riversong code showcase

Source/Riversong/Game/UI/Helpers/DraggableManipulator.cs

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+using UnityEngine;
+using UnityEngine.UIElements;
+
+namespace DanieleMarotta.RiversongCodeShowcase
+{
+    public class DraggableManipulator : PointerManipulator
+    {
+        private const string DraggedUssClassName = "dragged";
+
+        private Vector2 _startMousePosition;
+
+        private Vector2 _startElementPosition;
+
+        private VisualElement _draggedElement;
+
+        public DraggableManipulator(VisualElement draggedElement)
+        {
+            _draggedElement = draggedElement;
+        }
+
+        protected override void RegisterCallbacksOnTarget()
+        {
+            target.RegisterCallback<PointerDownEvent>(OnPointerDown);
+            target.RegisterCallback<PointerMoveEvent>(OnPointerMove);
+            target.RegisterCallback<PointerUpEvent>(OnPointerUp);
+        }
+
+        protected override void UnregisterCallbacksFromTarget()
+        {
+            target.UnregisterCallback<PointerDownEvent>(OnPointerDown);
+            target.UnregisterCallback<PointerMoveEvent>(OnPointerMove);
+            target.UnregisterCallback<PointerUpEvent>(OnPointerUp);
+        }
+
+        private void OnPointerDown(PointerDownEvent evt)
+        {
+            if (evt.button != 0) return;
+
+            target.CapturePointer(evt.pointerId);
+            evt.StopPropagation();
+
+            _startMousePosition = evt.position;
+            _startElementPosition = new Vector2(_draggedElement.resolvedStyle.left, _draggedElement.resolvedStyle.top);
+
+            _draggedElement.AddToClassList(DraggedUssClassName);
+        }
+
+        private void OnPointerMove(PointerMoveEvent evt)
+        {
+            if (!target.HasPointerCapture(evt.pointerId)) return;
+
+            var delta = (Vector2)evt.position - _startMousePosition;
+            _draggedElement.style.left = _startElementPosition.x + delta.x;
+            _draggedElement.style.top = _startElementPosition.y + delta.y;
+        }
+
+        private void OnPointerUp(PointerUpEvent evt)
+        {
+            if (!target.HasPointerCapture(evt.pointerId)) return;
+
+            target.ReleasePointer(evt.pointerId);
+
+            _draggedElement.RemoveFromClassList(DraggedUssClassName);
+        }
+    }
+}