Keep the place in view when a late zoom out catches a tilt

From 400 km, a tilt to -5° that a zoom out x2.5 caught 70 frames in eased down from the camera's old pitch at the new range. That put the camera below the place's horizon: the first frame's crosshair hit the ground 186 km from London, and London stayed hidden for about 11 frames. The re-solve also left the pivot pitch at 0°, so a zoom in before the next frame computed an infinite clearance floor, was refused, and stayed at 1,000 km.

The re-solved pivot pitch now stops at the place's horizon limit, or where the pivot already was. A camera that the zoom leaves past that limit steps down to it with the zoom and holds it, and the zoom still reports that angle. A zoom in straight after brings the range back to 400 km.

src/cameraTilt.test.mjs

@@ -688,15 +688,18 @@ test('a voice zoom during a tilt to an angle passes on the new end angle', async
 });
 
 // Late in the tilt the camera is already past the angle the new range's
-// horizon allows (from 400 km at -8°, a zoom out x2.5 reported -8° and the
-// next frame jumped to -9.4°): it eases to that limit with no jump, and the
-// zoom's reply names the angle it ends at, not the one it stood at.
-test('a late zoom out during a tilt eases to the new limit and reports it', (t) => {
+// horizon allows (from 400 km at -8°, a zoom out x2.5 reported -8°): past it
+// the place is behind the Earth, so the camera steps down to that limit with
+// the zoom, then holds it with no further jump, and the zoom's reply names
+// the angle it ends at, not the one it stood at.
+test('a late zoom out during a tilt steps to the new limit and reports it', (t) => {
   const h = harness(t, { height: 400_000 });
   moveCamera({ motion: 'tilt', pitchDeg: -5 });
   for (let i = 0; i < 70; i += 1) h.tick();
   const zoom = adjustOrbitRange(2.5);
   assert.equal(zoom.changed, true);
+  h.tick();
+  assert.equal(zoom.pitchDeg, Math.round(pitchDeg(h.camera)));
   let last = pitchDeg(h.camera);
   let maxStep = 0;
   for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) {
@@ -705,7 +708,7 @@ test('a late zoom out during a tilt eases to the new limit and reports it', (t)
     last = pitchDeg(h.camera);
   }
   assert.equal(getActiveCameraMotion(), null, 'tilt must finish');
-  assert.ok(maxStep < 0.5, `pitch jumped ${maxStep}° in one frame`);
+  assert.ok(maxStep < 0.1, `pitch jumped ${maxStep}° in one frame`);
   assert.ok(h.viewTarget(), 'the crosshair is on the sky');
   // Replies give whole degrees: the reported angle is the reached one rounded.
   assert.equal(
@@ -715,3 +718,56 @@ test('a late zoom out during a tilt eases to the new limit and reports it', (t)
   );
   assert.match(zoom.note, /horizon/);
 });
+
+// Easing from the camera's old pitch at the zoomed-out range put the camera
+// below the place's horizon: the first frame's crosshair hit the ground
+// 186 km from London, and London stayed hidden for ~11 frames.
+test('a late zoom out during a tilt keeps the place under the crosshair', (t) => {
+  const h = harness(t, { height: 400_000 });
+  moveCamera({ motion: 'tilt', pitchDeg: -5 });
+  for (let i = 0; i < 70; i += 1) h.tick();
+  const zoom = adjustOrbitRange(2.5);
+  assert.equal(zoom.changed, true);
+  for (let i = 0; i < 600 && getActiveCameraMotion(); i += 1) {
+    h.tick();
+    const hit = h.viewTarget();
+    assert.ok(hit, `frame ${i}: the crosshair is on the sky`);
+    const drift = centreDrift(h);
+    assert.ok(
+      drift < 100,
+      `frame ${i}: crosshair ${Math.round(drift)} m off the place`,
+    );
+  }
+  assert.equal(getActiveCameraMotion(), null, 'tilt must finish');
+  assert.ok(
+    Math.abs(pivotRange(h) - 1_000_000) < 1,
+    `range ${pivotRange(h)} m`,
+  );
+  assert.equal(
+    zoom.pitchDeg,
+    Math.round(pitchDeg(h.camera)),
+    `camera at ${pitchDeg(h.camera)}°, zoom reported ${zoom.pitchDeg}°`,
+  );
+  assert.match(zoom.note, /horizon/);
+});
+
+// The zoom out left the pivot pitch level with the place, so the zoom in's
+// clearance floor came out infinite and it was refused at 1,000 km.
+test('a zoom in right after a late zoom out brings the tilt back in', (t) => {
+  const h = harness(t, { height: 400_000 });
+  moveCamera({ motion: 'tilt', pitchDeg: -5 });
+  for (let i = 0; i < 70; i += 1) h.tick();
+  const range = pivotRange(h);
+  assert.equal(adjustOrbitRange(2.5).changed, true);
+  const zoomIn = adjustOrbitRange(0.4);
+  assert.equal(zoomIn.changed, true, 'the zoom in must not be refused');
+  h.finish();
+  assert.ok(
+    Math.abs(pivotRange(h) - range) < 1,
+    `range ${pivotRange(h)} m, wanted ${range} m`,
+  );
+  assert.ok(
+    centreDrift(h) < 100,
+    `crosshair ${centreDrift(h)} m off the place`,
+  );
+});

src/cameraVerbs.js

@@ -2109,20 +2109,27 @@ export function adjustOrbitRange(factor) {
 function retargetTiltAfterZoom(m) {
   if (m.kind !== 'tilt' || m.mode !== 'once' || m.askedPitch === undefined)
     return {};
-  const from = _viewer.camera.pitch;
+  let from = _viewer.camera.pitch;
   if (!(m.askedPitch > from)) return {};
   if (m.hpr) {
     // At the same pivot pitch a longer range looks down more steeply (the
     // Earth curves away): find the pivot pitch that holds this camera pitch.
+    // It stays below the place's horizon limit (or where the pivot already
+    // was): past it the place drops behind the Earth, so a camera the zoom
+    // leaves past that limit steps down to it with the zoom.
+    const cap = Math.max(m.hpr.pitch, tiltPivotPitchMax(m.hpr.range));
     for (let i = 0; i < 4; i += 1) {
       const error = from - pivotCameraPitch(m.target, m.hpr, m.hpr.pitch);
       if (Math.abs(error) < 1e-7) break;
-      m.hpr.pitch = Cesium.Math.clamp(
+      const pitch = Cesium.Math.clamp(
         m.hpr.pitch + error,
         -Cesium.Math.PI_OVER_TWO,
-        0,
+        cap,
       );
+      if (pitch === m.hpr.pitch) break;
+      m.hpr.pitch = pitch;
     }
+    from = Math.min(from, pivotCameraPitch(m.target, m.hpr, m.hpr.pitch));
   }
   const limit =
     m.hpr && !tiltClearanceBinds(m.hpr.range)