[mob] Show face visibility score in debug mode

mobile/lib/face/model/detection.dart

@@ -3,6 +3,9 @@ import "package:photos/face/model/landmark.dart";
 
 /// Stores the face detection data, notably the bounding box and landmarks.
 ///
+/// - Bounding box: [FaceBox] with xMin, yMin (so top left corner), width, height
+/// - Landmarks: list of [Landmark]s, namely leftEye, rightEye, nose, leftMouth, rightMouth
+///
 /// WARNING: All coordinates are relative to the image size, so in the range [0, 1]!
 class Detection {
   FaceBox box;
@@ -39,4 +42,38 @@ class Detection {
       ),
     );
   }
+
+  // TODO: iterate on better scoring logic, current is a placeholder
+  int getVisibilityScore() {
+    final double aspectRatio = box.width / box.height;
+    final double eyeDistance = (landmarks[1].x - landmarks[0].x).abs();
+    final double mouthDistance = (landmarks[4].x - landmarks[3].x).abs();
+    final double noseEyeDistance =
+        (landmarks[2].y - ((landmarks[0].y + landmarks[1].y) / 2)).abs();
+
+    final double normalizedEyeDistance = eyeDistance / box.width;
+    final double normalizedMouthDistance = mouthDistance / box.width;
+    final double normalizedNoseEyeDistance = noseEyeDistance / box.height;
+
+    const double aspectRatioThreshold = 0.8;
+    const double eyeDistanceThreshold = 0.2;
+    const double mouthDistanceThreshold = 0.3;
+    const double noseEyeDistanceThreshold = 0.1;
+
+    double score = 0;
+    if (aspectRatio >= aspectRatioThreshold) {
+      score += 50;
+    }
+    if (normalizedEyeDistance >= eyeDistanceThreshold) {
+      score += 20;
+    }
+    if (normalizedMouthDistance >= mouthDistanceThreshold) {
+      score += 20;
+    }
+    if (normalizedNoseEyeDistance >= noseEyeDistanceThreshold) {
+      score += 10;
+    }
+
+    return score.clamp(0, 100).toInt();
+  }
 }

mobile/lib/ui/viewer/file_details/face_widget.dart

@@ -168,6 +168,12 @@ class _FaceWidgetState extends State<FaceWidget> {
                       style: Theme.of(context).textTheme.bodySmall,
                       maxLines: 1,
                     ),
+                  if (kDebugMode)
+                    Text(
+                      'V: ${widget.face.detection.getVisibilityScore()}',
+                      style: Theme.of(context).textTheme.bodySmall,
+                      maxLines: 1,
+                    ),
                   // if (kDebugMode)
                   //   if (highlight)
                   //     const Text(