Optimize viewer shaders and camera controls; sample GPU profiles asynchronously

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b382-1e79-712b-abd1-d29201c9bb5e
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

core/profile.js

@@ -0,0 +1,42 @@
+// Single-writer/single-reader latest-sample mailbox. Header: state, UTF-8 byte length.
+// State 0 = empty, 1 = owned by a reader/writer, 2 = complete sample.
+// Neither side waits: an unread sample can be replaced, and a busy publication is skipped.
+export class SharedProfile {
+  constructor(buffer = new SharedArrayBuffer(1024 * 1024)) {
+    this.buffer = buffer;
+    this.header = new Int32Array(buffer, 0, 2);
+    this.bytes = new Uint8Array(buffer, 8);
+    this.encoder = new TextEncoder();
+    this.decoder = new TextDecoder();
+  }
+
+  write(json) {
+    const bytes = this.encoder.encode(json);
+    if (bytes.length > this.bytes.length) return false;
+    const state = Atomics.load(this.header, 0);
+    if (
+      state === 1 ||
+      Atomics.compareExchange(this.header, 0, state, 1) !== state
+    )
+      return false;
+    this.bytes.set(bytes);
+    this.header[1] = bytes.length;
+    Atomics.store(this.header, 0, 2);
+    return true;
+  }
+
+  read() {
+    if (Atomics.compareExchange(this.header, 0, 2, 1) !== 2) return;
+    let bytes;
+    try {
+      bytes = this.bytes.slice(0, this.header[1]);
+    } finally {
+      Atomics.store(this.header, 0, 0);
+    }
+    return JSON.parse(this.decoder.decode(bytes));
+  }
+
+  clear() {
+    Atomics.compareExchange(this.header, 0, 2, 0);
+  }
+}