Implement camera startup emulation in FakeCameraSystem

core/camera/build.gradle.kts

@@ -126,6 +126,7 @@ dependencies {
     // CameraX
     implementation(libs.camera.core)
     implementation(libs.camera.camera2)
+    implementation(libs.camera.viewfinder.core)
     implementation(libs.camera.lifecycle)
     implementation(libs.camera.video)
 

core/camera/src/androidTest/java/com/google/jetpackcamera/core/camera/CameraXCameraSystemTest.kt

@@ -409,7 +409,9 @@ class CameraXCameraSystemTest {
     private fun CameraXCameraSystem.providePreviewSurface() {
         cameraSystemScope.launch {
             getSurfaceRequest().filterNotNull().collect {
-                it.provideUpdatingSurface()
+                if (it is PreviewSurfaceRequest.CameraX) {
+                    it.surfaceRequest.provideUpdatingSurface()
+                }
             }
         }
     }

core/camera/src/main/java/com/google/jetpackcamera/core/camera/CameraSession.kt

@@ -773,7 +773,7 @@ private fun createPreviewUseCase(
 }.build()
     .apply {
         setSurfaceProvider { surfaceRequest ->
-            surfaceRequests.update { surfaceRequest }
+            surfaceRequests.update { PreviewSurfaceRequest.CameraX(surfaceRequest) }
         }
     }
 

core/camera/src/main/java/com/google/jetpackcamera/core/camera/CameraSessionContext.kt

@@ -16,7 +16,6 @@
 package com.google.jetpackcamera.core.camera
 
 import android.content.Context
-import androidx.camera.core.SurfaceRequest
 import androidx.camera.lifecycle.ProcessCameraProvider
 import com.google.jetpackcamera.core.camera.lowlight.LowLightBoostEffectProvider
 import com.google.jetpackcamera.core.common.FilePathGenerator
@@ -41,7 +40,7 @@ internal data class CameraSessionContext(
     val focusMeteringEvents: Channel<CameraEvent.FocusMeteringEvent>,
     val videoCaptureControlEvents: Channel<VideoCaptureControlEvent>,
     val currentCameraState: MutableStateFlow<CameraState>,
-    val surfaceRequests: MutableStateFlow<SurfaceRequest?>,
+    val surfaceRequests: MutableStateFlow<PreviewSurfaceRequest?>,
     val transientSettings: StateFlow<TransientSessionSettings?>,
     val lowLightBoostEffectProvider: LowLightBoostEffectProvider? = null
 )

core/camera/src/main/java/com/google/jetpackcamera/core/camera/CameraSystem.kt

@@ -91,7 +91,12 @@ interface CameraSystem {
 
     fun getCurrentCameraState(): StateFlow<CameraState>
 
-    fun getSurfaceRequest(): StateFlow<SurfaceRequest?>
+    /**
+     * Returns the current [PreviewSurfaceRequest].
+     *
+     * This will be null if no surface is currently requested.
+     */
+    fun getSurfaceRequest(): StateFlow<PreviewSurfaceRequest?>
 
     fun getScreenFlashEvents(): ReceiveChannel<ScreenFlashEvent>
 

core/camera/src/main/java/com/google/jetpackcamera/core/camera/CameraXCameraSystem.kt

@@ -31,7 +31,6 @@ import androidx.camera.core.CameraXConfig
 import androidx.camera.core.DynamicRange as CXDynamicRange
 import androidx.camera.core.ImageCapture
 import androidx.camera.core.ImageCapture.OutputFileOptions
-import androidx.camera.core.SurfaceRequest
 import androidx.camera.core.takePicture
 import androidx.camera.lifecycle.ExperimentalCameraProviderConfiguration
 import androidx.camera.lifecycle.ProcessCameraProvider
@@ -135,9 +134,10 @@ constructor(
     private var currentCameraState = MutableStateFlow(CameraState())
     override fun getCurrentCameraState(): StateFlow<CameraState> = currentCameraState.asStateFlow()
 
-    private val _surfaceRequest = MutableStateFlow<SurfaceRequest?>(null)
+    private val _surfaceRequest = MutableStateFlow<PreviewSurfaceRequest?>(null)
 
-    override fun getSurfaceRequest(): StateFlow<SurfaceRequest?> = _surfaceRequest.asStateFlow()
+    override fun getSurfaceRequest(): StateFlow<PreviewSurfaceRequest?> =
+        _surfaceRequest.asStateFlow()
 
     private val lowLightBoostAvailabilityChecker: LowLightBoostAvailabilityChecker?
     private val lowLightBoostEffectProvider: LowLightBoostEffectProvider?

core/camera/src/main/java/com/google/jetpackcamera/core/camera/FocusMetering.kt

@@ -44,7 +44,9 @@ internal suspend fun CameraSessionContext.processFocusMeteringEvents(
     cameraInfo: CameraInfo,
     cameraControl: CameraControl
 ) {
-    surfaceRequests.flatMapLatest { surfaceRequest ->
+    surfaceRequests.flatMapLatest { previewSurfaceRequest ->
+        val surfaceRequest =
+            (previewSurfaceRequest as? PreviewSurfaceRequest.CameraX)?.surfaceRequest
         surfaceRequest?.let { request ->
             Log.d(
                 TAG,

core/camera/src/main/java/com/google/jetpackcamera/core/camera/PreviewSurfaceRequest.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2026 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.jetpackcamera.core.camera
+
+import android.view.Surface
+import androidx.camera.core.SurfaceRequest
+import androidx.camera.viewfinder.core.ViewfinderSurfaceRequest
+import kotlinx.coroutines.CompletableDeferred
+
+/**
+ * A sealed interface representing a request for a preview surface, abstracting the specific
+ * viewfinder implementation required.
+ */
+sealed interface PreviewSurfaceRequest {
+    /**
+     * Wraps a CameraX [SurfaceRequest] for the production CameraXViewfinder.
+     *
+     * @property surfaceRequest The CameraX [SurfaceRequest].
+     */
+    data class CameraX(val surfaceRequest: SurfaceRequest) : PreviewSurfaceRequest
+
+    /**
+     * Wraps a [ViewfinderSurfaceRequest] for the standalone Viewfinder composable.
+     *
+     * @property surfaceRequest The standalone [ViewfinderSurfaceRequest].
+     * @property surfaceDeferred A [CompletableDeferred] that will be completed with the [Surface]
+     * once provided by the UI.
+     */
+    data class Viewfinder(
+        val surfaceRequest: ViewfinderSurfaceRequest,
+        val surfaceDeferred: CompletableDeferred<Surface> = CompletableDeferred()
+    ) : PreviewSurfaceRequest
+}

core/camera/testing/build.gradle.kts

@@ -52,10 +52,10 @@ dependencies {
     implementation(project(":core:camera"))
     implementation(project(":core:model"))
     implementation(project(":data:settings"))
-    
+
     implementation(libs.camera.core)
+    implementation(libs.camera.viewfinder.core)
     implementation(libs.kotlinx.coroutines.core)
-
     // Testing
     testImplementation(libs.junit)
     testImplementation(libs.truth)

core/camera/testing/src/main/java/com/google/jetpackcamera/core/camera/testing/FakeCameraSystem.kt

@@ -17,11 +17,14 @@ package com.google.jetpackcamera.core.camera.testing
 
 import android.annotation.SuppressLint
 import android.content.ContentResolver
+import android.view.Surface
 import androidx.camera.core.ImageCapture
-import androidx.camera.core.SurfaceRequest
+import androidx.camera.viewfinder.core.ImplementationMode
+import androidx.camera.viewfinder.core.ViewfinderSurfaceRequest
 import com.google.jetpackcamera.core.camera.CameraState
 import com.google.jetpackcamera.core.camera.CameraSystem
 import com.google.jetpackcamera.core.camera.OnVideoRecordEvent
+import com.google.jetpackcamera.core.camera.PreviewSurfaceRequest
 import com.google.jetpackcamera.model.AspectRatio
 import com.google.jetpackcamera.model.CameraZoomRatio
 import com.google.jetpackcamera.model.CaptureMode
@@ -38,6 +41,7 @@ import com.google.jetpackcamera.model.StreamConfig
 import com.google.jetpackcamera.model.TestPattern
 import com.google.jetpackcamera.model.VideoQuality
 import com.google.jetpackcamera.settings.model.CameraAppSettings
+import kotlinx.coroutines.CompletableDeferred
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.channels.Channel.Factory.UNLIMITED
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -53,12 +57,19 @@ class FakeCameraSystem(defaultCameraSettings: CameraAppSettings = CameraAppSetti
     private var initialized = false
     private var useCasesBinded = false
 
+    /** Whether the preview has started. */
     var previewStarted = false
+
+    /** Number of pictures taken. */
     var numPicturesTaken = 0
 
+    /** Whether a recording is in progress. */
     var recordingInProgress = false
+
+    /** Whether the current recording is paused. */
     var isRecordingPaused = false
 
+    /** Whether the lens facing is front. */
     var isLensFacingFront = false
 
     private var isScreenFlash = true
@@ -85,9 +96,11 @@ class FakeCameraSystem(defaultCameraSettings: CameraAppSettings = CameraAppSetti
 
         currentSettings
             .onCompletion {
+                _surfaceRequest.value = null
                 useCasesBinded = false
                 previewStarted = false
                 recordingInProgress = false
+                _currentCameraState.update { CameraState() }
             }.collectLatest {
                 useCasesBinded = true
                 previewStarted = true
@@ -96,6 +109,22 @@ class FakeCameraSystem(defaultCameraSettings: CameraAppSettings = CameraAppSetti
                 isScreenFlash =
                     isLensFacingFront &&
                     (it.flashMode == FlashMode.AUTO || it.flashMode == FlashMode.ON)
+
+                val aspectRatio = it.aspectRatio
+                val request = ViewfinderSurfaceRequest(
+                    1080 * aspectRatio.denominator / aspectRatio.numerator,
+                    1080,
+                    ImplementationMode.EXTERNAL
+                )
+                val deferred = CompletableDeferred<Surface>()
+                _currentCameraState.update { state ->
+                    state.copy(isCameraRunning = false)
+                }
+                _surfaceRequest.value = PreviewSurfaceRequest.Viewfinder(request, deferred)
+                deferred.await()
+                _currentCameraState.update { state ->
+                    state.copy(isCameraRunning = true)
+                }
             }
     }
 
@@ -163,8 +192,9 @@ class FakeCameraSystem(defaultCameraSettings: CameraAppSettings = CameraAppSetti
 
     override fun getCurrentCameraState(): StateFlow<CameraState> = _currentCameraState.asStateFlow()
 
-    private val _surfaceRequest = MutableStateFlow<SurfaceRequest?>(null)
-    override fun getSurfaceRequest(): StateFlow<SurfaceRequest?> = _surfaceRequest.asStateFlow()
+    private val _surfaceRequest = MutableStateFlow<PreviewSurfaceRequest?>(null)
+    override fun getSurfaceRequest(): StateFlow<PreviewSurfaceRequest?> =
+        _surfaceRequest.asStateFlow()
 
     override fun getScreenFlashEvents() = screenFlashEvents
     override fun getCurrentSettings(): StateFlow<CameraAppSettings?> = currentSettings.asStateFlow()