perf(weather): wake a staged frame on a 150 ms timer, not every render (#1345)

Wake staged weather imagery on a bounded timer instead of requesting every render.

Contribution by @nu-stats.

changelog.d/1345-weather-staging-wake.md

@@ -0,0 +1,3 @@
+- Wake staged weather imagery on a 150 ms timer while waiting for readiness,
+  avoiding a continuous render loop and cancelling the wake when work ends
+  (@nu-stats, #1345).

docs/CURRENT-STATE.md

@@ -306,6 +306,10 @@ catalog construction owns each instance.
 Wind animates one forecast without advancing forecast time. Separate Weather
 observation layers provide radar and satellite history; none claims measured cloud volume.
 Weather imagery releases its camera move listener on disable and registers it once on re-enable. Disabling also clears active imagery work.
+A staged weather frame with loaded tiles and no pending requests rechecks
+readiness on a single 150 ms wake timer instead of requesting every render.
+The existing readiness conditions and two settled frames still govern promotion;
+completion, cancellation, replacement and teardown clear the wake timer.
 Weather imagery drapes onto the globe basemap. On photorealistic 3D Tiles each
 observed product is instead a raised, translucent shell: one rectangle over the
 product bounds at a fixed height (global infrared 5.5 km, regional infrared

src/layers/weather/rendering.js

@@ -14,6 +14,8 @@ const GLOBAL_TILE_MAXIMUM_LEVEL = 3;
 // Six decoded 2048×1024 canvases (8 MiB each) bound the cache below 50 MiB.
 const MAX_MOSAICS = 6;
 const MAX_PREFETCH_TILES = 8;
+// How often a staged frame waiting out its quiet interval rechecks readiness.
+export const READY_WAKE_MS = 150;
 
 /** Globe imagery: own at most a displayed and a staging frame. Use native Cesium
  * tile scheduling, projection and texture disposal; the application clock is never touched. */
@@ -126,6 +128,7 @@ function createGlobeRendering({
     frame.offRender?.();
     frame.offCamera?.();
     clearTimeout(frame.timeout);
+    clearTimeout(frame.wake);
     for (const request of frame.requests) request.cancel?.();
     frame.requests.clear();
     frame.retries.clear();
@@ -277,6 +280,8 @@ function createGlobeRendering({
         frame.offCamera?.();
         frame.offCamera = null;
         clearTimeout(frame.timeout);
+        clearTimeout(frame.wake);
+        frame.wake = null;
         frame.offAbort?.();
         if (ok) {
           lastError = null;
@@ -450,8 +455,20 @@ function createGlobeRendering({
             if (++settled >= 2) finish(true);
             else viewer.scene.requestRender();
           } else settled = 0;
-          if (incoming === frame && frame.pending === 0 && frame.loaded > 0)
+          // Waiting out the quiet interval needs another readiness check
-            viewer.scene.requestRender();
+          // later, not a render every frame: wake on a timer so the render
+          // governor's frame cap still holds while a frame is staged.
+          if (
+            incoming === frame &&
+            frame.pending === 0 &&
+            frame.loaded > 0 &&
+            !frame.wake
+          )
+            frame.wake = setTimeout(() => {
+              frame.wake = null;
+              if (!frame.closed && incoming === frame)
+                viewer.scene.requestRender();
+            }, READY_WAKE_MS);
         });
         viewer.scene.requestRender();
         onChange();

src/layers/weather/weather.test.mjs

@@ -1,6 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
-import { createWeatherRendering } from './rendering.js';
+import { createWeatherRendering, READY_WAKE_MS } from './rendering.js';
 import { createWeatherLayer } from './index.js';
 import { createWeatherClock } from './clock.js';
 import * as Cesium from 'cesium';
@@ -242,6 +242,50 @@ test('a ready weather frame does not wait for unrelated terrain, but requires su
   h.rendering.clear();
 });
 
+test('a staged frame waiting out its quiet interval wakes on a timer, not every render', async (t) => {
+  t.mock.timers.enable({ apis: ['setTimeout'] });
+  let now = 0;
+  const h = renderingHarness({ now: () => now });
+  h.viewer.scene.globe.tilesLoaded = false;
+  const loaded = h.rendering.setFrame(snapshot, times[0]);
+  const tile = deferred();
+  h.providers[0].response = tile;
+  const request = h.providers[0].requestImage(0, 0, 0, {});
+  tile.resolve({});
+  await request;
+  const before = h.renders();
+  for (let i = 0; i < 10; i++) h.postRender.emit();
+  assert.equal(
+    h.renders(),
+    before,
+    'renders while waiting do not request further renders',
+  );
+  t.mock.timers.tick(READY_WAKE_MS - 1);
+  assert.equal(h.renders(), before);
+  t.mock.timers.tick(1);
+  assert.equal(h.renders(), before + 1, 'one wake per interval');
+  now = 200;
+  h.postRender.emit();
+  h.postRender.emit();
+  assert.equal(await loaded, true);
+  const settledRenders = h.renders();
+  t.mock.timers.tick(READY_WAKE_MS * 4);
+  assert.equal(h.renders(), settledRenders, 'commit clears the wake timer');
+
+  const abandoned = h.rendering.setFrame(snapshot, times[1]);
+  const second = deferred();
+  h.providers.at(-1).response = second;
+  const secondRequest = h.providers.at(-1).requestImage(0, 0, 0, {});
+  second.resolve({});
+  await secondRequest;
+  h.postRender.emit();
+  h.rendering.clear();
+  assert.equal(await abandoned, false);
+  const clearedRenders = h.renders();
+  t.mock.timers.tick(READY_WAKE_MS * 4);
+  assert.equal(h.renders(), clearedRenders, 'clear cancels the wake timer');
+});
+
 test('camera movement drops abandoned deferred tiles but still waits for admitted requests', async () => {
   let now = 0;
   const h = renderingHarness({ now: () => now });