fix(vessels): world-clock motion moves only drawn vessels, once per world time

Vessels out of view move on every 250 ms so one coming into view is current;
vessels at the end of their fixes ask for no frames; nothing moves while the
layer is off; 2D views judge the half-pixel step across the view's width; a
re-floor redraws vessels where they are on the next pass.

docs/CURRENT-STATE.md

@@ -2001,7 +2001,7 @@ snapshot still loading for more than 8 seconds. Those snapshots apply as polls
 do, so contacts move on smoothly: aircraft are drawn at the clock's time
 rather than behind it, and vessels between two fixes move along the great
 circle, never past the newer one, redrawn every frame with frames asked for
-as for placed live vessels. Records, absences and the Layers panel's age
+as for placed live vessels (vessels out of view move on every 250 ms). Records, absences and the Layers panel's age
 are judged at the clock's time. Outside the coverage the layer shows no
 contacts and loads nothing; while the coverage is unknown it loads nothing and
 clears nothing. A snapshot that fails clears the time and is asked again after

src/layers/vessels/renderGovernor.test.mjs

@@ -5,9 +5,9 @@ import { VISIBILITY_UPDATE_MS } from './policy.js';
 import { layerPlacement } from '../../data/placementProvider.js';
 import * as Cesium from 'cesium';
 
-// Vessels move only when a poll lands, so the layer must let the scene idle:
-// it asks for frames for forced passes and one trailing frame after the camera
-// stops, and never schedules a frame from a pass the camera did not cause.
+// The layer must let the scene idle: it asks for frames for forced passes,
+// for vessels that move, and one trailing frame after the camera stops, and
+// never schedules a frame from a pass nothing caused.
 
 const noop = () => {};
 
@@ -252,4 +252,106 @@ test('a vessel moving visibly asks for its next frame as soon as it moves half a
   assert.ok(waitAfterStep(0.0001) <= 16);
   // About 1 cm in a frame: half a pixel takes seconds, so once a second.
   assert.equal(waitAfterStep(0.0000001), 1000);
+  // A 2D view 40 km across in 1,000 px: 11 m is over a quarter pixel, so the
+  // next frame comes within two frames.
+  camera.frustum = { left: -20_000, right: 20_000 };
+  layer.testing._setVesselStateForTest({
+    viewer: { camera, scene: {}, canvas: { clientWidth: 1000 } },
+    records: [record],
+  });
+  layer.testing._prepareVesselVisualForTest(record);
+  assert.ok(waitAfterStep(0.0001) <= 32);
+});
+
+test('following the clock moves drawn vessels in place each world time, prepares missing ones and leaves hidden ones be', (t) => {
+  let mono = 0;
+  t.mock.method(performance, 'now', () => mono);
+  const originalDocument = globalThis.document;
+  globalThis.document = { getElementById: () => null };
+  t.after(() => {
+    if (originalDocument === undefined) delete globalThis.document;
+    else globalThis.document = originalDocument;
+  });
+  const { layer, camera, timers, advance } = setup();
+  camera.positionWC = Cesium.Cartesian3.fromDegrees(4.05, 51.93, 20_000);
+  camera.frustum = { fovy: 1 };
+  const motion = {
+    fromLat: 51.93,
+    fromLon: 4.05,
+    fromMs: 0,
+    toLat: 51.94,
+    toLon: 4.05,
+    toMs: 60_000,
+  };
+  const vessel = (mmsi, show) => ({
+    mmsi,
+    lat: 51.94,
+    lon: 4.05,
+    motion: { ...motion },
+    billboard: { show, position: null },
+  });
+  const drawn = vessel('111', true);
+  const hidden = vessel('222', false);
+  const owned = vessel('333', false);
+  const missing = vessel('444', true);
+  layer.testing._setVesselStateForTest({
+    viewer: { camera, scene: {}, canvas: { clientHeight: 1000 } },
+    records: [drawn, hidden, owned, missing],
+  });
+  const visuals = [drawn, hidden, owned].map((record) =>
+    layer.testing._prepareVesselVisualForTest(record),
+  );
+  visuals[2].modelOwnsVisual = true;
+  const before = visuals.map((visual) => ({ ...visual.position }));
+  const positions = visuals.map((visual) => visual.position);
+
+  // The first pass also moves hidden vessels, so the next stays within
+  // HIDDEN_FOLLOW_MS of it.
+  layer.testing._runClockPassForTest(10_000);
+  mono += 16;
+  layer.testing._runClockPassForTest(20_000);
+  assert.equal(visuals[0].position, positions[0], 'written in place');
+  assert.notDeepEqual({ ...visuals[0].position }, before[0]);
+  assert.notDeepEqual({ ...visuals[2].position }, before[2], 'model moves');
+  const hiddenAt = { ...visuals[1].position };
+  assert.ok(missing.billboard.position, 'a missing visual is prepared');
+  assert.equal(timers.size, 1, 'moving vessels ask for a frame');
+
+  // The hidden vessel waits for HIDDEN_FOLLOW_MS.
+  mono += 16;
+  layer.testing._runClockPassForTest(30_000);
+  assert.deepEqual({ ...visuals[1].position }, hiddenAt);
+  mono += 250;
+  layer.testing._runClockPassForTest(40_000);
+  assert.notDeepEqual({ ...visuals[1].position }, hiddenAt);
+
+  // The same world time again moves nothing and asks for no frame.
+  advance(1_000);
+  assert.equal(timers.size, 0);
+  const still = { ...visuals[0].position };
+  mono += 16;
+  layer.testing._runClockPassForTest(40_000);
+  assert.deepEqual({ ...visuals[0].position }, still);
+  assert.equal(timers.size, 0);
+
+  // Scrubbed back, a vessel moves back.
+  mono += 16;
+  layer.testing._runClockPassForTest(20_000);
+  assert.notDeepEqual({ ...visuals[0].position }, still);
+
+  // Each vessel moves once per world time: new fixes at the same world time
+  // are drawn when the snapshot that brings them prepares the visual.
+  const backAt = { ...visuals[0].position };
+  drawn.motion = { ...motion, toLat: 52 };
+  mono += 16;
+  layer.testing._runClockPassForTest(20_000);
+  assert.deepEqual({ ...visuals[0].position }, backAt);
+
+  // Past the newest fix, vessels hold still and ask for nothing.
+  mono += 16;
+  layer.testing._runClockPassForTest(70_000);
+  advance(1_000);
+  mono += 16;
+  layer.testing._runClockPassForTest(80_000);
+  assert.equal(timers.size, 0);
 });

src/layers/vessels/rendering.js

@@ -37,6 +37,9 @@ import { isAidToNavigation } from '../../data/vesselTypes.js';
 const VESSEL_STEP_PX = 0.5;
 /** A frame is asked for at least this often while any drawn vessel moves. */
 const PLACEMENT_FRAME_MS = 1000;
+/** How often vessels not drawn move on as the world clock plays (wall ms),
+ * so one that comes into view is judged where it is. */
+const HIDDEN_FOLLOW_MS = 250;
 
 /** How often the vessels near enough for a model are gathered again (wall ms). */
 const MODEL_CANDIDATES_MS = 500;
@@ -87,10 +90,8 @@ export function createRendering({
       visual.position,
       new Cesium.Cartesian3(),
     );
-    if (services.placement) {
-      visual.drawnLat = lat;
-      visual.drawnLon = lon;
-    }
+    visual.drawnLat = lat;
+    visual.drawnLon = lon;
     return visual;
   }
 
@@ -429,39 +430,51 @@ export function createRendering({
     modelCandidatesAtMs = -Infinity;
   }
 
-  // Vessels move only when a poll lands, so the layer does not hold the
-  // continuous render loop. Its passes run in preRender, which idle mode fires
-  // only for rendered frames: a forced pass (new data, selection) requests its
-  // frame, a frame that moved the camera but fell inside the 800 ms cadence
-  // leaves a trailing frame so the view the camera stopped on is always
+  // The layer does not hold the continuous render loop. Its passes run in
+  // preRender, which idle mode fires only for rendered frames: moving vessels
+  // ask for the frame that next moves them visibly (askMotionFrame), a forced
+  // pass (new data, selection) requests its frame, a frame that moved the
+  // camera but fell inside the 800 ms cadence leaves a trailing frame so the view the camera stopped on is always
   // evaluated, and the continuous hold is kept only while focus emphasis is
   // animating. The trailing frame is keyed to camera motion alone: the pass's
   // own label publication requests a frame, and scheduling on that would loop.
   function installRuntime(viewer) {
     if (state.preRenderRemover || !viewer) return;
     state.preRenderRemover = viewer.scene.preRender.addEventListener(() => {
-      if (followsClock(vesselState)) followClockPositions();
-      else if (services.placement && state.feed.enabled) followPlacements();
+      if (state.feed.enabled) {
+        if (followsClock(vesselState)) followClockPositions();
+        else if (services.placement) followPlacements();
+      }
       updateVisibility();
       if (state.feed.enabled) updateModels();
     });
   }
 
-  // As the world clock plays, vessels between two fixes move on along them,
-  // every frame.
-  let followedAtMs = null;
+  // As the world clock plays, vessels between two fixes move on along them:
+  // drawn ones every frame, each once per world time, hidden ones (which may
+  // come into view) every HIDDEN_FOLLOW_MS.
+  let hiddenFollowedAtWallMs = -Infinity;
   function followClockPositions() {
     const atMs = vesselState.worldNow();
-    if (atMs === followedAtMs) return;
-    followedAtMs = atMs;
     const motion = startMotionPass();
+    const moveHidden =
+      motion.wallMs - hiddenFollowedAtWallMs >= HIDDEN_FOLLOW_MS;
+    if (moveHidden) hiddenFollowedAtWallMs = motion.wallMs;
     for (const record of state.records.all) {
       if (!record.motion) continue;
       let visual = visualRecords.get(record);
-      if (visual?.position) {
+      if (!visual?.position) {
+        visual = prepareRecordVisual(record);
+        visual.followedAtMs = atMs;
+      } else {
+        const drawn = visual.billboard?.show || visual.modelOwnsVisual;
+        if (visual.followedAtMs === atMs || (!drawn && !moveHidden)) continue;
+        visual.followedAtMs = atMs;
         const { lat, lon } = vesselPositionAt(record, atMs);
+        // At either end of its fixes a vessel holds still.
+        if (lat === visual.drawnLat && lon === visual.drawnLon) continue;
         moveDrawnVisual(visual, lat, lon, motion);
-      } else visual = prepareRecordVisual(record);
+      }
       if (visual.billboard) visual.billboard.position = visual.position;
     }
     askMotionFrame(motion);
@@ -490,18 +503,27 @@ export function createRendering({
     askMotionFrame(motion);
   }
 
-  // One pass of moving vessels: whether any drawn vessel is moving, the
-  // largest angle one moved through as seen from the camera (radians), and
-  // the wall time since the pass before.
+  // One pass of moving vessels: whether any drawn vessel is moving, how far
+  // the fastest moved (as an angle seen from the camera, radians, and in
+  // metres), the pass's wall time and the wall time since the pass before.
   let motionPassWallMs = null;
-  const motionPass = { camera: null, sinceMs: 0, moving: false, angle: 0 };
+  const motionPass = {
+    camera: null,
+    wallMs: 0,
+    sinceMs: 0,
+    moving: false,
+    angle: 0,
+    metres: 0,
+  };
   function startMotionPass() {
     const wallMs = performance.now();
     motionPass.camera = state.viewer?.camera ?? null;
+    motionPass.wallMs = wallMs;
     motionPass.sinceMs =
       motionPassWallMs === null ? 0 : wallMs - motionPassWallMs;
     motionPass.moving = false;
     motionPass.angle = 0;
+    motionPass.metres = 0;
     motionPassWallMs = wallMs;
     return motionPass;
   }
@@ -512,14 +534,28 @@ export function createRendering({
     moveRecordVisual(visual, lat, lon);
     if (!visual.billboard?.show && !visual.modelOwnsVisual) return;
     motion.moving = true;
+    const metres = Cesium.Cartesian3.distance(from, visual.position);
+    motion.metres = Math.max(motion.metres, metres);
     const eye = motion.camera?.positionWC;
     if (!eye) return;
     const distance = Cesium.Cartesian3.distance(eye, from);
-    if (distance > 0)
-      motion.angle = Math.max(
-        motion.angle,
-        Cesium.Cartesian3.distance(from, visual.position) / distance,
+    if (distance > 0) motion.angle = Math.max(motion.angle, metres / distance);
+  }
+
+  /** How far the fastest drawn vessel moved on screen in a pass (pixels):
+   * through the perspective view's angle, or across the 2D view's width. */
+  function movedPixels(motion) {
+    const canvas = state.viewer?.canvas;
+    const frustum = motion.camera?.frustum;
+    if (!canvas || !frustum) return 0;
+    if (frustum.fovy > 0 && canvas.clientHeight > 0)
+      return (
+        (motion.angle * canvas.clientHeight) / (2 * Math.tan(frustum.fovy / 2))
       );
+    const width = frustum.right - frustum.left;
+    if (!(frustum.fovy > 0) && width > 0 && canvas.clientWidth > 0)
+      return (motion.metres * canvas.clientWidth) / width;
+    return 0;
   }
 
   // The timer for the next vessel frame while one is asked for, and when it
@@ -534,17 +570,9 @@ export function createRendering({
   function askMotionFrame(motion) {
     if (!motion.moving) return;
     let waitMs = PLACEMENT_FRAME_MS;
-    const canvasHeight = state.viewer?.canvas?.clientHeight;
-    const fovy = motion.camera?.frustum?.fovy;
-    if (
-      canvasHeight > 0 &&
-      fovy > 0 &&
-      motion.angle > 0 &&
-      motion.sinceMs > 0
-    ) {
-      const movedPx = (motion.angle * canvasHeight) / (2 * Math.tan(fovy / 2));
+    const movedPx = movedPixels(motion);
+    if (movedPx > 0 && motion.sinceMs > 0)
       waitMs = Math.min(waitMs, (VESSEL_STEP_PX * motion.sinceMs) / movedPx);
-    }
     // A frame already asked for no later than this one stands.
     const runtime = vesselState._aisRuntime;
     const dueMs = runtime.now() + waitMs;
@@ -943,6 +971,7 @@ export function createRendering({
     cancelTrailingVisibilityPass,
     cancelPlacementFrame,
     followPlacements,
+    followClockPositions,
     applyVesselFocusDeemphasis,
     makeOccluder,
     isVisible,

src/layers/vessels/testing.js

@@ -174,6 +174,13 @@ export function createTesting({
     components.rendering.followPlacements();
   }
 
+  /** Run one world-clock pass at world time `atMs`. Test-only seam. */
+
+  function _runClockPassForTest(atMs) {
+    vesselState.worldNow = () => atMs;
+    components.rendering.followClockPositions();
+  }
+
   /** True while a trailing visibility frame is scheduled. Test-only seam. */
 
   function _hasTrailingVisibilityPassForTest() {
@@ -208,6 +215,7 @@ export function createTesting({
     _runVisibilityPassForTest,
     _prepareVesselVisualForTest,
     _runPlacementPassForTest,
+    _runClockPassForTest,
     _hasTrailingVisibilityPassForTest,
   };
 }

src/layers/vessels/tracking.js

@@ -73,11 +73,10 @@ export function createTracking({
         heightM,
       );
       if (visual.billboard) visual.billboard.position = visual.position;
-      // A placed vessel is drawn again at its placement on the next pass.
-      if (services.placement) {
-        visual.drawnLat = NaN;
-        visual.drawnLon = NaN;
-      }
+      // A moving vessel is drawn again where it is on the next pass.
+      visual.drawnLat = NaN;
+      visual.drawnLon = NaN;
+      visual.followedAtMs = undefined;
     }
   }