SteelXR2/src/devkit/SceneStatsProbe.tsx

/**
 * DEVKIT — samples scene + XR session every frame, writes to sceneStatsStore.
 * Mounted inside <Canvas>. No visual output.
 */
import { useEffect, useRef } from 'react';
import { useFrame, useThree } from '@react-three/fiber';
import { useXR } from '@react-three/xr';
import { sceneStats, updateModelStats } from './sceneStatsStore';

export function SceneStatsProbe() {
  const { scene } = useThree();
  const session = useXR((s) => s.session);
  const frameCount = useRef(0);
  const lastFpsTime = useRef(performance.now());

  useEffect(() => {
    sceneStats.xrMode = session ? 'immersive-ar' : null;
  }, [session]);

  useFrame((_state, _dt, frame: XRFrame | undefined) => {
    frameCount.current++;
    const now = performance.now();
    if (now - lastFpsTime.current >= 500) {
      sceneStats.fps = Math.round((frameCount.current * 1000) / (now - lastFpsTime.current));
      frameCount.current = 0;
      lastFpsTime.current = now;
    }

    // Find the grabbable model group by traversing for first userData marker, fallback: scan
    let modelGroup: import('three').Object3D | null = null;
    scene.traverse((o) => {
      if (!modelGroup && o.userData?.__xrModelRoot) modelGroup = o;
    });
    updateModelStats(modelGroup);

    if (frame) {
      try {
        // @ts-expect-error detectedPlanes is experimental
        const planes = frame.detectedPlanes;
        sceneStats.xrPlanesCount = planes ? (planes.size ?? planes.length ?? 0) : 0;
      } catch { sceneStats.xrPlanesCount = 0; }
      sceneStats.xrInputCount = frame.session?.inputSources?.length ?? 0;
    }
    sceneStats.lastUpdate = now;
  });

  return null;
}