Optimize large lists rendering

Author: vanifatovvlad

Editor/Elements/TriListElement.cs

@@ -12,6 +12,8 @@ namespace TriInspector.Elements
 {
     public class TriListElement : TriElement
     {
+        private const int MinElementsForVirtualization = 25;
+
         private const float ListExtraWidth = 7f;
         private const float DraggableAreaExtraWidth = 14f;
 
@@ -21,6 +23,8 @@ public class TriListElement : TriElement
         private readonly bool _showElementLabels;
 
         private float _lastContentWidth;
+        private int? _lastInvisibleElement;
+        private int? _lastVisibleElement;
 
         protected ReorderableList ListGui => _reorderableListGui;
 
@@ -109,13 +113,22 @@ public override void OnGUI(Rect position)
         {
             if (!_property.IsExpanded)
             {
+                _lastInvisibleElement = null;
+                _lastVisibleElement = null;
+
                 ReorderableListProxy.DoListHeader(_reorderableListGui, new Rect(position)
                 {
                     yMax = position.yMax - 4,
                 });
                 return;
             }
 
+            if (_reorderableListGui.count < MinElementsForVirtualization)
+            {
+                _lastInvisibleElement = null;
+                _lastVisibleElement = null;
+            }
+
             var labelWidthExtra = ListExtraWidth + DraggableAreaExtraWidth;
 
             using (TriGuiHelper.PushLabelWidth(EditorGUIUtility.labelWidth - labelWidthExtra))
@@ -403,6 +416,36 @@ private void DrawElementCallback(Rect rect, int index, bool isActive, bool isFoc
                 return;
             }
 
+            if (_lastInvisibleElement.HasValue && index + 1 < _lastInvisibleElement.Value ||
+                _lastVisibleElement.HasValue && index - 1 > _lastVisibleElement.Value)
+            {
+                return;
+            }
+
+            if (_reorderableListGui.count > MinElementsForVirtualization)
+            {
+                if (Event.current.type == EventType.Repaint)
+                {
+                    var windowRect = GUIClipProxy.VisibleRect;
+                    var rectInWindow = GUIClipProxy.UnClipToWindow(rect);
+
+                    if (rectInWindow.yMax < 0)
+                    {
+                        _lastInvisibleElement = index;
+                    } else if (_lastInvisibleElement == index)
+                    {
+                        _lastInvisibleElement = index / 2;
+                        _lastVisibleElement = index / 2 + 1;
+                        _property.PropertyTree.RequestRepaint();
+                    }
+
+                    if (rectInWindow.y < windowRect.height)
+                    {
+                        _lastVisibleElement = index;
+                    }
+                }
+            }
+
             if (!_reorderableListGui.draggable)
             {
                 rect.xMin += DraggableAreaExtraWidth;
@@ -421,6 +464,12 @@ private float ElementHeightCallback(int index)
                 return EditorGUIUtility.singleLineHeight;
             }
 
+            if (_lastInvisibleElement.HasValue && index + 1 < _lastInvisibleElement.Value ||
+                _lastVisibleElement.HasValue && index - 1 > _lastVisibleElement.Value)
+            {
+                return Mathf.Max(EditorGUIUtility.singleLineHeight, GetChild(index).CachedHeight);
+            }
+
             return GetChild(index).GetHeight(_lastContentWidth);
         }
 

Editor/TriElement.cs

@@ -9,6 +9,7 @@ public class TriElement
     {
         private static readonly List<TriElement> Empty = new List<TriElement>();
 
+        private float _cachedHeight;
         private bool _attached;
         private List<TriElement> _children = Empty;
 
@@ -17,6 +18,8 @@ public class TriElement
 
         public bool IsAttached => _attached;
 
+        internal float CachedHeight => _cachedHeight;
+
         [PublicAPI]
         public virtual bool Update()
         {
@@ -43,24 +46,29 @@ public virtual float GetHeight(float width)
                 Debug.LogError($"{GetType().Name} not attached");
             }
 
+            if (Event.current.type != EventType.Layout)
+            {
+                return _cachedHeight;
+            }
+
             switch (_children.Count)
             {
                 case 0:
-                    return 0f;
+                    return _cachedHeight = 0f;
 
                 case 1:
-                    return _children[0].GetHeight(width);
+                    return _cachedHeight = _children[0].GetHeight(width);
 
                 default:
                 {
-                    var height = (_children.Count - 1) * EditorGUIUtility.standardVerticalSpacing;
+                    _cachedHeight = (_children.Count - 1) * EditorGUIUtility.standardVerticalSpacing;
 
                     foreach (var child in _children)
                     {
-                        height += child.GetHeight(width);
+                        _cachedHeight += child.GetHeight(width);
                     }
 
-                    return height;
+                    return _cachedHeight;
                 }
             }
         }

Unity.InternalAPIEditorBridge.012/GUIClipProxy.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reflection;
 using UnityEditor;
 using UnityEngine;
 
@@ -7,6 +8,8 @@ namespace TriInspectorUnityInternalBridge
     internal static class GUIClipProxy
     {
         private static Func<Vector2, Vector2> _guiClipUnClipVector2;
+        private static Func<Rect, Rect> _guiClipUnClipToWindowRect;
+        private static Func<Rect> _guiClipVisibleRect;
 
         [InitializeOnLoadMethod]
         private static void Setup()
@@ -16,11 +19,24 @@ private static void Setup()
 
             _guiClipUnClipVector2 = (Func<Vector2, Vector2>) Delegate.CreateDelegate(typeof(Func<Vector2, Vector2>),
                 guiClipType.GetMethod("Unclip", new[] {typeof(Vector2)}));
+
+            _guiClipUnClipToWindowRect = (Func<Rect, Rect>) Delegate.CreateDelegate(typeof(Func<Rect, Rect>),
+                guiClipType.GetMethod("UnclipToWindow", new[] {typeof(Rect)}));
+
+            _guiClipVisibleRect = (Func<Rect>) Delegate.CreateDelegate(typeof(Func<Rect>),
+                guiClipType.GetProperty("visibleRect", BindingFlags.Static | BindingFlags.NonPublic).GetMethod);
         }
 
+        public static Rect VisibleRect => _guiClipVisibleRect.Invoke();
+
         public static Vector2 UnClip(Vector2 pos)
         {
             return _guiClipUnClipVector2.Invoke(pos);
         }
+
+        public static Rect UnClipToWindow(Rect rect)
+        {
+            return _guiClipUnClipToWindowRect.Invoke(rect);
+        }
     }
 }