fix(director): seek camera longitude across the shortest dateline arc

src/director/director-dateline-seek.test.mjs

@@ -0,0 +1,26 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { cameraAtProgress } from './timeline.js';
+const camera = (lon) => ({
+  lat: 10,
+  lon,
+  alt: 1000,
+  heading: 0,
+  pitch: -40,
+  roll: 0,
+});
+test('director seek follows the short dateline arc in both directions', () => {
+  for (const [a, b] of [
+    [179, -179],
+    [-179, 179],
+  ]) {
+    assert.equal(
+      Math.abs(cameraAtProgress(camera(a), camera(b), 0.5).lon),
+      180,
+    );
+    assert.equal(cameraAtProgress(camera(a), camera(b), 0).lon, a);
+    assert.equal(cameraAtProgress(camera(a), camera(b), 1).lon, b);
+    assert.ok(Math.abs(cameraAtProgress(camera(a), camera(b), 0.25).lon) > 179);
+  }
+  assert.equal(cameraAtProgress(camera(20), camera(24), 0.5).lon, 22);
+});

src/director/timeline.js

@@ -45,7 +45,13 @@ export function cameraAtProgress(fromCamera, toCamera, progress) {
   };
   return {
     lat: lerp(source.lat, target.lat),
-    lon: lerp(source.lon, target.lon),
+    lon:
+      t === 0
+        ? Number(source.lon)
+        : t === 1
+          ? Number(target.lon)
+          : ((((lerpAngle(source.lon, target.lon) + 180) % 360) + 360) % 360) -
+            180,
     alt: lerp(source.alt, target.alt),
     heading: lerpAngle(source.heading, target.heading),
     pitch: lerp(source.pitch, target.pitch),