docs(changelog): add the #1706 fragment

Co-Authored-By: Claude Fable 5.2 <[email protected]>

changelog.d/1706-alpr-anchor-sampling.md

@@ -0,0 +1,4 @@
+- ALPR camera badges no longer take depth samples while the overlay paints, or
+  again each time the layer is switched back on. On a terrain globe their
+  height comes from the loaded terrain and is remembered per camera; some
+  badges move a few metres onto the drawn surface (mazy1998, #1706).

changelog.d/1713-clouds-infrared-lut.md

@@ -1,3 +0,0 @@
-- Halve the time the satellite cloud image takes to prepare on the 3D Tiles
-  map by applying its transparency curve from a lookup table, in place
-  (mazy1998, #1713).

docs/CURRENT-STATE.md

@@ -1513,10 +1513,14 @@ tile streamed in; floors resolve before new badges appear (bounded wait), and a
 badge whose cell has not resolved clamps until it does, then moves in place.
 Overlay anchors start on the same floor and write marker properties only on
 change. Once the camera is still and tiles have settled, each overlay anchor is
-replaced once by the rendered surface under it (two depth samples per paint,
-accepted only within -30/+40 m of the floor cell), so badges do not float or
-sink on slopes; wedge corners follow their own floor cells instead of staying
-level with the apex. Unknown bearings never acquire a wedge. The selected
+replaced once by the rendered surface under it (accepted only within -30/+40 m
+of the floor cell), so badges do not float or sink on slopes; wedge corners
+follow their own floor cells instead of staying level with the apex. The
+surface is read outside the overlay paint, one camera per frame: a terrain
+globe answers from its loaded mesh (`globe.getHeight`) and only photoreal
+tiles are depth-sampled (`scene.sampleHeight`). Answers are kept per camera
+until the map source changes, so a refresh or turning the layer off and on
+samples nothing again. Unknown bearings never acquire a wedge. The selected
 card's `DIRECTION` wraps after rounding to whole degrees, so a mapped bearing
 of 359.5° or more reads `0°` rather than `360°`. The row reads
 `N nearby · M on screen`; when every loaded camera is outside the view it adds

src/layers/alpr/overlay.js

@@ -4,10 +4,10 @@ import {
   MARKER_ICON_SIZE,
   SELECTED_MARKER_ICON_SIZE,
   MARKER_FLOOR_LIFT_M,
-  ANCHOR_SAMPLES_PER_PAINT,
+  REMEMBERED_ANCHORS,
   SURFACE_BELOW_FLOOR_M,
   SURFACE_ABOVE_FLOOR_M,
-  SURFACE_SAMPLES_PER_PAINT,
+  SURFACE_SAMPLES_PER_FRAME,
 } from './policy.js';
 import {
   MARKER_IMAGE,
@@ -19,11 +19,17 @@ import {
   validAlprGroundHeight,
 } from './visuals.js';
 
+const nextAnimationFrame = (step) =>
+  typeof requestAnimationFrame === 'function'
+    ? requestAnimationFrame(step)
+    : setTimeout(step, 16);
+
 /** Per-layer presentation on a caller-owned overlay; Cesium remains the fallback. */
 export function createAlprOverlay({
   state,
   services,
   onSurfaceChange = () => {},
+  requestFrame = nextAnimationFrame,
 }) {
   let lane,
     removeMapListener,
@@ -33,7 +39,12 @@ export function createAlprOverlay({
     hits = [],
     images = [],
     destroyed = false,
-    lastCamera = null;
+    lastCamera = null,
+    sampling = false;
+  // Rendered-surface answers by camera id. Entities are rebuilt by a refresh
+  // and by turning the layer off and on; keeping the answers on them meant
+  // every rebuild sampled the same cameras again.
+  const surfaceAnswers = new Map();
   const requestPaint = () => {
     if (!destroyed && state.enabled) lane?.requestPaint();
   };
@@ -92,38 +103,72 @@ export function createAlprOverlay({
       entity.gevAlprDisplayPosition = null;
       nativeVisible(entity, true);
     }
+    surfaceAnswers.clear();
     state.lastAnchorSampleAt = 0;
     retryUntil = Date.now() + 15000;
     requestPaint();
   }
 
-  function anchorFor(record, entity, budget) {
-    if (entity.gevAlprCanvasPosition) return entity.gevAlprCanvasPosition;
+  function rememberSurface(record, height, checked) {
+    surfaceAnswers.delete(record.id);
+    surfaceAnswers.set(record.id, {
+      latitude: record.latitude,
+      longitude: record.longitude,
+      height,
+      checked,
+    });
+    if (surfaceAnswers.size > REMEMBERED_ANCHORS)
+      surfaceAnswers.delete(surfaceAnswers.keys().next().value);
+  }
+
+  /**
+   * Rendered surface height under a camera. A terrain globe answers from its
+   * loaded mesh; only photoreal tiles need `sampleHeight`, which renders depth
+   * and compiles its shaders on first use (a freeze of up to 1.9 s at load).
+   */
+  function surfaceHeight(record, entity) {
     const scene = state.viewer.scene;
     const location = Cesium.Cartographic.fromDegrees(
       record.longitude,
       record.latitude,
     );
-    // A floor-placed marker anchors where its native badge sits; only a
-    // marker still waiting for its floor samples the rendered surface, and
-    // each paint samples a few at most (each sample is a depth render).
+    if (scene.globe?.show) return scene.globe.getHeight?.(location);
+    if (!scene.sampleHeightSupported) return undefined;
+    try {
+      return scene.sampleHeight(location, [entity]);
+    } catch {
+      /* streaming tiles */
+      return undefined;
+    }
+  }
+
+  /** The anchor a paint can have without sampling, or null while it waits for one. */
+  function anchorFor(record, entity) {
+    if (entity.gevAlprCanvasPosition) return entity.gevAlprCanvasPosition;
+    const scene = state.viewer.scene;
+    const answer = surfaceAnswers.get(record.id);
+    if (
+      answer?.latitude === record.latitude &&
+      answer.longitude === record.longitude
+    ) {
+      setAnchor(record, entity, answer.height);
+      if (answer.checked)
+        entity.gevAlprSurfaceCheckedFor = entity.gevAlprCanvasPosition;
+      return entity.gevAlprCanvasPosition;
+    }
+    // A floor-placed marker anchors where its native badge sits. A marker
+    // still waiting for its floor reads the terrain globe, or on photoreal
+    // tiles waits for sampleAnchors().
     let height;
     const floor = services.groundFloor.cachedGroundFloor(
       record.latitude,
       record.longitude,
     );
     if (validAlprGroundHeight(floor)) height = floor + MARKER_FLOOR_LIFT_M;
-    else if (scene.sampleHeightSupported) {
-      if (budget.samples <= 0) return null;
-      budget.samples -= 1;
-      try {
-        height = scene.sampleHeight(location, [entity]);
-      } catch {
-        /* streaming tiles */
-      }
-    }
-    if (!validAlprGroundHeight(height) && scene.globe.show)
-      height = scene.globe.getHeight?.(location);
+    else if (scene.globe.show)
+      height = scene.globe.getHeight?.(
+        Cesium.Cartographic.fromDegrees(record.longitude, record.latitude),
+      );
     if (!validAlprGroundHeight(height)) return null;
     setAnchor(record, entity, height);
     return entity.gevAlprCanvasPosition;
@@ -158,14 +203,19 @@ export function createAlprOverlay({
   }
 
   /**
-   * Replace floor anchors with the rendered surface under each overlay camera.
-   * Floors come from ~111 m cells, so on a slope a badge could float or sink
-   * by tens of metres. Runs only while the camera is still and tiles have
-   * settled, a few depth samples per paint, and each anchor at most once;
-   * samples far outside the floor prior (a roof or a streaming tile) are
-   * rejected. Returns whether anchors remain to check.
+   * Sample the rendered surface for the overlay cameras, outside the paint.
+   *
+   * A camera with no floor yet gets its anchor from a sample. An anchored one
+   * is checked against the surface once: floors come from ~111 m cells, so on
+   * a slope a badge could float or sink by tens of metres. Checks run only
+   * while the camera is still and tiles have settled, and samples far outside
+   * the floor prior (a roof or a streaming tile) are rejected. Each frame
+   * takes SURFACE_SAMPLES_PER_FRAME samples, so no frame carries the whole
+   * cohort; sampling inside paint() put up to six depth renders in one frame.
    */
-  function refineAnchors(budget) {
+  function sampleAnchors() {
+    sampling = false;
+    if (destroyed || !state.enabled) return;
     const camera = state.viewer.camera;
     const scene = state.viewer.scene;
     const still =
@@ -188,27 +238,41 @@ export function createAlprOverlay({
         position: Cesium.Cartesian3.clone(camera.positionWC),
         direction: Cesium.Cartesian3.clone(camera.directionWC),
       };
-    if (!scene.sampleHeightSupported) return false;
-    let pending = false;
+    const canSample = scene.globe?.show || scene.sampleHeightSupported;
+    let samples = SURFACE_SAMPLES_PER_FRAME,
+      pending = false,
+      progressed = false,
+      moved = false;
+    // Cameras with no anchor come first: they are not on the overlay yet.
+    for (const record of records) {
+      const entity = state.dataSource.entities.getById(record.id);
+      if (!entity || entity.gevAlprCanvasPosition) continue;
+      // The floor may have resolved since the paint that found none.
+      if (anchorFor(record, entity)) moved = true;
+      else if (!canSample || samples <= 0) pending = true;
+      else {
+        samples -= 1;
+        const sample = surfaceHeight(record, entity);
+        if (validAlprGroundHeight(sample)) {
+          setAnchor(record, entity, sample);
+          rememberSurface(record, sample, false);
+          moved = progressed = true;
+        } else pending = true;
+      }
+    }
     for (const record of records) {
       const entity = state.dataSource.entities.getById(record.id);
       const anchor = entity?.gevAlprCanvasPosition;
-      if (!anchor || entity.gevAlprSurfaceCheckedFor === anchor) continue;
-      if (!still || !surfaceSettled(scene) || budget.samples <= 0) {
+      if (!anchor || !canSample || entity.gevAlprSurfaceCheckedFor === anchor)
+        continue;
+      if (!still || !surfaceSettled(scene) || samples <= 0) {
         pending = true;
         continue;
       }
-      budget.samples -= 1;
-      let sample;
-      try {
-        sample = scene.sampleHeight(
-          Cesium.Cartographic.fromDegrees(record.longitude, record.latitude),
-          [entity],
-        );
-      } catch {
-        /* streaming tiles */
-      }
-      const current = Cesium.Cartographic.fromCartesian(anchor).height;
+      samples -= 1;
+      progressed = true;
+      const sample = surfaceHeight(record, entity);
+      let height = Cesium.Cartographic.fromCartesian(anchor).height;
       const floor = services.groundFloor.cachedGroundFloor(
         record.latitude,
         record.longitude,
@@ -218,21 +282,43 @@ export function createAlprOverlay({
         (!validAlprGroundHeight(floor) ||
           (sample >= floor - SURFACE_BELOW_FLOOR_M &&
             sample <= floor + SURFACE_ABOVE_FLOOR_M));
-      if (accepted && Math.abs(sample + MARKER_FLOOR_LIFT_M - current) > 1)
-        setAnchor(record, entity, sample + MARKER_FLOOR_LIFT_M);
+      if (accepted && Math.abs(sample + MARKER_FLOOR_LIFT_M - height) > 1) {
+        height = sample + MARKER_FLOOR_LIFT_M;
+        setAnchor(record, entity, height);
+        moved = true;
+      }
       entity.gevAlprSurfaceCheckedFor = entity.gevAlprCanvasPosition;
+      // A surface that did not answer is asked again after a rebuild.
+      if (validAlprGroundHeight(sample)) rememberSurface(record, height, true);
       if (entity.id === state.selectedId)
         entity.gevAlprDisplayPosition = entity.gevAlprCanvasPosition;
     }
-    return pending;
+    if (moved) requestPaint();
+    if (!pending || Date.now() >= retryUntil) return;
+    // Take the next ration on the next frame; when nothing could be sampled
+    // (camera moving, tiles streaming, no floor yet) look again in 250 ms.
+    if (progressed) scheduleSampling();
+    else if (!retryTimer)
+      retryTimer = setTimeout(() => {
+        retryTimer = null;
+        scheduleSampling();
+      }, 250);
+  }
+
+  function scheduleSampling() {
+    if (sampling || destroyed) return;
+    sampling = true;
+    requestFrame(sampleAnchors);
   }
 
   function paint({ ctx, width, height, keyhole, occluder }) {
     hits = [];
     if (!state.enabled || destroyed) return;
-    let unresolved = false;
+    let waiting = false;
     const painted = [];
-    const budget = { samples: ANCHOR_SAMPLES_PER_PAINT };
+    const canSample =
+      state.viewer.scene.globe?.show ||
+      state.viewer.scene.sampleHeightSupported;
     for (const record of records) {
       const entity = state.dataSource.entities.getById(record.id);
       if (!entity) continue;
@@ -246,12 +332,14 @@ export function createAlprOverlay({
         nativeVisible(entity, true);
         continue;
       }
-      const anchor = anchorFor(record, entity, budget);
+      const anchor = anchorFor(record, entity);
       if (!anchor) {
         nativeVisible(entity, true);
-        unresolved = true;
+        waiting = true;
         continue;
       }
+      if (canSample && entity.gevAlprSurfaceCheckedFor !== anchor)
+        waiting = true;
       canvasOwned(entity, true);
       if (occluder && !occluder.isPointVisible(anchor)) {
         setShown(entity, false);
@@ -335,15 +423,9 @@ export function createAlprOverlay({
       ctx.restore();
       hits.push({ id: record.id, x: origin.x, y: origin.y, radius: size / 2 });
     }
-    const refining = refineAnchors({
-      samples: Math.min(budget.samples, SURFACE_SAMPLES_PER_PAINT),
-    });
-    if ((unresolved || refining) && !retryTimer && Date.now() < retryUntil) {
-      retryTimer = setTimeout(() => {
-        retryTimer = null;
-        requestPaint();
-      }, 250);
-    }
+    // Anchors still to find or to check are sampled after this paint, a few
+    // per frame, never inside it.
+    if (waiting && !retryTimer && Date.now() < retryUntil) scheduleSampling();
   }
 
   return {

src/layers/alpr/overlay.test.mjs

@@ -45,8 +45,10 @@ function harness(t, count = 2, { floor = null } = {}) {
     active,
     removed = 0,
     paints = 0;
+  const frames = [];
   const overlay = createAlprOverlay({
     state,
+    requestFrame: (step) => frames.push(step),
     services: {
       groundFloor: { cachedGroundFloor: () => floor },
       overlays: {
@@ -106,6 +108,12 @@ function harness(t, count = 2, { floor = null } = {}) {
     entities,
     draw,
     paint: (occluder) => paint({ ctx, width: 800, height: 600, occluder }),
+    /** Run the sampling step queued for the next animation frame, if any. */
+    frame() {
+      const step = frames.shift();
+      step?.();
+      return Boolean(step);
+    },
     mapChanged() {
       mapListener({ detail: { status: 'ready' } });
     },
@@ -243,41 +251,149 @@ test('overlay glyphs and native badges shrink alike with distance', () => {
   assert.ok(Math.abs(markerScale(20_250) - 0.8) < 1e-9);
 });
 
-test('a still view replaces floor anchors with the rendered surface, within the floor window', (t) => {
-  // Floors come from ~111 m cells; on a slope a badge floated above the mesh.
-  const h = harness(t, 2, { floor: 150 });
+/** A photoreal scene: no globe, the rendered surface read by depth samples. */
+function photoreal(h, heightAt = () => 172) {
   const scene = h.state.viewer.scene;
-  const camera = h.state.viewer.camera;
-  camera.directionWC = Cesium.Cartesian3.UNIT_X;
+  h.state.viewer.camera.directionWC = Cesium.Cartesian3.UNIT_X;
+  scene.globe.show = false;
   scene.sampleHeightSupported = true;
   scene.primitives = { length: 0, get: () => null };
-  let samples = 0;
+  const sampled = [];
   scene.sampleHeight = (carto) => {
-    samples++;
-    return Cesium.Math.toDegrees(carto.latitude) > 30.00005 ? 400 : 172;
+    sampled.push(carto);
+    return heightAt(Cesium.Math.toDegrees(carto.latitude));
   };
+  return sampled;
+}
+
+const anchorHeight = (h, id) =>
+  Cesium.Cartographic.fromCartesian(
+    h.entities.getById(id).gevAlprCanvasPosition,
+  ).height;
+
+/** Run sampling frames until none is queued, waiting out the 250 ms look-again. */
+function settle(t, h) {
+  for (let i = 0; i < 400; i++) if (!h.frame()) t.mock.timers.tick(250);
+}
+
+test('a still view replaces floor anchors with the rendered surface, within the floor window', (t) => {
+  // Floors come from ~111 m cells; on a slope a badge floated above the mesh.
+  t.mock.timers.enable({ apis: ['setTimeout', 'Date'] });
+  const h = harness(t, 2, { floor: 150 });
+  const sampled = photoreal(h, (latitude) => (latitude > 30.00005 ? 400 : 172));
   h.overlay.sync(h.records);
   h.paint();
-  const height = (id) =>
-    Cesium.Cartographic.fromCartesian(
-      h.entities.getById(id).gevAlprCanvasPosition,
-    ).height;
+  assert.ok(
+    Math.abs(anchorHeight(h, 'camera:0') - 151.5) < 0.01,
+    'floor anchor first',
+  );
+  assert.equal(h.frame(), true, 'the paint queued a sampling frame');
   assert.equal(
-    samples,
+    sampled.length,
     0,
     'no depth samples while the camera may still be moving',
   );
-  assert.ok(Math.abs(height('camera:0') - 151.5) < 0.01, 'floor anchor first');
-  h.paint();
+  settle(t, h);
   assert.ok(
-    Math.abs(height('camera:0') - 173.5) < 0.01,
+    Math.abs(anchorHeight(h, 'camera:0') - 173.5) < 0.01,
     'rendered surface once still',
   );
   assert.ok(
-    Math.abs(height('camera:1') - 151.5) < 0.01,
+    Math.abs(anchorHeight(h, 'camera:1') - 151.5) < 0.01,
     'a rooftop-height sample is rejected',
   );
-  const taken = samples;
+  assert.equal(sampled.length, 2);
   h.paint();
-  assert.equal(samples, taken, 'each anchor is checked once');
+  settle(t, h);
+  assert.equal(sampled.length, 2, 'each anchor is checked once');
+});
+
+test('a paint never samples the surface; frames take one sample each', (t) => {
+  // Sampling inside paint() put up to six depth renders into one frame, and
+  // the first of them compiles shaders: a freeze of 0.8 to 1.9 s at load.
+  t.mock.timers.enable({ apis: ['setTimeout', 'Date'] });
+  const h = harness(t, 8);
+  const sampled = photoreal(h);
+  h.overlay.sync(h.records);
+  h.paint();
+  h.paint();
+  assert.equal(sampled.length, 0, 'no sample inside a paint');
+  assert.equal(h.draw.length, 0, 'unanchored cameras keep their native badge');
+  for (let taken = 1; taken <= 8; taken++) {
+    assert.equal(h.frame(), true);
+    assert.equal(sampled.length, taken, 'one sample per frame');
+  }
+  for (const record of h.records)
+    assert.ok(Math.abs(anchorHeight(h, record.id) - 172) < 0.01);
+  h.paint();
+  assert.ok(h.draw.length > 0, 'anchored cameras paint on the overlay');
+});
+
+test('a terrain globe is read from its mesh, never depth-sampled', (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout', 'Date'] });
+  const h = harness(t, 3, { floor: 150 });
+  const sampled = photoreal(h);
+  const scene = h.state.viewer.scene;
+  scene.globe.show = true;
+  scene.globe.tilesLoaded = true;
+  let reads = 0;
+  scene.globe.getHeight = () => {
+    reads++;
+    return 172;
+  };
+  h.overlay.sync(h.records);
+  h.paint();
+  settle(t, h);
+  assert.equal(sampled.length, 0);
+  assert.equal(reads, 3);
+  // The same anchor the depth sample gave: the surface plus the marker lift.
+  for (const record of h.records)
+    assert.ok(Math.abs(anchorHeight(h, record.id) - 173.5) < 0.01);
+});
+
+test('surface answers outlive rebuilt markers and a re-enable, until the map changes', (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout', 'Date'] });
+  const h = harness(t, 4, { floor: 150 });
+  const sampled = photoreal(h);
+  h.overlay.sync(h.records);
+  h.paint();
+  settle(t, h);
+  assert.equal(sampled.length, 4);
+  const before = h.records.map((record) => anchorHeight(h, record.id));
+
+  // A refresh or a toggle removes the entities and builds new ones.
+  const rebuild = () => {
+    h.overlay.clear();
+    h.entities.removeAll();
+    for (const record of h.records)
+      h.entities.add({
+        id: record.id,
+        billboard: { image: 'fallback', show: true },
+        polyline: { show: true },
+        polygon: { show: true },
+      });
+    h.overlay.sync(h.records);
+    h.paint();
+    settle(t, h);
+  };
+  rebuild();
+  h.state.enabled = false;
+  h.overlay.clear();
+  h.state.enabled = true;
+  rebuild();
+  assert.equal(sampled.length, 4, 'no camera is sampled again');
+  assert.deepEqual(
+    h.records.map((record) => anchorHeight(h, record.id)),
+    before,
+  );
+
+  // A camera that moved is a different question.
+  h.records[0] = { ...h.records[0], latitude: h.records[0].latitude + 0.001 };
+  rebuild();
+  assert.equal(sampled.length, 5);
+
+  h.mapChanged();
+  h.paint();
+  settle(t, h);
+  assert.equal(sampled.length, 9, 'a new map surface is sampled afresh');
 });

src/layers/alpr/policy.js

@@ -66,14 +66,15 @@ export const MAX_CANVAS_FRUSTUMS = 64;
 /** Metres a floor-placed marker sits above its resolved ground cell. */
 export const MARKER_FLOOR_LIFT_M = 1.5;
 
-/** Rendered-surface samples one overlay paint may take (each is a depth render). */
-export const ANCHOR_SAMPLES_PER_PAINT = 4;
+/** Rendered-surface samples one frame may take (on photoreal tiles each is a
+ * depth render of several milliseconds, so they are spread over frames). */
+export const SURFACE_SAMPLES_PER_FRAME = 1;
+/** Surface answers kept by camera id, so a refresh or re-enable asks nothing. */
+export const REMEMBERED_ANCHORS = 2048;
 
 /** Accepted rendered-surface window around a floor cell (a cut or an embankment
  * sits within it; a rooftop or an unstreamed tile usually does not). */
 export const SURFACE_BELOW_FLOOR_M = 30;
-/** Rendered-surface refinements per paint while the camera is still. */
-export const SURFACE_SAMPLES_PER_PAINT = 2;
 export const SURFACE_ABOVE_FLOOR_M = 40;
 
 /** OSM attribution may collapse after five seconds; full credit stays in Data attribution. */

src/layers/weather/infraredAlpha.js

@@ -1,29 +1,22 @@
 export const INFRARED_ALPHA_T0 = 0.4;
 export const INFRARED_ALPHA_T1 = 0.7;
 
-function infraredAmount(strength) {
-  return strength === 'full'
-    ? 0
-    : strength === 'filtered' || !Number.isFinite(strength)
-      ? 1
-      : Math.max(0, Math.min(100, strength)) / 100;
-}
-
-/** Scale each pixel's alpha in place; RGB is left as it is. The scale depends
- * only on the brightest channel, so it is worked out once for each of the 256
- * byte values instead of once per pixel: a 4096×2048 image has 8.4 million
- * pixels and the power curve per pixel held the page for over 100 ms. The
- * table holds the same numbers the per-pixel formula produced, so the output
- * bytes are unchanged.
+/** Return display pixels without changing RGB or the source RGBA bytes.
  * `strength` is 0–100: zero is the full image and 100 is the cloud key.
  */
-export function applyInfraredAlpha(pixels, strength = 'filtered') {
-  const amount = infraredAmount(strength);
+export function infraredAlpha(rgba, strength = 'filtered') {
+  const pixels = new Uint8ClampedArray(rgba);
+  const amount =
+    strength === 'full'
+      ? 0
+      : strength === 'filtered' || !Number.isFinite(strength)
+        ? 1
+        : Math.max(0, Math.min(100, strength)) / 100;
   if (amount === 0) return pixels;
-  const scale = new Float64Array(256);
-  for (let value = 0; value < 256; value++) {
+  for (let i = 0; i < pixels.length; i += 4) {
     // Match Cesium's czm_srgbToLinear conversion in draped imagery.
-    const linearMax = (value / 255) ** 2.2;
+    const linearMax =
+      (Math.max(rgba[i], rgba[i + 1], rgba[i + 2]) / 255) ** 2.2;
     const t = Math.max(
       0,
       Math.min(
@@ -33,21 +26,7 @@ export function applyInfraredAlpha(pixels, strength = 'filtered') {
       ),
     );
     const filtered = t * t * (3 - 2 * t);
-    scale[value] = 1 - amount + filtered * amount;
-  }
-  for (let i = 0; i < pixels.length; i += 4) {
-    const r = pixels[i];
-    const g = pixels[i + 1];
-    const b = pixels[i + 2];
-    const max = r > g ? (r > b ? r : b) : g > b ? g : b;
-    pixels[i + 3] = pixels[i + 3] * scale[max];
+    pixels[i + 3] = rgba[i + 3] * (1 - amount + filtered * amount);
   }
   return pixels;
 }
-
-/** Return display pixels without changing RGB or the source RGBA bytes.
- * `strength` is 0–100: zero is the full image and 100 is the cloud key.
- */
-export function infraredAlpha(rgba, strength = 'filtered') {
-  return applyInfraredAlpha(new Uint8ClampedArray(rgba), strength);
-}

src/layers/weather/infraredAlpha.test.mjs

@@ -1,7 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import {
-  applyInfraredAlpha,
   infraredAlpha,
   INFRARED_ALPHA_T0,
   INFRARED_ALPHA_T1,
@@ -62,43 +61,3 @@ test('full infrared preserves every channel including partial and zero alpha', (
   ]);
   assert.deepEqual(infraredAlpha(pixels, 'full'), pixels);
 });
-
-test('the lookup table gives the per-pixel curve byte for byte, in place', () => {
-  // The transfer as it was written per pixel, before the table.
-  const perPixel = (rgba, amount) => {
-    const out = new Uint8ClampedArray(rgba);
-    for (let i = 0; i < out.length; i += 4) {
-      const linearMax =
-        (Math.max(rgba[i], rgba[i + 1], rgba[i + 2]) / 255) ** 2.2;
-      const t = Math.max(
-        0,
-        Math.min(
-          1,
-          (linearMax - INFRARED_ALPHA_T0) /
-            (INFRARED_ALPHA_T1 - INFRARED_ALPHA_T0),
-        ),
-      );
-      out[i + 3] = rgba[i + 3] * (1 - amount + t * t * (3 - 2 * t) * amount);
-    }
-    return out;
-  };
-  // Every brightest-channel value in each channel, against a spread of alphas.
-  const bytes = [];
-  for (let value = 0; value < 256; value++)
-    for (const alpha of [0, 1, 37, 128, 200, 254, 255]) {
-      bytes.push(value, 0, 0, alpha);
-      bytes.push(value >> 1, value, 0, alpha);
-      bytes.push(0, value >> 2, value, alpha);
-    }
-  const source = new Uint8ClampedArray(bytes);
-  for (const strength of [1, 33, 50, 99, 100, 'filtered', Number.NaN]) {
-    const amount = Number.isFinite(strength) ? strength / 100 : 1;
-    const pixels = source.slice();
-    assert.equal(applyInfraredAlpha(pixels, strength), pixels);
-    assert.deepEqual(pixels, perPixel(source, amount), `strength ${strength}`);
-  }
-  for (const strength of [0, 'full']) {
-    const pixels = source.slice();
-    assert.deepEqual(applyInfraredAlpha(pixels, strength), source);
-  }
-});

src/layers/weather/infraredImage.js

@@ -6,7 +6,7 @@ import {
   drawWeatherPixels,
   closeWeatherPixels,
 } from './source.js';
-import { applyInfraredAlpha } from './infraredAlpha.js';
+import { infraredAlpha } from './infraredAlpha.js';
 
 export const MAX_MOSAIC_BYTES = 4 * 1024 * 1024;
 
@@ -31,8 +31,7 @@ export function processInfraredImage(
 
 function applyInfraredTransfer(context, canvas, mode) {
   const pixels = context.getImageData(0, 0, canvas.width, canvas.height);
-  // In place: a copy of a 4096×2048 image is 33 MB, made and written back.
-  applyInfraredAlpha(pixels.data, mode);
+  pixels.data.set(infraredAlpha(pixels.data, mode));
   context.putImageData(pixels, 0, 0);
 }
 

src/layers/weather/infraredImage.test.mjs

@@ -26,28 +26,6 @@ function canvas() {
   return output;
 }
 
-test('the transfer is applied to the canvas pixels in place, with no copy written back', () => {
-  let read = null;
-  const output = {};
-  output.getContext = () => ({
-    drawImage() {},
-    getImageData: () => {
-      read = { data: new Uint8ClampedArray([194, 0, 0, 200]) };
-      // A second full-size buffer copied over the first is what this guards.
-      read.data.set = () => {
-        throw new Error('the canvas pixels were overwritten from a copy');
-      };
-      return read;
-    },
-    putImageData: (pixels) => {
-      output.pixels = pixels;
-    },
-  });
-  processInfraredImage({ width: 1, height: 1 }, 'filtered', () => output);
-  assert.equal(output.pixels, read);
-  assert.deepEqual([...read.data], [194, 0, 0, 98]);
-});
-
 test('decoded pixels are processed once on a same-sized canvas', () => {
   const image = { width: 1, height: 1 };
   const output = processInfraredImage(image, 'filtered', canvas);