New dirty flag system. Avoid calling updates in rendering (yuck!)

TestGame/TestGame.cs

@@ -20,7 +20,7 @@ public class TestGame : Game
         InitializeSystemsDefault();
 
         _uiSystem = new UISystem(Input);
-        _uiSystem.RenderDebugRects = true;
+        _uiSystem.RenderDebugRects = false;
 
         ResourceManager.EnableFileWatching();
 
@@ -73,7 +73,7 @@ public class TestGame : Game
 
         _uiSystem.SetStyleSheet(_styleSheet);
 
-        var addButton = new Button("", _defaultFontSet);
+        var addButton = new Button("Default button", _defaultFontSet);
 
         var removeButton = new Button("Danger button", _defaultFontSet);
 
@@ -90,7 +90,7 @@ public class TestGame : Game
         {
             StyleVariant = "Layer01",
             ConfineToContents = true,
-            Anchor = Anchor.TopCenter
+            Anchor = Anchor.TopCenter,
         };
 
         var inputField = new InputField(string.Empty, _defaultFontSet)
@@ -124,6 +124,8 @@ public class TestGame : Game
             // ResourceManager.Reload();
             // _particleSystem!.RestartEmitter(_emitterId);
         }
+
+        _uiSystem.SetWindowSize(Renderer.WindowSize);
     }
 
     protected override void Render(double deltaTime)

Voile/Source/UI/Containers/Container.cs

@@ -40,19 +40,21 @@ public abstract class Container : UIElement, IParentableElement
         MarkDirty();
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
-        foreach (var child in _children)
+        for (int i = 0; i < _children.Count; i++)
         {
-            if (child is not IUpdatableElement updatable) continue;
+            var child = _children[i];
 
-            updatable.Update();
+            if (!child.Visible)
+                continue;
+
+            if (child is IUpdatableElement updatable && updatable.Dirty)
+                updatable.Update(layoutContext);
 
             if (child is IAnchorableElement anchorable)
-            {
                 anchorable.ApplyAnchor(GlobalPosition, Size);
         }
-        }
 
         Arrange();
 
@@ -62,15 +64,15 @@ public abstract class Container : UIElement, IParentableElement
         }
     }
 
-    public override void MarkDirty()
+    public override void MarkDirty(DirtyFlags flags = DirtyFlags.Layout)
     {
-        base.MarkDirty();
+        base.MarkDirty(flags);
 
         foreach (var child in _children)
         {
             if (child is not IUpdatableElement updatable) continue;
 
-            updatable.MarkDirty();
+            updatable.MarkDirty(flags);
         }
     }
 
@@ -85,6 +87,9 @@ public abstract class Container : UIElement, IParentableElement
     /// </summary>
     public void RecalculateSizes()
     {
+        if (_children.Count == 0)
+            return;
+
         float minX = float.MaxValue;
         float minY = float.MaxValue;
         float maxX = float.MinValue;
@@ -113,31 +118,45 @@ public abstract class Container : UIElement, IParentableElement
 
         if (finalSize != Size)
         {
-            Size = finalSize;
+            LayoutSize = finalSize;
         }
 
         if (_minimumSize > Size)
         {
-            Size = _minimumSize;
+            LayoutSize = _minimumSize;
         }
     }
 
+    /// <summary>
+    /// Adds an <see cref="UIElement"/> to the list of children.
+    /// </summary>
+    /// <param name="child">Child <see cref="UIElement"/> to add.</param>
+    /// <exception cref="InvalidOperationException"></exception>
     public void AddChild(UIElement child)
     {
         // child.StyleSheetOverride = StyleSheet;
+        if (child.Parent != null)
+            throw new InvalidOperationException("This UIElement already contains a parent.");
+
         _children.Add(child);
         child.SetParent(this);
 
         MarkDirty();
-        Update();
     }
 
+    /// <summary>
+    /// Removes an <see cref="UIElement"/> from the list of children.
+    /// </summary>
+    /// <param name="child">Child <see cref="UIElement"/> to remove.</param>
+    /// <exception cref="InvalidOperationException"></exception>
     public void RemoveChild(UIElement child)
     {
+        if (child.Parent != this)
+            throw new InvalidOperationException("This UIElement is not a child of this Container.");
+
         _children.Remove(child);
 
         MarkDirty();
-        Update();
     }
 
     protected override void OnRender(RenderSystem renderer, Style style)

Voile/Source/UI/Containers/FillContainer.cs

@@ -1,5 +1,3 @@
-using Voile.Rendering;
-
 namespace Voile.UI.Containers;
 
 /// <summary>
@@ -8,56 +6,18 @@ namespace Voile.UI.Containers;
 /// </summary>
 public class FillContainer : Container
 {
-    public FillContainer()
-    {
-
-    }
-
-    public FillContainer(Rect minimumSize) : base(minimumSize)
-    {
-
-    }
-
     public override void Arrange()
     {
-
+        // FillContainer does not position children.
+        // Children handle their own layout or are absolute.
     }
 
-    protected override void OnRender(RenderSystem renderer, Style style)
+    protected override void OnUpdate(LayoutContext layout)
     {
-        base.OnRender(renderer, style);
+        Size = Parent != null
+            ? Parent.Size
+            : new Rect(layout.WindowSize.X, layout.WindowSize.Y);
 
-        Rect parentSize;
+        base.OnUpdate(layout);
-
-        if (Parent != null)
-        {
-            parentSize = Parent.Size;
     }
-        else
-        {
-            var windowSize = renderer.WindowSize;
-            var windowRect = new Rect(windowSize.X, windowSize.Y);
-
-            parentSize = windowRect;
-        }
-
-        if (_lastParentSize != parentSize)
-        {
-            Size = parentSize;
-            _lastParentSize = parentSize;
-        }
-    }
-
-    protected override void OnUpdate()
-    {
-        base.OnUpdate();
-        Size = _lastParentSize;
-
-        if (Children.Count != 0)
-        {
-            Children[0].Size = Size;
-        }
-    }
-
-    private Rect _lastParentSize = Rect.Zero;
 }

Voile/Source/UI/Containers/FlexContainer.cs

@@ -124,7 +124,7 @@ public class FlexContainer : Container
             float justifyOffset = GetJustifyOffset(containerMainSize, lineMainLength, line.Count);
 
             float currentMain = mainPos + justifyOffset;
-            float maxLineCross = line.Select(child => GetCrossSize(GetChildSize(child))).Max();
+            float maxLineCross = line.Max(child => GetCrossSize(GetChildSize(child)));
 
             foreach (var child in line)
             {

Voile/Source/UI/Containers/MarginContainer.cs

@@ -21,9 +21,10 @@ public class MarginContainer : Container
         Margin = margin;
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
-        base.OnUpdate();
+        base.OnUpdate(layoutContext);
+
         if (Parent == null) return;
 
         if (Size != Parent.Size)

Voile/Source/UI/DirtyFlags.cs

@@ -0,0 +1,10 @@
+namespace Voile.UI;
+
+[Flags]
+public enum DirtyFlags
+{
+    None = 0,
+    Layout = 1 << 0,
+    Content = 1 << 1,
+    Style = 1 << 2,
+}

Voile/Source/UI/IElement.cs

@@ -25,7 +25,7 @@ public interface IElement
 public interface ITickableElement
 {
     /// <summary>
-    /// Excutes unconditionally on every frame engine loop step.
+    /// Executes unconditionally on every frame engine loop step.
     /// </summary>
     /// <param name="dt">Elapsed delta frame time in seconds.</param>
     /// <param name="input">InputSystem that this tickable element should use to poll input events.</param> 
@@ -77,11 +77,12 @@ public interface IUpdatableElement
     /// <summary>
     /// Update this element.
     /// </summary>
-    void Update(float dt = 0.0f);
+    void Update(LayoutContext layoutContext);
     /// <summary>
-    /// Marks this element as changed, requiring an update.
+    /// Marks this element as dirty (i.e. requiring an update).
     /// </summary>
-    void MarkDirty();
+    /// <param name="flags">The parts that were updated, as flags.</param>
+    void MarkDirty(DirtyFlags flags = DirtyFlags.Layout);
 }
 
 /// <summary>

Voile/Source/UI/LayoutContext.cs

@@ -0,0 +1,13 @@
+using System.Numerics;
+
+namespace Voile.UI;
+
+public readonly struct LayoutContext
+{
+    public Vector2 WindowSize { get; }
+
+    public LayoutContext(Vector2 windowSize)
+    {
+        WindowSize = windowSize;
+    }
+}

Voile/Source/UI/UIElement.cs

@@ -55,7 +55,7 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
             _size.Width = width;
             _size.Height = height;
 
-            MarkDirty();
+            MarkDirty(DirtyFlags.Layout);
         }
     }
 
@@ -63,57 +63,112 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
     public Anchor Anchor { get; set; } = Anchor.TopLeft;
 
     public abstract Rect MinimumSize { get; }
-    public bool Dirty => _dirty;
+    public bool Dirty => _dirty != DirtyFlags.None || _pendingDirty != DirtyFlags.None;
 
     public bool TryGetStyle(StyleSheet styleSheet, [NotNullWhen(true)] out Style? style)
     {
         return styleSheet.TryGet(StyleName, out style);
     }
 
-    public virtual void MarkDirty()
+    public virtual void MarkDirty(DirtyFlags flags = DirtyFlags.Layout) => _pendingDirty |= flags;
-    {
-        if (Parent != null && !Parent.Dirty)
-        {
-            Parent.MarkDirty();
-        }
-
-        _dirty = true;
-    }
 
     /// <summary>
     /// Sets a parent element for this <see cref="UIElement"/>.
     /// </summary>
     /// <param name="parent">Element to parent this <see cref="UIElement"/> to.</param>
+
     public void SetParent(UIElement parent)
     {
         _parent = parent;
-        MarkDirty();
+        MarkDirty(DirtyFlags.Layout);
     }
 
-    public void Update(float dt = 0.0f)
+    public void Update(LayoutContext layoutContext)
     {
-        if (!_dirty) return;
+        _dirty |= _pendingDirty;
-        _dirty = false;
+        _pendingDirty = DirtyFlags.None;
 
-        if (Size == Rect.Zero)
+        if (_dirty == DirtyFlags.None)
-            Size = MinimumSize;
+            return;
 
-        OnUpdate();
+        if (HasDirty(DirtyFlags.Layout))
+            OnLayoutUpdate();
 
-        if (_parent is not null && _parent.Size != Rect.Zero)
+        if (HasDirty(DirtyFlags.Content))
-        {
+            OnContentUpdate();
-            ApplyAnchor(_parent.GlobalPosition, _parent.Size);
+
-        }
+        if (HasDirty(DirtyFlags.Style))
+            OnStyleUpdate();
+
+        _dirty = DirtyFlags.None;
+
+        OnUpdate(layoutContext);
     }
 
+
     public void Render(RenderSystem renderer, Style style)
     {
         RenderStyleBox(renderer, style);
         OnRender(renderer, style);
     }
 
+    public void DrawSize(RenderSystem renderer)
+    {
+        renderer.SetTransform(GlobalPosition, Vector2.Zero);
+        renderer.DrawRectangleOutline(new Vector2(Size.Width, Size.Height), Color.Red, 2.0f);
+    }
+
+    /// <summary>
+    /// Determines if this <see cref="UIElement"/> contains a point within its confines.
+    /// </summary>
+    /// <param name="pointPosition">A global position of the point.</param>
+    /// <returns>True if the point is inside the widget; otherwise, false.</returns>
+    public bool ContainsPoint(Vector2 point)
+    {
+        return point.X >= GlobalPosition.X && point.Y >= GlobalPosition.Y &&
+               point.X <= GlobalPosition.X + Size.Width &&
+               point.Y <= GlobalPosition.Y + Size.Height;
+    }
+
+    /// <summary>
+    /// Applies this <see cref="UIElement"/> anchor.
+    /// </summary>
+    public virtual void ApplyAnchor(Vector2 parentPosition, Rect parentRect)
+    {
+        LocalPosition = Anchor.Calculate(parentPosition, parentRect, Size) + new Vector2(AnchorOffset.X, AnchorOffset.Y);
+    }
+
+    /// <summary>
+    /// Helper method for determining if this <see cref="UIElement"/> has a specific dirty flag.
+    /// </summary>
+    /// <param name="flags"></param>
+    /// <returns></returns>
+    public bool HasDirty(DirtyFlags flags) =>
+    (_dirty & flags) != 0 || (_pendingDirty & flags) != 0;
+
+    /// <summary>
+    /// The layout-computed size of this UI element that doesn't trigger
+    /// dirty state propagation.
+    /// </summary>
+    /// <remarks>
+    /// This property is intended to be used exclusively by the layout system
+    /// (e.g. containers during <c>RecalculateSizes</c>).
+    ///
+    /// Unlike the <see cref="Size"/> property setter, this property does not call
+    /// <c>MarkDirty</c>, and therefore will not trigger layout invalidation or
+    /// parent propagation.
+    /// </remarks>
+    protected Rect LayoutSize
+    {
+        get => _size; set => _size = value;
+    }
+
     protected abstract void OnRender(RenderSystem renderer, Style style);
-    protected abstract void OnUpdate();
+
+    protected virtual void OnLayoutUpdate() { }
+    protected virtual void OnContentUpdate() { }
+    protected virtual void OnStyleUpdate() { }
+    protected abstract void OnUpdate(LayoutContext layoutContext);
 
     /// <summary>
     /// Renders a stylebox from a given style.
@@ -174,32 +229,6 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
         }
     }
 
-    public void DrawSize(RenderSystem renderer)
-    {
-        renderer.SetTransform(GlobalPosition, Vector2.Zero);
-        renderer.DrawRectangleOutline(new Vector2(Size.Width, Size.Height), Color.Red, 2.0f);
-    }
-
-    /// <summary>
-    /// Determines if this <see cref="UIElement"/> contains a point within its confines.
-    /// </summary>
-    /// <param name="pointPosition">A global position of the point.</param>
-    /// <returns>True if the point is inside the widget; otherwise, false.</returns>
-    public bool ContainsPoint(Vector2 point)
-    {
-        return point.X >= GlobalPosition.X && point.Y >= GlobalPosition.Y &&
-               point.X <= GlobalPosition.X + Size.Width &&
-               point.Y <= GlobalPosition.Y + Size.Height;
-    }
-
-    /// <summary>
-    /// Applies this <see cref="UIElement"/> anchor.
-    /// </summary>
-    public virtual void ApplyAnchor(Vector2 parentPosition, Rect parentRect)
-    {
-        LocalPosition = Anchor.Calculate(parentPosition, parentRect, Size) + new Vector2(AnchorOffset.X, AnchorOffset.Y);
-    }
-
     private string ConstructStyleModifiers(string[]? modifiers)
     {
         if (modifiers == null)
@@ -225,7 +254,8 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
         return $".{StyleVariant}";
     }
 
-    private bool _dirty = true;
+    private DirtyFlags _dirty = DirtyFlags.Layout;
+    private DirtyFlags _pendingDirty = DirtyFlags.None;
     private Rect _size = Rect.Zero;
 
     private UIElement? _parent;

Voile/Source/UI/UISystem.cs

@@ -1,7 +1,6 @@
 using System.Numerics;
 using Voile.Input;
 using Voile.Rendering;
-using Voile.Resources;
 
 namespace Voile.UI;
 
@@ -33,10 +32,20 @@ public class UISystem : IUpdatableSystem, IRenderableSystem, IReloadableSystem
     {
         element.StyleSheetOverride = _styleSheet;
         _elements.Add(element);
-        _inputElementIndices.Add(element.GlobalPosition, _elements.Count - 1);
     }
     public void RemoveElement(UIElement element) => _elements.Remove(element);
 
+    public void SetWindowSize(Vector2 size)
+    {
+        if (_windowSize == size)
+            return;
+
+        _windowSize = size;
+
+        foreach (var element in _elements)
+            element.MarkDirty(DirtyFlags.Layout);
+    }
+
     public void Update(double deltaTime)
     {
         float dt = (float)deltaTime;
@@ -46,7 +55,11 @@ public class UISystem : IUpdatableSystem, IRenderableSystem, IReloadableSystem
         foreach (var element in _elements)
         {
             if (element is not IUpdatableElement updatable) continue;
-            updatable.Update();
+
+            if (!updatable.Dirty)
+                continue;
+
+            updatable.Update(new LayoutContext(_windowSize));
         }
     }
 
@@ -213,11 +226,10 @@ public class UISystem : IUpdatableSystem, IRenderableSystem, IReloadableSystem
         return false;
     }
 
+    private Vector2 _windowSize;
     private ResourceRef<StyleSheet> _styleSheet;
     private List<UIElement> _elements = new();
     private InputSystem _input;
 
-    private GridSet<int> _inputElementIndices = new();
-
     private Vector2 _lastMousePosition = Vector2.Zero;
 }

Voile/Source/UI/Widgets/Button.cs

@@ -23,7 +23,7 @@ public class Button : Widget
         get => _text; set
         {
             _text = value;
-            MarkDirty();
+            MarkDirty(DirtyFlags.Content);
         }
     }
 
@@ -57,7 +57,6 @@ public class Button : Widget
         FontSet.AddFont(fontOverride);
 
         MarkDirty();
-        Update();
     }
 
     public Button(string text, FontSet fontSet)
@@ -67,7 +66,6 @@ public class Button : Widget
         FontSet = fontSet;
 
         MarkDirty();
-        Update();
     }
 
     public Button(string text, FontSet fontSet, Action pressedAction)
@@ -78,25 +76,23 @@ public class Button : Widget
         FontSet = fontSet;
 
         MarkDirty();
-        Update();
     }
 
     protected override void OnRender(RenderSystem renderer, Style style)
     {
-        if (_padding != style.Padding)
-        {
-            MarkDirty();
-        }
-
         _padding = style.Padding ?? Voile.Size.Zero;
-        var textColor = style.TextColor ?? Color.Black;
 
-        var textPosition = new Vector2(GlobalPosition.X + Padding.Left, GlobalPosition.Y + Padding.Top);
+        var color = style.TextColor ?? Color.Black;
-        renderer.SetTransform(textPosition, Vector2.Zero);
 
-        if (_suitableFont.HasValue)
+        var pos = new Vector2(
+            GlobalPosition.X + _padding.Left,
+            GlobalPosition.Y + _padding.Top);
+
+        renderer.SetTransform(pos, Vector2.Zero);
+
+        if (_font.HasValue)
         {
-            renderer.DrawText(_suitableFont, _text, textColor);
+            renderer.DrawText(_font, _text, color);
         }
     }
 
@@ -139,39 +135,55 @@ public class Button : Widget
         }
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
-        ResourceRef<Font> fontRef = ResourceRef<Font>.Empty();
+        ResolveFont();
 
-        foreach (var c in _text)
+        if (!_font.HasValue)
-        {
+            return;
-            if (FontSet.TryGetFontFor(c, out var fallbackFont))
+
-            {
+        var font = _font.Value;
-                if (fallbackFont != fontRef)
+
-                {
+        var newSize = font.Measure(_text);
-                    fontRef = fallbackFont;
+        _textSize = newSize;
-                }
+
-            }
+        var final = _textSize + _padding;
+
+        if (_cachedSize.Width == final.Width &&
+            _cachedSize.Height == final.Height)
+            return;
+
+        _cachedSize = final;
+
+        Size = final;
+
+        MarkDirty(DirtyFlags.Layout);
     }
 
-        if (fontRef.HasValue)
+    private void ResolveFont()
     {
-            _suitableFont = fontRef;
+        if (_font.HasValue)
+            return;
 
-            var font = _suitableFont.Value;
+        var text = _text;
-            _textSize = font.Measure(_text);
+
+        for (int i = 0; i < text.Length; i++)
+        {
+            if (FontSet.TryGetFontFor(text[i], out var f))
+            {
+                _font = f;
+                break;
+            }
         }
-
-        Size = _padding + _textSize;
     }
 
     private Action? _pressedAction;
-
+    private Rect _cachedSize = Rect.Zero;
-    private ResourceRef<Font> _suitableFont = ResourceRef<Font>.Empty();
-
     private string _text = "Hello, World!";
     private Rect _textSize = Rect.Zero;
 
+    private ResourceRef<Font> _font = ResourceRef<Font>.Empty();
+
     private Size _padding;
 
     private bool _isHeldDown;

Voile/Source/UI/Widgets/InputField.cs

@@ -27,7 +27,8 @@ public class InputField : Widget, ITickableElement
         {
             _input = value ?? string.Empty;
             _cursor = Math.Clamp(_cursor, 0, _input.Length);
-            MarkDirty();
+
+            MarkDirty(DirtyFlags.Content);
         }
     }
 
@@ -43,7 +44,6 @@ public class InputField : Widget, ITickableElement
         FontSet = fontSet;
 
         MarkDirty();
-        Update();
     }
 
     public void Tick(float dt, InputSystem input)
@@ -94,7 +94,8 @@ public class InputField : Widget, ITickableElement
         {
             _input = _input.Insert(_cursor, c.ToString());
             _cursor++;
-            MarkDirty();
+
+            MarkDirty(DirtyFlags.Content);
         }
 
         context.SetHandled();
@@ -149,7 +150,7 @@ public class InputField : Widget, ITickableElement
                 {
                     _input = _input.Remove(_cursor - 1, 1);
                     _cursor--;
-                    MarkDirty();
+                    MarkDirty(DirtyFlags.Content);
                 }
                 break;
 
@@ -157,7 +158,7 @@ public class InputField : Widget, ITickableElement
                 if (_cursor > 0)
                 {
                     _cursor--;
-                    MarkDirty();
+                    MarkDirty(DirtyFlags.Content);
                 }
                 break;
 
@@ -165,7 +166,7 @@ public class InputField : Widget, ITickableElement
                 if (_cursor < _input.Length)
                 {
                     _cursor++;
-                    MarkDirty();
+                    MarkDirty(DirtyFlags.Content);
                 }
                 break;
         }
@@ -178,97 +179,96 @@ public class InputField : Widget, ITickableElement
 
     protected override void OnRender(RenderSystem renderer, Style style)
     {
-        if (_padding != style.Padding)
-        {
-            MarkDirty();
-        }
-
         _padding = style.Padding ?? Voile.Size.Zero;
 
         var textColor = style.TextColor ?? Color.Black;
         var caretColor = style.BorderColor ?? Color.Black;
 
-        var textPosition = new Vector2(GlobalPosition.X + _padding.Left, GlobalPosition.Y + _padding.Top);
+        var pos = new Vector2(GlobalPosition.X + _padding.Left,
-        renderer.SetTransform(textPosition, Vector2.Zero);
+                              GlobalPosition.Y + _padding.Top);
 
-        // Placeholder
+        renderer.SetTransform(pos, Vector2.Zero);
-        // TODO: use a color from the style instead of making it less transparent.
+
-        if (string.IsNullOrEmpty(_input) && !string.IsNullOrEmpty(PlaceholderText))
+        string text = string.IsNullOrEmpty(_input)
-        {
+            ? PlaceholderText
+            : _input;
+
+        // TODO: use a placeholder color from the style instead of making it lighter than the original text color.
         var placeholderColor = textColor.Lightened(0.5f);
 
-            if (_suitableFont.HasValue)
+        var color = string.IsNullOrEmpty(_input)
-            {
+            ? placeholderColor
-                renderer.DrawText(_suitableFont, PlaceholderText, placeholderColor);
+            : textColor;
-            }
+
-        }
+        if (_font.HasValue)
-        else
+            renderer.DrawText(_font, text, color);
-        {
-            if (_suitableFont.HasValue)
-            {
-                renderer.DrawText(_suitableFont, _input, textColor);
-            }
-        }
 
-        // Caret
         if (_isFocused && _blink)
         {
-            var caretX = MeasureTextWidth(_input.AsSpan(0, _cursor));
+            float caretX = GetCaretX(_cursor);
 
             renderer.SetTransform(
-                new Vector2(GlobalPosition.X + caretX + _padding.Left, GlobalPosition.Y + _padding.Top),
+                new Vector2(GlobalPosition.X + _padding.Left + caretX,
-                Vector2.Zero
+                            GlobalPosition.Y + _padding.Top),
-            );
+                Vector2.Zero);
 
-            var caretHeight = Math.Max(_placeholderSize.Height, _textSize.Height);
+            float h = Math.Max(_textSize.Height, _placeholderSize.Height);
-
+            renderer.DrawRectangle(new Vector2(1, h), caretColor);
-            renderer.DrawRectangle(
-                new Vector2(1, caretHeight),
-                caretColor
-            );
         }
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
-        ResourceRef<Font> fontRef = ResourceRef<Font>.Empty();
+        if (!_font.HasValue)
+            ResolveFont();
+
+        if (!_font.HasValue)
+            return;
+
+        var font = _font.Value;
+
+        _textSize = font.Measure(_input);
+
+        if (_input.Length == 0)
+            _placeholderSize = font.Measure(PlaceholderText);
+
+        var content = Rect.MaxWidth(_textSize, _placeholderSize);
+
+        float width = content.Width + _padding.Left + _padding.Right;
+        float height = content.Height + _padding.Top + _padding.Bottom;
+
+        if (LayoutSize.Width == width && LayoutSize.Height == height)
+            return;
+
+        LayoutSize = new Rect(width, height);
+
+        MarkDirty(DirtyFlags.Layout);
+    }
+
+    private float GetCaretX(int index)
+    {
+        var span = _input.AsSpan(0, index);
+
+        if (!_font.HasValue)
+            return 0.0f;
+
+        return _font.Value.Measure(span).Width;
+    }
+
+    private void ResolveFont()
+    {
+        if (_font.HasValue)
+            return;
 
         var text = string.IsNullOrEmpty(_input) ? PlaceholderText : _input;
 
         foreach (var c in text)
         {
-            if (FontSet.TryGetFontFor(c, out var fallbackFont))
+            if (FontSet.TryGetFontFor(c, out var f))
-            {
+                _font = f;
-                fontRef = fallbackFont;
         }
     }
 
-        if (fontRef.HasValue)
-        {
-            _suitableFont = fontRef;
-            var font = _suitableFont.Value;
-
-            _textSize = font.Measure(_input);
-
-            if (string.IsNullOrEmpty(_input))
-                _placeholderSize = font.Measure(PlaceholderText);
-        }
-
-        var size = Rect.MaxWidth(_placeholderSize, _textSize);
-
-        Size = _padding + size;
-    }
-
-    private float MeasureTextWidth(ReadOnlySpan<char> chars)
-    {
-        if (!_suitableFont.HasValue)
-        {
-            return 0.0f;
-        }
-
-        return _suitableFont.Value.Measure(chars).Width;
-    }
-
     private float _repeatTimer = 0.0f;
     private ActionType _lastActiveAction = ActionType.None;
     private const float INITIAL_DELAY = 0.5f;
@@ -281,7 +281,7 @@ public class InputField : Widget, ITickableElement
 
     private bool _blink = true;
 
-    private ResourceRef<Font> _suitableFont = ResourceRef<Font>.Empty();
+    private ResourceRef<Font> _font = ResourceRef<Font>.Empty();
 
     private Size _padding = Voile.Size.Zero;
     private Rect _textSize = Rect.Zero;

Voile/Source/UI/Widgets/Label.cs

@@ -32,7 +32,6 @@ public class Label : Widget
         FontSet.AddFont(fontOverride);
 
         MarkDirty();
-        Update();
     }
 
     public Label(string text, FontSet fontSet)
@@ -42,7 +41,6 @@ public class Label : Widget
         FontSet = fontSet;
 
         MarkDirty();
-        Update();
     }
 
     protected override void OnInput(UIInputContext action)
@@ -56,7 +54,7 @@ public class Label : Widget
         renderer.DrawText(_suitableFont, _text, style.TextColor ?? Color.Black);
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
         ResourceRef<Font> fontRef = ResourceRef<Font>.Empty();
         foreach (var c in _text)

Voile/Source/UI/Widgets/RectangleWidget.cs

@@ -65,7 +65,7 @@ public class RectangleWidget : Widget
         }
     }
 
-    protected override void OnUpdate()
+    protected override void OnUpdate(LayoutContext layoutContext)
     {
 
     }