perf(renderer): a nebula of patches stays under the opacity ceiling; Cassiopeia A's zoom goes from a 291 ms frame to 51 ms on an iPad

docs/performance/motion-freezes-membership.md

@@ -31,10 +31,9 @@ held differently while coasting:
   2026-10-04). A stack's opacity in the mix stops at 0.999: Safari painted every slice under a stack again each time its
   opacity left or reached 1 (54 ms for 88 slices with the camera still, nothing for 0.99 to 0.98).
   A galaxy's or nebula's picture layers follow the same two rules (`image-layers/prepared-image-layer-runtime.ts`,
-  `universe/universe-catalog-banks.ts`): a bank of sheets stops its own opacity at 0.999 too. A bank of patches draws
-  at 1, since a group under 1 lost a wedge of the picture at the Homunculus's nearest view, and pays the repaint each
-  time it crosses 1 (180 to 208 ms for Cassiopeia A's 1,397 patches). A stack the camera turns to, or a bank shown
-  again, stays hidden until its
+  `universe/universe-catalog-banks.ts`): the bank's own opacity stops at 0.999 too, for sheets and for patches
+  (Cassiopeia A's 1,397 patches repainted in one frame of 291 ms each time the bank crossed 1 on a zoom out, 51 ms
+  under the ceiling). A stack the camera turns to, or a bank shown again, stays hidden until its
   images are decoded off the page's thread, then shows whole: decoded inside the paint, NGC 2392's 57 layers made a
   frame of 235 ms on a turn and 270 ms on a dataset switch, against 34 and 31 ms decoded first (iPad, 2026-10-05).
   Joining such a stack a share a frame was measured and rejected: each joining frame painted the layers already shown.

packages/renderer/src/image-layers/prepared-image-layer-runtime.test.ts

@@ -244,8 +244,8 @@ test('a stack mounts a camera for each of its scenes, and a stack without leaves
   assert.ok(first!.style.transform === camera && second!.style.transform === camera && cameras.every(each => each.style.perspective === '600px'));
   // Seen edge-on the stack is still the only one that draws: it keeps the whole weight.
   publish([Math.SQRT1_2, 0, 0, Math.SQRT1_2]);
-  // A stack of patches is drawn at 1, not under the ceiling a stack of sheets is held to.
-  assert.equal(named('css-volume-projection')[0]!.style.opacity, '1');
+  // A stack of patches stays under the ceiling too, as a stack of sheets does.
+  assert.equal(named('css-volume-projection')[0]!.style.opacity, '0.999');
   assert.equal(named('css-volume-projection')[0]!.style.visibility, 'visible');
   assert.deepEqual(imageLayerAxisWeights([Math.SQRT1_2, 0, 0, Math.SQRT1_2], views.filter(view => view.axis === 'z')), { z: 1 });
 });

packages/renderer/src/image-layers/prepared-image-layer-runtime.ts

@@ -127,9 +127,6 @@ export function mountPreparedCssImageLayers({ host, before, payload, resolveReso
   let destroyed = false;
   const quotable = (address: string) => address.replace(/["\\\n\r]/g, char => `\\${char}`);
   return Object.freeze({ root,
-    /** The opacity the bank's root stops at, as its stacks do (`publish`): 1 for a bank of patches, under 1
-     * (STACK_OPACITY_CEILING) for any other. */
-    ceiling: banks.every(bank => bank.patches) ? 1 : STACK_OPACITY_CEILING,
     /** The bank root is shown again: each stack it draws waits for its images' decode, as one the camera turns to does. */
     resume() { for (const bank of banks) { bank.drawn = false; bank.turn++; } },
     /** `around`: the bank is drawn around a body that stands inside it, at that place (reference metres). The sheets the
@@ -196,12 +193,14 @@ export function mountPreparedCssImageLayers({ host, before, payload, resolveReso
           const shown = body && texture.sheet && (withinReach(texture.sheet, local.positionUnits, bank.reach) || withinReach(texture.sheet, body, bank.reach)) ? '0' : '';
           if (texture.shown !== shown) { texture.shown = shown; texture.element.style.opacity = shown; }
         }
-        // Never 1 for a stack of sheets (STACK_OPACITY_CEILING): a drag across M31 had its longest frame at 108 to 111 ms
-        // with a bank's opacity reaching 1, and 67 to 72 ms under the ceiling (iPad, 2026-10-04). A stack of patches is
-        // the only stack of its bank and keeps the whole weight, so it is drawn at 1: under the ceiling the browser
-        // composites the stack as one group, and at the Homunculus's nearest view a wedge of that group, a third of the
-        // picture, was black for one step of a drag, at the same camera places on every pass (headless Chrome, 2026-10-05).
-        set(bank.projection, 'opacity', String(Math.min(bank.patches ? 1 : STACK_OPACITY_CEILING, weight)));
+        // Never 1 (STACK_OPACITY_CEILING): a drag across M31 had its longest frame at 108 to 111 ms with a bank's opacity
+        // reaching 1, and 67 to 72 ms under the ceiling (iPad, 2026-10-04). A stack of patches was drawn at 1 for a day:
+        // under the ceiling a wedge of the Homunculus had gone black for a step of a drag at its nearest view, in headless
+        // Chrome. That was looked for again and not found. At the nearest view, on the nebula's page and around its star,
+        // the picture under the ceiling matched the picture at 1 at every step: 580 steps in Chrome on a GPU, 90 in the
+        // software-rendered shell, 11 on an iPad. And at 1 the bank crossed 1 on every zoom out: Cassiopeia A's 1,397
+        // patches repainted in one frame of 291 ms on the iPad, 51 ms under the ceiling (2026-10-05).
+        set(bank.projection, 'opacity', String(Math.min(STACK_OPACITY_CEILING, weight)));
         set(bank.projection, 'visibility', wanted && bank.ready ? 'visible' : 'hidden');
         // A zero-weight axis contributes nothing; its 3D leaves leave compositing.
         set(bank.projection, 'display', wanted ? '' : 'none');

packages/renderer/src/universe/universe-catalog-banks.test.ts

@@ -11,7 +11,7 @@ mock.module('../image-layers/prepared-image-layer-runtime.js', { namedExports: {
   mountPreparedCssImageLayers: ({ host, before }: { host: HTMLElement; before: Element }) => {
     const root = host.ownerDocument.createElement('div');
     host.insertBefore(root, before);
-    return { root, ceiling: 0.999, publish(_publication: unknown, around: readonly number[] | false = false) { drawnAround.push(around !== false); }, resume() {}, destroy() { root.remove(); } };
+    return { root, publish(_publication: unknown, around: readonly number[] | false = false) { drawnAround.push(around !== false); }, resume() {}, destroy() { root.remove(); } };
   },
 } });
 // The modules under test import the mocked ones, so they load after the mocks.

packages/renderer/src/universe/universe-catalog-banks.ts

@@ -1,4 +1,5 @@
 import { createImageFocusBank, createPointFocusBank } from './prepared-focus-bank.js';
+import { STACK_OPACITY_CEILING } from '../volume/prepared-volume-runtime.js';
 import type { SceneLifetime } from '@cssearth/engine';
 import { type PreparedCatalogObject, type DensityVolumeFrame } from '@cssearth/objects';
 import { type WorldCameraPose } from '@cssearth/engine';
@@ -225,11 +226,10 @@ export function createUniverseCatalogBanks({ root, end, stage, lifetime, declara
           bank.dotsShown = dotOpacity > 0;
         }
         if (opacity !== bank.publishedOpacity) {
-          // The root stops where its stacks do (the bank's `ceiling`). Under 1 for a bank of sheets: Safari paints every leaf
-          // under the root again when its opacity leaves or reaches 1. At 1 for a bank of patches, which a group under 1
-          // draws with a wedge missing at its nearest view (prepared-image-layer-runtime.ts); such a bank pays that repaint,
-          // 180 to 208 ms each way for Cassiopeia A's 1,397 patches with the camera still on an iPad (2026-10-05).
-          bank.mounted.root.style.opacity = String(Math.min(bank.mounted.ceiling, opacity));
+          // Never 1 (STACK_OPACITY_CEILING), as a stack's own opacity: Safari paints every leaf under the root again when its
+          // opacity leaves or reaches 1. Cassiopeia A's 1,397 patches made a frame of 180 to 208 ms each way with the camera
+          // still on an iPad, and none between 0.999 and 0.99 (2026-10-05): the first frames of every zoom out of a nebula.
+          bank.mounted.root.style.opacity = String(Math.min(STACK_OPACITY_CEILING, opacity));
           if (opacity > 0 && bank.mounted.root.style.display === 'none') bank.mounted.resume();
           bank.mounted.root.style.display = opacity > 0 ? '' : 'none';
           bank.publishedOpacity = opacity;