wip: layout.

src/Ursa/Controls/Timeline/Timeline.cs

@@ -6,12 +6,15 @@ using Avalonia.Controls.Presenters;
 using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
+using Avalonia.Layout;
 using Avalonia.Metadata;
 
 namespace Ursa.Controls;
 
 public class Timeline: ItemsControl
 {
+    private static readonly FuncTemplate<Panel?> DefaultPanel = new((Func<Panel>)(() => new TimelinePanel()));
+    
     public static readonly StyledProperty<IBinding?> IconMemberBindingProperty = AvaloniaProperty.Register<Timeline, IBinding?>(
         nameof(IconMemberBinding));
 
@@ -66,6 +69,29 @@ public class Timeline: ItemsControl
         set => SetValue(DescriptionTemplateProperty, value);
     }
 
+    public static readonly StyledProperty<TimelineDisplayMode> ModeProperty = AvaloniaProperty.Register<Timeline, TimelineDisplayMode>(
+        nameof(Mode));
+
+    public TimelineDisplayMode Mode
+    {
+        get => GetValue(ModeProperty);
+        set => SetValue(ModeProperty, value);
+    }
+
+    static Timeline()
+    {
+        ItemsPanelProperty.OverrideDefaultValue<Timeline>(DefaultPanel);
+        ModeProperty.Changed.AddClassHandler<Timeline, TimelineDisplayMode>((t, e) => { t.OnDisplayModeChanged(e); });
+    }
+
+    private void OnDisplayModeChanged(AvaloniaPropertyChangedEventArgs<TimelineDisplayMode> e)
+    {
+        if (this.ItemsPanelRoot is TimelinePanel panel)
+        {
+            panel.Mode = e.NewValue.Value;
+        }
+    }
+
     protected override bool NeedsContainerOverride(object? item, int index, out object? recycleKey)
     {
         recycleKey = null;

src/Ursa/Controls/Timeline/TimelineDisplayMode.cs

@@ -0,0 +1,9 @@
+namespace Ursa.Controls;
+
+public enum TimelineDisplayMode
+{
+    Left,
+    Center,
+    Right,
+    Alternate,
+}

src/Ursa/Controls/Timeline/TimelineItem.cs

@@ -8,9 +8,13 @@ using Avalonia.Media;
 
 namespace Ursa.Controls;
 
-[PseudoClasses(":first", ":last")]
+[PseudoClasses(PC_First, PC_Last, PC_EmptyIcon)]
 public class TimelineItem: HeaderedContentControl
 {
+    public const string PC_First = ":first";
+    public const string PC_Last = ":last";
+    public const string PC_EmptyIcon = ":empty-icon";
+    
     public static readonly StyledProperty<object?> IconProperty = AvaloniaProperty.Register<TimelineItem, object?>(
         nameof(Icon));
 
@@ -37,10 +41,47 @@ public class TimelineItem: HeaderedContentControl
         get => GetValue(TypeProperty);
         set => SetValue(TypeProperty, value);
     }
+    
+    public static readonly DirectProperty<TimelineItem, double> LeftWidthProperty = AvaloniaProperty.RegisterDirect<TimelineItem, double>(
+        nameof(LeftWidth), o => o.LeftWidth, (o, v) => o.LeftWidth = v);
+    private double _leftWidth;
+    public double LeftWidth
+    {
+        get => _leftWidth;
+        set => SetAndRaise(LeftWidthProperty, ref _leftWidth, value);
+    }
+    
+    public static readonly DirectProperty<TimelineItem, double> IconWidthProperty = AvaloniaProperty.RegisterDirect<TimelineItem, double>(
+        nameof(IconWidth), o => o.IconWidth, (o, v) => o.IconWidth = v);
+    private double _iconWidth;
+    public double IconWidth
+    {
+        get => _iconWidth;
+        set => SetAndRaise(IconWidthProperty, ref _iconWidth, value);
+    }
+    
+    public static readonly DirectProperty<TimelineItem, double> RightWidthProperty = AvaloniaProperty.RegisterDirect<TimelineItem, double>(
+        nameof(RightWidth), o => o.RightWidth, (o, v) => o.RightWidth = v);
+    private double _rightWidth;
+    public double RightWidth
+    {
+        get => _rightWidth;
+        set => SetAndRaise(RightWidthProperty, ref _rightWidth, value);
+    }
+
+    static TimelineItem()
+    {
+        IconProperty.Changed.AddClassHandler<TimelineItem, object?>((item, args) => { item.OnIconChanged(args); });
+    }
+
+    private void OnIconChanged(AvaloniaPropertyChangedEventArgs<object?> args)
+    {
+        PseudoClasses.Set(PC_EmptyIcon, args.NewValue.Value is null);
+    }
 
     internal void SetEnd(bool start, bool end)
     {
-        PseudoClasses.Set(":first", start);
-        PseudoClasses.Set(":last", end);
+        PseudoClasses.Set(PC_First, start);
+        PseudoClasses.Set(PC_Last, end);
     }
 }

src/Ursa/Controls/Timeline/TimelinePanel.cs

@@ -0,0 +1,43 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Layout;
+
+namespace Ursa.Controls;
+
+public class TimelinePanel: Panel
+{
+    public static readonly StyledProperty<TimelineDisplayMode> ModeProperty =
+        Timeline.ModeProperty.AddOwner<TimelinePanel>();
+
+    public TimelineDisplayMode Mode
+    {
+        get => GetValue(ModeProperty);
+        set => SetValue(ModeProperty, value);
+    }
+
+    static TimelinePanel()
+    {
+        AffectsMeasure<TimelinePanel>(ModeProperty);
+    }
+    
+    protected override Size MeasureOverride(Size availableSize)
+    {
+        double left = 0;
+        double right = 0;
+        double icon = 0;
+        foreach (var child in Children)
+        {
+            if (child is TimelineItem t)
+            {
+                
+            }
+        }
+        return base.MeasureOverride(availableSize);
+    }
+
+    protected override Size ArrangeOverride(Size finalSize)
+    {
+        return base.ArrangeOverride(finalSize);
+        
+    }
+}