[mob] Refactor

mobile/lib/services/machine_learning/face_ml/face_detection/face_detection_service.dart

@@ -37,7 +37,9 @@ class FaceDetectionService extends MlModel {
 
   // Singleton pattern
   FaceDetectionService._privateConstructor();
+
   static final instance = FaceDetectionService._privateConstructor();
+
   factory FaceDetectionService() => instance;
 
   /// Detects faces in the given image data.
@@ -141,17 +143,19 @@ class FaceDetectionService extends MlModel {
       inputImageList,
       _modelName,
     );
-    final List<List<List<double>>> reconstructedTensor = [];
-    for (int i = 0; i < result!.length; i += 25200 * 16) {
-      final List<List<double>> outerArray = [];
-      for (int j = 0; j < 25200; j++) {
-        final List<double> innerArray =
-            result.sublist(i + j * 16, i + (j + 1) * 16).cast<double>();
-        outerArray.add(innerArray);
-      }
-      reconstructedTensor.add(outerArray);
-    }
-    return reconstructedTensor;
+
+    final int resultLength = result!.length;
+    assert(resultLength % 25200 * 16 == 0);
+    const int outerLength = 1;
+    const int middleLength = 25200;
+    const int innerLength = 16;
+    return List.generate(
+      outerLength,
+      (_) => List.generate(
+        middleLength,
+        (j) => result.sublist(j * innerLength, (j + 1) * innerLength).toList(),
+      ),
+    );
   }
 
   static List<FaceDetectionRelative> _yoloPostProcessOutputs(

mobile/plugins/onnx_dart/android/src/main/kotlin/io/ente/photos/onnx_dart/OnnxDartPlugin.kt

@@ -175,8 +175,8 @@ class OnnxDartPlugin: FlutterPlugin, MethodCallHandler {
         val inputs = mapOf("input" to inputTensor)
         val outputs = session.run(inputs)
         Log.d(TAG, "Output shape: ${outputs.size()}")
-        val outputTensor = outputs[0].value as Array<Array<FloatArray>>
-        val flatList = outputTensor.flatMapToFloatArray()
+        val outputTensor = (outputs[0].value as Array<Array<FloatArray>>).get(0)
+        val flatList = outputTensor.flattenToFloatArray()
         withContext(Dispatchers.Main) {
           result.success(flatList)
         }
@@ -217,4 +217,15 @@ class OnnxDartPlugin: FlutterPlugin, MethodCallHandler {
     }
     return result
   }
+  fun Array<FloatArray>.flattenToFloatArray(): FloatArray {
+    val outputSize = this.sumOf { it.size }
+    val result = FloatArray(outputSize)
+    var index = 0
+    for (inner in this) {
+      for (value in inner) {
+        result[index++] = value
+      }
+    }
+    return result
+  }
 }