Simple Drag Window Script

DragWindow.cs

using UnityEngine;
using UnityEngine.EventSystems;

namespace TC._Project.TestSystems.Debugging {
    /// <summary>
    /// A class that allows a UI window to be dragged within the bounds of its parent canvas.
    /// </summary>
    public class DragWindow : MonoBehaviour, IDragHandler, IPointerDownHandler {
        [Tooltip("The RectTransform of the window to be dragged.")]
        [SerializeField] RectTransform m_dragRectTransform;
        
        [Tooltip("The Canvas in which the window is contained.")]
        [SerializeField] Canvas m_canvas;
        
        Vector2 m_canvasSize;
        
        void Awake() {
            EnsureRectTransformIsSet();
            FindCanvasInHierarchy();
            if (m_canvas) {
                m_canvasSize = m_canvas.GetComponent<RectTransform>().sizeDelta;
            }
        }

        /// <summary>
        /// Ensures that the RectTransform is set, assigning it from the parent if not.
        /// </summary>
        void EnsureRectTransformIsSet() {
            if (!m_dragRectTransform) {
                m_dragRectTransform = transform.parent.GetComponent<RectTransform>();
            }
        }

        /// <summary>
        /// Finds the Canvas in the hierarchy, assigning it from the parent if not set.
        /// </summary>
        void FindCanvasInHierarchy() {
            if (!m_canvas) {
                m_canvas = GetComponentInParent<Canvas>();
            }
        }

        /// <summary>
        /// Called when the object is dragged.
        /// </summary>
        /// <param name="eventData">Current event data.</param>
        public void OnDrag(PointerEventData eventData) {
            var newPosition = m_dragRectTransform.anchoredPosition + eventData.delta / m_canvas.scaleFactor;
            newPosition = ConstrainWithinCanvas(newPosition);
            m_dragRectTransform.anchoredPosition = newPosition;
        }

        /// <summary>
        /// Constrains the position within the bounds of the canvas.
        /// </summary>
        /// <param name="position">The new position to be constrained.</param>
        /// <returns>The constrained position.</returns>
        Vector2 ConstrainWithinCanvas(Vector2 position) {
            var minPosition = -0.5f * m_canvasSize;
            var maxPosition = 0.5f * m_canvasSize;

            position.x = Mathf.Clamp(position.x, minPosition.x, maxPosition.x);
            position.y = Mathf.Clamp(position.y, minPosition.y, maxPosition.y);

            return position;
        }

        /// <summary>
        /// Called when a pointer down event is detected.
        /// </summary>
        /// <param name="eventData">Current event data.</param>
        public void OnPointerDown(PointerEventData eventData)
            => m_dragRectTransform.SetAsLastSibling();
    }
}