feat(globe): mover sets report ready(); Navara scales by distance as Cesium

Task 10b foundation.
- MoverSet.ready(): whether what the set draws has loaded (Navara: the
  model set's glTF, a URL atlas; Cesium: every instance's Model, the cropped
  atlas; parts without it draw at once). The aircraft renderer keeps the 2D
  glyph until a model set is ready, as the Cesium path waits on Model.ready.
  Contract suite: a drawn model set is ready() (both engines); unit test of
  the neutral store.
- Navara sprites and points interpolate scaleByDistance as Cesium's
  NearFarScalar (over the squared camera distance, eased by ^0.2) instead
  of linearly in distance, so aircraft glyphs have Cesium's size at every
  range; the CPU pick radius follows (distanceScale, tested equal to
  focusDeemphasis' port of czm_nearFarScalar). The contract text says so.

src/globe/cesium/movers.js

@@ -139,6 +139,7 @@ function spritePart(scene, options, store, factories, requestRender, owners) {
     .catch((error) => console.warn(`[movers] ${id}: atlas failed`, error));
   return {
     primitive: collection,
+    ready: () => cells !== null,
     commit(range) {
       if (cells && range) apply(range.from, range.to);
       requestRender('movers');
@@ -254,6 +255,11 @@ function modelPart(options, store, factories, requestRender, owners) {
   };
   return {
     primitive: collection,
+    ready() {
+      for (let index = 0; index < store.count; index++)
+        if (!models[index]?.ready) return false;
+      return true;
+    },
     commit(range) {
       if (range)
         for (let index = range.from; index < range.to; index++) {
@@ -308,6 +314,7 @@ export function createCesiumMovers(
     rootCollection().add(primitive, at);
     return {
       primitive,
+      ready: part.ready,
       commit: () => part.commit(store.dirty()),
       destroy() {
         part.destroy();

src/globe/contract.js

@@ -317,7 +317,8 @@
  *   sizePx: number, scaleByDistance?: number[] }} [sprite] An image atlas
  *   whose cells are [u0, v0, u1, v1] in 0..1 (v down from the image top);
  *   each sprite is a square of sizePx CSS px times its scale, times the
- *   NearFarScalar [nearM, nearScale, farM, farScale] when given.
+ *   NearFarScalar [nearM, nearScale, farM, farScale] when given (Cesium's
+ *   interpolation: over the squared camera distance, eased by ^0.2).
  * @property {{ sizePx: number, outlinePx?: number, scaleByDistance?: number[] }} [point]
  *   A filled disc of sizePx CSS px diameter with a dark outline.
  * @property {{ url: string, minimumPixelSize?: number, maximumScale?: number,
@@ -348,6 +349,9 @@
  *   requests a render; nothing else draws a frame.
  * @property {() => Float64Array} positionsView x, y, z of the drawn
  *   instances (a view on the set's own array; read-only).
+ * @property {() => boolean} ready Whether what the set draws has loaded: a
+ *   model set's glTF (Cesium: every instance's model), a sprite set's atlas.
+ *   A layer keeps its fallback visual until then.
  * @property {() => void} destroy
  *
  * @typedef {object} GlobeMovers

src/globe/cpuPicks.js

@@ -42,14 +42,22 @@ const segmentT = (p, a, b) => {
     : 0;
 };
 
-// scaleByDistance [nearM, nearScale, farM, farScale] at `distance`, linear
-// between near and far as the Navara mover shader draws it.
-function distanceScale(scaleByDistance, distance) {
+// scaleByDistance [nearM, nearScale, farM, farScale] at `distance`, as
+// Cesium's NearFarScalar and the Navara mover shader draw it: over the
+// squared distance, eased by ^0.2.
+export function distanceScale(scaleByDistance, distance) {
   if (!scaleByDistance) return 1;
   const [near, nearScale, far, farScale] = scaleByDistance;
-  const t = Math.min(
-    1,
-    Math.max(0, (distance - near) / Math.max(far - near, 1e-6)),
+  const t = Math.pow(
+    Math.min(
+      1,
+      Math.max(
+        0,
+        (distance * distance - near * near) /
+          Math.max(far * far - near * near, 1e-6),
+      ),
+    ),
+    0.2,
   );
   return nearScale + (farScale - nearScale) * t;
 }

src/globe/cpuPicks.test.mjs

@@ -46,8 +46,28 @@ test('the CPU pick radius follows scaleByDistance', () => {
   const shrink = [1_000, 1, 10_000, 0.25];
   assert.equal(pickAt(22, shrink), 0);
   assert.equal(pickAt(7, shrink), 1);
-  // Halfway between near and far: linear, as the Navara shader draws it.
+  // Halfway between near and far: Cesium's NearFarScalar (squared distance,
+  // eased by ^0.2): t = 0.25^0.2 = 0.758, scale 0.621, radius 12.4 + 3 px.
   const half = [0, 1, 20_000, 0.5];
-  assert.equal(pickAt(17, half), 1, '15 + 3 px');
-  assert.equal(pickAt(19, half), 0);
+  assert.equal(pickAt(15, half), 1, '12.4 + 3 px');
+  assert.equal(pickAt(16, half), 0);
+});
+
+test('distanceScale is Cesium.NearFarScalar interpolation', async () => {
+  const Cesium = await import('cesium');
+  const { distanceScale } = await import('./cpuPicks.js');
+  const scalar = [1000, 3.0, 8_000_000, 0.5];
+  // Cesium's czm_nearFarScalar on the CPU (focusDeemphasis ports it too).
+  const { nearFarScalarValueAtDistance } =
+    await import('../data/focusDeemphasis.js');
+  for (const distance of [0, 1000, 5000, 1e5, 2e6, 8e6, 2e7]) {
+    const expected = nearFarScalarValueAtDistance(
+      new Cesium.NearFarScalar(...scalar),
+      distance,
+    );
+    assert.ok(
+      Math.abs(distanceScale(scalar, distance) - expected) < 1e-12,
+      `${distance} m`,
+    );
+  }
 });

src/globe/movers.js

@@ -309,7 +309,10 @@ export function createMoverStore(options) {
  * destroy. commit() hands the engine the changed range and cleans the store;
  * a destroyed set refuses every call but destroy().
  */
-export function createMoverSet(store, { id, commit, destroy }) {
+export function createMoverSet(
+  store,
+  { id, commit, destroy, ready = () => true },
+) {
   let destroyed = false;
   const alive = () => {
     if (destroyed) throw new Error('Mover set was destroyed');
@@ -332,6 +335,8 @@ export function createMoverSet(store, { id, commit, destroy }) {
       store.clean();
     },
     positionsView: () => store.positionsView(),
+    // Whether what it draws has loaded (a model's glTF, an atlas image).
+    ready: () => !destroyed && ready() === true,
     destroy() {
       if (destroyed) return;
       destroyed = true;
@@ -367,6 +372,7 @@ export function createMoverRegistry(build) {
           sets.delete(options.id);
           part.destroy();
         },
+        ready: () => (part.ready ? part.ready() : true),
       });
       sets.set(options.id, entry);
       return entry.set;

src/globe/movers.test.mjs

@@ -2,6 +2,7 @@ import assert from 'node:assert/strict';
 import test from 'node:test';
 import {
   MOVER_KINDS,
+  createMoverRegistry,
   createMoverSet,
   createMoverStore,
   normalizeMoverSetOptions,
@@ -207,3 +208,31 @@ test('a destroyed set releases its instance arrays', () => {
   assert.equal(set.positionsView().length, 0);
   assert.equal(store.dirty(), null);
 });
+
+test('a set is ready() once what it draws has loaded, never once destroyed', () => {
+  let loaded = false;
+  const registry = createMoverRegistry(() => ({
+    commit() {},
+    destroy() {},
+    ready: () => loaded,
+  }));
+  const set = registry.movers.createSet({
+    id: 'r',
+    kind: 'point',
+    capacity: 1,
+    point: { sizePx: 4 },
+  });
+  assert.equal(set.ready(), false);
+  loaded = true;
+  assert.equal(set.ready(), true);
+  set.destroy();
+  assert.equal(set.ready(), false);
+  const plain = createMoverRegistry(() => ({ commit() {}, destroy() {} }));
+  assert.equal(
+    plain.movers
+      .createSet({ id: 'p', kind: 'point', capacity: 1, point: { sizePx: 4 } })
+      .ready(),
+    true,
+    'an engine part without ready() draws at once',
+  );
+});

src/globe/navara/movers/index.js

@@ -129,6 +129,7 @@ export function createNavaraMovers(view, { overlay }) {
     }
     overlay.add(mover.mesh, () => updateMover(view, overlay.ctx, mover));
     return {
+      ready: mover.ready,
       commit() {
         mover.commit(store.dirty());
         request();
@@ -158,6 +159,7 @@ export function createNavaraMovers(view, { overlay }) {
       },
     });
     return {
+      ready: mover.ready,
       commit() {
         mover.commit(store.dirty());
         request();

src/globe/navara/movers/modelMover.js

@@ -176,6 +176,7 @@ export function createModelMover(options, store, { load, onLoad = () => {} }) {
   return {
     group,
     uniforms,
+    ready: () => loaded,
     origin: () => origin,
     commit(range) {
       if (!origin && store.count > 0)

src/globe/navara/movers/moverMesh.js

@@ -50,12 +50,15 @@ vec4 mvCenter = modelViewMatrix * instanceMatrix * vec4(0.0, 0.0, 0.0, 1.0);
 float gevScale = gevStyle.y;
 float gevDistance = length(mvCenter.xyz);
 if (uGevHasScaleByDistance > 0.5) {
+  // Cesium's czm_nearFarScalar: over the squared distance, eased by ^0.2.
+  float gevNearSq = uGevScaleByDistance.x * uGevScaleByDistance.x;
+  float gevFarSq = uGevScaleByDistance.z * uGevScaleByDistance.z;
   float t = clamp(
-    (gevDistance - uGevScaleByDistance.x) /
-      max(uGevScaleByDistance.z - uGevScaleByDistance.x, 1e-6),
+    (gevDistance * gevDistance - gevNearSq) / max(gevFarSq - gevNearSq, 1e-6),
     0.0,
     1.0
   );
+  t = pow(t, 0.2);
   gevScale *= mix(uGevScaleByDistance.y, uGevScaleByDistance.w, t);
 }
 float gevSizePx = uGevSizePx * gevScale;
@@ -213,8 +216,15 @@ export function createMoverMesh(
     tGevSceneDepth: overlayUniforms.tGevSceneDepth,
     uGevResolution: overlayUniforms.uGevResolution,
   };
+  // A canvas atlas is there at once; a URL one once its image loads.
+  let textureReady = point || Boolean(options.sprite.atlas.canvas);
   const material = new MeshBasicMaterial({
-    map: point ? null : atlasTexture(options.sprite.atlas, onTextureLoad),
+    map: point
+      ? null
+      : atlasTexture(options.sprite.atlas, () => {
+          textureReady = true;
+          onTextureLoad();
+        }),
     transparent: true,
     alphaTest: 0.02,
     // Drawn after tone mapping, with no depth buffer: the shader tests the
@@ -260,6 +270,7 @@ export function createMoverMesh(
   return {
     mesh,
     uniforms,
+    ready: () => textureReady,
     origin: () => origin,
     /** Writes the changed instances; the origin starts at the first one. */
     commit(range) {

src/globe/testing/contractSuite.mjs

@@ -1210,6 +1210,7 @@ export function createContractSuite(
             return count;
           };
           await until(() => modelPixels() > 150, 'the model drawn');
+          ensure(models.ready(), 'a drawn model set is not ready()');
         } finally {
           for (const set of sets) set.destroy();
         }