#323: ZIndex fixes

samples/UI/zindex.xmmp

@@ -0,0 +1,7 @@
+<Project>
+  <Panel>
+    <TextButton Text="Button 3" Left="20"  />
+    <TextButton Text="Button 1" ZIndex="2" />
+    <TextButton Text="Button 2" Left="10" Top="10" ZIndex="4" />
+  </Panel>
+</Project>

src/Myra.Tests/CustomTests.cs

@@ -1,8 +1,10 @@
 using Myra.Graphics2D.TextureAtlases;
 using Myra.Graphics2D.UI;
 using Myra.Graphics2D.UI.Styles;
+using Myra.Utility;
 using NUnit.Framework;
 using System;
+using System.Collections.Generic;
 
 namespace Myra.Tests
 {
@@ -49,5 +51,40 @@ public void MyraEnvironmentReset()
 			Assert.AreNotEqual(oldStylesheet, newStylesheet);
 			Assert.AreNotEqual(oldTexture, newTexture);
 		}
+
+		[Test]
+		public void TestZIndexSort()
+		{
+			var widgets = new List<Widget>();
+			var button1 = new TextButton
+			{
+				ZIndex = 10
+			};
+			var button2 = new TextButton
+			{
+				ZIndex = 6
+			};
+			var button3 = new TextButton
+			{
+				ZIndex = 4
+			};
+			var button4 = new TextButton
+			{
+				ZIndex = 2
+			};
+
+			widgets.Add(button1);
+			widgets.Add(button2);
+			widgets.Add(button3);
+			widgets.Add(button4);
+
+			widgets.SortWidgetsByZIndex();
+
+			// The list should become reversed
+			Assert.AreEqual(widgets[0], button4);
+			Assert.AreEqual(widgets[1], button3);
+			Assert.AreEqual(widgets[2], button2);
+			Assert.AreEqual(widgets[3], button1);
+		}
 	}
 }

src/Myra/Graphics2D/UI/Container.cs

@@ -110,7 +110,7 @@ private void UpdateWidgets()
 				_childrenCopy.Add(GetChild(i));
 			}
 
-			_childrenCopy.Sort((a, b) => Comparer<int>.Default.Compare(a.ZOrder, b.ZOrder));
+			_childrenCopy.SortWidgetsByZIndex();
 
 			_childrenDirty = false;
 		}

src/Myra/Graphics2D/UI/Desktop.cs

@@ -1171,7 +1171,7 @@ private void UpdateWidgetsCopy()
 			_widgetsCopy.Clear();
 			_widgetsCopy.AddRange(Widgets);
 
-			_widgetsCopy.Sort((a, b) => Comparer<int>.Default.Compare(a.ZOrder, b.ZOrder));
+			_widgetsCopy.SortWidgetsByZIndex();
 
 			_widgetsDirty = false;
 		}

src/Myra/Graphics2D/UI/Widget.cs

@@ -34,6 +34,7 @@ private enum LayoutState
 		private int _left, _top;
 		private int? _minWidth, _minHeight, _maxWidth, _maxHeight, _width, _height;
 		private int _gridColumn, _gridRow, _gridColumnSpan = 1, _gridRowSpan = 1;
+		private int _zIndex;
 		private HorizontalAlignment _horizontalAlignment = HorizontalAlignment.Left;
 		private VerticalAlignment _verticalAlignment = VerticalAlignment.Top;
 		private LayoutState _layoutState = LayoutState.Invalid;
@@ -531,15 +532,26 @@ public virtual bool Visible
 		[DefaultValue(DragDirection.None)]
 		public virtual DragDirection DragDirection { get; set; } = DragDirection.None;
 
+		[XmlIgnore]
+		[Browsable(false)]
+		internal bool IsDraggable { get => DragDirection != DragDirection.None; }
+
 		[Category("Behavior")]
 		[DefaultValue(0)]
-		public int ZOrder { get; set; }
-
+		public int ZIndex
+		{
+			get => _zIndex;
+			set
+			{
+				if (value == _zIndex)
+				{
+					return;
+				}
 
-		[Obsolete("Use DragDirection instead")]
-		[XmlIgnore]
-		[Browsable(false)]
-		public bool IsDraggable => DragDirection != DragDirection.None;
+				_zIndex = value;
+				InvalidateMeasure();
+			}
+		}
 
 		[XmlIgnore]
 		[Browsable(false)]

src/Myra/Utility/UIUtils.cs

@@ -1,5 +1,6 @@
 using Myra.Graphics2D.UI;
 using System;
+using System.Collections.Generic;
 
 namespace Myra.Utility
 {
@@ -32,5 +33,32 @@ public static bool ProcessWidgets(this Widget root, Func<Widget, bool> operation
 
 			return true;
 		}
+
+		/// <summary>
+		/// Sorts widgets by ZIndex using bubble sort
+		/// </summary>
+		/// <param name="list"></param>
+		public static void SortWidgetsByZIndex(this List<Widget> list)
+		{
+			var n = list.Count;
+			do
+			{
+				var newN = 0;
+				for (var i = 1; i < n; ++i)
+				{
+					if (list[i - 1].ZIndex > list[i].ZIndex)
+					{
+						// Swap
+						var temp = list[i - 1];
+						list[i - 1] = list[i];
+						list[i] = temp;
+
+						newN = i;
+					}
+				}
+
+				n = newN;
+			} while (n > 1);
+		}
 	}
 }