Update arrangement logic for containers, remove position property from Rect, add Size property to IElement.

Voile/Source/Input/InputSystem.cs

@@ -134,6 +134,9 @@ namespace Voile.Input
                 new KeyInputAction(KeyboardKey.D),
                 new KeyInputAction(KeyboardKey.Right),
             ]);
+            AddInputMapping("accept", [
+                new KeyInputAction(KeyboardKey.Enter),
+            ]);
         }
 
         protected bool TryGetInputMappings(string forAction, [NotNullWhen(true)] out List<IInputAction>? inputActions)

Voile/Source/UI/Containers/Container.cs

@@ -9,6 +9,7 @@ public abstract class Container : IElement, IParentableElement, IUpdatableElemen
 {
     public IReadOnlyList<IElement> Children => _children;
     public Vector2 Position { get; set; }
+    public Rect Size { get; set; } = Rect.Zero;
 
     public Container()
     {

Voile/Source/UI/Containers/HorizontalContainer.cs

@@ -1,3 +1,4 @@
+using System.Numerics;
 using Voile.Rendering;
 
 namespace Voile.UI.Containers;
@@ -19,15 +20,20 @@ public class HorizontalContainer : Container, IRenderableElement
 
     public override void Arrange()
     {
-        int i = 0;
-        foreach (var child in Children)
-        {
-            var pos = Position;
-            pos.X += i * Spacing;
+        float currentX = Position.X;
 
+        for (int i = 0; i < Children.Count; i++)
+        {
+            var child = Children[i];
+            var pos = new Vector2(currentX, Position.Y);
             child.Position = pos;
 
-            i++;
+            currentX += child.Size.Width;
+
+            if (i < Children.Count - 1)
+            {
+                currentX += Spacing;
+            }
         }
     }
 

Voile/Source/UI/Containers/VerticalContainer.cs

@@ -1,3 +1,4 @@
+using System.Numerics;
 using Voile.Rendering;
 
 namespace Voile.UI.Containers;
@@ -19,15 +20,20 @@ public class VerticalContainer : Container, IRenderableElement
 
     public override void Arrange()
     {
-        int i = 0;
-        foreach (var child in Children)
-        {
-            var pos = Position;
-            pos.Y += i * Spacing;
+        float currentY = Position.Y;
 
+        for (int i = 0; i < Children.Count; i++)
+        {
+            var child = Children[i];
+            var pos = new Vector2(Position.X, currentY);
             child.Position = pos;
 
-            i++;
+            currentY += child.Size.Height;
+
+            if (i < Children.Count - 1)
+            {
+                currentY += Spacing;
+            }
         }
     }
 

Voile/Source/UI/IElement.cs

@@ -7,6 +7,7 @@ namespace Voile.UI;
 public interface IElement
 {
     public Vector2 Position { get; set; }
+    public Rect Size { get; set; }
 }
 
 public interface IParentableElement
@@ -15,6 +16,14 @@ public interface IParentableElement
     public void AddChild(IElement child);
 }
 
+public interface IResizeableElement
+{
+    /// <summary>
+    /// Get a minimum rectangle size for this element.
+    /// </summary>
+    public abstract Rect MinimumRect { get; }
+}
+
 public interface IUpdatableElement
 {
     void Update();

Voile/Source/UI/Rect.cs

@@ -1,8 +1,9 @@
-using System.Numerics;
-
 namespace Voile.UI;
 
 /// <summary>
 /// Represents a rectangle. Used to determine widget confines for UI layout.
 /// </summary>
-public record Rect(Vector2 Position, float Width, float Height);
+public record Rect(float Width = 0.0f, float Height = 0.0f)
+{
+    public static Rect Zero => new Rect(0.0f, 0.0f);
+}

Voile/Source/UI/Widgets/Button.cs

@@ -18,7 +18,7 @@ public enum ButtonState
 public class Button : Widget
 {
     public string Label { get; set; } = "Button";
-    public override Rect MinimumRect => new Rect(Position, Width: 128.0f, Height: 64.0f);
+    public override Rect MinimumRect => new Rect(Width: 128.0f, Height: 64.0f);
 
     public Button(string label, Action pressedAction)
     {

Voile/Source/UI/Widgets/Widget.cs

@@ -7,11 +7,12 @@ namespace Voile.UI.Widgets;
 /// <summary>
 /// A base class for all UI widgets.
 /// </summary>
-public abstract class Widget : IElement, IRenderableElement, IInputElement
+public abstract class Widget : IElement, IRenderableElement, IInputElement, IResizeableElement, IUpdatableElement
 {
     public bool Visible { get; set; } = true;
     public bool IgnoreInput { get; set; }
     public Vector2 Position { get; set; } = Vector2.Zero;
+    public Rect Size { get; set; } = new();
 
     public Widget()
     {
@@ -23,9 +24,7 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement
         Position = position;
     }
 
-    /// <summary>
-    /// Get a minimum rectangle size for this widget.
-    /// </summary>
+    /// </inheritdoc>
     public abstract Rect MinimumRect { get; }
 
     /// <summary>
@@ -38,4 +37,12 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement
     /// </summary>
     /// <param name="action">An input action this widget received.</param>
     public abstract void Input(IInputAction action);
+
+    public void Update()
+    {
+        if (Size == Rect.Zero)
+        {
+            Size = MinimumRect;
+        }
+    }
 }