Document GridSet, fix resource hot reload on every frame.

TODO.md

@@ -92,10 +92,14 @@
   - ~~Positioning (anchors)~~
 - ~~Move layouting to Render instead of Update, use Update for input.~~
 - Input propagation
-  - Use GridSet to efficiently query inputtable UI elements.
+  - ~~Pass input to widgets.~~
   - Add element focus logic, make them focusable with action inputs.
-- Basic input elements (button, text field, toggle).
+- Basic input elements (~~button~~, text field, toggle).
 - Styling
-  - Add style settings for UI panels (for buttons, labels, etc.).
+  - ~~Style sheet~~
+  - ~~Add style settings for UI panels (for buttons, labels, etc.).~~
+  - ~~Parse StyleSheet from TOML file.~~
+  - Animated styles
+  - (stretch goal) Style variables
   - Find a way to reference external assets in the style (fonts, textures).
   - Create a default style for widgets.

TestGame/Resources/default.style.toml

@@ -0,0 +1,63 @@
+[Button]
+BackgroundColor = "#0f62fe"
+TextColor = "#ffffff"
+Padding = 16.0
+
+# Creates an empty rule for Button.Normal.
+# This will inherit style from Button, this is a temporary workaround.
+[Button.Normal]
+
+[Button.Hovered]
+BackgroundColor = "#0353e9"
+
+[Button.Pressed]
+BackgroundColor = "#002d9c"
+
+[Button.Danger]
+TextColor = "#ffffff"
+
+[Button.Danger.Normal]
+BackgroundColor = "#da1e28"
+
+[Button.Danger.Hovered]
+BackgroundColor = "#ba1b23"
+
+[Button.Danger.Pressed]
+BackgroundColor = "#750e13"
+
+[Button.Outline]
+BackgroundColor = [0, 0, 0, 0]
+BorderSize = 1.0
+BorderColor = "#0f62fe"
+
+[Button.Outline.Normal]
+TextColor = "#0353e9"
+
+[Button.Outline.Hovered]
+BackgroundColor = "#0353e9"
+
+[Button.Outline.Pressed]
+BackgroundColor = "#002d9c"
+BorderColor = [0, 0, 0, 0]
+
+[Button.Link]
+BackgroundColor = [0, 0, 0, 0]
+TextColor = "#0f62fe"
+Padding = 0.0
+
+[Button.Link.Normal]
+
+[Button.Link.Hovered]
+BorderColor = "#0043ce"
+TextColor = "#0043ce"
+BorderSize = [0, 0, 0, 1]
+
+[Button.Link.Pressed]
+TextColor = "#161616"
+BorderSize = [0, 0, 0, 1]
+BorderColor = "#161616"
+
+
+# Default background color for all Container derived classes.
+[Container]
+BackgroundColor = "#e0e0e0"

TestGame/TestGame.cs

@@ -19,8 +19,10 @@ public class TestGame : Game
     {
         InitializeSystemsDefault();
 
-        _uiSystem = new UISystem(Input, ResourceRef<Style>.Empty());
+        _uiSystem = new UISystem(Input);
-        _uiSystem.RenderDebugRects = true;
+        // _uiSystem.RenderDebugRects = true;
+
+        ResourceManager.EnableFileWatching();
 
         _particleSystem = new ParticleSystem();
 
@@ -36,6 +38,7 @@ public class TestGame : Game
     protected override void LoadResources()
     {
         ResourceManager.AddResourceLoaderAssociation(new ParticleEmitterSettingsResourceLoader());
+        ResourceManager.AddResourceLoaderAssociation(new StyleSheetLoader());
 
         if (!ResourceManager.TryLoad("fonts/Inter-Regular.ttf", out _font))
         {
@@ -55,18 +58,56 @@ public class TestGame : Game
             throw new Exception("Failed to load emitter settings!");
         }
 
+        if (ResourceManager.TryLoad("default.style.toml", out _styleSheet))
+        {
+
+        }
+
         _defaultFontSet = new([_font, _jpFont]);
     }
 
     protected override void Ready()
     {
         Input.AddInputMapping("reload", new IInputAction[] { new KeyInputAction(KeyboardKey.R) });
-        _emitterId = _particleSystem.CreateEmitter(Renderer.WindowSize / 2, _fireEffect);
+        // _emitterId = _particleSystem.CreateEmitter(Renderer.WindowSize / 2, _fireEffect);
 
-        // _fillContainer.AddChild(_container);
+        _uiSystem.SetStyleSheet(_styleSheet);
-        // _marginContainer.AddChild(_container);
 
-        _uiSystem.AddElement(_container);
+        var addButton = new Button("Default button", _defaultFontSet);
+
+        var removeButton = new Button("Danger button", _defaultFontSet);
+
+        removeButton.StyleVariant = "Danger";
+
+        var outlineButton = new Button("Outline button", _defaultFontSet);
+        outlineButton.StyleVariant = "Outline";
+
+        var linkButton = new Button("Link button", _defaultFontSet);
+        linkButton.StyleVariant = "Link";
+
+
+        var c = new HorizontalContainer()
+        {
+            StyleVariant = "Layer01",
+            ConfineToContents = true,
+            Anchor = Anchor.TopCenter
+        };
+
+        c.AddChild(addButton);
+        c.AddChild(removeButton);
+        c.AddChild(outlineButton);
+        c.AddChild(linkButton);
+
+        var vc = new VerticalContainer(0.0f);
+        vc.AddChild(c);
+
+        var f = new MarginContainer(new Size(0.0f));
+        f.AddChild(_container);
+
+        vc.AddChild(f);
+
+        _rootFill.AddChild(vc);
+        _uiSystem.AddElement(_rootFill);
     }
 
 
@@ -74,19 +115,8 @@ public class TestGame : Game
     {
         if (Input.IsActionPressed("reload"))
         {
-            ResourceManager.Reload();
+            // ResourceManager.Reload();
-            _particleSystem!.RestartEmitter(_emitterId);
+            // _particleSystem!.RestartEmitter(_emitterId);
-        }
-
-        if (Input.IsActionPressed("accept"))
-        {
-            _container.AddChild(new Label("こんにちは世界！", _defaultFontSet));
-        }
-
-        if (Input.IsActionPressed("cancel") && _container.Children.Count != 0)
-        {
-            var lastChild = _container.Children.Last();
-            _container.RemoveChild(lastChild);
         }
     }
 
@@ -128,6 +158,7 @@ public class TestGame : Game
     private ResourceRef<ParticleEmitterSettingsResource> _fireEffect;
     private ResourceRef<Font> _font;
     private ResourceRef<Font> _jpFont;
+    private ResourceRef<StyleSheet> _styleSheet;
 
     private FontSet _defaultFontSet;
 
@@ -141,17 +172,15 @@ public class TestGame : Game
         Justify = JustifyContent.Start,
         Align = AlignItems.Center,
         Wrap = true,
-        Gap = 8.0f
+        Gap = 8.0f,
+        StyleVariant = "Layer02",
     };
 
     [NotNull] private Label _label;
 
-    private FillContainer _fillContainer = new();
+    private FillContainer _rootFill = new();
-    private MarginContainer _marginContainer = new(new Margin(32.0f))
+    private HorizontalContainer _buttonContainer = new(16)
     {
+        ConfineToContents = true,
     };
-    // private HorizontalContainer _container = new(new Rect(128.0f, 64.0f), new(), 16)
-    // {
-    //     ConfineToContents = true,
-    // };
 }

Voile/GridSet.cs

@@ -7,15 +7,23 @@ namespace Voile;
 
 public class GridSet<T>
 {
-    public float GridSize { get; }
+    /// <summary>
-    public GridSet(float gridSize = 32.0f)
+    /// The size of a cell of this <see cref="GridSet"/>.
+    /// </summary>
+    public float CellSize { get; }
+    public GridSet(float cellSize = 32.0f)
     {
-        GridSize = gridSize;
+        CellSize = cellSize;
     }
 
+    /// <summary>
+    /// Add an element to this <see cref="GridSet"/>.
+    /// </summary>
+    /// <param name="position">Position of the element in this <see cref="GridSet"/>.</param>
+    /// <param name="child">Element to add.</param>
     public void Add(Vector2 position, T child)
     {
-        var snap = Vector2.One * GridSize;
+        var snap = Vector2.One * CellSize;
         position = position.Snapped(snap);
 
         if (_values.TryGetValue(position, out var list))
@@ -28,10 +36,11 @@ public class GridSet<T>
         }
     }
 
-    public void Remove(T child)
+    /// <summary>
-    {
+    /// Removes an element from this <see cref="GridSet"/>.
-
+    /// </summary>
-    }
+    /// <param name="child">Element to remove.</param>
+    public void Remove(T child) => throw new NotImplementedException();
 
     private Dictionary<Vector2, List<T>> _values = new();
 }

Voile/Source/Color.cs

@@ -6,6 +6,7 @@ namespace Voile
     /// </summary>
     public record struct Color
     {
+        public static readonly Color Transparent = new(1.0f, 1.0f, 1.0f, 0.0f);
         public static readonly Color AliceBlue = new(0xF0F8FF);
         public static readonly Color AntiqueWhite = new(0xFAEBD7);
         public static readonly Color Aqua = new(0x00FFFF);

Voile/Source/Input/InputAction.cs

@@ -45,7 +45,7 @@ namespace Voile.Input
 
         public bool IsPressed(InputSystem inputSystem)
         {
-            return inputSystem.IsMousePressed(MouseButton);
+            return inputSystem.IsMouseButtonPressed(MouseButton);
         }
 
         public bool IsDown(InputSystem inputSystem)

Voile/Source/Input/InputSystem.cs

@@ -108,7 +108,7 @@ namespace Voile.Input
 
         public abstract int GetCharPressed();
 
-        public abstract bool IsMousePressed(MouseButton button);
+        public abstract bool IsMouseButtonPressed(MouseButton button);
         public abstract bool IsMouseButtonDown(MouseButton button);
         public abstract bool IsMouseButtonReleased(MouseButton button);
         public abstract float GetMouseWheelMovement();

Voile/Source/Input/RaylibInputSystem.cs

@@ -50,7 +50,7 @@ namespace Voile.Input
         public override bool KeyboardKeyJustPressed(KeyboardKey key) => _justPressedKeys.Contains(key);
         public override bool KeyboardKeyJustReleased(KeyboardKey key) => _justReleasedKeys.Contains(key);
 
-        public override bool IsMousePressed(MouseButton button) => _pressedMouseButtons.Contains(button);
+        public override bool IsMouseButtonPressed(MouseButton button) => _pressedMouseButtons.Contains(button);
         public override bool IsMouseButtonReleased(MouseButton button) => _releasedMouseButtons.Contains(button);
         public override bool IsMouseButtonDown(MouseButton button) => _downMouseButtons.Contains(button);
 

Voile/Source/Rect.cs

@@ -21,3 +21,61 @@ public record Rect(float Width = 0.0f, float Height = 0.0f)
     public static bool operator >=(Rect left, Rect right) => left.CompareTo(right) >= 0;
     public static bool operator <=(Rect left, Rect right) => left.CompareTo(right) <= 0;
 }
+
+/// <summary>
+/// Represents the size offsets applied around a rectangle.
+/// </summary>
+public struct Size : IEquatable<Size>
+{
+    public float Left;
+    public float Right;
+    public float Top;
+    public float Bottom;
+
+    public Size(float uniform)
+    {
+        Left = Right = Top = Bottom = uniform;
+    }
+
+    public Size(float horizontal, float vertical)
+    {
+        Left = Right = horizontal;
+        Top = Bottom = vertical;
+    }
+
+    public Size(float left, float right, float top, float bottom)
+    {
+        Left = left;
+        Right = right;
+        Top = top;
+        Bottom = bottom;
+    }
+
+    public static Size Zero => new Size(0);
+
+    public static Rect operator +(Size margin, Rect rect) =>
+        new Rect(rect.Width + margin.Left + margin.Right,
+                 rect.Height + margin.Top + margin.Bottom);
+
+    public static Rect operator +(Rect rect, Size margin) =>
+        margin + rect;
+
+
+    public static bool operator ==(Size a, Size b) =>
+a.Equals(b);
+
+    public static bool operator !=(Size a, Size b) =>
+        !a.Equals(b);
+
+    public bool Equals(Size other) =>
+        Left == other.Left &&
+        Right == other.Right &&
+        Top == other.Top &&
+        Bottom == other.Bottom;
+
+    public override bool Equals(object? obj) =>
+        obj is Size other && Equals(other);
+
+    public override int GetHashCode() =>
+        HashCode.Combine(Left, Right, Top, Bottom);
+}

Voile/Source/Resources/DataReaders/IDataReader.cs

@@ -65,6 +65,9 @@ namespace Voile.Resources.DataReaders
         /// <param name="defaultValue">Default value in case this getter fails to get data.</param>
         /// <returns></returns>
         double GetDouble(string key, double defaultValue = 0.0);
+
+        string GetString(string key, string defaultValue);
+
         /// <summary>
         /// Get a Voile.Color from this data getter.
         /// </summary>
@@ -79,5 +82,15 @@ namespace Voile.Resources.DataReaders
         /// <param name="defaultValue">Default value in case this getter fails to get data.</param>
         /// <returns></returns>
         Vector2 GetVector2(string key, Vector2 defaultValue);
+
+        /// <summary>
+        /// Get a <see cref="Size"/> from this data getter.
+        /// </summary>
+        /// <param name="key">Key of the value.</param>
+        /// <param name="defaultValue">Default value in case this getter fails to get data.</param>
+        /// <returns></returns>
+        Size GetSize(string key, Size defaultValue);
+
+        T[] GetArray<T>(string key, T[] defaultValue);
     }
 }

Voile/Source/Resources/DataReaders/TomlDataReader.cs

@@ -9,163 +9,129 @@ namespace Voile.Resources.DataReaders;
 /// </summary>
 public class TomlDataReader : IStreamDataReader, IDataValidator, IStreamKeyValueGetter
 {
-    public string ExpectedHeader { get; private set; } = string.Empty;
+    public TomlDataReader() { }
-    public TomlDataReader(string expectedHeader)
-    {
-        ExpectedHeader = expectedHeader;
-    }
 
     public void Read(Stream data)
     {
-        using (var reader = new StreamReader(data))
+        using var reader = new StreamReader(data);
+        _table = TOML.Parse(reader);
+        _valid = _table != null;
+    }
+
+    public bool Valid() => _valid;
+
+    public bool HasKey(string key)
+    {
+        return _table != null &&
+               _table.HasKey(key);
+    }
+
+    public IEnumerable<string> GetSubKeys()
+    {
+        if (_table == null)
+            return Enumerable.Empty<string>();
+
+        return _table.Keys
+            .Where(k => _table[k].IsTable)
+            .ToList();
+    }
+
+    public IEnumerable<string> GetSubKeysRecursive(string prefix = "")
+    {
+        if (_table == null)
+            yield break;
+
+        foreach (var key in _table.Keys)
         {
-            _table = TOML.Parse(reader);
+            var fullKey = string.IsNullOrEmpty(prefix) ? key : $"{prefix}.{key}";
-            _valid = _table.HasKey(ExpectedHeader);
+            if (_table[key].IsTable)
+            {
+                var subReader = GetSubReader(key);
+                if (subReader != null)
+                {
+                    foreach (var subKey in subReader.GetSubKeysRecursive(fullKey))
+                        yield return subKey;
+
+                    yield return fullKey;
+                }
+            }
         }
     }
 
+    public IEnumerable<string> GetSubKeys(string subPath)
+    {
+        var subReader = GetSubReader(subPath);
+        if (subReader?._table == null)
+            return Enumerable.Empty<string>();
+
+        return subReader._table.Keys
+            .Where(k => subReader._table[k].IsTable)
+            .ToList();
+    }
+
+    public TomlDataReader? GetSubReader(string path)
+    {
+        var current = _table;
+        foreach (var part in path.Split('.'))
+        {
+            if (current == null || !current.HasKey(part) || !current[part].IsTable)
+                return null;
+
+            current = current[part].AsTable;
+        }
+
+        return new TomlDataReader { _table = current, _valid = true };
+    }
+
     public bool GetBool(string key, bool defaultValue = false)
-    {
+        => TryGetNode(key, out var node) && node.IsBoolean ? node.AsBoolean : defaultValue;
-        if (_table is null)
-        {
-            return defaultValue;
-        }
-
-        var dataTable = _table[ExpectedHeader];
-
-        if (!dataTable.HasKey(key))
-        {
-            return defaultValue;
-        }
-
-        var tableValue = dataTable[key];
-
-        if (!tableValue.IsBoolean)
-        {
-            return defaultValue;
-        }
-
-        return tableValue.AsBoolean;
-    }
 
     public int GetInt(string key, int defaultValue = 0)
-    {
+        => TryGetNode(key, out var node) && node.IsInteger ? node.AsInteger : defaultValue;
-        if (_table is null)
-        {
-            return defaultValue;
-        }
-
-        var dataTable = _table[ExpectedHeader];
-
-        if (!dataTable.HasKey(key))
-        {
-            return defaultValue;
-        }
-
-        var tableValue = dataTable[key];
-
-        if (!tableValue.IsInteger)
-        {
-            return defaultValue;
-        }
-
-        return tableValue.AsInteger;
-    }
 
     public long GetLong(string key, long defaultValue = 0)
-    {
+        => TryGetNode(key, out var node) && node.IsInteger ? node.AsInteger.Value : defaultValue;
-        if (_table is null)
-        {
-            return defaultValue;
-        }
-
-        var dataTable = _table[ExpectedHeader];
-
-        if (!dataTable.HasKey(key))
-        {
-            return defaultValue;
-        }
-
-        var tableValue = dataTable[key];
-
-        if (!tableValue.IsInteger)
-        {
-            return defaultValue;
-        }
-
-        return tableValue.AsInteger.Value;
-    }
 
     public float GetFloat(string key, float defaultValue = 0)
     {
-        if (_table is null)
+        if (!TryGetNode(key, out var node))
-        {
             return defaultValue;
-        }
 
-        var dataTable = _table[ExpectedHeader];
+        if (node.IsFloat) return node.AsFloat;
-
+        if (node.IsInteger) return node.AsInteger;
-        if (!dataTable.HasKey(key))
+        return defaultValue;
-        {
-            return defaultValue;
-        }
-
-        var tableValue = dataTable[key];
-
-        if (!tableValue.IsFloat)
-        {
-            if (tableValue.IsInteger) return (float)tableValue.AsInteger.Value;
-            return defaultValue;
-        }
-
-        return tableValue.AsFloat;
     }
 
     public double GetDouble(string key, double defaultValue = 0)
+        => TryGetNode(key, out var node) && node.IsFloat ? node.AsFloat : defaultValue;
+
+    public string GetString(string key, string defaultValue)
     {
-        if (_table is null)
+        if (!TryGetNode(key, out var node))
         {
             return defaultValue;
         }
 
-        var dataTable = _table[ExpectedHeader];
+        if (node.IsString)
-
-        if (!dataTable.HasKey(key))
         {
-            return defaultValue;
+            return node.AsString;
         }
 
-        if (!dataTable.IsFloat)
+        return defaultValue;
-        {
-            return defaultValue;
-        }
-
-        return dataTable.AsFloat.Value;
     }
 
     public Color GetColor(string key, Color defaultValue)
     {
-        if (_table is null)
+        if (!TryGetNode(key, out var node))
-        {
             return defaultValue;
-        }
 
-        var dataTable = _table[ExpectedHeader];
+        if (node.IsInteger)
-
-        if (!dataTable.HasKey(key))
         {
-            return defaultValue;
+            return new Color(node.AsInteger);
         }
-
+        else if (node.IsArray)
-        var colorNode = dataTable[key];
-
-        if (colorNode.IsInteger)
         {
-            return new Color(colorNode.AsInteger);
+            var colorArray = node.AsArray;
-        }
-        else if (colorNode.IsArray)
-        {
-            var colorArray = colorNode.AsArray;
 
             var rNode = colorArray[0];
             var gNode = colorArray[1];
@@ -185,45 +151,102 @@ public class TomlDataReader : IStreamDataReader, IDataValidator, IStreamKeyValue
 
             return new Color((byte)r, (byte)g, (byte)b, (byte)a);
         }
-        else if (colorNode.IsString)
+        else if (node.IsString)
         {
-            var colorHexString = colorNode.AsString.Value;
+            var colorHexString = node.AsString.Value;
             return Color.FromHexString(colorHexString);
         }
         else
         {
-            throw new ArgumentException("Color can only be represented as an array of integers in the range of 0-255, array of floats (0-1), hexadecimal, or hex string.");
+            return defaultValue;
         }
     }
 
     public Vector2 GetVector2(string key, Vector2 defaultValue)
     {
-        if (_table is null)
+        if (!TryGetNode(key, out var node) || !node.IsArray || node.AsArray.RawArray.Count != 2)
-        {
             return defaultValue;
-        }
 
-        var dataTable = _table[ExpectedHeader];
+        var arr = node.AsArray;
-
+        return new Vector2(arr[0], arr[1]);
-        if (!dataTable.HasKey(key))
-        {
-            return defaultValue;
-        }
-
-        var vector2Node = dataTable[key];
-
-        if (!vector2Node.IsArray)
-        {
-            return defaultValue;
-        }
-
-        var vector2Array = vector2Node.AsArray;
-
-        return new Vector2(vector2Array[0], vector2Array[1]);
     }
 
-    public bool Valid() => _valid;
+    public Size GetSize(string key, Size defaultValue)
+    {
+        if (!TryGetNode(key, out var node))
+            return defaultValue;
+
+        if (node.IsInteger)
+        {
+            return new Size(node.AsInteger);
+        }
+        else if (node.IsFloat)
+        {
+            return new Size(node.AsFloat);
+        }
+        else if (node.IsArray)
+        {
+            var sizeArray = node.AsArray;
+
+            var lNode = sizeArray[0];
+            var rNode = sizeArray[1];
+            var tNode = sizeArray[2];
+            var bNode = sizeArray[3];
+
+            var l = lNode.IsInteger ? lNode.AsInteger : 0;
+            var t = tNode.IsInteger ? tNode.AsInteger : 0;
+            var r = rNode.IsInteger ? rNode.AsInteger : 0;
+            var b = bNode.IsInteger ? bNode.AsInteger : 0;
+
+            return new Size(l, r, t, b);
+        }
+
+        return defaultValue;
+    }
+
+    public T[] GetArray<T>(string key, T[] defaultValue)
+    {
+        throw new NotImplementedException("Generic array reading not implemented yet.");
+    }
+
+    private bool TryGetNode(string key, out TomlNode node)
+    {
+        node = null!;
+        if (_table == null)
+            return false;
+
+        var current = _table;
+        var parts = key.Split('.');
+
+        for (int i = 0; i < parts.Length; i++)
+        {
+            if (!current.HasKey(parts[i]))
+                return false;
+
+            var child = current[parts[i]];
+
+            if (i == parts.Length - 1)
+            {
+                node = child;
+                return true;
+            }
+
+            if (!child.IsTable)
+                return false;
+
+            current = child.AsTable;
+        }
+
+        return false;
+    }
 
     private TomlTable? _table;
     private bool _valid;
+
+    // Internal use for subreaders
+    private TomlDataReader(TomlTable table)
+    {
+        _table = table;
+        _valid = true;
+    }
 }

Voile/Source/Resources/Font.cs

@@ -104,7 +104,7 @@ public class Font : Resource, IUpdatableResource, IDisposable
             }
         }
 
-        float totalHeight = maxAscent + maxDescent;
+        float totalHeight = Size;
         return new Rect(totalWidth, totalHeight);
     }
 

Voile/Source/Resources/Loaders/StyleLoader.cs

@@ -1,17 +0,0 @@
-using Voile.UI;
-
-namespace Voile.Resources;
-
-public class StyleLoader : ResourceLoader<Style>
-{
-    public override IEnumerable<string> SupportedExtensions =>
-    [
-        ".toml"
-    ];
-
-    protected override Style LoadResource(string path)
-    {
-        // TODO: implement loading styles.
-        return new Style(string.Empty);
-    }
-}

Voile/Source/Resources/ResourceManager.cs

@@ -269,7 +269,6 @@ namespace Voile.Resources
                          | NotifyFilters.CreationTime
                          | NotifyFilters.DirectoryName
                          | NotifyFilters.FileName
-                         | NotifyFilters.LastAccess
                          | NotifyFilters.LastWrite
                          | NotifyFilters.Security
                          | NotifyFilters.Size;
@@ -351,7 +350,6 @@ namespace Voile.Resources
             { typeof(Sound), new SoundLoader()},
             {typeof(Texture2d), new Texture2dLoader()},
             {typeof(Font), new FontLoader()},
-            { typeof(Style), new StyleLoader()}
         };
 
         private static readonly Dictionary<Type, object> _resourceSaverAssociations = new()

Voile/Source/Systems/ParticleSystem.cs

@@ -62,7 +62,7 @@ public class ParticleEmitterSettingsResourceLoader : ResourceLoader<ParticleEmit
     {
         var settings = new ParticleEmitterSettings();
 
-        var reader = new TomlDataReader("ParticleEmitterSettings");
+        var reader = new TomlDataReader();
         reader.Read(VirtualFileSystem.Read(path));
 
         settings.Local = reader.GetBool("Local", true);

Voile/Source/UI/Containers/Container.cs

@@ -16,6 +16,8 @@ public abstract class Container : UIElement, IParentableElement
     /// </summary>
     public bool ConfineToContents { get; set; } = false;
 
+    public override string? StyleElementName => nameof(Container);
+
     public override Rect MinimumSize => _minimumSize;
 
     public Container()
@@ -122,6 +124,7 @@ public abstract class Container : UIElement, IParentableElement
 
     public void AddChild(UIElement child)
     {
+        // child.StyleSheetOverride = StyleSheet;
         _children.Add(child);
         child.SetParent(this);
 
@@ -137,12 +140,18 @@ public abstract class Container : UIElement, IParentableElement
         Update();
     }
 
-    public override void Render(RenderSystem renderer, Style style)
+    protected override void OnRender(RenderSystem renderer, Style style)
     {
         foreach (var child in Children)
         {
             if (child is not IRenderableElement renderable) continue;
-            renderable.Render(renderer, style);
+
+            if (!child.TryGetStyle(StyleSheet.Value, out var childStyle))
+            {
+                childStyle = new Style();
+            }
+
+            renderable.Render(renderer, childStyle);
         }
     }
 

Voile/Source/UI/Containers/FillContainer.cs

@@ -23,9 +23,9 @@ public class FillContainer : Container
 
     }
 
-    public override void Render(RenderSystem renderer, Style style)
+    protected override void OnRender(RenderSystem renderer, Style style)
     {
-        base.Render(renderer, style);
+        base.OnRender(renderer, style);
 
         Rect parentSize;
 
@@ -52,6 +52,11 @@ public class FillContainer : Container
     {
         base.OnUpdate();
         Size = _lastParentSize;
+
+        if (Children.Count != 0)
+        {
+            Children[0].Size = Size;
+        }
     }
 
     private Rect _lastParentSize = Rect.Zero;

Voile/Source/UI/Containers/MarginContainer.cs

@@ -2,53 +2,21 @@ using System.Numerics;
 
 namespace Voile.UI.Containers;
 
-/// <summary>
-/// Represents the margin offsets applied around an element.
-/// </summary>
-public struct Margin
-{
-    public float Left;
-    public float Right;
-    public float Top;
-    public float Bottom;
-
-    public Margin(float uniform)
-    {
-        Left = Right = Top = Bottom = uniform;
-    }
-
-    public Margin(float horizontal, float vertical)
-    {
-        Left = Right = horizontal;
-        Top = Bottom = vertical;
-    }
-
-    public Margin(float left, float right, float top, float bottom)
-    {
-        Left = left;
-        Right = right;
-        Top = top;
-        Bottom = bottom;
-    }
-
-    public static Margin Zero => new Margin(0);
-}
-
 public class MarginContainer : Container
 {
     /// <summary>
     /// The margin to apply around the contents of this container.
     /// </summary>
-    public Margin Margin { get; set; }
+    public Size Margin { get; set; }
 
     /// <summary>
     /// Specifies if this <see cref="MarginContainer"/> will fill to parent size.
     /// </summary>
     public bool Fill { get; set; } = true;
 
-    public MarginContainer() : this(new Margin()) { }
+    public MarginContainer() : this(new Size()) { }
 
-    public MarginContainer(Margin margin)
+    public MarginContainer(Size margin)
     {
         Margin = margin;
     }
@@ -58,7 +26,10 @@ public class MarginContainer : Container
         base.OnUpdate();
         if (Parent == null) return;
 
-        Size = Parent.Size;
+        if (Size != Parent.Size)
+        {
+            Size = Parent.Size;
+        }
     }
 
     public override void Arrange()

Voile/Source/UI/IElement.cs

@@ -63,7 +63,7 @@ public interface IUpdatableElement
     /// <summary>
     /// Update this element.
     /// </summary>
-    void Update();
+    void Update(float dt = 0.0f);
     /// <summary>
     /// Marks this element as changed, requiring an update.
     /// </summary>

Voile/Source/UI/Style.cs

@@ -1,13 +1,230 @@
+using System.Diagnostics.CodeAnalysis;
 using Voile.Resources;
+using Voile.Resources.DataReaders;
+using Voile.UI.Containers;
+using Voile.VFS;
 
 namespace Voile.UI;
 
 /// <summary>
-/// A resource containing UI style settings.
+/// UI style settings.
 /// </summary>
-public class Style : TextDataResource
+public class Style
 {
-    public Style(string path) : base(path)
+    public enum AnimationType
     {
+        Linear,
+        EaseIn,
+        EaseOut,
+        EaseInOut
+    }
+
+    public float TransitionDuration = 0f;
+    public AnimationType TransitionType = AnimationType.Linear;
+
+    public Style() { }
+
+    public Size? Padding { get; set; }
+    public Color? BackgroundColor { get; set; }
+    public Size? BorderSize { get; set; }
+    public Color? BorderColor { get; set; }
+    public float CornerRadius { get; set; }
+    public Color? TextColor { get; set; }
+
+    /// <summary>
+    /// Merges this <see cref="Style"/> with a different one.<br />
+    /// Properties that are not set for this <see cref="Style"/> will be inherited from <paramref name="overrideStyle"/>.
+    /// </summary>
+    /// <param name="overrideStyle"></param>
+    /// <returns>A merged <see cref="Style"/>.</returns>
+    public Style Merge(Style overrideStyle)
+    {
+        return new Style
+        {
+            BackgroundColor = overrideStyle.BackgroundColor != default ? overrideStyle.BackgroundColor : BackgroundColor,
+            TextColor = overrideStyle.TextColor != default ? overrideStyle.TextColor : TextColor,
+            Padding = overrideStyle.Padding != default ? overrideStyle.Padding : Padding,
+            BorderSize = overrideStyle.BorderSize != default ? overrideStyle.BorderSize : BorderSize,
+            BorderColor = overrideStyle.BorderColor != default ? overrideStyle.BorderColor : BorderColor,
+        };
     }
 }
+
+public class StyleSheetLoader : ResourceLoader<StyleSheet>
+{
+    public override IEnumerable<string> SupportedExtensions => [".toml"];
+
+    protected override StyleSheet LoadResource(string path)
+    {
+        var result = new StyleSheet(path);
+        var allStyles = new Dictionary<string, Style>();
+
+        using var stream = VirtualFileSystem.Read(path);
+        _reader.Read(stream);
+
+        foreach (var styleKey in _reader.GetSubKeysRecursive())
+        {
+            var subReader = _reader.GetSubReader(styleKey);
+            if (subReader == null || !subReader.Valid())
+                continue;
+
+            var style = ParseStyle(subReader, styleKey);
+            if (style != null)
+            {
+                allStyles[styleKey] = style;
+            }
+        }
+
+        foreach (var kvp in allStyles)
+        {
+            var finalStyle = GetMergedStyle(kvp.Key, allStyles);
+            result.Add(kvp.Key, finalStyle);
+        }
+
+        return result;
+    }
+
+    private Style ParseStyle(TomlDataReader reader, string input)
+    {
+        var style = new Style();
+
+        string easingName = reader.GetString("TransitionType", "Linear");
+
+        if (!Enum.TryParse<Style.AnimationType>(easingName, true, out var easing))
+            easing = Style.AnimationType.Linear;
+
+        style.TransitionType = easing;
+
+
+        if (reader.HasKey("BackgroundColor"))
+            style.BackgroundColor = reader.GetColor("BackgroundColor", Color.Transparent);
+
+        if (reader.HasKey("TextColor"))
+            style.TextColor = reader.GetColor("TextColor", Color.Black);
+
+        if (reader.HasKey("Padding"))
+            style.Padding = reader.GetSize("Padding", Size.Zero);
+
+        if (reader.HasKey("BorderSize"))
+            style.BorderSize = reader.GetSize("BorderSize", Size.Zero);
+
+        if (reader.HasKey("BorderColor"))
+            style.BorderColor = reader.GetColor("BorderColor", Color.Transparent);
+
+        return style;
+    }
+
+    private Style GetMergedStyle(string fullKey, Dictionary<string, Style> allStyles)
+    {
+        var parts = fullKey.Split('.');
+        var merged = new Style();
+
+        for (int i = 1; i <= parts.Length; i++)
+        {
+            var subKey = string.Join('.', parts.Take(i));
+            if (allStyles.TryGetValue(subKey, out var parentStyle))
+            {
+                merged = merged.Merge(parentStyle);
+            }
+        }
+
+        return merged;
+    }
+
+    private readonly TomlDataReader _reader = new();
+}
+
+public class StyleSheet : Resource
+{
+    public StyleSheet(string path) : base(path)
+    {
+    }
+
+    public StyleSheet(Dictionary<string, Style> styles) : base(string.Empty)
+    {
+        _styles = styles;
+    }
+
+    public void Add(string key, Style style) => _styles.Add(key, style);
+
+    public bool TryGet(string styleName, [NotNullWhen(true)] out Style? style)
+    {
+        return _styles.TryGetValue(styleName, out style);
+    }
+
+    public static StyleSheet Default => new(new Dictionary<string, Style>()
+    {
+        {"Label", new Style()
+        {
+            TextColor = Color.FromHexString("#161616"),
+            BackgroundColor = Color.DarkRed,
+            BorderSize = new Size(2.0f),
+            BorderColor = Color.Red
+        }},
+        { "Button", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#0f62fe"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Normal", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#0f62fe"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Hovered", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#0353e9"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Pressed", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#002d9c"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Danger", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#da1e28"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Danger.Normal", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#da1e28"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Danger.Hovered", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#ba1b23"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Button.Danger.Pressed", new Style()
+        {
+            Padding = new Size(8.0f),
+            BackgroundColor = Color.FromHexString("#750e13"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Container", new Style()
+        {
+            BackgroundColor = Color.FromHexString("#ffffff"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Container.Layer01", new Style()
+        {
+            BackgroundColor = Color.FromHexString("#f4f4f4"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+        {"Container.Layer02", new Style()
+        {
+            BackgroundColor = Color.FromHexString("#e8e8e8"),
+            TextColor = Color.FromHexString("#ffffff"),
+        }},
+    });
+
+    private Dictionary<string, Style> _styles = new();
+}

Voile/Source/UI/StyleAnimator.cs

@@ -0,0 +1,56 @@
+namespace Voile.UI;
+
+public class StyleAnimator
+{
+    public bool IsComplete => _elapsed >= _duration;
+
+    public StyleAnimator(Style from, Style to, float duration)
+    {
+        _from = from;
+        _to = to;
+
+        _duration = duration;
+        _elapsed = 0f;
+    }
+
+    public static float Ease(float t, Style.AnimationType type)
+    {
+        return type switch
+        {
+            Style.AnimationType.Linear => t,
+            Style.AnimationType.EaseIn => t * t,
+            Style.AnimationType.EaseOut => t * (2 - t),
+            Style.AnimationType.EaseInOut => t < 0.5f
+                ? 2 * t * t
+                : -1 + (4 - 2 * t) * t,
+            _ => t
+        };
+    }
+
+    public Style Update(float deltaTime)
+    {
+        _elapsed = MathF.Min(_elapsed + deltaTime, _duration);
+        float t = _duration == 0 ? 1 : _elapsed / _duration;
+        float easedT = Ease(t, _to.TransitionType);
+
+        return LerpStyle(_from, _to, easedT);
+    }
+
+    private static Style LerpStyle(Style from, Style to, float t)
+    {
+        var result = new Style()
+        {
+            BackgroundColor = MathUtils.LerpColor(from.BackgroundColor ?? Color.Transparent, to.BackgroundColor ?? Color.Transparent, t),
+            TextColor = MathUtils.LerpColor(from.TextColor ?? Color.Black, to.TextColor ?? Color.Black, t),
+            Padding = MathUtils.LerpSize(from.Padding ?? Size.Zero, to.Padding ?? Size.Zero, t),
+            BorderColor = MathUtils.LerpColor(from.BorderColor ?? Color.Transparent, to.BorderColor ?? Color.Transparent, t),
+            BorderSize = MathUtils.LerpSize(from.BorderSize ?? Size.Zero, to.BorderSize ?? Size.Zero, t),
+            TransitionType = to.TransitionType
+        };
+
+        return result;
+    }
+
+    private Style _from, _to;
+    private float _duration, _elapsed;
+}

Voile/Source/UI/UIElement.cs

@@ -1,4 +1,6 @@
+using System.Diagnostics.CodeAnalysis;
 using System.Numerics;
+using System.Text;
 using Voile.Rendering;
 
 namespace Voile.UI;
@@ -13,6 +15,23 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
     public Vector2 LocalPosition { get; set; } = Vector2.Zero;
     public Vector2 GlobalPosition => _parent?.GlobalPosition + LocalPosition ?? LocalPosition;
 
+    public string StyleName => $"{StyleElementName ?? "UIElement"}{GetStyleVariantString()}{ConstructStyleModifiers(StyleModifiers)}";
+
+    /// <summary>
+    /// An element name for style.
+    /// </summary>
+    public virtual string? StyleElementName { get; }
+
+    public string StyleVariant { get; set; } = string.Empty;
+
+    /// <summary>
+    /// List of style modifiers for this <see cref="UIElement"/>.
+    /// </summary>
+    public virtual string[]? StyleModifiers { get; }
+
+    public ResourceRef<StyleSheet> StyleSheet => Parent?.StyleSheet ?? StyleSheetOverride;
+    public ResourceRef<StyleSheet> StyleSheetOverride { get; set; } = ResourceRef<StyleSheet>.Empty();
+
     /// <summary>
     /// Parent <see cref="UIElement"/> of this element.
     /// </summary>
@@ -47,6 +66,11 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
     public abstract Rect MinimumSize { get; }
     public bool Dirty => _dirty;
 
+    public bool TryGetStyle(StyleSheet styleSheet, [NotNullWhen(true)] out Style? style)
+    {
+        return styleSheet.TryGet(StyleName, out style);
+    }
+
     public virtual void MarkDirty()
     {
         if (Parent != null && !Parent.Dirty)
@@ -67,7 +91,7 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
         MarkDirty();
     }
 
-    public void Update()
+    public void Update(float dt = 0.0f)
     {
         if (!_dirty) return;
         _dirty = false;
@@ -83,9 +107,74 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
         }
     }
 
-    public abstract void Render(RenderSystem renderer, Style style);
+    public void Render(RenderSystem renderer, Style style)
+    {
+        RenderStyleBox(renderer, style);
+        OnRender(renderer, style);
+    }
+
+    protected abstract void OnRender(RenderSystem renderer, Style style);
     protected abstract void OnUpdate();
 
+    /// <summary>
+    /// Renders a stylebox from a given style.
+    /// </summary>
+    /// <param name="renderer"></param>
+    /// <param name="style"></param>
+    protected void RenderStyleBox(RenderSystem renderer, Style style)
+    {
+        var backgroundColor = style.BackgroundColor ?? Color.Transparent;
+        var borderColor = style.BorderColor ?? Color.Transparent;
+        var borderSize = style.BorderSize;
+
+        var borderLeft = borderSize?.Left ?? 0;
+        var borderRight = borderSize?.Right ?? 0;
+        var borderTop = borderSize?.Top ?? 0;
+        var borderBottom = borderSize?.Bottom ?? 0;
+
+        renderer.SetTransform(GlobalPosition, Vector2.Zero);
+
+        renderer.DrawRectangle(new Vector2(Size.Width, Size.Height), backgroundColor);
+
+        if (borderLeft > 0)
+        {
+            renderer.SetTransform(GlobalPosition, Vector2.Zero);
+            renderer.DrawRectangle(
+                new Vector2(borderLeft, Size.Height),
+                borderColor
+            );
+        }
+
+        if (borderTop > 0)
+        {
+            renderer.SetTransform(GlobalPosition, Vector2.Zero);
+            renderer.DrawRectangle(
+                new Vector2(Size.Width, borderTop),
+                borderColor
+            );
+        }
+
+        if (borderRight > 0)
+        {
+            var rightX = GlobalPosition.X + Size.Width - borderRight;
+            renderer.SetTransform(new Vector2(rightX, GlobalPosition.Y), Vector2.Zero);
+            renderer.DrawRectangle(
+                new Vector2(borderRight, Size.Height),
+                borderColor
+            );
+        }
+
+        if (borderBottom > 0)
+        {
+            var bottomY = GlobalPosition.Y + Size.Height - borderBottom;
+            renderer.SetTransform(new Vector2(GlobalPosition.X, bottomY), Vector2.Zero);
+            renderer.DrawRectangle(
+                new Vector2(Size.Width, borderBottom),
+                borderColor
+            );
+        }
+    }
+
     public void DrawSize(RenderSystem renderer)
     {
         renderer.SetTransform(GlobalPosition, Vector2.Zero);
@@ -112,6 +201,30 @@ public abstract class UIElement : IElement, IRenderableElement, IResizeableEleme
         LocalPosition = Anchor.Calculate(parentPosition, parentRect, Size) + new Vector2(AnchorOffset.X, AnchorOffset.Y);
     }
 
+    private string ConstructStyleModifiers(string[]? modifiers)
+    {
+        if (modifiers == null)
+        {
+            return string.Empty;
+        }
+
+        var sb = new StringBuilder();
+        foreach (var modifier in modifiers)
+        {
+            sb.Append($".{modifier}");
+        }
+
+        return sb.ToString();
+    }
+
+    private string GetStyleVariantString()
+    {
+        if (string.IsNullOrEmpty(StyleVariant))
+            return string.Empty;
+
+        return $".{StyleVariant}";
+    }
+
     private bool _dirty = true;
     private Rect _size = Rect.Zero;
 

Voile/Source/UI/UIInputContext.cs

@@ -3,19 +3,48 @@ using Voile.Input;
 
 namespace Voile.UI;
 
+/// <summary>
+/// Input information for UI elements.
+/// </summary>
 public class UIInputContext
 {
+    /// <summary>
+    /// Current action handled by this <see cref="UIElement"/>.
+    /// </summary>
     public IInputAction Action { get; }
+    /// <summary>
+    /// Current mouse position.
+    /// </summary>
     public Vector2 MousePosition { get; }
+    /// <summary>
+    /// Determines if a mouse button was pressed.
+    /// </summary>
     public bool MousePressed { get; set; }
+    /// <summary>
+    /// Determines if a mouse button was released.
+    /// </summary>
     public bool MouseReleased { get; set; }
+    /// <summary>
+    /// Determines if a mouse button is currently held.
+    /// </summary>
     public bool MouseDown { get; set; }
-
+    /// <summary>
+    /// Name of the current <see cref="IInputAction"/>.
+    /// </summary>
     public string ActionName { get; }
-
+    /// <summary>
+    /// Keycode of a currently pressed character.
+    /// </summary>
     public int CharPressed { get; }
+
+    /// <summary>
+    /// Determines if this <see cref="UIInputContext"/> registered any character input from keyboard.
+    /// </summary>
     public bool HasCharInput => CharPressed != 0;
 
+    /// <summary>
+    /// Determines if this context's input was already handled and no longer needs to be processed.
+    /// </summary>
     public bool Handled => _handled;
 
     /// <summary>

Voile/Source/UI/UISystem.cs

@@ -1,10 +1,11 @@
 using System.Numerics;
 using Voile.Input;
 using Voile.Rendering;
+using Voile.Resources;
 
 namespace Voile.UI;
 
-public class UISystem : IUpdatableSystem, IRenderableSystem
+public class UISystem : IUpdatableSystem, IRenderableSystem, IReloadableSystem
 {
     public IReadOnlyList<IElement> Elements => _elements;
 
@@ -14,25 +15,23 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
 
     public UISystem(InputSystem inputSystem)
     {
-        _style = ResourceRef<Style>.Empty();
         _input = inputSystem;
     }
 
-    public UISystem(InputSystem inputSystem, ResourceRef<Style> style)
+    public UISystem(InputSystem inputSystem, List<UIElement> elements)
     {
         _input = inputSystem;
-        _style = style;
-    }
-
-    public UISystem(InputSystem inputSystem, ResourceRef<Style> style, List<UIElement> elements)
-    {
-        _input = inputSystem;
-        _style = style;
         _elements = elements;
     }
 
+    public void SetStyleSheet(ResourceRef<StyleSheet> styleSheet)
+    {
+        _styleSheet = styleSheet;
+    }
+
     public void AddElement(UIElement element)
     {
+        element.StyleSheetOverride = _styleSheet;
         _elements.Add(element);
         _inputElementIndices.Add(element.GlobalPosition, _elements.Count - 1);
     }
@@ -40,30 +39,33 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
 
     public void Update(double deltaTime)
     {
-        HandleInput();
+        // HandleInput();
     }
 
     public void Render(RenderSystem renderer)
     {
         // Update elements each time UI system is rendered.
+        HandleInput();
+
         foreach (var element in _elements)
         {
             if (element is not IUpdatableElement updatable) continue;
             updatable.Update();
         }
 
+
         foreach (var element in _elements)
         {
             if (element is IRenderableElement renderable)
             {
-                // TODO: normally you'd load a default style if the one supplied is empty,
+                var styleSheet = _styleSheet.Value;
-                // but for now this will do.
+
-                if (!_style.TryGetValue(out var value))
+                if (!styleSheet.TryGet(element.StyleName, out var style))
                 {
-                    value = new Style(string.Empty);
+                    style = new Style();
                 }
 
-                renderable.Render(renderer, value);
+                renderable.Render(renderer, style);
             }
         }
 
@@ -76,6 +78,11 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
         }
     }
 
+    public void Reload()
+    {
+        throw new NotImplementedException();
+    }
+
     private void DrawDebugForElement(RenderSystem renderer, UIElement element)
     {
         var size = new Vector2(element.Size.Width, element.Size.Height);
@@ -138,7 +145,7 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
             {
                 MouseDown = _input.IsMouseButtonDown(MouseButton.Left),
                 MouseReleased = _input.IsMouseButtonReleased(MouseButton.Left),
-                MousePressed = _input.IsMouseButtonReleased(MouseButton.Left),
+                MousePressed = _input.IsMouseButtonPressed(MouseButton.Left),
             };
             PropagateInput(_elements, context);
         }
@@ -150,6 +157,8 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
         {
             var element = elements[i];
 
+            // if (!element.ContainsPoint(context.MousePosition)) continue;
+
             if (element is IInputElement inputElement && !inputElement.IgnoreInput)
             {
                 inputElement.Input(context);
@@ -167,7 +176,7 @@ public class UISystem : IUpdatableSystem, IRenderableSystem
         return false;
     }
 
-    private ResourceRef<Style> _style;
+    private ResourceRef<StyleSheet> _styleSheet;
     private List<UIElement> _elements = new();
     private InputSystem _input;
 

Voile/Source/UI/Widgets/Button.cs

@@ -1,6 +1,7 @@
 using System.Numerics;
-using Voile.Input;
 using Voile.Rendering;
+using Voile.Resources;
+using Voile.UI.Containers;
 
 namespace Voile.UI.Widgets;
 
@@ -17,31 +18,153 @@ public enum ButtonState
 /// </summary>
 public class Button : Widget
 {
-    public string Label { get; set; } = "Button";
+    public string Text
-    public override Rect MinimumSize => new Rect(Width: 128.0f, Height: 64.0f);
-
-    public Button(string label, Action pressedAction)
     {
-        Label = label;
+        get => _text; set
+        {
+            _text = value;
+            MarkDirty();
+        }
+    }
+
+    public ButtonState CurrentState { get; private set; } = ButtonState.Normal;
+
+    public override Rect MinimumSize => Padding + _textSize;
+
+    /// <summary>
+    /// <see cref="FontSet"/> to use with this button.
+    /// </summary>
+    public FontSet FontSet { get; set; } = new();
+    public Size Padding
+    {
+        get => _padding; set
+        {
+            _padding = value;
+        }
+    }
+
+    public override string? StyleElementName => nameof(Button);
+    public override string[]? StyleModifiers =>
+    [
+        CurrentState.ToString()
+    ];
+
+    public Button(string text, ResourceRef<Font> fontOverride, Action pressedAction)
+    {
+        _text = text;
         _pressedAction = pressedAction;
+
+        FontSet.AddFont(fontOverride);
+
+        MarkDirty();
+        Update();
     }
 
-    public override void Render(RenderSystem renderer, Style style)
+    public Button(string text, FontSet fontSet)
     {
-        // TODO: use a button color from style.
+        _text = text;
-        renderer.SetTransform(GlobalPosition, Vector2.Zero);
+
-        renderer.DrawRectangle(new Vector2(MinimumSize.Width, MinimumSize.Height), new Color(0.25f, 0.25f, 0.25f));
+        FontSet = fontSet;
+
+        MarkDirty();
+        Update();
     }
 
+    public Button(string text, FontSet fontSet, Action pressedAction)
+    {
+        _text = text;
+        _pressedAction = pressedAction;
+
+        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);
+        renderer.SetTransform(textPosition, Vector2.Zero);
+        renderer.DrawText(_suitableFont, _text, textColor);
+    }
+
+    protected virtual void Pressed() { }
+
     protected override void OnInput(UIInputContext action)
     {
+        bool isHovering = ContainsPoint(action.MousePosition);
 
+        if (action.MousePressed && isHovering)
+        {
+            _isHeldDown = true;
+            CurrentState = ButtonState.Pressed;
+        }
+        else if (action.MouseReleased)
+        {
+            if (_isHeldDown && isHovering)
+            {
+                _pressedAction?.Invoke();
+                Pressed();
+            }
+
+            _isHeldDown = false;
+            CurrentState = isHovering ? ButtonState.Hovered : ButtonState.Normal;
+        }
+        else
+        {
+            if (_isHeldDown)
+            {
+                CurrentState = ButtonState.Pressed; // keep showing as pressed
+            }
+            else if (isHovering)
+            {
+                CurrentState = ButtonState.Hovered;
+            }
+            else
+            {
+                CurrentState = ButtonState.Normal;
+            }
+        }
     }
 
     protected override void OnUpdate()
     {
-        throw new NotImplementedException();
+        ResourceRef<Font> fontRef = ResourceRef<Font>.Empty();
+        foreach (var c in _text)
+        {
+            if (FontSet.TryGetFontFor(c, out var fallbackFont))
+            {
+                if (fallbackFont != fontRef)
+                {
+                    fontRef = fallbackFont;
+                }
+            }
+        }
+
+        _suitableFont = fontRef;
+
+        var font = _suitableFont.Value;
+        _textSize = font.Measure(_text);
+
+        Size = _padding + _textSize;
     }
 
-    private Action _pressedAction;
+    private Action? _pressedAction;
+
+    private ResourceRef<Font> _suitableFont = ResourceRef<Font>.Empty();
+
+    private string _text = "Hello, World!";
+    private Rect _textSize = Rect.Zero;
+
+    private Size _padding;
+
+    private bool _isHeldDown;
 }

Voile/Source/UI/Widgets/Label.cs

@@ -18,6 +18,8 @@ public class Label : Widget
         }
     }
 
+    public override string? StyleElementName => nameof(Label);
+
     /// <summary>
     /// <see cref="FontSet"/> to use with this label.
     /// </summary>
@@ -48,12 +50,10 @@ public class Label : Widget
 
     }
 
-    public override void Render(RenderSystem renderer, Style style)
+    protected override void OnRender(RenderSystem renderer, Style style)
     {
-        // TODO: use style here.
-
         renderer.SetTransform(GlobalPosition, Vector2.Zero);
-        renderer.DrawText(_suitableFont, _text, Color.White);
+        renderer.DrawText(_suitableFont, _text, style.TextColor ?? Color.Black);
     }
 
     protected override void OnUpdate()

Voile/Source/UI/Widgets/RectangleWidget.cs

@@ -20,7 +20,7 @@ public class RectangleWidget : Widget
         _hoverColor = color.Lightened(0.25f);
     }
 
-    public override void Render(RenderSystem renderer, Style style)
+    protected override void OnRender(RenderSystem renderer, Style style)
     {
         renderer.SetTransform(GlobalPosition, Vector2.Zero);
         renderer.DrawRectangle(new Vector2(Size.Width, Size.Height), Color);

Voile/Source/UI/Widgets/Widget.cs

@@ -29,10 +29,7 @@ public abstract class Widget : UIElement, IInputElement
     public void Input(UIInputContext context)
     {
         if (context.Handled || IgnoreInput) return;
-        if (ContainsPoint(context.MousePosition))
+        OnInput(context);
-        {
-            OnInput(context);
-        }
     }
 
     /// <summary>

Voile/Source/Utils/MathUtils.cs

@@ -15,6 +15,18 @@ namespace Voile
         [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
         public static float Lerp(float a, float b, float t) => t <= 0f ? a : t >= 1f ? b : LerpUnclamped(a, b, t);
 
+        public static Size LerpSize(Size a, Size b, float t)
+        {
+            t = Math.Clamp(t, 0f, 1f);
+
+            float left = Lerp(a.Left, b.Left, t);
+            float right = Lerp(a.Right, b.Right, t);
+            float top = Lerp(a.Top, b.Top, t);
+            float bottom = Lerp(a.Bottom, b.Bottom, t);
+
+            return new Size(left, right, top, bottom);
+        }
+
         public static Color LerpColor(Color colorA, Color colorB, float t)
         {
             t = Math.Clamp(t, 0f, 1f);

Voile/Source/VFS/FileSystemMountPoint.cs

@@ -14,7 +14,7 @@ public class FileSystemFile : VirtualFile
 
     public override Stream GetStream()
     {
-        return new FileStream(_fsPath, FileMode.Open, FileAccess.Read);
+        return new FileStream(_fsPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
     }
 
     private string _fsPath;