docs(changelog): add the #1721 fragment

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

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

@@ -0,0 +1,3 @@
+- 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).

changelog.d/1721-clouds-infrared-shader.md

@@ -0,0 +1,3 @@
+- Satellite clouds on the 3D Tiles map apply their transparency in the shader
+  instead of rewriting each 4096 x 2048 image on the page, and changing the
+  cloud strength no longer builds a new image (mazy1998, #1721).

docs/CURRENT-STATE.md

@@ -891,9 +891,11 @@ image proxy accepts `bbox=west,south,east,north` for every product: inside the
 product bounds, 2:1 within 1 %, rounded to 0.25°, up to 4096×2048 (the
 default), cached by product, time, size and bbox. Diagnostics report
 `shell.detail` (`bbox`, `size`, `ready`, `enabled`).
-Clouds only applies a soft brightness ramp to decoded pixels once, using
+Clouds only applies a soft brightness ramp, using
 Cesium's sRGB-to-linear conversion (`channel ** 2.2`) and smoothstep from 0.40
-to 0.70. The old 0.55 threshold is the ramp midpoint. RGB and source alpha are
+to 0.70. Globe hosts apply it to decoded pixels once; a shell applies the same
+ramp in its fragment shader from a strength uniform, so its images are drawn
+as decoded and a strength change neither fetches nor rewrites an image. The old 0.55 threshold is the ramp midpoint. RGB and source alpha are
 preserved in Full image mode; both modes use the chosen layer opacity. This
 is a display filter, not a cloud mask. The cloud-filter slider is a continuous
 0–100% strength: 0% is Full, 100% is the existing Clouds only key, and
@@ -909,13 +911,13 @@ and processes it before staging. Globe hosts crop that canvas into 256 px tiles
 to maximum level 3 on a geographic 2×1 root grid bounded to the manifest extent,
 avoiding request-dependent contrast seams.
 On globe hosts, regional infrared retains network tiles and processes each
-decoded tile once; shells process each whole frame once.
+decoded tile once; shells never read a frame's pixels back.
 Exact-time tile and image responses are immutable for 24 hours; manifests and
 errors remain uncached. Each globe renderer retains up to 6 processed global
 mosaics in a least-recently-used cache keyed by observation time and infrared
 mode (up to 48 MiB of canvas pixels). Each shell keeps decoded full-extent and
 detail images in one least-recently-used cache bounded at 128 MiB, keyed by
-time, mode and window: the shown frame and the warmed next frame, each
+time and window: the shown frame and the warmed next frame, each
 full-extent and detail; nothing older survives them. Disable clears the caches.
 Cache hits skip
 fetch/decode and report `mosaic.cached: true` with zero decode time.

src/layers/weather/infraredAlpha.js

@@ -1,22 +1,31 @@
 export const INFRARED_ALPHA_T0 = 0.4;
 export const INFRARED_ALPHA_T1 = 0.7;
 
-/** Return display pixels without changing RGB or the source RGBA bytes.
+/** How much of the cloud key applies, 0–1, for a display mode or a 0–100
+ * strength. The weather shell passes it to its fragment shader. */
+export 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.
  * `strength` is 0–100: zero is the full image and 100 is the cloud key.
  */
-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;
+export function applyInfraredAlpha(pixels, strength = 'filtered') {
+  const amount = infraredAmount(strength);
   if (amount === 0) return pixels;
-  for (let i = 0; i < pixels.length; i += 4) {
+  const scale = new Float64Array(256);
+  for (let value = 0; value < 256; value++) {
     // Match Cesium's czm_srgbToLinear conversion in draped imagery.
-    const linearMax =
-      (Math.max(rgba[i], rgba[i + 1], rgba[i + 2]) / 255) ** 2.2;
+    const linearMax = (value / 255) ** 2.2;
     const t = Math.max(
       0,
       Math.min(
@@ -26,7 +35,21 @@ export function infraredAlpha(rgba, strength = 'filtered') {
       ),
     );
     const filtered = t * t * (3 - 2 * t);
-    pixels[i + 3] = rgba[i + 3] * (1 - amount + filtered * amount);
+    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];
   }
   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

@@ -1,6 +1,7 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import {
+  applyInfraredAlpha,
   infraredAlpha,
   INFRARED_ALPHA_T0,
   INFRARED_ALPHA_T1,
@@ -61,3 +62,43 @@ 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 { infraredAlpha } from './infraredAlpha.js';
+import { applyInfraredAlpha } from './infraredAlpha.js';
 
 export const MAX_MOSAIC_BYTES = 4 * 1024 * 1024;
 
@@ -31,13 +31,22 @@ export function processInfraredImage(
 
 function applyInfraredTransfer(context, canvas, mode) {
   const pixels = context.getImageData(0, 0, canvas.width, canvas.height);
-  pixels.data.set(infraredAlpha(pixels.data, mode));
+  // In place: a copy of a 4096×2048 image is 33 MB, made and written back.
+  applyInfraredAlpha(pixels.data, mode);
   context.putImageData(pixels, 0, 0);
 }
 
 /** Draw pixels a frame source supplied into a new canvas, with the display
  * transfer for infrared products, and release them. They must be `size`. */
-function drawSuppliedImage(pixels, product, mode, size, signal, createCanvas) {
+function drawSuppliedImage(
+  pixels,
+  product,
+  mode,
+  size,
+  signal,
+  createCanvas,
+  transfer,
+) {
   try {
     signal.throwIfAborted();
     const { width, height } = weatherPixelSize(pixels);
@@ -48,7 +57,7 @@ function drawSuppliedImage(pixels, product, mode, size, signal, createCanvas) {
     texture.height = height;
     const context = texture.getContext('2d');
     drawWeatherPixels(context, pixels);
-    if (product === 'clouds' || product === 'clouds-regional')
+    if (transfer && (product === 'clouds' || product === 'clouds-regional'))
       applyInfraredTransfer(context, texture, mode);
     return texture;
   } finally {
@@ -88,7 +97,8 @@ export function decodeInfraredImage(blob, signal) {
 }
 
 /** Fetch one capped whole-extent frame, or a `bbox` detail window of it, and draw
- * it into a canvas. Infrared frames get the display transfer; a canvas also keeps
+ * it into a canvas. Infrared frames get the display transfer unless `transfer`
+ * is false, for a caller that applies it when drawing; a canvas also keeps
  * Cesium's texture row order, which an ImageBitmap upload would not. The decoded
  * image is always released. With a `frameSource` that has `getImage`, the host
  * supplies the decoded pixels instead and nothing is fetched or decoded here. */
@@ -107,6 +117,7 @@ export async function acquireWeatherImage(
     now = () => performance.now(),
     onFetched = () => {},
     frameSource = null,
+    transfer = true,
   },
 ) {
   if (frameSource?.getImage) {
@@ -127,6 +138,7 @@ export async function acquireWeatherImage(
       size,
       signal,
       createCanvas,
+      transfer,
     );
     return { texture, decodeMs: now() - started };
   }
@@ -147,7 +159,7 @@ export async function acquireWeatherImage(
     if (image.width !== size.width || image.height !== size.height)
       throw new Error('Invalid weather image dimensions');
     let texture;
-    if (product === 'clouds' || product === 'clouds-regional')
+    if (transfer && (product === 'clouds' || product === 'clouds-regional'))
       texture = processInfraredImage(image, mode, createCanvas);
     else {
       texture = createCanvas();

src/layers/weather/infraredImage.test.mjs

@@ -26,6 +26,75 @@ 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('with transfer off an infrared frame is drawn and never read back', async () => {
+  const drawn = [];
+  const createCanvas = () => {
+    const output = {};
+    output.getContext = () => ({
+      drawImage: (image) => drawn.push(image),
+      getImageData: () => {
+        throw new Error('the frame was read back on the page');
+      },
+      putImageData: () => {
+        throw new Error('the frame was rewritten on the page');
+      },
+    });
+    return output;
+  };
+  const size = { width: 4096, height: 2048 };
+  const image = { ...size, close() {} };
+  const options = {
+    signal: new AbortController().signal,
+    mode: 'filtered',
+    size,
+    maxBytes: 1024,
+    createCanvas,
+    transfer: false,
+  };
+  const fetched = await acquireWeatherImage(
+    'clouds-regional',
+    '2026-09-15T20:00:00.000Z',
+    {
+      ...options,
+      fetchImpl: async () => ({
+        ok: true,
+        headers: new Headers(),
+        arrayBuffer: async () => new ArrayBuffer(1),
+      }),
+      decodeImage: async () => image,
+    },
+  );
+  assert.equal(fetched.texture.width, 4096);
+  const supplied = { ...size };
+  await acquireWeatherImage('clouds-regional', '2026-09-15T20:00:00.000Z', {
+    ...options,
+    frameSource: { getImage: async () => supplied },
+  });
+  assert.deepEqual(drawn, [image, supplied]);
+});
+
 test('decoded pixels are processed once on a same-sized canvas', () => {
   const image = { width: 1, height: 1 };
   const output = processInfraredImage(image, 'filtered', canvas);

src/layers/weather/shellRendering.js

@@ -1,4 +1,9 @@
 import { acquireWeatherImage } from './infraredImage.js';
+import {
+  INFRARED_ALPHA_T0,
+  INFRARED_ALPHA_T1,
+  infraredAmount,
+} from './infraredAlpha.js';
 import { imageryHostStatus } from './imageryHost.js';
 import { WEATHER_DETAIL_SIZE, WEATHER_IMAGE_SIZES } from './source.js';
 import { msg } from '../../i18n/index.js';
@@ -36,6 +41,10 @@ const LIFT_STEP = 500;
 // draw nothing until the full-extent image has arrived, and sample the detail
 // image only once it has arrived. The window is west, south, east, north in the
 // full-extent image's texture coordinates.
+// `infrared` is how much of the cloud key applies, 0–1 (infraredAlpha.js has
+// the same curve for the globe's draped imagery). It is applied here, to the
+// image as it was decoded, so a 4096×2048 frame is never read back and
+// rewritten on the page, and a strength change is one uniform, not a new image.
 const MATERIAL_SOURCE = `czm_material czm_getMaterial(czm_materialInput materialInput)
 {
   czm_material material = czm_getDefaultMaterial(materialInput);
@@ -46,7 +55,8 @@ const MATERIAL_SOURCE = `czm_material czm_getMaterial(czm_materialInput material
   float useDetail = inside * step(1.5, float(detailDimensions.x));
   vec4 c = mix(coarse, texture(detail, clamp(dst, 0.0, 1.0)), useDetail);
   material.diffuse = czm_gammaCorrect(c.rgb);
-  material.alpha = c.a * alpha * step(1.5, float(imageDimensions.x));
+  float key = smoothstep(${INFRARED_ALPHA_T0.toFixed(4)}, ${INFRARED_ALPHA_T1.toFixed(4)}, pow(max(c.r, max(c.g, c.b)), 2.2));
+  material.alpha = c.a * mix(1.0, key, infrared) * alpha * step(1.5, float(imageDimensions.x));
   return material;
 }
 `;
@@ -63,6 +73,7 @@ function registerMaterial(cesium) {
         image: cesium.Material.DefaultImageId,
         detail: cesium.Material.DefaultImageId,
         alpha: 1,
+        infrared: 0,
         window: { type: 'vec4', x: 0, y: 0, z: -1, w: -1 },
       },
       // Diffuse and alpha share these samples, so one source, not components.
@@ -245,6 +256,12 @@ export function createShellSurface({
       material.uniforms.alpha = value;
       scene.requestRender();
     },
+    /** How much of the infrared cloud key applies, 0–1. */
+    setInfrared(value) {
+      if (destroyed || material.uniforms.infrared === value) return;
+      material.uniforms.infrared = value;
+      scene.requestRender();
+    },
     /** Draw `next` inside `rect` (west, south, east, north in the full-extent
      * image's texture coordinates, 0–1); null clears it. In the same window only
      * the image changes, and Cesium keeps drawing the previous texture until
@@ -438,10 +455,11 @@ export function createWeatherShell({
   const visible = () => !hidden && !suspended();
   const boundsKey = ({ west, south, east, north }) =>
     `${west},${south},${east},${north}`;
-  const cacheKey = (time, mode, box = null) =>
-    `${time}|${infrared ? mode : 'none'}${box ? `|${boundsKey(box)}` : ''}`;
+  // One image per time and window: the infrared mode is a uniform, not pixels.
+  const cacheKey = (time, box = null) =>
+    box ? `${time}|${boundsKey(box)}` : time;
   const wantedDetail = () =>
-    current && view ? cacheKey(current.time, current.infrared, view) : null;
+    current && view ? cacheKey(current.time, view) : null;
 
   function evict(keep = []) {
     const kept = new Set([...keep, current?.key, detail?.key]);
@@ -454,12 +472,11 @@ export function createWeatherShell({
   }
   async function acquire(
     time,
-    mode,
     signal,
     { box = null, keep = [], onFetched } = {},
   ) {
     signal.throwIfAborted();
-    const key = cacheKey(time, mode, box);
+    const key = cacheKey(time, box);
     const entry = images.get(key);
     if (entry) {
       images.delete(key);
@@ -468,7 +485,8 @@ export function createWeatherShell({
     }
     const result = await acquireWeatherImage(product, time, {
       signal,
-      mode,
+      // The surface's shader applies the infrared transfer.
+      transfer: false,
       size: box ? detailSize : size,
       bbox: box,
       maxBytes: MAX_IMAGE_BYTES,
@@ -564,9 +582,7 @@ export function createWeatherShell({
     const job = { key, box: view, controller: new AbortController() };
     detailJob = job;
     job.timeout = setTimeout(() => job.controller.abort(), timeoutMs);
-    void acquire(current.time, current.infrared, job.controller.signal, {
-      box: view,
-    })
+    void acquire(current.time, job.controller.signal, { box: view })
       .then(({ texture }) => installDetail(job, texture))
       .catch(() => failDetail(job));
   }
@@ -661,6 +677,7 @@ export function createWeatherShell({
       loadMs: now() - frame.startedAt,
     };
     surface.setAlpha(alpha);
+    surface.setInfrared(infrared ? infraredAmount(frame.infrared) : 0);
     applyVisibility();
     lastError = null;
     evict();
@@ -715,7 +732,7 @@ export function createWeatherShell({
       return changed;
     },
     cancelPrefetch,
-    async prefetch(snapshot, time, { infrared: mode = 'filtered' } = {}) {
+    async prefetch(snapshot, time) {
       let job;
       try {
         if (
@@ -729,8 +746,8 @@ export function createWeatherShell({
         // Warm the next frame's detail window too while the window stays put.
         const box =
           view && viewBounds === boundsKey(snapshot.bounds) ? view : null;
-        const coarse = cacheKey(time, mode);
-        const key = box ? cacheKey(time, mode, box) : coarse;
+        const coarse = cacheKey(time);
+        const key = box ? cacheKey(time, box) : coarse;
         if (prefetchJob?.key === key || prefetchedKey === key) return false;
         cancelPrefetch();
         job = { key, controller: new AbortController() };
@@ -739,8 +756,8 @@ export function createWeatherShell({
         job.timeout = setTimeout(() => job.controller.abort(), timeoutMs);
         // Both images at once: one after the other would outlast playback's step.
         await Promise.all([
-          acquire(time, mode, signal, { keep: box ? [key] : [] }),
-          box ? acquire(time, mode, signal, { box, keep: [coarse] }) : null,
+          acquire(time, signal, { keep: box ? [key] : [] }),
+          box ? acquire(time, signal, { box, keep: [coarse] }) : null,
         ]);
         signal.throwIfAborted();
         if (prefetchJob === job) prefetchedKey = key;
@@ -782,7 +799,7 @@ export function createWeatherShell({
         infrared: mode,
         bounds,
         product: snapshot.product,
-        key: cacheKey(time, mode),
+        key: cacheKey(time),
         mosaic: { fetched: false, decodeMs: null, cached: false },
         controller: new AbortController(),
         startedAt: now(),
@@ -797,7 +814,7 @@ export function createWeatherShell({
       });
       watch(frame, signal);
       frame.timeout = setTimeout(() => fail(frame), timeoutMs);
-      void acquire(time, mode, frame.controller.signal, {
+      void acquire(time, frame.controller.signal, {
         onFetched: () => {
           frame.mosaic.fetched = true;
         },

src/layers/weather/shellRendering.test.mjs

@@ -11,6 +11,7 @@ import {
   WEATHER_SHELL_HEIGHTS,
 } from './shellRendering.js';
 import { NO_IMAGERY_HOST } from './imageryHost.js';
+import { INFRARED_ALPHA_T0, INFRARED_ALPHA_T1 } from './infraredAlpha.js';
 import {
   createShellCesium,
   createShellScene,
@@ -147,12 +148,13 @@ test('surface builds a flat raised rectangle drawn in primitive order without de
     image: Cesium.Material.DefaultImageId,
     detail: Cesium.Material.DefaultImageId,
     alpha: 1,
+    infrared: 0,
     window: { type: 'vec4', x: 0, y: 0, z: -1, w: -1 },
   });
   const { source } = template.fabric;
   assert.match(
     source,
-    /material\.alpha = c\.a \* alpha \* step\(1\.5, float\(imageDimensions\.x\)\);/,
+    /material\.alpha = c\.a \* mix\(1\.0, key, infrared\) \* alpha \* step\(1\.5, float\(imageDimensions\.x\)\);/,
     'nothing draws before the full-extent image',
   );
   assert.match(
@@ -373,6 +375,7 @@ test('real Cesium builds the two-texture material, the opaque-pass appearance an
     /uniform sampler2D image_\d+;/,
     /uniform sampler2D detail_\d+;/,
     /uniform float alpha_\d+;/,
+    /uniform float infrared_\d+;/,
     /uniform vec4 window_\d+;/,
     /uniform ivec3 imageDimensions_\d+;/,
     /uniform ivec3 detailDimensions_\d+;/,
@@ -384,9 +387,16 @@ test('real Cesium builds the two-texture material, the opaque-pass appearance an
   assert.match(shader, /step\(1\.5, float\(detailDimensions_\d+\.x\)\)/);
   assert.match(
     shader,
-    /material\.alpha = c\.a \* alpha_\d+ \* step\(1\.5, float\(imageDimensions_\d+\.x\)\);/,
+    /material\.alpha = c\.a \* mix\(1\.0, key, infrared_\d+\) \* alpha_\d+ \* step\(1\.5, float\(imageDimensions_\d+\.x\)\);/,
     'the uniform is renamed, the material field is not',
   );
+  // The cloud key the globe's draped imagery gets from infraredAlpha.js:
+  // brightest channel, 2.2 power, the shared thresholds.
+  assert.ok(
+    shader.includes(
+      `float key = smoothstep(${INFRARED_ALPHA_T0.toFixed(4)}, ${INFRARED_ALPHA_T1.toFixed(4)}, pow(max(c.r, max(c.g, c.b)), 2.2));`,
+    ),
+  );
   assert.match(shader, /float useDetail = inside \* step/, 'locals keep names');
   const detail = { width: 4096, height: 2048 };
   surface.setDetail(detail, { west: 0.1, south: 0.2, east: 0.3, north: 0.4 });
@@ -743,12 +753,12 @@ test('prefetch warms a decoded frame without staging and cancels cleanly', async
   h.shell.clear();
 });
 
-test('infrared frames get the display transfer; radar and lightning keep their pixels', async () => {
-  for (const [product, transfer] of [
-    ['clouds-regional', true],
-    ['clouds', true],
-    ['radar', false],
-    ['lightning', false],
+test('infrared frames reach the shader as decoded, with the cloud key as a uniform; radar and lightning get none', async () => {
+  for (const [product, amount] of [
+    ['clouds-regional', 1],
+    ['clouds', 1],
+    ['radar', 0],
+    ['lightning', 0],
   ]) {
     const h = harness({ product });
     const pending = h.shell.setFrame(snapshot(product), times[0]);
@@ -756,11 +766,10 @@ test('infrared frames get the display transfer; radar and lightning keep their p
     const image = h.material().uniforms.image;
     assert.equal(image.source, h.decoded[0], 'drawn into a canvas');
     assert.equal(h.decoded[0].closed, true);
-    assert.equal(image.pixels !== undefined, transfer, product);
-    if (transfer)
-      assert.deepEqual([...image.pixels], [194, 0, 0, 98], 'clouds only');
+    assert.equal(image.pixels, undefined, `${product}: pixels never rewritten`);
     h.render();
     assert.equal(await pending, true);
+    assert.equal(h.material().uniforms.infrared, amount, product);
     assert.equal(
       h.shell.getDiagnostics().height,
       WEATHER_SHELL_HEIGHTS[product],
@@ -769,20 +778,28 @@ test('infrared frames get the display transfer; radar and lightning keep their p
   }
 });
 
-test('an infrared mode change restages the same time with its own cached canvas', async () => {
+test('an infrared mode change is a uniform on the same image: no fetch, no new canvas', async () => {
   const h = harness({ product: 'clouds' });
   assert.equal(await show(h, times[0]), true);
-  const filtered = h.material().uniforms.image;
+  const image = h.material().uniforms.image;
+  assert.equal(h.material().uniforms.infrared, 1);
   assert.equal(await show(h, times[0]), true, 'same frame is a no-op');
   assert.equal(h.fetches.length, 1);
+  const renders = h.scene.renders;
   assert.equal(await show(h, times[0], { infrared: 'full' }), true);
-  const full = h.material().uniforms.image;
-  assert.notEqual(full, filtered);
-  assert.deepEqual([...full.pixels], [194, 0, 0, 200]);
+  assert.equal(h.material().uniforms.image, image);
+  assert.equal(h.material().uniforms.infrared, 0);
   assert.equal(h.shell.getDiagnostics().infrared, 'full');
+  assert.ok(h.scene.renders > renders, 'the new strength is drawn');
+  assert.equal(await show(h, times[0], { infrared: 40 }), true);
+  assert.equal(h.material().uniforms.infrared, 0.4);
+  assert.equal(h.shell.getDiagnostics().infrared, 40);
   assert.equal(await show(h, times[0], { infrared: 'filtered' }), true);
-  assert.equal(h.material().uniforms.image, filtered, 'cache hit');
-  assert.equal(h.fetches.length, 2);
+  assert.equal(h.material().uniforms.image, image);
+  assert.equal(h.material().uniforms.infrared, 1);
+  assert.equal(h.fetches.length, 1);
+  assert.equal(h.decoded.length, 1);
+  assert.equal(h.shell.getDiagnostics().cache.mosaics, 1);
   h.shell.clear();
 });