perf(capture): render exports off the shutter path via FIFO background queue

App.tsx

@@ -95,6 +95,22 @@ export default function App() {
   const [shutterSound, setShutterSound] = useState<ShutterSound>('on');
   const photoSeq = useRef(0);
   const [isProcessing, setIsProcessing] = useState(false);
+  // Short shutter-burst lock: guards the capturePhotoToFile calls from
+  // overlapping. Released as soon as the frames are written — NOT after the
+  // render, so a new shot can start while the previous photo is still being
+  // processed in the background.
+  const captureBusyRef = useRef(false);
+  // FIFO background render queue: processAndExportPhoto (Skia render + gallery
+  // save, ~1s) runs OFF the shutter path, one at a time, so the next photo can
+  // be taken immediately. FIFO keeps history order == shutter order. Renders
+  // are heavy on the JS thread but yield between awaits — UI keeps responding.
+  const exportQueueRef = useRef<Promise<void>>(Promise.resolve());
+  const enqueueExport = (task: () => Promise<void>) => {
+    exportQueueRef.current = exportQueueRef.current
+      .catch(() => {}) // a failed render must not stall the queue
+      .then(task)
+      .catch((e) => console.error('Background export failed:', e));
+  };
 
   // Hardware Permissions (vision-camera)
   const { hasPermission: cameraPermissionGranted, requestPermission: requestCameraPermission } = useCameraPermission();
@@ -435,7 +451,7 @@ export default function App() {
         Alert.alert('Camera Not Ready', 'Please wait for the camera to start, then try again.');
         return;
       }
-      setIsProcessing(true);
+      captureBusyRef.current = true;
       Haptics.impactAsync(Haptics.ImpactFeedbackStyle.Medium);
       try {
         // A photo taken now is at the device's current spot — resolve device GPS
@@ -449,7 +465,6 @@ export default function App() {
           }
         }
 
-        const tShot = Date.now();
         // Hardware AE bias for this shot (best-effort, bounded retries inside).
         // Applied here — right before the capture — instead of live during EV
         // slider drags, which re-locked AE on the Xiaomi and flashed preview.
@@ -478,42 +493,56 @@ export default function App() {
           }
         }
 
-        const tExp = Date.now();
+        // Snapshot the look at shutter time, then render OFF the shutter path:
-        const result = await processAndExportPhoto(
+        // processAndExportPhoto (~1s Skia render + gallery save) is enqueued on
-          sourceUri,
+        // the FIFO background queue — the shutter returns in tens of ms and the
-          { ...activeRecipe, adjustments: renderAdj, frameId: selectedFrame, useGeotag },
+        // next shot can be taken immediately; no full-screen RENDERING overlay.
-          selectedFrame,
+        // Finished photos land in history (and the gallery) when their turn
-          useGeotag,
+        // completes; the thumbnail button shows each as it arrives.
-          captureGps,
+        const recipeName = activeRecipe.name;
-          // 300dpi header + full-res screen sharpen. evFromCamera: the AE bias
+        const render = () =>
-          // already applied exposure compensation at capture — don't add 2^EV.
+          processAndExportPhoto(
-          // aspect: crop to the on-screen composition ratio (full = keep 4:3 native).
+            sourceUri,
-          {
+            { ...activeRecipe, adjustments: renderAdj, frameId: selectedFrame, useGeotag },
-            dpi: 300,
+            selectedFrame,
-            sharpen: true,
+            useGeotag,
-            evFromCamera: true,
+            captureGps,
-            aspect: aspectRatio === 'full' ? undefined : aspectRatio,
+            // 300dpi header + full-res screen sharpen. evFromCamera: the AE bias
+            // already applied exposure compensation at capture — don't add 2^EV.
+            // aspect: crop to the on-screen composition ratio (full = keep 4:3 native).
+            {
+              dpi: 300,
+              sharpen: true,
+              evFromCamera: true,
+              aspect: aspectRatio === 'full' ? undefined : aspectRatio,
+            }
+          );
+        enqueueExport(async () => {
+          try {
+            const result = await render();
+            if (result) {
+              // No auto preview after a capture — the thumbnail button opens
+              // the swipe viewer. Saved to session history either way.
+              pushPhoto({
+                uri: result.uri,
+                recipeName,
+                savedToLibrary: result.savedToLibrary,
+                assetId: result.assetId,
+              });
+              Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
+            } else {
+              Alert.alert('Failed', 'Error occurred while processing the captured photo.');
+            }
+          } catch (error) {
+            console.error('Camera export failed:', error);
+            Alert.alert('Failed', 'Error occurred while processing the captured photo.');
           }
-        );
+        });
-
-        if (result) {
-          // No auto preview after a capture — the thumbnail button opens the
-          // swipe viewer. Saved to session history either way.
-          pushPhoto({
-            uri: result.uri,
-            recipeName: activeRecipe.name,
-            savedToLibrary: result.savedToLibrary,
-            assetId: result.assetId,
-          });
-          Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
-        } else {
-          Alert.alert('Failed', 'Error occurred while processing the captured photo.');
-        }
       } catch (error) {
         console.error('Camera capture failed:', error);
         Alert.alert('Capture Failed', 'Could not take the photo. See logs for details.');
       } finally {
-        setIsProcessing(false);
+        captureBusyRef.current = false;
       }
       return;
     }