Merge branch 'master' into upstream-wrap-layout-fixes

samples/ControlCatalog/App.xaml.cs

@@ -39,6 +39,10 @@ namespace ControlCatalog
 
         public static Styles DefaultLight = new Styles
         {
+            new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
+            {
+                Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/AccentColors.xaml")
+            },
             new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
             {
                 Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/Base.xaml")
@@ -60,6 +64,10 @@ namespace ControlCatalog
 
         public static Styles DefaultDark = new Styles
         {
+            new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
+            {
+                Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/AccentColors.xaml")
+            },
             new StyleInclude(new Uri("resm:Styles?assembly=ControlCatalog"))
             {
                 Source = new Uri("avares://Avalonia.Themes.Fluent/Accents/Base.xaml")

samples/ControlCatalog/Pages/ViewboxPage.xaml

@@ -1,66 +1,36 @@
 <UserControl xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              x:Class="ControlCatalog.Pages.ViewboxPage">
-    <UserControl.Resources>
-        <StreamGeometry x:Key="Acorn">
-            F1 M 16.6309,18.6563C 17.1309,
-            8.15625 29.8809,14.1563 29.8809,
-            14.1563C 30.8809,11.1563 34.1308,
-            11.4063 34.1308,11.4063C 33.5,12
-            34.6309,13.1563 34.6309,13.1563C
-            32.1309,13.1562 31.1309,14.9062
-            31.1309,14.9062C 41.1309,23.9062
-            32.6309,27.9063 32.6309,27.9062C
-            24.6309,24.9063 21.1309,22.1562
-            16.6309,18.6563 Z M 16.6309,19.9063C
-            21.6309,24.1563 25.1309,26.1562
-            31.6309,28.6562C 31.6309,28.6562
-            26.3809,39.1562 18.3809,36.1563C
-            18.3809,36.1563 18,38 16.3809,36.9063C
-            15,36 16.3809,34.9063 16.3809,34.9063C
-            16.3809,34.9063 10.1309,30.9062 16.6309,19.9063 Z
-        </StreamGeometry>
-    </UserControl.Resources>
 
-    <Grid RowDefinitions="Auto,*">
+    <Grid RowDefinitions="Auto,*,*">
         <StackPanel Orientation="Vertical" Spacing="4">
             <TextBlock Classes="h1">Viewbox</TextBlock>
             <TextBlock Classes="h2">A control used to scale single child.</TextBlock>
         </StackPanel>
-        <Grid ColumnDefinitions="Auto,*,*"
-              RowDefinitions="*,*,*,*"
-              Grid.Row="1" Margin="48"
-              MaxWidth="400">
-            <TextBlock Grid.Row="0" VerticalAlignment="Center">None</TextBlock>
-            <TextBlock Grid.Row="1" VerticalAlignment="Center">Fill</TextBlock>
-            <TextBlock Grid.Row="2" VerticalAlignment="Center">Uniform</TextBlock>
-            <TextBlock Grid.Row="3" VerticalAlignment="Center">UniformToFill</TextBlock>
 
-            <Viewbox Grid.Row="0" Grid.Column="1" Stretch="None">
+        <Grid Grid.Row="1" ColumnDefinitions="*,Auto" HorizontalAlignment="Center" Margin="0,10,0,0">
-                <TextBlock>Hello World!</TextBlock>
-            </Viewbox>
-            <Viewbox Grid.Row="1" Grid.Column="1" Stretch="Fill">
-                <TextBlock>Hello World!</TextBlock>
-            </Viewbox>
-            <Viewbox Grid.Row="2" Grid.Column="1" Stretch="Uniform">
-                <TextBlock>Hello World!</TextBlock>
-            </Viewbox>
-            <Viewbox Grid.Row="3" Grid.Column="1" Stretch="UniformToFill">
-                <TextBlock>Hello World!</TextBlock>
-            </Viewbox>
 
-            <Viewbox Grid.Row="0" Grid.Column="2" Stretch="None">
+          <Border HorizontalAlignment="Center" Grid.Column="0" BorderThickness="1" BorderBrush="Orange" Width="200" Height="200">
-                <Path Fill="Blue" Data="{StaticResource Acorn}"/>
+            <Border VerticalAlignment="Center" HorizontalAlignment="Center" Grid.Column="0" BorderThickness="1" BorderBrush="CornflowerBlue" Width="{Binding #WidthSlider.Value}" Height="{Binding #HeightSlider.Value}" >
-            </Viewbox>
+              <Viewbox
-            <Viewbox Grid.Row="1" Grid.Column="2" Stretch="Fill">
+                  Stretch="{Binding #StretchSelector.SelectedItem}"
-                <Path Fill="Blue" Data="{StaticResource Acorn}"/>
+                  StretchDirection="{Binding #StretchDirectionSelector.SelectedItem}">
-            </Viewbox>
+                <Ellipse Width="50" Height="50" Fill="CornflowerBlue" />
-            <Viewbox Grid.Row="2" Grid.Column="2" Stretch="Uniform">
+              </Viewbox>
-                <Path Fill="Blue" Data="{StaticResource Acorn}"/>
+            </Border>
-            </Viewbox>
+          </Border>
-            <Viewbox Grid.Row="3" Grid.Column="2" Stretch="UniformToFill">
+
-                <Path Fill="Blue" Data="{StaticResource Acorn}"/>
+          <StackPanel HorizontalAlignment="Left" Orientation="Vertical" Grid.Column="1" Margin="8,0,0,0" Width="150">
-            </Viewbox>
+            <TextBlock Text="Width" />
+            <Slider Minimum="10" Maximum="200" Value="100" x:Name="WidthSlider" TickFrequency="25" TickPlacement="TopLeft" />
+            <TextBlock Text="Height" />
+            <Slider Minimum="10" Maximum="200" Value="100" x:Name="HeightSlider" TickFrequency="25" TickPlacement="TopLeft" />
+            <TextBlock Text="Stretch" />
+            <ComboBox x:Name="StretchSelector" HorizontalAlignment="Stretch" Margin="0,0,0,2" />
+            <TextBlock Text="Stretch Direction" />
+            <ComboBox x:Name="StretchDirectionSelector" HorizontalAlignment="Stretch" />
+          </StackPanel>
         </Grid>
+
     </Grid>
 </UserControl>

samples/ControlCatalog/Pages/ViewboxPage.xaml.cs

@@ -1,5 +1,6 @@
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
+using Avalonia.Media;
 
 namespace ControlCatalog.Pages
 {
@@ -7,7 +8,25 @@ namespace ControlCatalog.Pages
     {
         public ViewboxPage()
         {
-            this.InitializeComponent();
+            InitializeComponent();
+
+            var stretchSelector = this.FindControl<ComboBox>("StretchSelector");
+
+            stretchSelector.Items = new[]
+            {
+                Stretch.Uniform, Stretch.UniformToFill, Stretch.Fill, Stretch.None
+            };
+
+            stretchSelector.SelectedIndex = 0;
+
+            var stretchDirectionSelector = this.FindControl<ComboBox>("StretchDirectionSelector");
+
+            stretchDirectionSelector.Items = new[]
+            {
+                StretchDirection.Both, StretchDirection.DownOnly, StretchDirection.UpOnly
+            };
+
+            stretchDirectionSelector.SelectedIndex = 0;
         }
 
         private void InitializeComponent()

samples/RenderDemo/Pages/AnimationsPage.xaml

@@ -1,7 +1,8 @@
 <UserControl 
   xmlns="https://github.com/avaloniaui" 
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
-  x:Class="RenderDemo.Pages.AnimationsPage">
+  x:Class="RenderDemo.Pages.AnimationsPage"
+  MaxWidth="600">
   <UserControl.Styles>
     <Styles>
       <Styles.Resources>
@@ -167,8 +168,8 @@
       <StackPanel.Clock>
         <Clock />
       </StackPanel.Clock>
-      <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
+      <StackPanel Orientation="Horizontal" VerticalAlignment="Center" Spacing="20">
-        <TextBlock VerticalAlignment="Center">Hover to activate Transform Keyframe Animations.</TextBlock>
+        <TextBlock VerticalAlignment="Center">Hover to activate Keyframe Animations.</TextBlock>
         <Button Content="{Binding PlayStateText}" Command="{Binding TogglePlayState}" Click="ToggleClock" />
       </StackPanel>
       <WrapPanel ClipToBounds="False">

samples/RenderDemo/Pages/TransitionsPage.xaml

@@ -1,7 +1,8 @@
 <UserControl 
   xmlns="https://github.com/avaloniaui" 
-  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
+  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-  x:Class="RenderDemo.Pages.TransitionsPage">
+  x:Class="RenderDemo.Pages.TransitionsPage"
+  MaxWidth="600">
   <UserControl.Styles>
     <Styles>
       <Styles.Resources>
@@ -90,6 +91,56 @@
         <Setter Property="RenderTransform" Value="none" />
       </Style>
 
+      <Style Selector="Border.Rect7">
+        <Setter Property="Transitions">
+          <Transitions>
+            <DoubleTransition Property="Height" Duration="0:0:0.5" />
+          </Transitions>
+        </Setter>
+      </Style>
+
+      <Style Selector="Border.Rect7:pointerover">
+        <Setter Property="Height" Value="50" />
+      </Style>
+
+      <Style Selector="Border.Rect8">
+        <Setter Property="Transitions">
+          <Transitions>
+            <CornerRadiusTransition Property="CornerRadius" Duration="0:0:0.5" />
+          </Transitions>
+        </Setter>
+      </Style>
+
+      <Style Selector="Border.Rect8:pointerover">
+        <Setter Property="CornerRadius" Value="50" />
+      </Style>
+
+      <Style Selector="Border.Rect9">
+        <Setter Property="Transitions">
+          <Transitions>
+            <ThicknessTransition Property="Padding" Duration="0:0:0.5" />
+          </Transitions>
+        </Setter>
+      </Style>
+
+      <Style Selector="Border.Rect9:pointerover">
+        <Setter Property="Padding" Value="10" />
+      </Style>
+
+      <Style Selector="Border.Shadow">
+        <Setter Property="Background" Value="Transparent"/>        
+        <Setter Property="BorderBrush" Value="Black"/>
+        <Setter Property="BorderThickness" Value="1"/>
+        <Setter Property="BoxShadow" Value="inset 0 0 0 2 Red, -15 -15 Green"/>
+        <Setter Property="Transitions">
+          <Transitions>
+            <BoxShadowsTransition Property="BoxShadow" Duration="0:0:0.5" />
+          </Transitions>
+        </Setter>
+      </Style>
+      <Style Selector="Border.Shadow:pointerover">
+        <Setter Property="BoxShadow" Value="inset 30 30 20 30 Green, 20 40 20 10 Red"/>
+      </Style>
     </Styles>
   </UserControl.Styles>
 
@@ -98,8 +149,8 @@
       <StackPanel.Clock>
         <Clock />
       </StackPanel.Clock>
-      <StackPanel Orientation="Horizontal" VerticalAlignment="Center">
+      <StackPanel Orientation="Horizontal" VerticalAlignment="Center" Spacing="20">
-        <TextBlock VerticalAlignment="Center">Hover to activate Transform Keyframe Animations.</TextBlock>
+        <TextBlock VerticalAlignment="Center">Hover to activate Transitions.</TextBlock>
         <Button Content="{Binding PlayStateText}" Command="{Binding TogglePlayState}" Click="ToggleClock" />
       </StackPanel>
       <WrapPanel ClipToBounds="False">
@@ -109,6 +160,12 @@
         <Border Classes="Test Rect4" Background="Navy"/>
         <Border Classes="Test Rect5" Background="SeaGreen"/>
         <Border Classes="Test Rect6" Background="Orange"/>
+        <Border Classes="Test Rect7" Background="Gold"/>
+        <Border Classes="Test Rect8" Background="Gray" />
+        <Border Classes="Test Rect9" Background="Red" />
+
+        <Border Classes="Test Shadow" CornerRadius="10" Child="{x:Null}" />
+        <Border Classes="Test Shadow" CornerRadius="0 30 60 0" Child="{x:Null}" />
       </WrapPanel>
     </StackPanel>
   </Grid>

src/Avalonia.Animation/Transitions/DoubleTransition.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,15 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class DoubleTransition : Transition<double>
     {
+        private static readonly DoubleAnimator s_animator = new DoubleAnimator();
+
         /// <inheritdocs/>
         public override IObservable<double> DoTransition(IObservable<double> progress, double oldValue, double newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-                    return ((newValue - oldValue) * f) + oldValue;
-                });
         }
     }
 }

src/Avalonia.Animation/Transitions/FloatTransition.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,12 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class FloatTransition : Transition<float>
     {
+        private static readonly FloatAnimator s_animator = new FloatAnimator();
+
         /// <inheritdocs/>
         public override IObservable<float> DoTransition(IObservable<double> progress, float oldValue, float newValue)
         {
-            var delta = newValue - oldValue;
             return progress
-                .Select(p => (float)Easing.Ease(p) * delta + oldValue);
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
         }
     }
 }

src/Avalonia.Animation/Transitions/IntegerTransition.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,12 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class IntegerTransition : Transition<int>
     {
+        private static readonly Int32Animator s_animator = new Int32Animator();
+
         /// <inheritdocs/>
         public override IObservable<int> DoTransition(IObservable<double> progress, int oldValue, int newValue)
         {
-            var delta = newValue - oldValue;
             return progress
-                .Select(p => (int)(Easing.Ease(p) * delta + oldValue));
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
         }
     }
 }

src/Avalonia.Base/PropertyStore/BindingEntry.cs

@@ -79,7 +79,7 @@ namespace Avalonia.PropertyStore
 
         public void OnError(Exception error)
         {
-            throw new NotImplementedException();
+            throw new NotImplementedException("BindingEntry.OnError is not implemented", error);
         }
 
         public void OnNext(BindingValue<T> value)

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -535,7 +535,8 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<DataGrid, int>(
                 nameof(SelectedIndex),
                 o => o.SelectedIndex,
-                (o, v) => o.SelectedIndex = v);
+                (o, v) => o.SelectedIndex = v,
+                defaultBindingMode: BindingMode.TwoWay);
 
         /// <summary>
         /// Gets or sets the index of the current selection.
@@ -553,7 +554,8 @@ namespace Avalonia.Controls
             AvaloniaProperty.RegisterDirect<DataGrid, object>(
                 nameof(SelectedItem),
                 o => o.SelectedItem,
-                (o, v) => o.SelectedItem = v);
+                (o, v) => o.SelectedItem = v,
+                defaultBindingMode: BindingMode.TwoWay);
 
         /// <summary>
         /// Gets or sets the data item corresponding to the selected row.

src/Avalonia.Controls/ApiCompatBaseline.txt

@@ -4,10 +4,11 @@ InterfacesShouldHaveSameMembers : Interface member 'public System.Boolean Avalon
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.IMenuItem.StaysOpenOnClick.set(System.Boolean)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.INativeMenuExporterEventsImplBridge.RaiseClosed()' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Controls.INativeMenuExporterEventsImplBridge.RaiseOpening()' is present in the implementation but not in the contract.
+MembersMustExist : Member 'public Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.AvaloniaProperty<Avalonia.Media.Stretch> Avalonia.Controls.Viewbox.StretchProperty' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Controls.Embedding.Offscreen.OffscreenTopLevelImplBase.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public Avalonia.AvaloniaProperty Avalonia.AvaloniaProperty Avalonia.Controls.Notifications.NotificationCard.CloseOnClickProperty' does not exist in the implementation but it does exist in the contract.
 EnumValuesMustMatch : Enum value 'Avalonia.Platform.ExtendClientAreaChromeHints Avalonia.Platform.ExtendClientAreaChromeHints.Default' is (System.Int32)2 in the implementation but (System.Int32)1 in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.ICursorImpl)' is present in the implementation but not in the contract.
 InterfacesShouldHaveSameMembers : Interface member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' is present in the contract but not in the implementation.
 MembersMustExist : Member 'public void Avalonia.Platform.ITopLevelImpl.SetCursor(Avalonia.Platform.IPlatformHandle)' does not exist in the implementation but it does exist in the contract.
-Total Issues: 11
+Total Issues: 12

src/Avalonia.Controls/Image.cs

@@ -31,8 +31,8 @@ namespace Avalonia.Controls
 
         static Image()
         {
-            AffectsRender<Image>(SourceProperty, StretchProperty);
+            AffectsRender<Image>(SourceProperty, StretchProperty, StretchDirectionProperty);
-            AffectsMeasure<Image>(SourceProperty, StretchProperty);
+            AffectsMeasure<Image>(SourceProperty, StretchProperty, StretchDirectionProperty);
         }
 
         /// <summary>

src/Avalonia.Controls/Viewbox.cs

@@ -1,40 +1,48 @@
-using System;
+using Avalonia.Media;
-using Avalonia.Media;
 
 namespace Avalonia.Controls
 {
     /// <summary>
-    /// Viewbox is used to scale single child.
+    /// Viewbox is used to scale single child to fit in the available space.
     /// </summary>
     /// <seealso cref="Avalonia.Controls.Decorator" />
     public class Viewbox : Decorator
     {
         /// <summary>
-        /// The stretch property
+        /// Defines the <see cref="Stretch"/> property.
         /// </summary>
-        public static readonly AvaloniaProperty<Stretch> StretchProperty =
+        public static readonly StyledProperty<Stretch> StretchProperty =
-                AvaloniaProperty.RegisterDirect<Viewbox, Stretch>(nameof(Stretch),
+            AvaloniaProperty.Register<Image, Stretch>(nameof(Stretch), Stretch.Uniform);
-                    v => v.Stretch, (c, v) => c.Stretch = v, Stretch.Uniform);
 
-        private Stretch _stretch = Stretch.Uniform;
+        /// <summary>
+        /// Defines the <see cref="StretchDirection"/> property.
+        /// </summary>
+        public static readonly StyledProperty<StretchDirection> StretchDirectionProperty =
+            AvaloniaProperty.Register<Viewbox, StretchDirection>(nameof(StretchDirection), StretchDirection.Both);
+
+        static Viewbox()
+        {
+            ClipToBoundsProperty.OverrideDefaultValue<Viewbox>(true);
+            AffectsMeasure<Viewbox>(StretchProperty, StretchDirectionProperty);
+        }
 
         /// <summary>
         /// Gets or sets the stretch mode, 
         /// which determines how child fits into the available space.
         /// </summary>
-        /// <value>
-        /// The stretch.
-        /// </value>
         public Stretch Stretch
         {
-            get => _stretch;
+            get => GetValue(StretchProperty);
-            set => SetAndRaise(StretchProperty, ref _stretch, value);
+            set => SetValue(StretchProperty, value);
         }
 
-        static Viewbox()
+        /// <summary>
+        /// Gets or sets a value controlling in what direction contents will be stretched.
+        /// </summary>
+        public StretchDirection StretchDirection
         {
-            ClipToBoundsProperty.OverrideDefaultValue<Viewbox>(true);
+            get => GetValue(StretchDirectionProperty);
-            AffectsMeasure<Viewbox>(StretchProperty);
+            set => SetValue(StretchDirectionProperty, value);
         }
 
         protected override Size MeasureOverride(Size availableSize)
@@ -47,9 +55,9 @@ namespace Avalonia.Controls
 
                 var childSize = child.DesiredSize;
 
-                var scale = GetScale(availableSize, childSize, Stretch);
+                var size = Stretch.CalculateSize(availableSize, childSize, StretchDirection);
 
-                return (childSize * scale).Constrain(availableSize);
+                return size.Constrain(availableSize);
             }
 
             return new Size();
@@ -62,7 +70,9 @@ namespace Avalonia.Controls
             if (child != null)
             {
                 var childSize = child.DesiredSize;
-                var scale = GetScale(finalSize, childSize, Stretch);
+                var scale = Stretch.CalculateScaling(finalSize, childSize, StretchDirection);
+
+                // TODO: Viewbox should have another decorator as a child so we won't affect other render transforms.
                 var scaleTransform = child.RenderTransform as ScaleTransform;
 
                 if (scaleTransform == null)
@@ -81,44 +91,5 @@ namespace Avalonia.Controls
 
             return new Size();
         }
-
-        private static Vector GetScale(Size availableSize, Size childSize, Stretch stretch)
-        {
-            double scaleX = 1.0;
-            double scaleY = 1.0;
-
-            bool validWidth = !double.IsPositiveInfinity(availableSize.Width);
-            bool validHeight = !double.IsPositiveInfinity(availableSize.Height);
-
-            if (stretch != Stretch.None && (validWidth || validHeight))
-            {
-                scaleX = childSize.Width <= 0.0 ? 0.0 : availableSize.Width / childSize.Width;
-                scaleY = childSize.Height <= 0.0 ? 0.0 : availableSize.Height / childSize.Height;
-
-                if (!validWidth)
-                {
-                    scaleX = scaleY;
-                }
-                else if (!validHeight)
-                {
-                    scaleY = scaleX;
-                }
-                else
-                {
-                    switch (stretch)
-                    {
-                        case Stretch.Uniform:
-                            scaleX = scaleY = Math.Min(scaleX, scaleY);
-                            break;
-
-                        case Stretch.UniformToFill:
-                            scaleX = scaleY = Math.Max(scaleX, scaleY);
-                            break;
-                    }
-                }
-            }
-
-            return new Vector(scaleX, scaleY);
-        }
     }
 }

src/Avalonia.Diagnostics/Diagnostics/ViewModels/ControlLayoutViewModel.cs

@@ -1,4 +1,6 @@
+using System;
 using System.ComponentModel;
+using System.Text;
 using Avalonia.Controls;
 using Avalonia.Layout;
 using Avalonia.VisualTree;
@@ -95,12 +97,27 @@ namespace Avalonia.Diagnostics.ViewModels
             {
                 string CreateConstraintInfo(StyledProperty<double> minProperty, StyledProperty<double> maxProperty)
                 {
-                    if (ao.IsSet(minProperty) || ao.IsSet(maxProperty))
+                    bool hasMin = ao.IsSet(minProperty);
+                    bool hasMax = ao.IsSet(maxProperty);
+
+                    if (hasMin || hasMax)
                     {
-                        var minValue = ao.GetValue(minProperty);
+                        var builder = new StringBuilder();
-                        var maxValue = ao.GetValue(maxProperty);
+
+                        if (hasMin)
+                        {
+                            var minValue = ao.GetValue(minProperty);
+                            builder.AppendFormat("Min: {0}", Math.Round(minValue, 2));
+                            builder.AppendLine();
+                        }
+
+                        if (hasMax)
+                        {
+                            var maxValue = ao.GetValue(maxProperty);
+                            builder.AppendFormat("Max: {0}", Math.Round(maxValue, 2));
+                        }
 
-                        return $"{minValue} < size < {maxValue}";
+                        return builder.ToString();
                     }
 
                     return null;
@@ -183,8 +200,8 @@ namespace Avalonia.Diagnostics.ViewModels
         {
             var size = _control.Bounds;
 
-            Width = size.Width;
+            Width = Math.Round(size.Width, 2);
-            Height = size.Height;
+            Height = Math.Round(size.Height, 2);
         }
     }
 }

src/Avalonia.Diagnostics/Diagnostics/Views/ControlDetailsView.xaml

@@ -8,11 +8,16 @@
 
   <UserControl.Resources>
     <SolidColorBrush x:Key="ThicknessBorderBrush" Color="#666666" />
+    <SolidColorBrush x:Key="HighlightBorderBrush" Color="CornflowerBlue" />
     <SolidColorBrush x:Key="SizeGuidelineBrush" Color="#333333" />
     <SolidColorBrush x:Key="MarginBackgroundBrush" Color="#D78965" />
+    <SolidColorBrush x:Key="MarginHighlightBrush" Color="#EA966F" />
     <SolidColorBrush x:Key="BorderBackgroundBrush" Color="#E3C381" />
+    <SolidColorBrush x:Key="BorderHighlightBrush" Color="#EFCD88" />
     <SolidColorBrush x:Key="PaddingBackgroundBrush" Color="#B8C47F" />
+    <SolidColorBrush x:Key="PaddingHighlightBrush" Color="#CEDA8E" />
     <SolidColorBrush x:Key="SizeBackgroundBrush" Color="#88B2BD" />
+    <SolidColorBrush x:Key="SizeHighlightBrush" Color="#9ED0DC" />
     <conv:BoolToOpacityConverter x:Key="BoolToOpacity" Opacity="0.6"/>
   </UserControl.Resources>
 
@@ -24,43 +29,60 @@
       <Setter Property="BorderBrush" Value="{StaticResource ThicknessBorderBrush}" />
       <Setter Property="Template">
         <ControlTemplate>
-          <Border
+          <Panel>
-            Background="{TemplateBinding Background}"
+            <Rectangle x:Name="PART_Background" Classes.no-content-pointerover="{Binding !#PART_ContentPresenter.IsPointerOver}" />
-            BorderBrush="{TemplateBinding BorderBrush}"
+            <Border
-            BorderThickness="{TemplateBinding BorderThickness}">
+              x:Name="PART_Border"
-            <Grid RowDefinitions="Auto,*,Auto" ColumnDefinitions="Auto,*,Auto">
+              Classes.no-content-pointerover="{Binding !#PART_ContentPresenter.IsPointerOver}"
-              <Grid.Styles>
+              BorderBrush="{TemplateBinding BorderBrush}"
-                <Style Selector="TextBox.thickness-edit">
+              BorderThickness="{TemplateBinding BorderThickness}">
-                  <Setter Property="Background" Value="Transparent" />
+              <Grid RowDefinitions="Auto,*,Auto" ColumnDefinitions="Auto,*,Auto">
-                  <Setter Property="BorderThickness" Value="0" />
+                <Grid.Styles>
-                  <Setter Property="Margin" Value="2" />
+                  <Style Selector="TextBox.thickness-edit">
-                  <Setter Property="HorizontalAlignment" Value="Stretch" />
+                    <Setter Property="Background" Value="Transparent" />
-                  <Setter Property="VerticalAlignment" Value="Stretch" />
+                    <Setter Property="BorderThickness" Value="0" />
-                  <Setter Property="HorizontalContentAlignment" Value="Center" />
+                    <Setter Property="Margin" Value="2" />
-                  <Setter Property="VerticalContentAlignment" Value="Center" />
+                    <Setter Property="HorizontalAlignment" Value="Stretch" />
-                  <Setter Property="(ScrollViewer.HorizontalScrollBarVisibility)" Value="Disabled" />
+                    <Setter Property="VerticalAlignment" Value="Stretch" />
-                  <Setter Property="(ScrollViewer.VerticalScrollBarVisibility)" Value="Disabled" />
+                    <Setter Property="HorizontalContentAlignment" Value="Center" />
-                  <Setter Property="IsVisible" Value="{Binding $parent[local:ThicknessEditor].IsPresent}" />
+                    <Setter Property="VerticalContentAlignment" Value="Center" />
-                </Style>
+                    <Setter Property="(ScrollViewer.HorizontalScrollBarVisibility)" Value="Disabled" />
-              </Grid.Styles>
+                    <Setter Property="(ScrollViewer.VerticalScrollBarVisibility)" Value="Disabled" />
-              <TextBlock IsVisible="{TemplateBinding IsPresent}" Margin="4,0,0,0" Text="{TemplateBinding Header}" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" />
+                    <Setter Property="IsVisible" Value="{Binding $parent[local:ThicknessEditor].IsPresent}" />
-              <TextBox Grid.Row="1" Grid.Column="0" Text="{Binding Left, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
+                  </Style>
-              <TextBox x:Name="Right"  Grid.Row="0" Grid.Column="1" Text="{Binding Top, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
+                </Grid.Styles>
-              <TextBox Grid.Row="1" Grid.Column="2" Text="{Binding Right, RelativeSource={RelativeSource TemplatedParent}}"  Classes="thickness-edit" />
+                <TextBlock IsVisible="{TemplateBinding IsPresent}" Margin="4,0,0,0" Text="{TemplateBinding Header}" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" />
-              <TextBox Grid.Row="2" Grid.Column="1" Text="{Binding Bottom, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
+                <TextBox Grid.Row="1" Grid.Column="0" Text="{Binding Left, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
-              <ContentPresenter Grid.Row="1" Grid.Column="1"
+                <TextBox x:Name="Right"  Grid.Row="0" Grid.Column="1" Text="{Binding Top, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
-                Name="PART_ContentPresenter"
+                <TextBox Grid.Row="1" Grid.Column="2" Text="{Binding Right, RelativeSource={RelativeSource TemplatedParent}}"  Classes="thickness-edit" />
-                                ContentTemplate="{TemplateBinding ContentTemplate}"
+                <TextBox Grid.Row="2" Grid.Column="1" Text="{Binding Bottom, RelativeSource={RelativeSource TemplatedParent}}" Classes="thickness-edit" />
-                                Content="{TemplateBinding Content}"
+                <ContentPresenter Grid.Row="1" Grid.Column="1"
-                                Padding="{TemplateBinding Padding}"
+                                  Name="PART_ContentPresenter"
-                                VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
+                                  ContentTemplate="{TemplateBinding ContentTemplate}"
-                                HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" />
+                                  Content="{TemplateBinding Content}"
-            </Grid>
+                                  Padding="{TemplateBinding Padding}"
-          </Border>
+                                  VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
+                                  HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" />
+              </Grid>
+            </Border>
+          </Panel>
 
         </ControlTemplate>
       </Setter>
     </Style>
+
+    <Style Selector="local|ThicknessEditor /template/ Rectangle#PART_Background">
+      <Setter Property="Fill" Value="{Binding Background, RelativeSource={RelativeSource TemplatedParent}}" />
+    </Style>
+
+    <Style Selector="local|ThicknessEditor:pointerover /template/ Rectangle#PART_Background.no-content-pointerover">
+      <Setter Property="Fill" Value="{Binding Highlight, RelativeSource={RelativeSource TemplatedParent}}" />
+    </Style>
+
+    <Style Selector="local|ThicknessEditor:pointerover /template/ Border#PART_Border.no-content-pointerover">
+      <Setter Property="BorderBrush" Value="{StaticResource HighlightBorderBrush}" />
+    </Style>
+
     <Style Selector="local|ThicknessEditor[IsPresent=False]">
       <Setter Property="BorderThickness" Value="0" />
     </Style>
@@ -110,47 +132,67 @@
 
     <Grid Grid.Column="2" RowDefinitions="Auto,*, Auto,*,Auto" >
       <TextBlock Grid.Row="0" Text="Layout Visualizer" Margin="4" />
-      
+
-      <Grid Grid.Row="1" x:Name="LayoutRoot" Margin="8,0,8,8" RowDefinitions="Auto,Auto" ColumnDefinitions="Auto,Auto">
+      <Viewbox Grid.Row="1" StretchDirection="DownOnly" >
-
+        <Grid Grid.Row="1" x:Name="LayoutRoot" Margin="8,0,8,8" RowDefinitions="Auto,Auto" ColumnDefinitions="Auto,Auto">
-        <Border x:Name="VerticalSize" Grid.Row="0" Grid.Column="1" >
+
-          <TextBlock VerticalAlignment="Center" FontWeight="Bold"
+          <Grid.Styles>
-                     TextDecorations="{Binding Layout.HeightConstraint, Converter={x:Static local:Converters.HasConstraintConverter}}"
+            <Style Selector="TextBlock.with-constraint">
-                     Text="{Binding Layout.Height}"
+              <Setter Property="TextDecorations" Value="Underline" />
-                     ToolTip.Tip="{Binding Layout.HeightConstraint}" />
+            </Style>
-        </Border>
+
-        
+          </Grid.Styles>
-        <Border x:Name="HorizontalSize" Grid.Row="1" Grid.Column="0" >
+
-          <TextBlock HorizontalAlignment="Center" FontWeight="Bold" 
+          <Border x:Name="VerticalSize" Grid.Row="0" Grid.Column="1" >
-                     TextDecorations="{Binding Layout.WidthConstraint, Converter={x:Static local:Converters.HasConstraintConverter}}"
+            <TextBlock VerticalAlignment="Center" FontWeight="Bold"
-                     Text="{Binding Layout.Width}" 
+                       Classes.with-constraint="{Binding Layout.HeightConstraint, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"
-                     ToolTip.Tip="{Binding Layout.WidthConstraint}" />
+                       Text="{Binding Layout.Height}"
-        </Border>
+                       ToolTip.Tip="{Binding Layout.HeightConstraint}" />
-        
+          </Border>
-        <local:ThicknessEditor Grid.Row="0" Grid.Column="0" Header="margin" VerticalAlignment="Top" HorizontalAlignment="Center" Background="{StaticResource MarginBackgroundBrush}" Thickness="{Binding Layout.MarginThickness}">
+
-          <local:ThicknessEditor x:Name="BorderArea" Header="border" Background="{StaticResource BorderBackgroundBrush}" Thickness="{Binding Layout.BorderThickness}" IsPresent="{Binding Layout.HasBorder}">
+          <Border x:Name="HorizontalSize" Grid.Row="1" Grid.Column="0" >
-            <local:ThicknessEditor x:Name="PaddingArea" Header="padding" Background="{StaticResource PaddingBackgroundBrush}" Thickness="{Binding Layout.PaddingThickness}" IsPresent="{Binding Layout.HasPadding}">
+            <TextBlock HorizontalAlignment="Center" FontWeight="Bold"
-              <Border x:Name="ContentArea" BorderThickness="1" BorderBrush="{StaticResource ThicknessBorderBrush}" MinWidth="100" MinHeight="16" Background="{StaticResource SizeBackgroundBrush}" VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
+                       Classes.with-constraint="{Binding Layout.WidthConstraint, Converter={x:Static StringConverters.IsNotNullOrEmpty}}"
-                <TextBlock Margin="2" HorizontalAlignment="Center" VerticalAlignment="Center" Text="content" />
+                       Text="{Binding Layout.Width}"
-              </Border>
+                       ToolTip.Tip="{Binding Layout.WidthConstraint}" />
+          </Border>
+
+          <local:ThicknessEditor Grid.Row="0" Grid.Column="0" Header="margin" VerticalAlignment="Top" HorizontalAlignment="Center" Background="{StaticResource MarginBackgroundBrush}" Highlight="{StaticResource MarginHighlightBrush}" Thickness="{Binding Layout.MarginThickness}">
+            <local:ThicknessEditor x:Name="BorderArea" Header="border" Background="{StaticResource BorderBackgroundBrush}" Highlight="{StaticResource BorderHighlightBrush}" Thickness="{Binding Layout.BorderThickness}" IsPresent="{Binding Layout.HasBorder}">
+              <local:ThicknessEditor x:Name="PaddingArea" Header="padding" Background="{StaticResource PaddingBackgroundBrush}" Highlight="{StaticResource PaddingHighlightBrush}" Thickness="{Binding Layout.PaddingThickness}" IsPresent="{Binding Layout.HasPadding}">
+                <Border x:Name="ContentArea" BorderThickness="1" MinWidth="100" MinHeight="16" VerticalAlignment="Stretch" HorizontalAlignment="Stretch">
+                  <Border.Styles>
+                    <Style Selector="Border">
+                      <Setter Property="Background" Value="{StaticResource SizeBackgroundBrush}" />
+                      <Setter Property="BorderBrush" Value="{StaticResource ThicknessBorderBrush}" />
+                    </Style>
+                    <Style Selector="Border:pointerover">
+                      <Setter Property="Background" Value="{StaticResource SizeHighlightBrush}" />
+                      <Setter Property="BorderBrush" Value="{StaticResource HighlightBorderBrush}" />
+                    </Style>
+                  </Border.Styles>
+                  <TextBlock Margin="2" HorizontalAlignment="Center" VerticalAlignment="Center" Text="content" />
+                </Border>
+              </local:ThicknessEditor>
             </local:ThicknessEditor>
           </local:ThicknessEditor>
-        </local:ThicknessEditor>
+
-
+          <Canvas Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Grid.ColumnSpan="2">
-        <Canvas Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" Grid.ColumnSpan="2">
+            <Canvas.Styles>
-          <Canvas.Styles>
+              <Style Selector="Rectangle">
-            <Style Selector="Rectangle">
+                <Setter Property="StrokeDashArray" Value="1,3" />
-              <Setter Property="StrokeDashArray" Value="1,3" />
+                <Setter Property="Stroke" Value="{StaticResource SizeGuidelineBrush}" />
-              <Setter Property="Stroke" Value="{StaticResource SizeGuidelineBrush}" />
+                <Setter Property="StrokeThickness" Value="1" />
-              <Setter Property="StrokeThickness" Value="1" />
+                <Setter Property="IsHitTestVisible" Value="False" />
-            </Style>
+              </Style>
-          </Canvas.Styles>
+            </Canvas.Styles>
-          <Rectangle x:Name="HorizontalSizeBegin" />
+            <Rectangle x:Name="HorizontalSizeBegin" />
-          <Rectangle x:Name="HorizontalSizeEnd" />
+            <Rectangle x:Name="HorizontalSizeEnd" />
-          <Rectangle x:Name="VerticalSizeBegin" />
+            <Rectangle x:Name="VerticalSizeBegin" />
-          <Rectangle x:Name="VerticalSizeEnd" />
+            <Rectangle x:Name="VerticalSizeEnd" />
-        </Canvas>
+          </Canvas>
-      </Grid>
+        </Grid>
+      </Viewbox>
 
       <Grid Grid.Row="2" Margin="4" RowDefinitions="Auto,Auto">
 

src/Avalonia.Diagnostics/Diagnostics/Views/ThicknessEditor.cs

@@ -1,21 +1,9 @@
 using Avalonia.Controls;
 using Avalonia.Data;
-using Avalonia.Data.Converters;
 using Avalonia.Media;
 
 namespace Avalonia.Diagnostics.Views
 {
-    internal static class Converters
-    {
-        public static IValueConverter HasConstraintConverter =
-            new FuncValueConverter<object, TextDecorationCollection>(ConvertToDecoration);
-
-        private static TextDecorationCollection ConvertToDecoration(object arg)
-        {
-            return arg != null ? TextDecorations.Underline : null;
-        }
-    }
-
     internal class ThicknessEditor : ContentControl
     {
         public static readonly DirectProperty<ThicknessEditor, Thickness> ThicknessProperty =
@@ -44,6 +32,14 @@ namespace Avalonia.Diagnostics.Views
             AvaloniaProperty.RegisterDirect<ThicknessEditor, double>(nameof(Bottom), o => o.Bottom,
                 (o, v) => o.Bottom = v);
 
+        public static readonly StyledProperty<IBrush> HighlightProperty =
+            AvaloniaProperty.Register<ThicknessEditor, IBrush>(nameof(Highlight));
+
+        public IBrush Highlight
+        {
+            get => GetValue(HighlightProperty);
+            set => SetValue(HighlightProperty, value);
+        }
         
         private Thickness _thickness;
         private string _header;
@@ -52,7 +48,6 @@ namespace Avalonia.Diagnostics.Views
         private double _top;
         private double _right;
         private double _bottom;
-
         private bool _isUpdatingThickness;
 
         public Thickness Thickness

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -70,6 +70,28 @@ namespace Avalonia.Headless
             return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
         public IBitmapImpl LoadBitmap(PixelFormat format, AlphaFormat alphaFormat, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
             return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));

src/Avalonia.Styling/Controls/Classes.cs

@@ -2,6 +2,8 @@ using System;
 using System.Collections.Generic;
 using Avalonia.Collections;
 
+#nullable enable
+
 namespace Avalonia.Controls
 {
     /// <summary>
@@ -90,7 +92,7 @@ namespace Avalonia.Controls
         }
 
         /// <summary>
-        /// Remvoes all non-pseudoclasses from the collection.
+        /// Removes all non-pseudoclasses from the collection.
         /// </summary>
         public override void Clear()
         {
@@ -135,7 +137,7 @@ namespace Avalonia.Controls
         /// </remarks>
         public override void InsertRange(int index, IEnumerable<string> names)
         {
-            var c = new List<string>();
+            List<string>? toInsert = null;
 
             foreach (var name in names)
             {
@@ -143,11 +145,16 @@ namespace Avalonia.Controls
 
                 if (!Contains(name))
                 {
-                    c.Add(name);
+                    toInsert ??= new List<string>();
+
+                    toInsert.Add(name);
                 }
             }
 
-            base.InsertRange(index, c);
+            if (toInsert != null)
+            {
+                base.InsertRange(index, toInsert);
+            }
         }
 
         /// <summary>
@@ -176,19 +183,21 @@ namespace Avalonia.Controls
         /// </remarks>
         public override void RemoveAll(IEnumerable<string> names)
         {
-            var c = new List<string>();
+            List<string>? toRemove = null;
 
             foreach (var name in names)
             {
                 ThrowIfPseudoclass(name, "removed");
 
-                if (Contains(name))
+                toRemove ??= new List<string>();
-                {
+
-                    c.Add(name);
+                toRemove.Add(name);
-                }
             }
 
-            base.RemoveAll(c);
+            if (toRemove != null)
+            {
+                base.RemoveAll(toRemove);
+            }
         }
 
         /// <summary>
@@ -223,7 +232,7 @@ namespace Avalonia.Controls
         /// <param name="source">The new contents of the collection.</param>
         public void Replace(IList<string> source)
         {
-            var toRemove = new List<string>();
+            List<string>? toRemove = null;
 
             foreach (var name in source)
             {
@@ -234,11 +243,17 @@ namespace Avalonia.Controls
             {
                 if (!name.StartsWith(":"))
                 {
+                    toRemove ??= new List<string>();
+
                     toRemove.Add(name);
                 }
             }
 
-            base.RemoveAll(toRemove);
+            if (toRemove != null)
+            {
+                base.RemoveAll(toRemove);
+            }
+
             base.AddRange(source);
         }
 

src/Avalonia.Themes.Fluent/Accents/Base.xaml

@@ -1,6 +1,7 @@
 <Style xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-       xmlns:sys="clr-namespace:System;assembly=netstandard">
+       xmlns:sys="using:System"
+       xmlns:converters="using:Avalonia.Controls.Converters">
   <Style.Resources>
     <!-- https://docs.microsoft.com/en-us/previous-versions/windows/apps/dn518235(v=win.10)?redirectedfrom=MSDN -->
     <!-- SystemColor Color Resources (Reflect OS High Contrast Settings) -->
@@ -30,5 +31,10 @@
     <!-- ScrollBar animation -->
     <TransformOperations x:Key="VerticalSmallScrollThumbScaleTransform">scaleX(0.125) translateX(-2px)</TransformOperations>
     <TransformOperations x:Key="HorizontalSmallScrollThumbScaleTransform">scaleY(0.125) translateY(-2px)</TransformOperations>
+
+    <converters:CornerRadiusFilterConverter x:Key="TopCornerRadiusFilterConverter" Filter="TopLeft, TopRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="RightCornerRadiusFilterConverter" Filter="TopRight, BottomRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="BottomCornerRadiusFilterConverter" Filter="BottomLeft, BottomRight"/>
+    <converters:CornerRadiusFilterConverter x:Key="LeftCornerRadiusFilterConverter" Filter="TopLeft, BottomLeft"/>
   </Style.Resources>
 </Style>

src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml

@@ -27,14 +27,12 @@
   <Style Selector="DataValidationErrors">
     <Style.Resources>
       <DataTemplate x:Key="InlineDataValidationErrorTemplate">
-        <ItemsControl Items="{Binding}">
+        <ItemsControl Items="{Binding}" TextBlock.Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}">
-          <ItemsControl.ItemTemplate>
+          <ItemsControl.Styles>
-            <DataTemplate>
+            <Style Selector="TextBlock">
-              <TextBlock Foreground="{DynamicResource SystemControlErrorTextForegroundBrush}"
+              <Setter Property="TextWrapping" Value="Wrap" />
-                         Text="{Binding}"
+            </Style>
-                         TextWrapping="Wrap" />
+          </ItemsControl.Styles>
-            </DataTemplate>
-          </ItemsControl.ItemTemplate>
         </ItemsControl>
       </DataTemplate>
       <ControlTemplate x:Key="InlineDataValidationContentTemplate" TargetType="DataValidationErrors">

src/Avalonia.Themes.Fluent/Controls/Expander.xaml

@@ -1,141 +1,232 @@
-<Styles xmlns="https://github.com/avaloniaui">
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+  <Design.PreviewWith>
+    <Border Padding="20">
+      <StackPanel Orientation="Vertical" Spacing="20">
+        <Expander ExpandDirection="Up" Header="Expand Up">
+          <StackPanel>
+            <TextBlock>Expanded content</TextBlock>
+          </StackPanel>
+        </Expander>
+        <Expander ExpandDirection="Down" Header="Expand Down">
+          <StackPanel>
+            <TextBlock>Expanded content</TextBlock>
+          </StackPanel>
+        </Expander>
+        <Expander ExpandDirection="Left" Header="Expand Left">
+          <StackPanel>
+            <TextBlock>Expanded content</TextBlock>
+          </StackPanel>
+        </Expander>
+        <Expander ExpandDirection="Right" Header="Expand Right">
+          <StackPanel>
+            <TextBlock>Expanded content</TextBlock>
+          </StackPanel>
+        </Expander>
+      </StackPanel>
+    </Border>
+  </Design.PreviewWith>
 
+  <Styles.Resources>
+    <Thickness x:Key="ExpanderHeaderPadding">16</Thickness>
+    <Thickness x:Key="ExpanderContentPadding">16</Thickness>
+
+    <Thickness x:Key="ExpanderBorderThickness">1</Thickness>
+
+    <Thickness x:Key="ExpanderDropdownLeftBorderThickness">1,1,0,1</Thickness>
+    <Thickness x:Key="ExpanderDropdownUpBorderThickness">1,1,1,0</Thickness>
+    <Thickness x:Key="ExpanderDropdownRightBorderThickness">0,1,1,1</Thickness>
+    <Thickness x:Key="ExpanderDropdownDownBorderThickness">1,0,1,1</Thickness>
+
+    <SolidColorBrush x:Key="ExpanderBackground" Color="{DynamicResource SystemAltMediumHighColor}" />
+    <SolidColorBrush x:Key="ExpanderBorderBrush" Color="{DynamicResource SystemBaseLowColor}" />
+
+    <SolidColorBrush x:Key="ExpanderDropDownBackground" Color="{DynamicResource SystemChromeMediumLowColor}" />
+    <SolidColorBrush x:Key="ExpanderDropDownBorderBrush" Color="{DynamicResource SystemBaseLowColor}" />
+
+    <SolidColorBrush x:Key="ExpanderForeground" Color="{DynamicResource SystemBaseHighColor}" />
+
+    <SolidColorBrush x:Key="ExpanderChevronForeground" Color="{DynamicResource SystemBaseHighColor}" />
+  </Styles.Resources>
   <Style Selector="Expander">
-    <Setter Property="ContentTransition">
+    <Setter Property="Background" Value="{DynamicResource ExpanderBackground}" />
-      <Setter.Value>
+    <Setter Property="BorderThickness" Value="{DynamicResource ExpanderBorderThickness}" />
-        <CrossFade Duration="00:00:00.25" />
+    <Setter Property="BorderBrush" Value="{DynamicResource ExpanderBorderBrush}" />
-      </Setter.Value>
+    <Setter Property="Padding" Value="{DynamicResource ExpanderHeaderPadding}" />
-    </Setter>
+    <Setter Property="HorizontalAlignment" Value="Stretch" />
+    <Setter Property="HorizontalContentAlignment" Value="Left" />
+    <Setter Property="VerticalContentAlignment" Value="Center" />
   </Style>
-  <Style Selector="Expander[ExpandDirection=Down]">
+  <Style Selector="Expander">
-    <Setter Property="Template">
-      <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
-          <Grid RowDefinitions="Auto,*">
-            <ToggleButton Name="PART_toggle" Grid.Row="0"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
-            <ContentPresenter Name="PART_ContentPresenter"
-                              Grid.Row="1"
-                              IsVisible="{TemplateBinding IsExpanded}"
-                              ContentTemplate="{TemplateBinding ContentTemplate}"
-                              Content="{TemplateBinding Content}"
-                              HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
-                              VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
-                              Padding="{TemplateBinding Padding}" />
-          </Grid>
-        </Border>
-      </ControlTemplate>
-    </Setter>
-  </Style>
-  <Style Selector="Expander[IsExpanded=true] /template/ ToggleButton#PART_toggle /template/ ContentPresenter#PART_ContentPresenter">
-    <Setter Property="TextBlock.Foreground" Value="{DynamicResource ToggleButtonForeground}"/>
-  </Style>
-  <Style Selector="Expander[ExpandDirection=Up]">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
+        <DockPanel>
-          <Grid RowDefinitions="*,Auto">
+          <ToggleButton x:Name="ExpanderHeader"
-            <ToggleButton Name="PART_toggle" Grid.Row="1"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+                        Padding="{TemplateBinding Padding}"
-            <ContentPresenter Name="PART_ContentPresenter"
+                        HorizontalAlignment="{TemplateBinding HorizontalAlignment}"
-                              Grid.Row="0"
+                        Background="{TemplateBinding Background}"
-                              IsVisible="{TemplateBinding IsExpanded}"
+                        BorderBrush="{TemplateBinding BorderBrush}"
-                              ContentTemplate="{TemplateBinding ContentTemplate}"
+                        BorderThickness="{TemplateBinding BorderThickness}"
-                              Content="{TemplateBinding Content}"
+                        Content="{TemplateBinding Header}"
+                        ContentTemplate="{TemplateBinding HeaderTemplate}"
+                        IsChecked="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
+                        IsEnabled="{TemplateBinding IsEnabled}" />
+          <Border x:Name="ExpanderContent"
+                  Padding="{DynamicResource ExpanderContentPadding}"
+                  Background="{DynamicResource ExpanderDropDownBackground}"
+                  BorderBrush="{DynamicResource ExpanderDropDownBorderBrush}"
+                  IsVisible="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}">
+            <ContentPresenter x:Name="PART_ContentPresenter"
                               HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                               VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
-                              Padding="{TemplateBinding Padding}" />
-          </Grid>
-        </Border>
-      </ControlTemplate>
-    </Setter>
-  </Style>
-  <Style Selector="Expander[ExpandDirection=Right]">
-    <Setter Property="Template">
-      <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
-          <Grid ColumnDefinitions="Auto,*">
-            <ToggleButton Name="PART_toggle" Grid.Column="0"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
-            <ContentPresenter Name="PART_ContentPresenter"
-                              Grid.Column="1"
-                              IsVisible="{TemplateBinding IsExpanded}"
-                              ContentTemplate="{TemplateBinding ContentTemplate}"
                               Content="{TemplateBinding Content}"
-                              HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
+                              ContentTemplate="{TemplateBinding ContentTemplate}" />
-                              VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
+          </Border>
-                              Padding="{TemplateBinding Padding}" />
+        </DockPanel>
-          </Grid>
-        </Border>
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="Expander[ExpandDirection=Left]">
+
+  <Style Selector="Expander /template/ ToggleButton#ExpanderHeader">
+    <Setter Property="HorizontalContentAlignment" Value="Left" />
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
+        <Border x:Name="ToggleButtonBackground">
           <Grid ColumnDefinitions="*,Auto">
-            <ToggleButton Name="PART_toggle" Grid.Column="1"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+            <ContentPresenter x:Name="PART_ContentPresenter"
-            <ContentPresenter Name="PART_ContentPresenter"
+                              Margin="{TemplateBinding Padding}"
-                              Grid.Column="0"
-                              IsVisible="{TemplateBinding IsExpanded}"
-                              ContentTemplate="{TemplateBinding ContentTemplate}"
-                              Content="{TemplateBinding Content}"
                               HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
-                              VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
+                              VerticalContentAlignment="Center"
-                              Padding="{TemplateBinding Padding}" />
+                              Background="Transparent"
-          </Grid>
+                              BorderBrush="Transparent"
-        </Border>
+                              BorderThickness="0"
-      </ControlTemplate>
+                              Content="{TemplateBinding Content}"
-    </Setter>
+                              ContentTemplate="{TemplateBinding ContentTemplate}"
-  </Style>
+                              TextBlock.Foreground="{DynamicResource ExpanderForeground}" />
-  <Style Selector="Expander /template/ ToggleButton#PART_toggle">
+            <Border x:Name="ExpandCollapseChevronBorder"
-    <Setter Property="Template">
+                    Grid.Column="1"
-      <ControlTemplate>
+                    Width="32"
-        <Border BorderThickness="1" Background="Transparent">
+                    Height="32"
-          <Grid ColumnDefinitions="Auto,Auto">
+                    Margin="7"
-            <Border Grid.Column="0" Width="20" Height="20" HorizontalAlignment="Center" VerticalAlignment="Center">
+                    RenderTransformOrigin="50%,50%">
-              <Path Fill="{DynamicResource SystemControlForegroundBaseHighBrush}"
+              <Path x:Name="ExpandCollapseChevron"
-                      HorizontalAlignment="Center"
+                    HorizontalAlignment="Center"
-                      VerticalAlignment="Center"
+                    VerticalAlignment="Center"
-                      Data="M 0 2 L 4 6 L 0 10 Z" />
+                    RenderTransformOrigin="50%,50%"
+                    Stretch="None"
+                    Stroke="{DynamicResource ExpanderChevronForeground}"
+                    StrokeThickness="1" />
+              <Border.RenderTransform>
+                <RotateTransform />
+              </Border.RenderTransform>
             </Border>
-            <ContentPresenter Name="PART_ContentPresenter"
-                              Grid.Column="1" 
-                              Background="Transparent" 
-                              Content="{TemplateBinding Content}" 
-                              VerticalAlignment="Center" 
-                              HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
-                              VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
-                              Padding="{TemplateBinding Padding}"/>
           </Grid>
         </Border>
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="Expander /template/ ToggleButton#PART_toggle:pointerover /template/ Border">
+  <Style Selector="Expander /template/ ToggleButton#ExpanderHeader:pressed">
-    <Setter Property="BorderBrush" Value="{DynamicResource SystemControlHighlightBaseMediumBrush}" />
+    <Setter Property="RenderTransform" Value="{x:Null}" />
   </Style>
-  <Style Selector="Expander:down:expanded /template/ ToggleButton#PART_toggle /template/ Path">
+
-    <Setter Property="RenderTransform">
+  <Style Selector="Expander:left /template/ ToggleButton#ExpanderHeader, Expander:right /template/ ToggleButton#ExpanderHeader">
-      <RotateTransform Angle="90" />
+    <Setter Property="VerticalAlignment" Value="Stretch" />
-    </Setter>
   </Style>
-  <Style Selector="Expander:up:expanded /template/ ToggleButton#PART_toggle /template/ Path">
+
-    <Setter Property="RenderTransform">
+
-      <RotateTransform Angle="-90" />
+  <Style Selector="Expander /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
-    </Setter>
+    <Setter Property="Background" Value="{TemplateBinding Background}" />
+    <Setter Property="BorderBrush" Value="{TemplateBinding BorderBrush}" />
+    <Setter Property="BorderThickness" Value="{TemplateBinding BorderThickness}" />
   </Style>
-  <Style Selector="Expander:left:expanded /template/ ToggleButton#PART_toggle /template/ Path">
+
-    <Setter Property="RenderTransform">
+  <Style Selector="Expander:not(:expanded) /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
-      <RotateTransform Angle="180" />
+    <Setter Property="CornerRadius" Value="{DynamicResource ControlCornerRadius}" />
-    </Setter>
   </Style>
-  <Style Selector="Expander:right /template/ ToggleButton#PART_toggle /template/ Path">
+  <Style Selector="Expander:expanded:up /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
-    <Setter Property="RenderTransform">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource BottomCornerRadiusFilterConverter}}" />
-      <RotateTransform Angle="180" />
-    </Setter>
   </Style>
-  <Style Selector="Expander:right:expanded /template/ ToggleButton#PART_toggle /template/ Path">
+  <Style Selector="Expander:expanded:up /template/ Border#ExpanderContent">
-    <Setter Property="RenderTransform">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource TopCornerRadiusFilterConverter}}" />
-      <RotateTransform Angle="0" />
+  </Style>
-    </Setter>
+  <Style Selector="Expander:expanded:down /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource TopCornerRadiusFilterConverter}}" />
+  </Style>
+  <Style Selector="Expander:expanded:down /template/ Border#ExpanderContent">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource BottomCornerRadiusFilterConverter}}" />
+  </Style>
+  <Style Selector="Expander:expanded:left /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource RightCornerRadiusFilterConverter}}" />
+  </Style>
+  <Style Selector="Expander:expanded:left /template/ Border#ExpanderContent">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource LeftCornerRadiusFilterConverter}}" />
+  </Style>
+  <Style Selector="Expander:expanded:right /template/ ToggleButton#ExpanderHeader /template/ Border#ToggleButtonBackground">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource LeftCornerRadiusFilterConverter}}" />
+  </Style>
+  <Style Selector="Expander:expanded:right /template/ Border#ExpanderContent">
+    <Setter Property="CornerRadius" Value="{Binding Source={StaticResource ControlCornerRadius}, Converter={StaticResource RightCornerRadiusFilterConverter}}" />
+  </Style>
+
+  <Style Selector="Expander:left /template/ ToggleButton#ExpanderHeader">
+    <Setter Property="DockPanel.Dock" Value="Right" />
+  </Style>
+  <Style Selector="Expander:up /template/ ToggleButton#ExpanderHeader">
+    <Setter Property="DockPanel.Dock" Value="Bottom" />
+  </Style>
+  <Style Selector="Expander:right /template/ ToggleButton#ExpanderHeader">
+    <Setter Property="DockPanel.Dock" Value="Left" />
+  </Style>
+  <Style Selector="Expander:down /template/ ToggleButton#ExpanderHeader">
+    <Setter Property="DockPanel.Dock" Value="Top" />
+  </Style>
+
+
+  <Style Selector="Expander:expanded /template/ ToggleButton#ExpanderHeader /template/ Border#ExpandCollapseChevronBorder">
+    <Style.Animations>
+      <Animation FillMode="Both" Duration="0:0:0.0625">
+        <KeyFrame Cue="100%">
+          <Setter Property="RotateTransform.Angle" Value="180" />
+        </KeyFrame>
+      </Animation>
+    </Style.Animations>
+  </Style>
+  <Style Selector="Expander:not(:expanded) /template/ ToggleButton#ExpanderHeader /template/ Border#ExpandCollapseChevronBorder">
+    <Style.Animations>
+      <Animation FillMode="Both" Duration="0:0:0.0625">
+        <KeyFrame Cue="0%">
+          <Setter Property="RotateTransform.Angle" Value="180" />
+        </KeyFrame>
+        <KeyFrame Cue="100%">
+          <Setter Property="RotateTransform.Angle" Value="0" />
+        </KeyFrame>
+      </Animation>
+    </Style.Animations>
+  </Style>
+
+  <Style Selector="Expander:left /template/ ToggleButton#ExpanderHeader /template/ Path#ExpandCollapseChevron">
+    <Setter Property="Data" Value="M 7 0 L 0 7 L 7 14" />
+  </Style>
+  <Style Selector="Expander:up /template/ ToggleButton#ExpanderHeader /template/ Path#ExpandCollapseChevron">
+    <Setter Property="Data" Value="M 0 7 L 7 0 L 14 7" />
+  </Style>
+  <Style Selector="Expander:right /template/ ToggleButton#ExpanderHeader /template/ Path#ExpandCollapseChevron">
+    <Setter Property="Data" Value="M 0 0 L 7 7 L 0 14" />
+  </Style>
+  <Style Selector="Expander:down /template/ ToggleButton#ExpanderHeader /template/ Path#ExpandCollapseChevron">
+    <Setter Property="Data" Value="M 0 0 L 7 7 L 14 0" />
+  </Style>
+
+
+  <Style Selector="Expander:left /template/ Border#ExpanderContent">
+    <Setter Property="BorderThickness" Value="{DynamicResource ExpanderDropdownLeftBorderThickness}" />
+  </Style>
+  <Style Selector="Expander:up /template/ Border#ExpanderContent">
+    <Setter Property="BorderThickness" Value="{DynamicResource ExpanderDropdownUpBorderThickness}" />
+  </Style>
+  <Style Selector="Expander:right /template/ Border#ExpanderContent">
+    <Setter Property="BorderThickness" Value="{DynamicResource ExpanderDropdownRightBorderThickness}" />
+  </Style>
+  <Style Selector="Expander:down /template/ Border#ExpanderContent">
+    <Setter Property="BorderThickness" Value="{DynamicResource ExpanderDropdownDownBorderThickness}" />
   </Style>
 </Styles>

src/Avalonia.Visuals/Animation/Animators/SolidColorBrushAnimator.cs

@@ -12,6 +12,11 @@ namespace Avalonia.Animation.Animators
     {
         public override ISolidColorBrush Interpolate(double progress, ISolidColorBrush oldValue, ISolidColorBrush newValue)
         {
+            if (oldValue is null || newValue is null)
+            {
+                return oldValue;
+            }
+
             return new ImmutableSolidColorBrush(ColorAnimator.InterpolateCore(progress, oldValue.Color, newValue.Color));
         }
 
@@ -26,6 +31,11 @@ namespace Avalonia.Animation.Animators
     {    
         public override SolidColorBrush Interpolate(double progress, SolidColorBrush oldValue, SolidColorBrush newValue)
         {
+            if (oldValue is null || newValue is null)
+            {
+                return oldValue;
+            }
+
             return new SolidColorBrush(ColorAnimator.InterpolateCore(progress, oldValue.Color, newValue.Color));
         }
     }

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

@@ -0,0 +1,23 @@
+using System;
+using System.Reactive.Linq;
+
+using Avalonia.Animation.Animators;
+using Avalonia.Media;
+
+namespace Avalonia.Animation
+{
+    /// <summary>
+    /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="BoxShadows"/> type.
+    /// </summary>  
+    public class BoxShadowsTransition : Transition<BoxShadows>
+    {
+        private static readonly BoxShadowsAnimator s_animator = new BoxShadowsAnimator();
+
+        /// <inheritdocs/>
+        public override IObservable<BoxShadows> DoTransition(IObservable<double> progress, BoxShadows oldValue, BoxShadows newValue)
+        {
+            return progress
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
+        }
+    }
+}

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

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,26 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class CornerRadiusTransition : Transition<CornerRadius>
     {
+        private static readonly CornerRadiusAnimator s_animator = new CornerRadiusAnimator();
+
         /// <inheritdocs/>
         public override IObservable<CornerRadius> DoTransition(IObservable<double> progress, CornerRadius oldValue, CornerRadius newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-
-                    var deltaTL = newValue.TopLeft - oldValue.TopLeft;
-                    var deltaTR = newValue.TopRight - oldValue.TopRight;
-                    var deltaBR = newValue.BottomRight - oldValue.BottomRight;
-                    var deltaBL = newValue.BottomLeft - oldValue.BottomLeft;
-
-                    var nTL = f * deltaTL + oldValue.TopLeft;
-                    var nTR = f * deltaTR + oldValue.TopRight;
-                    var nBR = f * deltaBR + oldValue.BottomRight;
-                    var nBL = f * deltaBL + oldValue.BottomLeft;
-
-                    return new CornerRadius(nTL, nTR, nBR, nBL);
-                });
         }
     }
 }

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

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,15 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class PointTransition : Transition<Point>
     {
+        private static readonly PointAnimator s_animator = new PointAnimator();
+
         /// <inheritdocs/>
         public override IObservable<Point> DoTransition(IObservable<double> progress, Point oldValue, Point newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-                    return ((newValue - oldValue) * f) + oldValue;
-                });
         }
     }
 }

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

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,15 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class SizeTransition : Transition<Size>
     {
+        private static readonly SizeAnimator s_animator = new SizeAnimator();
+
         /// <inheritdocs/>
         public override IObservable<Size> DoTransition(IObservable<double> progress, Size oldValue, Size newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-                    return ((newValue - oldValue) * f) + oldValue;
-                });
         }
     }
 }

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

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,15 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class ThicknessTransition : Transition<Thickness>
     {
+        private static readonly ThicknessAnimator s_animator = new ThicknessAnimator();
+
         /// <inheritdocs/>
         public override IObservable<Thickness> DoTransition(IObservable<double> progress, Thickness oldValue, Thickness newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-                    return ((newValue - oldValue) * f) + oldValue;
-                });
         }
     }
 }

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

@@ -1,6 +1,8 @@
 using System;
 using System.Reactive.Linq;
 
+using Avalonia.Animation.Animators;
+
 namespace Avalonia.Animation
 {
     /// <summary>
@@ -8,15 +10,13 @@ namespace Avalonia.Animation
     /// </summary>  
     public class VectorTransition : Transition<Vector>
     {
+        private static readonly VectorAnimator s_animator = new VectorAnimator();
+
         /// <inheritdocs/>
         public override IObservable<Vector> DoTransition(IObservable<double> progress, Vector oldValue, Vector newValue)
         {
             return progress
-                .Select(p =>
+                .Select(progress => s_animator.Interpolate(Easing.Ease(progress), oldValue, newValue));
-                {
-                    var f = Easing.Ease(p);
-                    return ((newValue - oldValue) * f) + oldValue;
-                });
         }
     }
 }

src/Avalonia.Visuals/ApiCompatBaseline.txt

@@ -64,3 +64,8 @@ InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IGl
 InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IGlyphRunImpl Avalonia.Platform.IPlatformRenderInterface.CreateGlyphRun(Avalonia.Media.GlyphRun, System.Double)' is present in the contract but not in the implementation.
 MembersMustExist : Member 'public Avalonia.Platform.IGlyphRunImpl Avalonia.Platform.IPlatformRenderInterface.CreateGlyphRun(Avalonia.Media.GlyphRun, System.Double)' does not exist in the implementation but it does exist in the contract.
 Total Issues: 64
+InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmap(System.IO.Stream)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmap(System.String)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmapToHeight(System.IO.Stream, System.Int32, Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode)' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Platform.IWriteableBitmapImpl Avalonia.Platform.IPlatformRenderInterface.LoadWriteableBitmapToWidth(System.IO.Stream, System.Int32, Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode)' is present in the implementation but not in the contract.
+Total Issues: 11

src/Avalonia.Visuals/Media/Imaging/WriteableBitmap.cs

@@ -1,5 +1,8 @@
 using System;
+using System.IO;
+using System.Threading.Tasks;
 using Avalonia.Platform;
+using Avalonia.Visuals.Media.Imaging;
 
 namespace Avalonia.Media.Imaging
 {
@@ -34,8 +37,50 @@ namespace Avalonia.Media.Imaging
         {
         }
 
+        private WriteableBitmap(IWriteableBitmapImpl impl) : base(impl)
+        {
+            
+        }
+
         public ILockedFramebuffer Lock() => ((IWriteableBitmapImpl) PlatformImpl.Item).Lock();
 
+        public static WriteableBitmap Decode(Stream stream)
+        {
+            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+
+            return new WriteableBitmap(ri.LoadWriteableBitmap(stream));
+        }
+        
+        /// <summary>
+        /// Loads a WriteableBitmap from a stream and decodes at the desired width. Aspect ratio is maintained.
+        /// This is more efficient than loading and then resizing.
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from. This can be any supported image format.</param>
+        /// <param name="width">The desired width of the resulting bitmap.</param>
+        /// <param name="interpolationMode">The <see cref="BitmapInterpolationMode"/> to use should any scaling be required.</param>
+        /// <returns>An instance of the <see cref="WriteableBitmap"/> class.</returns>
+        public new static WriteableBitmap DecodeToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+
+            return new WriteableBitmap(ri.LoadWriteableBitmapToWidth(stream, width, interpolationMode));
+        }
+
+        /// <summary>
+        /// Loads a Bitmap from a stream and decodes at the desired height. Aspect ratio is maintained.
+        /// This is more efficient than loading and then resizing.
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from. This can be any supported image format.</param>
+        /// <param name="height">The desired height of the resulting bitmap.</param>
+        /// <param name="interpolationMode">The <see cref="BitmapInterpolationMode"/> to use should any scaling be required.</param>
+        /// <returns>An instance of the <see cref="WriteableBitmap"/> class.</returns>
+        public new static WriteableBitmap DecodeToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+
+            return new WriteableBitmap(ri.LoadWriteableBitmapToHeight(stream, height, interpolationMode));
+        }
+
         private static IBitmapImpl CreatePlatformImpl(PixelSize size, in Vector dpi, PixelFormat? format, AlphaFormat? alphaFormat)
         {
             var ri = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();

src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs

@@ -100,6 +100,38 @@ namespace Avalonia.Platform
         /// <returns>An <see cref="IBitmapImpl"/>.</returns>
         IBitmapImpl LoadBitmap(Stream stream);
 
+        /// <summary>
+        /// Loads a WriteableBitmap implementation from a stream to a specified width maintaining aspect ratio.
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from.</param> 
+        /// <param name="width">The desired width of the resulting bitmap.</param>
+        /// <param name="interpolationMode">The <see cref="BitmapInterpolationMode"/> to use should resizing be required.</param>
+        /// <returns>An <see cref="IWriteableBitmapImpl"/>.</returns>
+        IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality);
+
+        /// <summary>
+        /// Loads a WriteableBitmap implementation from a stream to a specified height maintaining aspect ratio.
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from.</param> 
+        /// <param name="height">The desired height of the resulting bitmap.</param>
+        /// <param name="interpolationMode">The <see cref="BitmapInterpolationMode"/> to use should resizing be required.</param>
+        /// <returns>An <see cref="IBitmapImpl"/>.</returns>
+        IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality);
+        
+        /// <summary>
+        /// Loads a WriteableBitmap implementation from a file.
+        /// </summary>
+        /// <param name="fileName">The filename of the bitmap.</param>        
+        /// <returns>An <see cref="IBitmapImpl"/>.</returns>
+        IWriteableBitmapImpl LoadWriteableBitmap(string fileName);
+
+        /// <summary>
+        /// Loads a WriteableBitmap implementation from a file.
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from.</param>        
+        /// <returns>An <see cref="IBitmapImpl"/>.</returns>
+        IWriteableBitmapImpl LoadWriteableBitmap(Stream stream);
+
         /// <summary>
         /// Loads a bitmap implementation from a stream to a specified width maintaining aspect ratio.
         /// </summary>

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -77,6 +77,31 @@ namespace Avalonia.Skia
             return new ImmutableBitmap(stream);
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableBitmapImpl(stream, width, true, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableBitmapImpl(stream, height, false, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            using (var stream = File.OpenRead(fileName))
+            {
+                return LoadWriteableBitmap(stream);
+            }
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            return new WriteableBitmapImpl(stream);
+        }
+
         /// <inheritdoc />
         public IBitmapImpl LoadBitmap(PixelFormat format, AlphaFormat alphaFormat, IntPtr data, PixelSize size, Vector dpi, int stride)
         {

src/Skia/Avalonia.Skia/WriteableBitmapImpl.cs

@@ -1,8 +1,10 @@
 using System;
 using System.IO;
 using System.Threading;
+using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using Avalonia.Skia.Helpers;
+using Avalonia.Visuals.Media.Imaging;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -15,7 +17,70 @@ namespace Avalonia.Skia
         private static readonly SKBitmapReleaseDelegate s_releaseDelegate = ReleaseProc;
         private readonly SKBitmap _bitmap;
         private readonly object _lock = new object();
+        
+        /// <summary>
+        /// Create a WriteableBitmap from given stream.
+        /// </summary>
+        /// <param name="stream">Stream containing encoded data.</param>
+        public WriteableBitmapImpl(Stream stream)
+        {
+            using (var skiaStream = new SKManagedStream(stream))
+            {
+                _bitmap = SKBitmap.Decode(skiaStream);
+
+                if (_bitmap == null)
+                {
+                    throw new ArgumentException("Unable to load bitmap from provided data");
+                }
+
+                PixelSize = new PixelSize(_bitmap.Width, _bitmap.Height);
+                Dpi = SkiaPlatform.DefaultDpi;
+            }
+        }
+
+        public WriteableBitmapImpl(Stream stream, int decodeSize, bool horizontal, BitmapInterpolationMode interpolationMode)
+        {
+            using (var skStream = new SKManagedStream(stream))
+            using (var codec = SKCodec.Create(skStream))
+            {
+                var info = codec.Info;
 
+                // get the scale that is nearest to what we want (eg: jpg returned 512)
+                var supportedScale = codec.GetScaledDimensions(horizontal ? ((float)decodeSize / info.Width) : ((float)decodeSize / info.Height));
+
+                // decode the bitmap at the nearest size
+                var nearest = new SKImageInfo(supportedScale.Width, supportedScale.Height);
+                var bmp = SKBitmap.Decode(codec, nearest);
+
+                // now scale that to the size that we want
+                var realScale = horizontal ? ((double)info.Height / info.Width) : ((double)info.Width / info.Height);
+
+                SKImageInfo desired;
+
+
+                if (horizontal)
+                {
+                    desired = new SKImageInfo(decodeSize, (int)(realScale * decodeSize));
+                }
+                else
+                {
+                    desired = new SKImageInfo((int)(realScale * decodeSize), decodeSize);
+                }
+
+                if (bmp.Width != desired.Width || bmp.Height != desired.Height)
+                {
+                    var scaledBmp = bmp.Resize(desired, interpolationMode.ToSKFilterQuality());
+                    bmp.Dispose();
+                    bmp = scaledBmp;
+                }
+
+                _bitmap = bmp;
+
+                PixelSize = new PixelSize(bmp.Width, bmp.Height);
+                Dpi = SkiaPlatform.DefaultDpi;
+            }
+        }
+        
         /// <summary>
         /// Create new writeable bitmap.
         /// </summary>

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -188,6 +188,28 @@ namespace Avalonia.Direct2D1
             return new WicBitmapImpl(stream);
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableWicBitmapImpl(stream, width, true, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableWicBitmapImpl(stream, height, false, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            return new WriteableWicBitmapImpl(fileName);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            return new WriteableWicBitmapImpl(stream);
+        }
+
         /// <inheritdoc />
         public IBitmapImpl LoadBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {

src/Windows/Avalonia.Direct2D1/Media/Imaging/WriteableWicBitmapImpl.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using Avalonia.Platform;
 using SharpDX.WIC;
 using PixelFormat = Avalonia.Platform.PixelFormat;
@@ -7,11 +8,27 @@ namespace Avalonia.Direct2D1.Media.Imaging
 {
     class WriteableWicBitmapImpl : WicBitmapImpl, IWriteableBitmapImpl
     {
+        public WriteableWicBitmapImpl(Stream stream, int decodeSize, bool horizontal,
+            Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode interpolationMode)
+        : base(stream, decodeSize, horizontal, interpolationMode)
+        {
+        }
+        
         public WriteableWicBitmapImpl(PixelSize size, Vector dpi, PixelFormat? pixelFormat, AlphaFormat? alphaFormat) 
             : base(size, dpi, pixelFormat, alphaFormat)
         {
         }
 
+        public WriteableWicBitmapImpl(Stream stream)
+            : base(stream)
+        {
+        }
+
+        public WriteableWicBitmapImpl(string fileName)
+            : base(fileName)
+        {
+        }
+
         class LockedBitmap : ILockedFramebuffer
         {
             private readonly WriteableWicBitmapImpl _parent;

tests/Avalonia.Benchmarks/NullRenderingPlatform.cs

@@ -61,6 +61,28 @@ namespace Avalonia.Benchmarks
             throw new NotImplementedException();
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            throw new NotImplementedException();
+        }
+
         public IBitmapImpl LoadBitmap(PixelFormat format, AlphaFormat alphaFormat, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
             throw new NotImplementedException();

tests/Avalonia.Controls.UnitTests/ViewboxTests.cs

@@ -114,5 +114,61 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(2.0, scaleTransform.ScaleX);
             Assert.Equal(2.0, scaleTransform.ScaleY);
         }
+
+        [Theory]
+        [InlineData(50, 100, 50, 100, 50, 100, 1)]
+        [InlineData(50, 100, 150, 150, 50, 100, 1)]
+        [InlineData(50, 100, 25, 50, 25, 50, 0.5)]
+        public void Viewbox_Should_Return_Correct_SizeAndScale_StretchDirection_DownOnly(
+            double childWidth, double childHeight,
+            double viewboxWidth, double viewboxHeight,
+            double expectedWidth, double expectedHeight,
+            double expectedScale)
+        {
+            var target = new Viewbox
+            {
+                Child = new Control { Width = childWidth, Height = childHeight },
+                StretchDirection = StretchDirection.DownOnly
+            };
+
+            target.Measure(new Size(viewboxWidth, viewboxHeight));
+            target.Arrange(new Rect(default, target.DesiredSize));
+
+            Assert.Equal(new Size(expectedWidth, expectedHeight), target.DesiredSize);
+
+            var scaleTransform = target.Child.RenderTransform as ScaleTransform;
+
+            Assert.NotNull(scaleTransform);
+            Assert.Equal(expectedScale, scaleTransform.ScaleX);
+            Assert.Equal(expectedScale, scaleTransform.ScaleY);
+        }
+
+        [Theory]
+        [InlineData(50, 100, 50, 100, 50, 100, 1)]
+        [InlineData(50, 100, 25, 50, 25, 50, 1)]
+        [InlineData(50, 100, 150, 150, 75, 150, 1.5)]
+        public void Viewbox_Should_Return_Correct_SizeAndScale_StretchDirection_UpOnly(
+            double childWidth, double childHeight,
+            double viewboxWidth, double viewboxHeight,
+            double expectedWidth, double expectedHeight,
+            double expectedScale)
+        {
+            var target = new Viewbox
+            {
+                Child = new Control { Width = childWidth, Height = childHeight },
+                StretchDirection = StretchDirection.UpOnly
+            };
+
+            target.Measure(new Size(viewboxWidth, viewboxHeight));
+            target.Arrange(new Rect(default, target.DesiredSize));
+
+            Assert.Equal(new Size(expectedWidth, expectedHeight), target.DesiredSize);
+
+            var scaleTransform = target.Child.RenderTransform as ScaleTransform;
+
+            Assert.NotNull(scaleTransform);
+            Assert.Equal(expectedScale, scaleTransform.ScaleX);
+            Assert.Equal(expectedScale, scaleTransform.ScaleY);
+        }
     }
 }

tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs

@@ -66,6 +66,28 @@ namespace Avalonia.UnitTests
             return Mock.Of<IBitmapImpl>();
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            throw new NotImplementedException();
+        }
+
         public IBitmapImpl LoadBitmap(string fileName)
         {
             return Mock.Of<IBitmapImpl>();

tests/Avalonia.Visuals.UnitTests/VisualTree/MockRenderInterface.cs

@@ -42,6 +42,28 @@ namespace Avalonia.Visuals.UnitTests.VisualTree
             throw new NotImplementedException();
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            throw new NotImplementedException();
+        }
+
         public IBitmapImpl LoadBitmap(string fileName)
         {
             throw new NotImplementedException();