riversong code showcase

Source/Riversong/Game/UI/Panels/WorldUI/WorldUITrackingSystem.cs

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+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Pool;
+using UnityEngine.UIElements;
+
+namespace DanieleMarotta.RiversongCodeShowcase
+{
+    [Service(typeof(IWorldUIService))]
+    [GameSystemGroup(typeof(UISystemGroup))]
+    public class WorldUITrackingSystem : GameSystem, IUpdatable, IWorldUIService
+    {
+        [InjectService]
+        private IScene _scene;
+
+        private readonly Dictionary<VisualElement, TrackedElement> _trackedElements = new();
+
+        public WorldUITrackingSystem(IServiceLocator serviceLocator) : base(serviceLocator)
+        {
+        }
+
+        public void Register(VisualElement element, Transform target)
+        {
+            _trackedElements[element] = new TrackedElement { Target = target };
+        }
+
+        public void Unregister(VisualElement element)
+        {
+            _trackedElements.Remove(element);
+        }
+
+        public void SetWorldOffset(VisualElement element, Vector3 offset)
+        {
+            var trackedElement = _trackedElements[element];
+            trackedElement.Offset = offset;
+            _trackedElements[element] = trackedElement;
+        }
+
+        public void Update()
+        {
+            if (_trackedElements.Count == 0) return;
+
+            using var invalidScope = ListPool<VisualElement>.Get(out var invalidElements);
+            var camera = _scene.MainCamera;
+
+            foreach (var (element, trackedElement) in _trackedElements)
+            {
+                var target = trackedElement.Target;
+                if (element.panel == null || target == null)
+                {
+                    invalidElements.Add(element);
+                    continue;
+                }
+
+                var screenPoint = camera.WorldToScreenPoint(target.position + trackedElement.Offset);
+                var isVisible = screenPoint.x >= 0 && screenPoint.x <= Screen.width && screenPoint.y >= 0 && screenPoint.y <= Screen.height && screenPoint.z > 0;
+
+                element.style.visibility = isVisible ? Visibility.Visible : Visibility.Hidden;
+                if (isVisible) element.SetAbsoluteScreenPosition(screenPoint);
+            }
+
+            foreach (var invalidElement in invalidElements) _trackedElements.Remove(invalidElement);
+        }
+
+        private struct TrackedElement
+        {
+            public Transform Target;
+
+            public Vector3 Offset;
+        }
+    }
+}