feat: update selection handling, fix initial offset calculation.

src/Ursa.Themes.Semi/Controls/Anchor.axaml

@@ -1,31 +1,60 @@
 <ResourceDictionary
     xmlns="https://github.com/avaloniaui"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-    xmlns:u="https://irihi.tech/ursa"
+    xmlns:converters="clr-namespace:Ursa.Themes.Semi.Converters"
-    xmlns:iri="https://irihi.tech/shared">
+    xmlns:iri="https://irihi.tech/shared"
+    xmlns:u="https://irihi.tech/ursa">
+    <converters:TreeLevelToMarginConverter x:Key="LevelToMarginConverter" />
     <ControlTheme x:Key="{x:Type u:Anchor}" TargetType="{x:Type u:Anchor}">
         <Setter Property="Template">
             <ControlTemplate>
-                <ItemsPresenter
+                <Panel>
-                    Name="PART_ItemsPresenter"
+                    <Rectangle
-                    Margin="{TemplateBinding Padding}"
+                        Width="1"
-                    ItemsPanel="{TemplateBinding ItemsPanel}" />
+                        HorizontalAlignment="Left"
+                        VerticalAlignment="Stretch"
+                        Fill="{DynamicResource SemiColorBorder}" />
+                    <ItemsPresenter
+                        Name="PART_ItemsPresenter"
+                        Margin="{TemplateBinding Padding}"
+                        ItemsPanel="{TemplateBinding ItemsPanel}" />
+                </Panel>
             </ControlTemplate>
         </Setter>
     </ControlTheme>
 
-    <ControlTheme x:Key="{x:Type u:AnchorItem}" TargetType="u:AnchorItem" >
+    <ControlTheme x:Key="{x:Type u:AnchorItem}" TargetType="u:AnchorItem">
         <Setter Property="Background" Value="Transparent" />
+        <Setter Property="MinHeight" Value="20" />
         <Setter Property="Template">
             <ControlTemplate TargetType="u:AnchorItem">
                 <StackPanel>
-                    <ContentPresenter Name="{x:Static iri:PartNames.PART_HeaderPresenter}" Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" />
+                    <Panel>
-                    <ItemsPresenter Margin="8 0 0 0" ItemsPanel="{TemplateBinding ItemsPanel}" />
+                        <Rectangle
+                            Name="PART_Pipe"
+                            Width="2"
+                            HorizontalAlignment="Left"
+                            VerticalAlignment="Stretch" />
+                        <Panel Margin="8,0,0,0">
+                            <ContentPresenter
+                                Name="{x:Static iri:PartNames.PART_HeaderPresenter}"
+                                Content="{TemplateBinding Header}"
+                                ContentTemplate="{TemplateBinding HeaderTemplate}">
+                                <ContentPresenter.Margin>
+                                    <MultiBinding Converter="{StaticResource LevelToMarginConverter}">
+                                        <Binding Path="Level" RelativeSource="{RelativeSource AncestorType={x:Type u:AnchorItem}}" />
+                                        <DynamicResource ResourceKey="AnchorIndent" />
+                                    </MultiBinding>
+                                </ContentPresenter.Margin>
+                            </ContentPresenter>
+                        </Panel>
+                    </Panel>
+                    <ItemsPresenter ItemsPanel="{TemplateBinding ItemsPanel}" />
                 </StackPanel>
             </ControlTemplate>
         </Setter>
-        <Style Selector="^:selected /template/ ContentPresenter#PART_HeaderPresenter">
+        <Style Selector="^:selected /template/ Rectangle#PART_Pipe">
-            <Setter Property="Foreground" Value="{DynamicResource SemiBlue5}" />
+            <Setter Property="Fill" Value="{DynamicResource SemiBlue5}" />
         </Style>
     </ControlTheme>
 </ResourceDictionary>

src/Ursa.Themes.Semi/Converters/NavigationMenuItemLevelToMarginConverter.cs

@@ -1,23 +0,0 @@
-using System.Globalization;
-using Avalonia;
-using Avalonia.Data.Converters;
-
-namespace Ursa.Themes.Semi.Converters;
-
-public class NavigationMenuItemLevelToMarginConverter: IMultiValueConverter
-{
-    public int Indent { get; set; }
-
-    public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
-    {
-        if (values[0] is int i && values[1] is bool b)
-        {
-            if (b)
-            {
-                return new Thickness();
-            }
-            return new Thickness((i-1) * Indent, 0, 0, 0);
-        }
-        return new Thickness();
-    }
-}

src/Ursa.Themes.Semi/Converters/TreeLevelToMarginConverter.cs

@@ -0,0 +1,17 @@
+using System.Globalization;
+using Avalonia;
+using Avalonia.Data.Converters;
+
+namespace Ursa.Themes.Semi.Converters;
+
+public class TreeLevelToMarginConverter: IMultiValueConverter
+{
+    public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (values[0] is int i && values[1] is double indent)
+        {
+            return new Thickness((i-1) * indent, 0, 0, 0);
+        }
+        return new Thickness();
+    }
+}

src/Ursa.Themes.Semi/Themes/Shared/Anchor.axaml

@@ -0,0 +1,4 @@
+<ResourceDictionary xmlns="https://github.com/avaloniaui"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <x:Double x:Key="AnchorIndent">12</x:Double>
+</ResourceDictionary>

src/Ursa.Themes.Semi/Themes/Shared/_index.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
     <ResourceDictionary.MergedDictionaries>
         <ResourceInclude Source="Avatar.axaml" />
+        <ResourceInclude Source="Anchor.axaml" />
         <ResourceInclude Source="Badge.axaml" />
         <ResourceInclude Source="Banner.axaml" />
         <ResourceInclude Source="ButtonGroup.axaml" />

src/Ursa/Common/LogicalHelpers.cs

@@ -0,0 +1,21 @@
+using Avalonia.LogicalTree;
+using Ursa.Controls;
+
+namespace Ursa.Common;
+
+public static class LogicalHelpers
+{
+    public static int CalculateDistanceFromLogicalParent<T, TItem>(TItem? item, int @default = -1) 
+        where T : class 
+        where TItem : ILogical
+    {
+        var result = 0;
+        ILogical? logical = item;
+        while (logical is not null and not T)
+        {
+            if (logical is TItem) result++;
+            logical = logical.LogicalParent;
+        }
+        return item is not null ? result : @default;
+    }
+}

src/Ursa/Controls/Anchor/Anchor.cs

@@ -1,4 +1,3 @@
-using System.Diagnostics;
 using Avalonia;
 using Avalonia.Animation;
 using Avalonia.Animation.Easings;
@@ -47,7 +46,7 @@ public class Anchor: ItemsControl
     }
 
     private CancellationTokenSource _cts = new();
-    private bool _scrollingFromSelection = false;
+    private bool _scrollingFromSelection;
     
     private void ScrollToAnchor(Visual target)
     {
@@ -114,7 +113,7 @@ public class Anchor: ItemsControl
         {
             var anchorId = GetAnchorId(item);
             if (anchorId is null) continue;
-            var position = item.TransformToVisual(TargetContainer)?.M32;
+            var position = item.TransformToVisual(TargetContainer)?.M32 + TargetContainer.Offset.Y;
             if (position.HasValue)
             {
                 positions.Add((anchorId, position.Value));
@@ -127,22 +126,14 @@ public class Anchor: ItemsControl
     protected override void OnLoaded(RoutedEventArgs e)
     {
         base.OnLoaded(e);
-        var items = this.GetVisualDescendants().OfType<AnchorItem>().ToList();
         var target = this.TargetContainer;
         if (target is null) return;
-        var targetItems = target.GetVisualDescendants().Where(a => Anchor.GetAnchorId(a) is not null).ToList();
-        var tops = targetItems.Select(a => (a.TransformToVisual(target)?.M32, GetAnchorId(a)));
-        var isloaded = TargetContainer?.IsLoaded; 
         TargetContainer?.AddHandler(ScrollViewer.ScrollChangedEvent, OnScrollChanged);
-        if (isloaded is true)
+        TargetContainer?.AddHandler(LoadedEvent, OnTargetContainerLoaded);
+        if (TargetContainer?.IsLoaded == true)
         {
             InvalidateAnchorPositions();
         }
-        else
-        {
-            TargetContainer.Loaded += (s, args) => InvalidateAnchorPositions();
-        }
-
         MarkSelectedContainerByPosition();
     }
 
@@ -159,7 +150,7 @@ public class Anchor: ItemsControl
         if (source is null) return;
         MarkSelectedContainer(source);
         var target = TargetContainer?.GetVisualDescendants()
-                                    .FirstOrDefault(a => Anchor.GetAnchorId(a) == source?.AnchorId);
+                                    .FirstOrDefault(a => Anchor.GetAnchorId(a) == source.AnchorId);
         if (target is null) return;
         ScrollToAnchor(target);
     }
@@ -187,7 +178,7 @@ public class Anchor: ItemsControl
         ContainerForItemPreparedOverride(container, item, index);
     }
 
-    internal AnchorItem? _selectedContainer;
+    private AnchorItem? _selectedContainer;
     
     internal void MarkSelectedContainer(AnchorItem? item)
     {
@@ -211,4 +202,14 @@ public class Anchor: ItemsControl
         MarkSelectedContainer(item);
     }
 
+    protected override void OnUnloaded(RoutedEventArgs e)
+    {
+        base.OnUnloaded(e);
+        TargetContainer?.RemoveHandler(UnloadedEvent, OnTargetContainerLoaded);
+    }
+
+    private void OnTargetContainerLoaded(object? sender, RoutedEventArgs e)
+    {
+        InvalidateAnchorPositions();
+    }
 }

src/Ursa/Controls/Anchor/AnchorItem.cs

@@ -3,8 +3,8 @@ using Avalonia.Controls;
 using Avalonia.Controls.Mixins;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
-using Avalonia.Input;
 using Avalonia.LogicalTree;
+using Ursa.Common;
 
 namespace Ursa.Controls;
 
@@ -19,6 +19,12 @@ public class AnchorItem : HeaderedItemsControl, ISelectable
     private static readonly FuncTemplate<Panel?> DefaultPanel =
         new(() => new StackPanel());
 
+    internal static readonly DirectProperty<AnchorItem, int> LevelProperty =
+        AvaloniaProperty.RegisterDirect<AnchorItem, int>(
+            nameof(Level), o => o.Level, (o, v) => o.Level = v);
+
+    private int _level;
+
     private Anchor? _root;
 
     static AnchorItem()
@@ -28,6 +34,12 @@ public class AnchorItem : HeaderedItemsControl, ISelectable
         ItemsPanelProperty.OverrideDefaultValue<TreeViewItem>(DefaultPanel);
     }
 
+    public int Level
+    {
+        get => _level;
+        set => SetAndRaise(LevelProperty, ref _level, value);
+    }
+
     public string? AnchorId
     {
         get => GetValue(AnchorIdProperty);
@@ -44,15 +56,12 @@ public class AnchorItem : HeaderedItemsControl, ISelectable
     {
         base.OnAttachedToVisualTree(e);
         _root = this.GetLogicalAncestors().OfType<Anchor>().FirstOrDefault();
+        Level = LogicalHelpers.CalculateDistanceFromLogicalParent<Anchor, AnchorItem>(this);
         if (ItemTemplate is null && _root?.ItemTemplate is not null)
-        {
             SetCurrentValue(ItemTemplateProperty, _root.ItemTemplate);
-        }
 
         if (ItemContainerTheme is null && _root?.ItemContainerTheme is not null)
-        {
             SetCurrentValue(ItemContainerThemeProperty, _root.ItemContainerTheme);
-        }
     }
 
     protected override Control CreateContainerForItemOverride(object? item, int index, object? recycleKey)