Add front camera texture coordinate handling

- Add separate texture coordinates for front and back cameras
- Front camera uses mirrored coordinates for natural selfie view
- Add setFrontCamera() method to renderer for dynamic switching
- Update texture coord buffer on GL thread when camera changes
- CameraScreen observes isFrontCamera state to trigger updates

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/src/main/java/no/naiv/tiltshift/effect/TiltShiftRenderer.kt

@@ -36,6 +36,9 @@ class TiltShiftRenderer(
     @Volatile
     var blurParameters: BlurParameters = BlurParameters.DEFAULT
 
+    @Volatile
+    private var isFrontCamera: Boolean = false
+
     // Quad vertices (full screen)
     private val vertices = floatArrayOf(
         -1f, -1f,  // Bottom left
@@ -44,15 +47,26 @@ class TiltShiftRenderer(
          1f,  1f   // Top right
     )
 
-    // Texture coordinates rotated 90° for portrait mode
+    // Texture coordinates rotated 90° for portrait mode (back camera)
     // (Camera sensors are landscape-oriented, we rotate to portrait)
-    private val texCoords = floatArrayOf(
+    private val texCoordsBack = floatArrayOf(
         1f, 1f,  // Bottom left of screen  -> bottom right of texture
         1f, 0f,  // Bottom right of screen -> top right of texture
         0f, 1f,  // Top left of screen     -> bottom left of texture
         0f, 0f   // Top right of screen    -> top left of texture
     )
 
+    // Texture coordinates for front camera (mirrored + rotated)
+    // Front camera needs horizontal mirror for natural selfie view
+    private val texCoordsFront = floatArrayOf(
+        0f, 1f,  // Bottom left of screen
+        0f, 0f,  // Bottom right of screen
+        1f, 1f,  // Top left of screen
+        1f, 0f   // Top right of screen
+    )
+
+    private var currentTexCoords = texCoordsBack
+
     override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) {
         GLES20.glClearColor(0f, 0f, 0f, 1f)
 
@@ -68,10 +82,10 @@ class TiltShiftRenderer(
         vertexBuffer.position(0)
 
         // Create texture coordinate buffer
-        texCoordBuffer = ByteBuffer.allocateDirect(texCoords.size * 4)
+        texCoordBuffer = ByteBuffer.allocateDirect(currentTexCoords.size * 4)
             .order(ByteOrder.nativeOrder())
             .asFloatBuffer()
-            .put(texCoords)
+            .put(currentTexCoords)
         texCoordBuffer.position(0)
 
         // Create camera texture
@@ -101,6 +115,14 @@ class TiltShiftRenderer(
         // Update texture with latest camera frame
         surfaceTexture?.updateTexImage()
 
+        // Update texture coordinate buffer if camera changed
+        if (updateTexCoordBuffer) {
+            texCoordBuffer.clear()
+            texCoordBuffer.put(currentTexCoords)
+            texCoordBuffer.position(0)
+            updateTexCoordBuffer = false
+        }
+
         GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT)
 
         // Use shader and set parameters
@@ -143,6 +165,22 @@ class TiltShiftRenderer(
         blurParameters = params
     }
 
+    /**
+     * Sets whether using front camera. Updates texture coordinates accordingly.
+     * Thread-safe - actual buffer update happens on next frame.
+     */
+    fun setFrontCamera(front: Boolean) {
+        if (isFrontCamera != front) {
+            isFrontCamera = front
+            currentTexCoords = if (front) texCoordsFront else texCoordsBack
+            // Buffer will be updated on next draw
+            updateTexCoordBuffer = true
+        }
+    }
+
+    @Volatile
+    private var updateTexCoordBuffer = false
+
     /**
      * Releases OpenGL resources.
      * Must be called from GL thread.

app/src/main/java/no/naiv/tiltshift/ui/CameraScreen.kt

@@ -125,6 +125,12 @@ fun CameraScreen(
         glSurfaceView?.requestRender()
     }
 
+    // Update renderer when camera switches (front/back)
+    LaunchedEffect(isFrontCamera) {
+        renderer?.setFrontCamera(isFrontCamera)
+        glSurfaceView?.requestRender()
+    }
+
     // Start camera when surface texture is available
     LaunchedEffect(surfaceTexture) {
         surfaceTexture?.let {