From f53d6f0b1bfcbdfd96e336a6f4a41ed329350bed Mon Sep 17 00:00:00 2001
From: Ole-Morten Duesund <olemd@glemt.net>
Date: Fri, 27 Feb 2026 15:19:41 +0100
Subject: [PATCH] Fix runBlocking deadlock in ImageCaptureHandler

runBlocking on the camera callback thread could deadlock when
saveBitmap() needed the main thread. Split capturePhoto() into two
phases: synchronous CPU work (decode/rotate/effect) inside the
suspendCancellableCoroutine callback, and suspend-safe saveBitmap()
after the continuation resumes in coroutine context.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 .../tiltshift/camera/ImageCaptureHandler.kt   | 100 +++++++++++-------
 1 file changed, 60 insertions(+), 40 deletions(-)

diff --git a/app/src/main/java/no/naiv/tiltshift/camera/ImageCaptureHandler.kt b/app/src/main/java/no/naiv/tiltshift/camera/ImageCaptureHandler.kt
index aaa6279..b7a8d6b 100644
--- a/app/src/main/java/no/naiv/tiltshift/camera/ImageCaptureHandler.kt
+++ b/app/src/main/java/no/naiv/tiltshift/camera/ImageCaptureHandler.kt
@@ -3,9 +3,7 @@ package no.naiv.tiltshift.camera
 import android.content.Context
 import android.graphics.Bitmap
 import android.graphics.BitmapFactory
-import android.graphics.Canvas
 import android.graphics.Matrix
-import android.graphics.Paint
 import android.location.Location
 import androidx.camera.core.ImageCapture
 import androidx.camera.core.ImageCaptureException
@@ -30,8 +28,21 @@ class ImageCaptureHandler(
     private val photoSaver: PhotoSaver
 ) {
 
+    /**
+     * Holds the processed bitmap ready for saving, produced inside the
+     * camera callback (synchronous CPU work) and consumed afterwards
+     * in the caller's coroutine context.
+     */
+    private class ProcessedCapture(val bitmap: Bitmap)
+
     /**
      * Captures a photo and applies the tilt-shift effect.
+     *
+     * Phase 1 (inside suspendCancellableCoroutine / camera callback):
+     *   decode → rotate → apply effect  (synchronous CPU work only)
+     *
+     * Phase 2 (after continuation resumes, back in coroutine context):
+     *   save bitmap via PhotoSaver (suspend-safe)
      */
     suspend fun capturePhoto(
         imageCapture: ImageCapture,
@@ -40,55 +51,64 @@ class ImageCaptureHandler(
         deviceRotation: Int,
         location: Location?,
         isFrontCamera: Boolean
-    ): SaveResult = suspendCancellableCoroutine { continuation ->
+    ): SaveResult {
+        // Phase 1: capture and process the image synchronously in the callback
+        val captureResult = suspendCancellableCoroutine { continuation ->
+            imageCapture.takePicture(
+                executor,
+                object : ImageCapture.OnImageCapturedCallback() {
+                    override fun onCaptureSuccess(imageProxy: ImageProxy) {
+                        try {
+                            val imageRotation = imageProxy.imageInfo.rotationDegrees
 
-        imageCapture.takePicture(
-            executor,
-            object : ImageCapture.OnImageCapturedCallback() {
-                override fun onCaptureSuccess(imageProxy: ImageProxy) {
-                    try {
-                        // Get rotation from ImageProxy (sensor orientation)
-                        val imageRotation = imageProxy.imageInfo.rotationDegrees
+                            var bitmap = imageProxyToBitmap(imageProxy)
+                            imageProxy.close()
 
-                        // Convert ImageProxy to Bitmap
-                        var bitmap = imageProxyToBitmap(imageProxy)
-                        imageProxy.close()
+                            if (bitmap == null) {
+                                continuation.resume(
+                                    SaveResult.Error("Failed to convert image") as Any
+                                )
+                                return
+                            }
 
-                        if (bitmap == null) {
-                            continuation.resume(SaveResult.Error("Failed to convert image"))
-                            return
-                        }
+                            bitmap = rotateBitmap(bitmap, imageRotation, isFrontCamera)
 
-                        // Rotate bitmap to correct orientation
-                        // Camera sensor is landscape, we need to rotate for portrait
-                        bitmap = rotateBitmap(bitmap, imageRotation, isFrontCamera)
+                            val processedBitmap = applyTiltShiftEffect(bitmap, blurParams)
+                            bitmap.recycle()
 
-                        // Apply tilt-shift effect to the correctly oriented image
-                        val processedBitmap = applyTiltShiftEffect(bitmap, blurParams)
-                        bitmap.recycle()
-
-                        // Save with EXIF orientation as NORMAL (bitmap is already rotated)
-                        kotlinx.coroutines.runBlocking {
-                            val result = photoSaver.saveBitmap(
-                                processedBitmap,
-                                ExifInterface.ORIENTATION_NORMAL,
-                                location
+                            continuation.resume(ProcessedCapture(processedBitmap))
+                        } catch (e: Exception) {
+                            continuation.resume(
+                                SaveResult.Error("Capture failed: ${e.message}", e) as Any
                             )
-                            processedBitmap.recycle()
-                            continuation.resume(result)
                         }
-                    } catch (e: Exception) {
-                        continuation.resume(SaveResult.Error("Capture failed: ${e.message}", e))
+                    }
+
+                    override fun onError(exception: ImageCaptureException) {
+                        continuation.resume(
+                            SaveResult.Error(
+                                "Capture failed: ${exception.message}", exception
+                            ) as Any
+                        )
                     }
                 }
+            )
+        }
 
-                override fun onError(exception: ImageCaptureException) {
-                    continuation.resume(
-                        SaveResult.Error("Capture failed: ${exception.message}", exception)
-                    )
-                }
+        // Phase 2: save to disk in the caller's coroutine context (suspend-safe)
+        if (captureResult is ProcessedCapture) {
+            return try {
+                photoSaver.saveBitmap(
+                    captureResult.bitmap,
+                    ExifInterface.ORIENTATION_NORMAL,
+                    location
+                )
+            } finally {
+                captureResult.bitmap.recycle()
             }
-        )
+        }
+
+        return captureResult as SaveResult
     }
 
     /**