feat(3d-nds): lag detection

app/components/NDS3D.vue

@@ -195,7 +195,12 @@ watch(
   { immediate: true },
 );
 
-const { onRender } = useLoop();
+const { onRender, onBeforeRender } = useLoop();
+
+const LAG_FPS_THRESHOLD = 440;
+const LAG_DURATION_SECS = 1;
+let lagSeconds = 0;
+let lagCheckDone = false;
 
 const HINT_SPRITE_SCALE = 2;
 const HINT_SPRITE_DPR = 4;
@@ -337,10 +342,30 @@ useKeyUp(({ ndsButton }) => {
   }
 });
 
-onRender(({ delta }) => {
+// lag detection
+onBeforeRender(({ delta }) => {
+  if (!lagCheckDone) {
+    const fps = 1 / delta;
+    if (fps < LAG_FPS_THRESHOLD) {
+      lagSeconds += delta;
+      if (lagSeconds >= LAG_DURATION_SECS) {
+        lagCheckDone = true;
+        app.lagDetected = true;
+      }
+    } else {
+      lagSeconds = 0;
+    }
+  }
+});
+
+// upate screens
+onRender(() => {
   if (topScreenTexture) topScreenTexture.needsUpdate = true;
   if (bottomScreenTexture) bottomScreenTexture.needsUpdate = true;
+});
 
+// update physical buttons
+onBeforeRender(({ delta }) => {
   // cross
   const crossButton = meshes.get(CROSS_BUTTON);
   if (crossButton) {