lineCoverage.test.mjs

@@ -2,6 +2,7 @@ import assert from 'node:assert/strict';
 import test from 'node:test';
 import * as Cesium from 'cesium';
 import {
+  coverageZoom,
   createLineCoverage,
   freshCoverage,
   ZOOM_IN_HINT,
@@ -28,7 +29,7 @@ const { maxSequences: COVERAGE_MAX_SEQUENCES, maxTiles: COVERAGE_MAX_TILES } =
   COVERAGE_TUNING;
 
 /** Line coverage as the Mapillary provider builds it, over `source`. */
-function createCoverage({ state, source }) {
+function createCoverage({ state, source, zoomFor = coverageZoomForHeight }) {
   return createLineCoverage({
     state,
     fetchTile: async (tile, { signal }) =>
@@ -36,7 +37,7 @@ function createCoverage({ state, source }) {
         await source.getTile('coverage', tile.z, tile.x, tile.y, { signal }),
         tile,
       ),
-    zoomFor: coverageZoomForHeight,
+    zoomFor,
     colors: COLORS,
     pickPrefix: PICK_PREFIX.sequence,
     renderKey: 'mapillary-coverage',
@@ -123,7 +124,7 @@ function deferredSource() {
   };
 }
 
-function setup() {
+function setup({ zoomFor } = {}) {
   const centre = tileCentre(-121.4944, 38.5816);
   const viewer = fakeViewer({ lon: centre.lon, lat: centre.lat, height: 900 });
   const source = deferredSource();
@@ -146,7 +147,7 @@ function setup() {
     },
     sequence: { selectedId: null },
   };
-  const coverage = createCoverage({ state, source });
+  const coverage = createCoverage({ state, source, zoomFor });
   const bytes = encodeCoverageTile(centre.tile, {
     sequences: [
       {
@@ -239,6 +240,37 @@ test('panning off a tile that is still loading stops counting it as loading', as
   coverage.clear();
 });
 
+test('a zoomFor in the older {zoom, kind} shape still draws its lines', async () => {
+  // Providers written before the core went slim (#1139's Vegbilder) answer
+  // an object: it must not ask for no tiles and say nothing.
+  const { viewer, source, coverage, bytes } = setup({
+    zoomFor: (height) => {
+      const zoom = coverageZoomForHeight(height);
+      return zoom == null ? null : { zoom, kind: 'sequence' };
+    },
+  });
+  coverage.refresh();
+  assert.equal(source.calls.length, 1, 'the tile is asked for');
+  assert.equal(source.calls[0].z, 14);
+  source.calls[0].resolve(bytes);
+  await settle();
+  assert.equal(viewer.scene.groundPrimitives.items.size, 1, 'its line drawn');
+  assert.equal(coverage.stats().hint, '');
+  coverage.clear();
+});
+
+test('a zoom level is read from either shape; an overview or a bad answer draws nothing', () => {
+  assert.equal(coverageZoom(14), 14);
+  assert.equal(coverageZoom({ zoom: 15, kind: 'sequence' }), 15);
+  assert.equal(coverageZoom({ zoom: 12 }), 12);
+  assert.equal(coverageZoom({ zoom: 5, kind: 'overview' }), null, 'orbit');
+  assert.equal(coverageZoom(null), null);
+  assert.equal(coverageZoom(undefined), null);
+  assert.equal(coverageZoom({}), null);
+  assert.equal(coverageZoom(14.5), null);
+  assert.equal(coverageZoom('14'), null);
+});
+
 test('from orbit nothing is requested or drawn, and the hint says to zoom in', async () => {
   const { viewer, source, state, coverage, bytes } = setup();
   coverage.refresh();