Add ScrollToSelection script

Author: adamgraham

Runtime/ScrollToSelection.cs

@@ -0,0 +1,132 @@
+using UnityEngine;
+using UnityEngine.EventSystems;
+using UnityEngine.InputSystem;
+using UnityEngine.UI;
+
+namespace Zigurous.UI
+{
+    [RequireComponent(typeof(ScrollRect))]
+    [AddComponentMenu("Zigurous/UI/Navigation/Scroll To Selection")]
+    public class ScrollToSelection : MonoBehaviour
+    {
+        public enum ScrollDirection
+        {
+            Vertical,
+            Horizontal,
+            Both,
+        }
+
+        public ScrollDirection scrollDirection;
+        public float scrollSpeed = 10.0f;
+        public bool manualScrolling { get; private set; }
+
+        public ScrollRect scrollRect { get; private set; }
+        public RectTransform scrollTransform { get; private set; }
+        public GameObject selectedGameObject { get; private set; }
+        public RectTransform selectedTransform { get; private set; }
+
+        private void Awake()
+        {
+            this.scrollRect = GetComponent<ScrollRect>();
+            this.scrollTransform = this.scrollRect.GetComponent<RectTransform>();
+        }
+
+        private void Update()
+        {
+            CheckForManualScrolling();
+            SetSelectedGameObject();
+            SetScrollPosition();
+        }
+
+        private void CheckForManualScrolling()
+        {
+            if (Mouse.current != null && Mouse.current.scroll.y.IsActuated()) {
+                this.manualScrolling = true;
+            }
+        }
+
+        private void SetSelectedGameObject()
+        {
+            EventSystem eventSystem = EventSystem.current;
+
+            if (eventSystem == null || eventSystem.currentSelectedGameObject == null) {
+                return;
+            }
+
+            if (eventSystem.currentSelectedGameObject != this.selectedGameObject &&
+                eventSystem.currentSelectedGameObject.transform.parent == this.scrollRect.content)
+            {
+                this.selectedGameObject = eventSystem.currentSelectedGameObject;
+                this.selectedTransform = this.selectedGameObject.GetComponent<RectTransform>();
+                this.manualScrolling = false;
+            }
+        }
+
+        private void SetScrollPosition()
+        {
+            if (this.selectedTransform == null || this.manualScrolling) {
+                return;
+            }
+
+            switch (this.scrollDirection)
+            {
+                case ScrollDirection.Vertical:
+                    ScrollVertical(this.selectedTransform);
+                    break;
+
+                case ScrollDirection.Horizontal:
+                    ScrollHorizontal(this.selectedTransform);
+                    break;
+
+                case ScrollDirection.Both:
+                    ScrollVertical(this.selectedTransform);
+                    ScrollHorizontal(this.selectedTransform);
+                    break;
+            }
+        }
+
+        private void ScrollVertical(RectTransform selection)
+        {
+            // Calculate the scroll offset
+            float elementHeight = selection.rect.height;
+            float maskHeight = this.scrollTransform.rect.height;
+            float anchorPosition = this.scrollRect.content.anchoredPosition.y;
+            float selectionPosition = -selection.anchoredPosition.y - (elementHeight * (1.0f - selection.pivot.y));
+            float offset = GetScrollOffset(selectionPosition, anchorPosition, elementHeight, maskHeight);
+
+            // Move the target scroll rect
+            float position = this.scrollRect.verticalNormalizedPosition;
+            position = Mathf.Clamp01(position + (offset / this.scrollRect.content.rect.height) * Time.unscaledDeltaTime * this.scrollSpeed);
+            this.scrollRect.verticalNormalizedPosition = position;
+        }
+
+        private void ScrollHorizontal(RectTransform selection)
+        {
+            // Calculate the scroll offset
+            float selectionPosition = -selection.anchoredPosition.x - (selection.rect.width * (1.0f - selection.pivot.x));
+            float elementWidth = selection.rect.width;
+            float maskWidth = this.scrollTransform.rect.width;
+            float anchorPosition = -this.scrollRect.content.anchoredPosition.x;
+            float offset = -GetScrollOffset(selectionPosition, anchorPosition, elementWidth, maskWidth);
+
+            // Move the target scroll rect
+            float position = this.scrollRect.horizontalNormalizedPosition;
+            position = Mathf.Clamp01(position + (offset / this.scrollRect.content.rect.width) * Time.unscaledDeltaTime * this.scrollSpeed);
+            this.scrollRect.horizontalNormalizedPosition = position;
+        }
+
+        private float GetScrollOffset(float position, float anchorPosition, float targetLength, float maskLength)
+        {
+            if (position < anchorPosition + (targetLength * 0.5f)) {
+                return (anchorPosition + maskLength) - (position - targetLength);
+            }
+            else if (position + targetLength > anchorPosition + maskLength) {
+                return (anchorPosition + maskLength) - (position + targetLength);
+            }
+
+            return 0.0f;
+        }
+
+    }
+
+}