web: Mesa's WebGPU call counter only when asked for (?wgpustats=1)

countWebGpu wrapped every WebGPU call Mesa makes with a performance.now
pair and a Map update, always: 2.5% of the compositor worker's time in
Noita's page (F's co1 profile), 13% of a replayed frame's CPU. The stats
line keeps its per-frame call table when the page asks for it. The
eject site's launcher forwards ?glcapture and ?wgpustats to nt.html.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_d2453757b8a84fdbb4ee7c9e093141df

web/eject-site/index.html

@@ -93,7 +93,7 @@
     // `?direct=0` composites always.
     if (m.direct && q.get('direct') !== '0') p.set('direct', '1');
     // Diagnostics for the page itself, passed through.
-    for (const k of ['present', 'pointerlock', 'wgslcache', 'mesaenv', 'trapstack', 'sharetrace']) if (q.has(k)) p.set(k, q.get(k));
+    for (const k of ['present', 'pointerlock', 'wgslcache', 'mesaenv', 'trapstack', 'sharetrace', 'glcapture', 'wgpustats']) if (q.has(k)) p.set(k, q.get(k));
     location.replace(`nt.html?${p}`);
   } catch (e) {
     fail(String(e?.message ?? e));

web/src/compositor-worker.js

@@ -1404,6 +1404,7 @@ async function startGl(m, canvas) {
     env: m.mesaEnv,
     capture: m.glCapture,
     wgslCache: m.wgslCache,
+    wgpuStats: m.wgpuStats,
     gpu: await requestGexDevice(),
   });
   if (!glDevice.ok) throw new Error(glDevice.error || 'the GL device would not start');

web/src/compositor.js

@@ -73,8 +73,12 @@ export class Compositor {
       // `?wgslcache=all|site|0`: which shader translations Mesa starts with
       // (mesa-gl.js #loadWgslCache).
       const wgslCache = q?.get('wgslcache');
+      // `?wgpustats=1`: count Mesa's WebGPU calls for the stats line
+      // (mesa-gl.js countWebGpu); off by default, it costs time.
+      const wgpuStats = q?.get('wgpustats') === '1';
       this.#worker.postMessage({ kind: 'gl', channel, ...opts, ...(mesaEnv ? { mesaEnv } : {}),
-        ...(glCapture ? { glCapture } : {}), ...(wgslCache ? { wgslCache } : {}) });
+        ...(glCapture ? { glCapture } : {}), ...(wgslCache ? { wgslCache } : {}),
+        ...(wgpuStats ? { wgpuStats } : {}) });
     });
   }
 

web/src/mesa-gl.js

@@ -63,9 +63,10 @@ async function loadGlue(url) {
 
 /** The driver's WebGPU calls by name: [calls, ms inside, bytes, ms waited]
  *  ("waited" is a promise's time to settle: mapAsync, onSubmittedWorkDone).
- *  Mesa's own wasm is a few percent of a frame; its cost is these calls, so
- *  they are counted always -- one performance.now pair per call -- and
- *  `glState` reports them per frame since it was last asked. */
+ *  `glState` reports them per frame since it was last asked. Only when asked
+ *  for (`?wgpustats=1`, the `wgpuStats` option): the wrapper is a
+ *  performance.now pair and a Map lookup on each of a few thousand calls a
+ *  frame, which was 2.5% of the GL worker's time in Noita's page. */
 const wgpuCalls = new Map();
 function countWebGpu() {
   if (countWebGpu.done || typeof GPUQueue === 'undefined') return;
@@ -124,6 +125,16 @@ function countWebGpu() {
  *  message to whatever is listening (DevTools, a harness over CDP), on the
  *  thread that runs Mesa: two thousand batches in a seven-minute Noita run.
  *  `?gltrace=1` keeps them all. */
+/** A page's `?NAME=1`. In a Worker `location` is the worker script's, so
+ *  the compositor passes its page's switches in as options instead. */
+function pageFlag(name) {
+  try {
+    return globalThis.document !== undefined && new URLSearchParams(location.search).get(name) === '1';
+  } catch {
+    return false;
+  }
+}
+
 function quietReports(out) {
   let all = false;
   try {
@@ -224,7 +235,7 @@ export class MesaGlDevice {
       const { adapter, device } = options.gpu ?? await requestGexDevice();
       out.#adapter = adapter;
       out.#device = device;
-      countWebGpu();
+      if (options.wgpuStats ?? pageFlag('wgpustats')) countWebGpu();
       // And out of reach of the collector for as long as the page lives.
       //
       // The fields above were supposed to be enough, and are not: the device