From e069eb8014b931db4be695d89772c0ecb2175dd2 Mon Sep 17 00:00:00 2001
From: Eli Arbel <aelij@arbel.net>
Date: Sat, 2 Sep 2017 15:48:28 +0300
Subject: [PATCH] PR comments

---
 .../Rendering/DirtyVisuals.cs                 | 79 ++++---------------
 1 file changed, 17 insertions(+), 62 deletions(-)

diff --git a/src/Avalonia.Visuals/Rendering/DirtyVisuals.cs b/src/Avalonia.Visuals/Rendering/DirtyVisuals.cs
index 895b1679b0..00bc236b9c 100644
--- a/src/Avalonia.Visuals/Rendering/DirtyVisuals.cs
+++ b/src/Avalonia.Visuals/Rendering/DirtyVisuals.cs
@@ -17,8 +17,8 @@ namespace Avalonia.Rendering
     {
         private SortedDictionary<int, List<IVisual>> _inner = new SortedDictionary<int, List<IVisual>>();
         private Dictionary<IVisual, int> _index = new Dictionary<IVisual, int>();
-        private List<(DeferredChange change, IVisual visual)> _deferredChanges = new List<(DeferredChange, IVisual)>();
-        private bool _deferring;
+        private List<IVisual> _deferredChanges = new List<IVisual>();
+        private int _deferring;
 
         /// <summary>
         /// Gets the number of dirty visuals.
@@ -31,9 +31,9 @@ namespace Avalonia.Rendering
         /// <param name="visual">The dirty visual.</param>
         public void Add(IVisual visual)
         {
-            if (_deferring)
+            if (_deferring > 0)
             {
-                _deferredChanges.Add((DeferredChange.Add, visual));
+                _deferredChanges.Add(visual);
                 return;
             }
 
@@ -65,42 +65,23 @@ namespace Avalonia.Rendering
         /// </summary>
         public void Clear()
         {
-            if (_deferring)
+            if (_deferring > 0)
             {
-                _deferredChanges.Add((DeferredChange.Clear, null));
-                return;
+                throw new InvalidOperationException("Cannot clear while enumerating");
             }
 
             _inner.Clear();
             _index.Clear();
         }
 
-        /// <summary>
-        /// Removes a visual from the dirty list.
-        /// </summary>
-        /// <param name="visual">The visual.</param>
-        public void Remove(IVisual visual)
-        {
-            if (_deferring)
-            {
-                _deferredChanges.Add((DeferredChange.Remove, visual));
-                return;
-            }
-
-            if (_index.TryGetValue(visual, out var distance))
-            {
-                _inner[distance].Remove(visual);
-                _index.Remove(visual);
-            }
-        }
-
         /// <summary>
         /// Gets the dirty visuals, in ascending order of distance to their root.
         /// </summary>
         /// <returns>A collection of visuals.</returns>
         public IEnumerator<IVisual> GetEnumerator()
         {
-            using (DeferChanges())
+            BeginDefer();
+            try
             {
                 foreach (var i in _inner)
                 {
@@ -110,34 +91,24 @@ namespace Avalonia.Rendering
                     }
                 }
             }
+            finally
+            {
+                EndDefer();
+            }
         }
 
-        private DeferDisposer DeferChanges()
+        private void BeginDefer()
         {
-            _deferring = true;
-            return new DeferDisposer(this);
+            ++_deferring;
         }
 
         private void EndDefer()
         {
-            if (!_deferring) return;
+            if (--_deferring > 0) return;
 
-            _deferring = false;
-
-            foreach (var change in _deferredChanges)
+            foreach (var visual in _deferredChanges)
             {
-                switch (change.change)
-                {
-                    case DeferredChange.Add:
-                        Add(change.visual);
-                        break;
-                    case DeferredChange.Remove:
-                        Remove(change.visual);
-                        break;
-                    case DeferredChange.Clear:
-                        Clear();
-                        break;
-                }
+                Add(visual);
             }
 
             _deferredChanges.Clear();
@@ -148,21 +119,5 @@ namespace Avalonia.Rendering
         /// </summary>
         /// <returns>A collection of visuals.</returns>
         IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
-
-        private struct DeferDisposer : IDisposable
-        {
-            private DirtyVisuals _parent;
-
-            internal DeferDisposer(DirtyVisuals parent) => _parent = parent;
-
-            public void Dispose() => _parent?.EndDefer();
-        }
-
-        private enum DeferredChange
-        {
-            Add,
-            Remove,
-            Clear
-        }
     }
 }