tilt-shift-camera/CLAUDE.md

# Tilt-Shift Camera

Android camera app that applies a real-time tilt-shift (miniature/diorama) blur effect to the camera preview and to imported gallery images. Built with Kotlin, Jetpack Compose, CameraX, and OpenGL ES 2.0.

## What it does

- Live camera preview with GPU-accelerated tilt-shift blur via GLSL fragment shader
- Gallery import with CPU-based preview that updates in real time as you adjust parameters
- Supports both **linear** (band) and **radial** (elliptical) blur modes
- Gesture controls: drag to position, pinch to resize, two-finger rotate
- Slider panel for precise control of blur, falloff, size, angle, aspect ratio
- Multi-lens support on devices with multiple back cameras
- EXIF GPS tagging from device location
- Saves processed images to MediaStore (scoped storage)

## Architecture

```
no.naiv.tiltshift/
  MainActivity.kt              # Entry point, permissions, edge-to-edge setup
  ui/
    CameraScreen.kt            # Main Compose UI, GL surface, controls
    CameraViewModel.kt         # State management, gallery preview loop, bitmap lifecycle
    TiltShiftOverlay.kt        # Gesture handling and visual guides
    ZoomControl.kt             # Zoom presets and indicator
    LensSwitcher.kt            # Multi-lens picker
    theme/AppColors.kt         # Color constants
  camera/
    CameraManager.kt           # CameraX lifecycle, zoom, lens binding
    ImageCaptureHandler.kt     # Capture pipeline, CPU blur/mask, gallery processing
    LensController.kt          # Enumerates physical camera lenses
  effect/
    TiltShiftRenderer.kt       # GLSurfaceView.Renderer for live camera preview
    TiltShiftShader.kt         # Compiles GLSL, sets uniforms (incl. precomputed trig)
    BlurParameters.kt          # Data class for all effect parameters
  storage/
    PhotoSaver.kt              # MediaStore writes, EXIF metadata, IS_PENDING pattern
    SaveResult.kt              # Sealed class for save outcomes
  util/
    LocationProvider.kt         # FusedLocationProvider flow (accepts coarse or fine)
    OrientationDetector.kt      # Device rotation for EXIF
    HapticFeedback.kt           # Null-safe vibration wrapper
```

### Rendering pipeline

- **Camera preview**: OpenGL ES 2.0 via `GLSurfaceView` + `TiltShiftRenderer`. Camera frames arrive as `GL_TEXTURE_EXTERNAL_OES` from a `SurfaceTexture`. The fragment shader (`tiltshift_fragment.glsl`) applies blur per-fragment using precomputed `uCosAngle`/`uSinAngle` uniforms and an unrolled 9-tap Gaussian kernel.
- **Gallery preview**: CPU-based. A 1024px-max downscaled source is kept in `galleryPreviewSource`. `CameraViewModel.startPreviewLoop()` uses `collectLatest` on blur params (with 80ms debounce) to reactively recompute the preview via `ImageCaptureHandler.applyTiltShiftPreview()`.
- **Final save**: Full-resolution CPU pipeline — stack blur at 1/4 scale, gradient mask at 1/4 scale with bilinear upscale, per-pixel compositing. Camera captures save both original + processed; gallery imports save only the processed version (original already on device).

## Build & run

```bash
./gradlew assembleRelease          # Build release APK
./gradlew compileDebugKotlin       # Quick compile check
adb install -r app/build/outputs/apk/release/naiv-tilt-shift-release.apk
```

Signing config is loaded from `local.properties` (not committed).

## Key design decisions and patterns

### Bitmap lifecycle (important!)

Bitmaps emitted to `StateFlow`s are **never eagerly recycled** immediately after replacement. Compose may still be drawing the old bitmap in the current frame. Instead:

- A `pendingRecyclePreview` / `pendingRecycleThumbnail` field holds the bitmap from the *previous* update
- On the *next* update, the pending bitmap is recycled (Compose has had a full frame to finish)
- Final cleanup happens in `cancelGalleryPreview()` (which `join()`s the preview job first) and `onCleared()`

### Thread safety

- `galleryPreviewSource` is `@Volatile` (accessed from Main thread, IO dispatcher, and cancel path)
- `TiltShiftRenderer.currentTexCoords` is `@Volatile` (written by UI thread, read by GL thread)
- `cancelGalleryPreview()` cancels + `join()`s the preview job before recycling the source bitmap, because `applyTiltShiftEffect` is a long CPU loop with no suspension points
- GL resources are released via `glSurfaceView.queueEvent {}` (must run on GL thread)
- `CameraManager.captureExecutor` is shut down in `release()` to prevent thread leaks

### Error handling

- `bitmap.compress()` return value is checked; failure reported to user
- `loadBitmapFromUri()` logs all null-return paths (stream open, dimensions, decode)
- Error/success dismiss indicators use cancellable `Job` tracking to prevent race conditions
- `writeExifToUri()` returns boolean and logs at ERROR level on failure

## Permissions

| Permission | Purpose | Notes |
|-----------|---------|-------|
| `CAMERA` | Camera preview and capture | Required |
| `ACCESS_FINE_LOCATION` | GPS EXIF tagging | Optional; coarse-only grant also works |
| `ACCESS_COARSE_LOCATION` | GPS EXIF tagging | Fallback if fine denied |
| `ACCESS_MEDIA_LOCATION` | Read GPS from gallery images | Required on Android 10+ |
| `VIBRATE` | Haptic feedback | Always granted |

## Known limitations / future work

- `minSdk = 35` (Android 15) — intentional for personal use. Lower to 26-29 if distributing.
- Accompanist Permissions (`0.36.0`) is deprecated; should migrate to first-party `activity-compose` API.
- No user-facing toggle to disable GPS tagging — location is embedded whenever permission is granted.
- Dependencies are pinned to late-2024 versions; periodic bumps recommended.
- Fragment shader uses `int` uniform branching in GLSL ES 1.00 — works but could be cleaner with ES 3.00.