Add camera facing selection

app/src/main/kotlin/com/kimgo/posefit/MainActivity.kt

@@ -12,6 +12,7 @@ import androidx.compose.runtime.*
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.dp
+import com.kimgo.posefit.sender.CameraFacing
 import com.kimgo.posefit.sender.WebRtcSenderClient
 import timber.log.Timber
 
@@ -23,7 +24,8 @@ class MainActivity : ComponentActivity() {
         registerForActivityResult(ActivityResultContracts.RequestPermission()) { granted ->
             if (granted) {
                 val url = getSavedSignalingUrl()
-                startWebRtc(url)
+                val cameraFacing = getSavedCameraFacing()
+                startWebRtc(url, cameraFacing)
             } else {
                 Timber.w("Camera permission denied")
             }
@@ -48,6 +50,7 @@ class MainActivity : ComponentActivity() {
     @Composable
     fun ConfigScreen() {
         var url by remember { mutableStateOf(getSavedSignalingUrl()) }
+        var cameraFacing by remember { mutableStateOf(getSavedCameraFacing()) }
         var isStreaming by remember { mutableStateOf(false) }
 
         Column(
@@ -71,6 +74,32 @@ class MainActivity : ComponentActivity() {
                 enabled = !isStreaming
             )
             Spacer(modifier = Modifier.height(16.dp))
+            Text(
+                text = "选择摄像头",
+                style = MaterialTheme.typography.titleMedium,
+                modifier = Modifier.fillMaxWidth()
+            )
+            Spacer(modifier = Modifier.height(8.dp))
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                horizontalArrangement = Arrangement.spacedBy(12.dp)
+            ) {
+                CameraFacingButton(
+                    text = "前置摄像头",
+                    selected = cameraFacing == CameraFacing.FRONT,
+                    enabled = !isStreaming,
+                    modifier = Modifier.weight(1f),
+                    onClick = { cameraFacing = CameraFacing.FRONT }
+                )
+                CameraFacingButton(
+                    text = "后置摄像头",
+                    selected = cameraFacing == CameraFacing.BACK,
+                    enabled = !isStreaming,
+                    modifier = Modifier.weight(1f),
+                    onClick = { cameraFacing = CameraFacing.BACK }
+                )
+            }
+            Spacer(modifier = Modifier.height(16.dp))
             Button(
                 onClick = {
                     if (isStreaming) {
@@ -78,6 +107,7 @@ class MainActivity : ComponentActivity() {
                         isStreaming = false
                     } else {
                         saveSignalingUrl(url)
+                        saveCameraFacing(cameraFacing)
                         requestPermission.launch(Manifest.permission.CAMERA)
                         isStreaming = true
                     }
@@ -89,6 +119,40 @@ class MainActivity : ComponentActivity() {
         }
     }
 
+    @Composable
+    private fun CameraFacingButton(
+        text: String,
+        selected: Boolean,
+        enabled: Boolean,
+        modifier: Modifier = Modifier,
+        onClick: () -> Unit
+    ) {
+        val colors = if (selected) {
+            ButtonDefaults.buttonColors()
+        } else {
+            ButtonDefaults.outlinedButtonColors()
+        }
+
+        if (selected) {
+            Button(
+                onClick = onClick,
+                enabled = enabled,
+                modifier = modifier
+            ) {
+                Text(text)
+            }
+        } else {
+            OutlinedButton(
+                onClick = onClick,
+                enabled = enabled,
+                modifier = modifier,
+                colors = colors
+            ) {
+                Text(text)
+            }
+        }
+    }
+
     private fun getSavedSignalingUrl(): String {
         val prefs = getSharedPreferences("posefit_prefs", Context.MODE_PRIVATE)
         return prefs.getString("signaling_url", "ws://192.168.2.10:8765") ?: "ws://192.168.2.10:8765"
@@ -99,12 +163,25 @@ class MainActivity : ComponentActivity() {
         prefs.edit().putString("signaling_url", url).apply()
     }
 
-    private fun startWebRtc(url: String) {
-        Timber.i("startWebRtc: %s", url)
+    private fun getSavedCameraFacing(): CameraFacing {
+        val prefs = getSharedPreferences("posefit_prefs", Context.MODE_PRIVATE)
+        val value = prefs.getString("camera_facing", CameraFacing.FRONT.name)
+        return runCatching { CameraFacing.valueOf(value ?: CameraFacing.FRONT.name) }
+            .getOrDefault(CameraFacing.FRONT)
+    }
+
+    private fun saveCameraFacing(cameraFacing: CameraFacing) {
+        val prefs = getSharedPreferences("posefit_prefs", Context.MODE_PRIVATE)
+        prefs.edit().putString("camera_facing", cameraFacing.name).apply()
+    }
+
+    private fun startWebRtc(url: String, cameraFacing: CameraFacing) {
+        Timber.i("startWebRtc: %s, cameraFacing=%s", url, cameraFacing)
         webRtcClient?.release()
         webRtcClient = WebRtcSenderClient(
             context = this,
-            signalingUrl = url
+            signalingUrl = url,
+            cameraFacing = cameraFacing
         )
         webRtcClient?.start()
     }

app/src/main/kotlin/com/kimgo/posefit/sender/CameraFacing.kt

@@ -0,0 +1,6 @@
+package com.kimgo.posefit.sender
+
+enum class CameraFacing {
+    FRONT,
+    BACK
+}

app/src/main/kotlin/com/kimgo/posefit/sender/WebRtcSenderClient.kt

@@ -8,7 +8,8 @@ import timber.log.Timber
 
 class WebRtcSenderClient(
     private val context: Context,
-    private val signalingUrl: String
+    private val signalingUrl: String,
+    private val cameraFacing: CameraFacing = CameraFacing.FRONT
 ) {
 
     private val eglBase = EglBase.create()
@@ -24,7 +25,7 @@ class WebRtcSenderClient(
     private var surfaceTextureHelper: SurfaceTextureHelper? = null
 
     fun start() {
-        Timber.i("WebRTC starting, signalingUrl=%s", signalingUrl)
+        Timber.i("WebRTC starting, signalingUrl=%s, cameraFacing=%s", signalingUrl, cameraFacing)
         initPeerConnectionFactory()
         connectSignaling()
     }
@@ -129,9 +130,7 @@ class WebRtcSenderClient(
     private fun startCamera() {
         val enumerator = Camera2Enumerator(context)
 
-        val cameraName = enumerator.deviceNames.firstOrNull {
-            enumerator.isFrontFacing(it)
-        } ?: enumerator.deviceNames.first()
+        val cameraName = selectCamera(enumerator)
 
         videoCapturer = enumerator.createCapturer(cameraName, null)
 
@@ -160,6 +159,22 @@ class WebRtcSenderClient(
         Timber.d("Camera started: %s, resolution=1280x720@30fps", cameraName)
     }
 
+    private fun selectCamera(enumerator: Camera2Enumerator): String {
+        val preferredCamera = enumerator.deviceNames.firstOrNull { cameraName ->
+            when (cameraFacing) {
+                CameraFacing.FRONT -> enumerator.isFrontFacing(cameraName)
+                CameraFacing.BACK -> enumerator.isBackFacing(cameraName)
+            }
+        }
+
+        if (preferredCamera != null) {
+            return preferredCamera
+        }
+
+        Timber.w("Preferred camera not found: %s, falling back to first available camera", cameraFacing)
+        return enumerator.deviceNames.first()
+    }
+
     private fun createOffer() {
         val constraints = MediaConstraints().apply {
             mandatory.add(