Add minor performance improvements.

Include rotate 3d transition for carousel control.

samples/ControlCatalog/Pages/CarouselPage.xaml

@@ -29,6 +29,7 @@
         <ComboBoxItem>None</ComboBoxItem>
         <ComboBoxItem>Slide</ComboBoxItem>
         <ComboBoxItem>Crossfade</ComboBoxItem>
+        <ComboBoxItem>3D Rotation</ComboBoxItem>
       </ComboBox>
     </StackPanel>
 

samples/ControlCatalog/Pages/CarouselPage.xaml.cs

@@ -45,6 +45,9 @@ namespace ControlCatalog.Pages
                 case 2:
                     _carousel.PageTransition = new CrossFade(TimeSpan.FromSeconds(0.25));
                     break;
+                case 3:
+                    _carousel.PageTransition = new Rotate3DTransition(TimeSpan.FromSeconds(0.5), _orientation.SelectedIndex == 0 ? PageSlide.SlideAxis.Horizontal : PageSlide.SlideAxis.Vertical);
+                    break;
             }
         }
     }

src/Avalonia.Visuals/Animation/PageSlide.cs

@@ -10,7 +10,7 @@ using Avalonia.VisualTree;
 namespace Avalonia.Animation
 {
     /// <summary>
-    /// Transitions between two pages by sliding them horizontally.
+    /// Transitions between two pages by sliding them horizontally or vertically.
     /// </summary>
     public class PageSlide : IPageTransition
     {
@@ -62,7 +62,7 @@ namespace Avalonia.Animation
         public Easing SlideOutEasing { get; set; } = new LinearEasing();
 
         /// <inheritdoc />
-        public async Task Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken)
+        public virtual async Task Start(Visual? from, Visual? to, bool forward, CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {
@@ -155,7 +155,7 @@ namespace Avalonia.Animation
         /// <remarks>
         /// Any one of the parameters may be null, but not both.
         /// </remarks>
-        private static IVisual GetVisualParent(IVisual? from, IVisual? to)
+        protected static IVisual GetVisualParent(IVisual? from, IVisual? to)
         {
             var p1 = (from ?? to)!.VisualParent;
             var p2 = (to ?? from)!.VisualParent;

src/Avalonia.Visuals/Animation/Transitions/Rotate3DTransition.cs

@@ -0,0 +1,153 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Avalonia.Media;
+using Avalonia.Styling;
+
+namespace Avalonia.Animation;
+
+public class Rotate3DTransition: PageSlide
+{
+    
+    /// <summary>
+    ///  Creates a new instance if the <see cref="Rotate3DTransition"/>
+    /// </summary>
+    /// <param name="duration">How long the rotation should take place</param>
+    /// <param name="orientation">The orientation of the rotation</param>
+    public Rotate3DTransition(TimeSpan duration, SlideAxis orientation = SlideAxis.Horizontal) 
+        : base(duration, orientation)
+    {}
+
+    /// <summary>
+    ///  Creates a new instance if the <see cref="Rotate3DTransition"/>
+    /// </summary>
+    public Rotate3DTransition() { }
+
+    /// <inheritdoc />
+    public override async Task Start(Visual? @from, Visual? to, bool forward, CancellationToken cancellationToken)
+    {
+        if (cancellationToken.IsCancellationRequested)
+        {
+            return;
+        }
+
+        var tasks = new List<Task>();
+        var parent = GetVisualParent(from, to);
+        var (rotateProperty, center) = Orientation switch
+        {
+            SlideAxis.Vertical => (Rotate3DTransform.AngleXProperty, parent.Bounds.Height),
+            SlideAxis.Horizontal => (Rotate3DTransform.AngleYProperty, parent.Bounds.Width),
+            _ => throw new ArgumentOutOfRangeException()
+        };
+
+        var depthSetter = new Setter {Property = Rotate3DTransform.DepthProperty, Value = center};
+        var centerZSetter = new Setter {Property = Rotate3DTransform.CenterZProperty, Value = -center / 2};
+
+        if (from != null)
+        {
+            var animation = new Animation
+            {
+                Duration = Duration,
+                Children =
+                {
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = rotateProperty, Value = 0d },
+                            new Setter { Property = Visual.ZIndexProperty, Value = 2 },
+                            centerZSetter,
+                            depthSetter,
+                        },
+                        Cue = new Cue(0d)
+                    },
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = rotateProperty, Value = 45d * (forward ? -1 : 1) },
+                            new Setter { Property = Visual.ZIndexProperty, Value = 1 },
+                            centerZSetter,
+                            depthSetter
+                        },
+                        Cue = new Cue(0.5d)
+                    },
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = rotateProperty, Value = 90d * (forward ? -1 : 1) },
+                            new Setter { Property = Visual.ZIndexProperty, Value = 1 },
+                            centerZSetter,
+                            depthSetter
+                        },
+                        Cue = new Cue(1d)
+                    }
+                }
+            };
+
+            tasks.Add(animation.RunAsync(from, null, cancellationToken));
+        }
+
+        if (to != null)
+        {
+            to.IsVisible = true;
+            var animation = new Animation
+            {
+                Duration = Duration,
+                Children =
+                {
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = rotateProperty, Value = 90d * (forward ? 1 : -1) },
+                            new Setter { Property = Visual.ZIndexProperty, Value = 1 },
+                            centerZSetter,
+                            depthSetter
+                        },
+                        Cue = new Cue(0d)
+                    },
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = Visual.ZIndexProperty, Value = 1 },
+                            new Setter { Property = rotateProperty, Value = 45d * (forward ? 1 : -1) },
+                            centerZSetter,
+                            depthSetter
+                        },
+                        Cue = new Cue(0.5d)
+                    },
+                    new KeyFrame
+                    {
+                        Setters =
+                        {
+                            new Setter { Property = rotateProperty, Value = 0d },
+                            new Setter { Property = Visual.ZIndexProperty, Value = 2 },
+                            centerZSetter,
+                            depthSetter,
+                        },
+                        Cue = new Cue(1d)
+                    }
+                }
+            };
+
+            tasks.Add(animation.RunAsync(to, null, cancellationToken));
+        }
+
+        await Task.WhenAll(tasks);
+
+        if (from != null && !cancellationToken.IsCancellationRequested)
+        {
+            from.IsVisible = false;
+            from.ZIndex = 1;
+        }
+
+        if (to != null && !cancellationToken.IsCancellationRequested)
+        {
+            to.ZIndex = 2;
+        }
+    }
+}

src/Avalonia.Visuals/Media/Rotate3DTransform.cs

@@ -9,6 +9,8 @@ namespace Avalonia.Media;
 /// </summary>
 public class Rotate3DTransform : Transform
 {
+    private readonly bool _isInitializing;
+    
     /// <summary>
     /// Defines the <see cref="AngleX"/> property.
     /// </summary>
@@ -76,12 +78,14 @@ public class Rotate3DTransform : Transform
         double centerY,
         double centerZ) : this()
     {
+        _isInitializing = true;
         AngleX = angleX;
         AngleY = angleY;
         AngleZ = angleZ;
         CenterX = centerX;
         CenterY = centerY;
         CenterZ = centerZ;
+        _isInitializing = false;
     }
 
     /// <summary>
@@ -148,21 +152,22 @@ public class Rotate3DTransform : Transform
     }
 
     /// <summary>
-    /// Gets the transform's <see cref="Matrix"/>.
+    /// Gets the transform's <see cref="Matrix"/>. 
     /// </summary>
     public override Matrix Value
     {
         get
         {
             var matrix44 = Matrix4x4.Identity;
+            var centerSum = CenterX + CenterY + CenterZ;
+            
+            if (centerSum != 0) matrix44 *= Matrix4x4.CreateTranslation(-(float)CenterX, -(float)CenterY, -(float)CenterZ);
 
-            matrix44 *= Matrix4x4.CreateTranslation(-(float)CenterX, -(float)CenterY, -(float)CenterZ);
+            if (AngleX != 0) matrix44 *= Matrix4x4.CreateRotationX((float)Matrix.ToRadians(AngleX));
+            if (AngleY != 0) matrix44 *= Matrix4x4.CreateRotationY((float)Matrix.ToRadians(AngleY));
+            if (AngleZ != 0) matrix44 *= Matrix4x4.CreateRotationZ((float)Matrix.ToRadians(AngleZ));
 
-            matrix44 *= Matrix4x4.CreateRotationX((float)Matrix.ToRadians(AngleX));
-            matrix44 *= Matrix4x4.CreateRotationY((float)Matrix.ToRadians(AngleY));
-            matrix44 *= Matrix4x4.CreateRotationZ((float)Matrix.ToRadians(AngleZ));
-
-            matrix44 *= Matrix4x4.CreateTranslation((float)CenterX, (float)CenterY, (float)CenterZ);
+            if (centerSum != 0) matrix44 *= Matrix4x4.CreateTranslation((float)CenterX, (float)CenterY, (float)CenterZ);
 
             if (Depth != 0)
             {
@@ -186,5 +191,8 @@ public class Rotate3DTransform : Transform
         }
     }
 
-    protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change) => RaiseChanged();
+    protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
+    {
+        if (!_isInitializing) RaiseChanged();
+    } 
 }