Keep scaling the shared atmosphere vectors in place, and take a rebuilt globe's base from the value they had before any scaling

Pointing the scaled uniforms at the scaler's own vectors (bc1b56b6) left the atmosphere unscaled: takram's materials read the AtmosphereParameters.DEFAULT vectors themselves, so the frame dimmed (luma 161 against 214) and qa-navara-bloom found nothing to bloom. The scaler writes those vectors in place again, and a page-wide map keeps each one's value from before it was first scaled: a globe built later on the page takes its base from there instead of from the scaled value. Bloom measures as before (214.4 → 240.3), and qa-strict-context-loss passes 3 of 3 under eight busy threads.

src/globe/navara/look.js

@@ -253,70 +253,62 @@ const IRRADIANCE_OFF = Object.freeze({
 const VISIBLE = Object.freeze({ visible: true });
 const HIDDEN = Object.freeze({ visible: false });
 
+// Every luminance vector a scaler has written, with the value it had
+// before: one map for the page, as the vectors are.
+const unscaled = new WeakMap();
+
 /**
  * The atmosphere scale (viewOptions.js ATMOSPHERE_LUMINANCE_SCALE): each
  * luminance factor is set to `scale` times the base value recorded the
- * first time it is seen, so a vector Navara shares between materials, or
- * copies into a rebuilt one, is never scaled twice. A scaled uniform points
- * at this scaler's own vector; the vector Navara built it with is never
- * written. Those are takram's AtmosphereParameters.DEFAULT vectors, one per
- * page: written in place, the next globe on the page (a rebuild after a lost
- * context) recorded a scaled value as its base and drew the atmosphere
- * scale² bright. The stars keep the base value. Returns `apply()`, true
- * when it changed what a uniform holds.
+ * first time it is seen, never multiplied in place, so a vector Navara
+ * shares between materials, or copies into a rebuilt one, is never scaled
+ * twice. The stars keep the base value: when they share the sky's vector,
+ * they get their own. Returns `apply()`, true when it changed a uniform.
+ *
+ * The vectors are takram's AtmosphereParameters.DEFAULT ones, one per page
+ * and read by every globe's materials, so the base of a vector an earlier
+ * globe already scaled is the value it had before that (`unscaled`): a
+ * globe rebuilt on the page after a lost context took the scaled value as
+ * its base and drew the atmosphere scale² bright.
  */
 export function createLuminanceScaler(scale, forEachUniform, handles) {
   if (scale === 1 || !forEachUniform) return () => false;
-  // key -> the vectors uniforms point at, and the values they must hold
-  const bases = new Map();
+  const bases = new Map(); // key -> { base, target }
+  const scaledVectors = new WeakSet();
   let changed = false;
   const entry = (key, value) => {
     let found = bases.get(key);
     if (!found) {
-      const baseValue = value.clone();
-      const targetValue = value.clone().multiplyScalar(scale);
+      const base = unscaled.get(value) ?? value;
       found = {
-        base: baseValue.clone(),
-        target: targetValue.clone(),
-        baseValue,
-        targetValue,
+        base: base.clone(),
+        target: base.clone().multiplyScalar(scale),
       };
       bases.set(key, found);
     }
     return found;
   };
-  // A material may write into the vector its uniform holds.
-  const restore = () => {
-    for (const { base, target, baseValue, targetValue } of bases.values()) {
-      if (!base.equals(baseValue)) {
-        base.copy(baseValue);
-        changed = true;
-      }
-      if (!target.equals(targetValue)) {
-        target.copy(targetValue);
-        changed = true;
-      }
-    }
-  };
   let applyScale = true;
   const record = (key, uniform) => entry(key, uniform.value);
   const scaleOne = (key, uniform, scaled) => {
     if (!scaled) return;
     const { base, target } = entry(key, uniform.value);
     const desired = applyScale ? target : base;
-    if (uniform.value === desired) return;
-    if (!uniform.value.equals(desired)) changed = true;
-    uniform.value = desired;
+    scaledVectors.add(uniform.value);
+    if (uniform.value.equals(desired)) return;
+    if (!unscaled.has(uniform.value))
+      unscaled.set(uniform.value, uniform.value.clone());
+    uniform.value.copy(desired);
+    changed = true;
   };
   const keepBase = (key, uniform, scaled) => {
     if (scaled) return;
-    const { base, target } = entry(key, uniform.value);
-    // Never this scaler's own vectors: they change with the scale.
-    if (uniform.value === target || uniform.value === base) {
-      if (!uniform.value.equals(base)) changed = true;
+    const { base } = entry(key, uniform.value);
+    if (scaledVectors.has(uniform.value)) {
       uniform.value = base.clone();
+      changed = true;
     } else if (!uniform.value.equals(base)) {
-      uniform.value = base.clone();
+      uniform.value.copy(base);
       changed = true;
     }
   };
@@ -325,7 +317,6 @@ export function createLuminanceScaler(scale, forEachUniform, handles) {
     changed = false;
     // Bases first, from the values as Navara built them.
     forEachUniform(handles, record);
-    restore();
     forEachUniform(handles, scaleOne);
     forEachUniform(handles, keepBase);
     return changed;

src/globe/navara/look.test.mjs

@@ -568,17 +568,14 @@ test('a second look on the page scales the shared atmosphere vectors from their
   };
   const first = build();
   near(first.sky[SKY].value.x, 1.5 * k);
-  assert.equal(
-    pageDefault[SKY].value.x,
-    1.5,
-    'the shared vector is not written',
-  );
-  // The first globe's context is lost and a new one is built on the page.
+  // The first globe's context is lost and a new one is built on the page:
+  // its materials hold the vectors the first one scaled.
   const second = build();
   near(second.sky[SKY].value.x, 1.5 * k);
   near(second.clouds[SUN].value.x, 1.3 * k);
+  near(pageDefault[SKY].value.x, 1.5 * k);
   assert.equal(second.stars[SKY].value.x, 1.5);
-  near(first.sky[SKY].value.x, 1.5 * k);
+  assert.equal(second.stars[SUN].value.x, 1.3);
 });
 
 test('a value a material writes into the scaled vector is put back on the next frame', () => {