WIP: dirty flag for UI.

Voile/Source/UI/Containers/Container.cs

@@ -8,41 +8,65 @@ namespace Voile.UI.Containers;
 /// </summary>
 public abstract class Container : IElement, IParentableElement, IUpdatableElement, IResizeableElement, IRenderableElement
 {
+    /// <inheritdoc />
     public IReadOnlyList<IElement> Children => _children;
+    /// <inheritdoc />
     public Vector2 Position { get; set; }
+    /// <inheritdoc />
     public Rect MinimumRect { get; set; } = Rect.Zero;
+    /// <inheritdoc />
     public Rect Size { get; set; } = Rect.Zero;
+    /// <inheritdoc />
     public bool Visible { get; set; } = true;
+    /// <inheritdoc />
+    public bool Dirty => _isDirty;
 
     public Container()
     {
-
+        MarkDirty();
     }
 
     public Container(Rect minimumSize)
     {
         MinimumRect = minimumSize;
+
+        MarkDirty();
     }
 
     public Container(Rect minimumSize, List<IElement> children)
     {
         MinimumRect = minimumSize;
         _children = children;
+
+        MarkDirty();
     }
 
     public void Update()
     {
-        Arrange();
-        CalculateMinimumSize();
+        if (!_isDirty) return;
+        _isDirty = false;
+
 
         foreach (var child in _children)
         {
             if (child is not IUpdatableElement updatable) continue;
             updatable.Update();
         }
+
+        Arrange();
+        CalculateMinimumSize();
     }
+
+    public void MarkDirty() => _isDirty = true;
+
+    /// <summary>
+    /// Called when this <see cref="Container"/> has to rearrange its children.
+    /// </summary>
     public abstract void Arrange();
 
+    /// <summary>
+    /// Recalculates a minimum size for this <see cref="Container"/>.
+    /// </summary>
     public void CalculateMinimumSize()
     {
         if (Children.Count == 0)
@@ -81,12 +105,16 @@ public abstract class Container : IElement, IParentableElement, IUpdatableElemen
     public void AddChild(IElement child)
     {
         _children.Add(child);
+
+        MarkDirty();
         Update();
     }
 
     public void RemoveChild(IElement child)
     {
         _children.Remove(child);
+
+        MarkDirty();
         Update();
     }
 
@@ -106,4 +134,5 @@ public abstract class Container : IElement, IParentableElement, IUpdatableElemen
     }
 
     private List<IElement> _children = new();
+    private bool _isDirty;
 }

Voile/Source/UI/IElement.cs

@@ -6,14 +6,31 @@ namespace Voile.UI;
 
 public interface IElement
 {
+    /// <summary>
+    /// This element's position in pixels relative to the viewport top-left edge.
+    /// </summary>
     public Vector2 Position { get; set; }
+    /// <summary>
+    /// The size of this element.
+    /// </summary>
     public Rect Size { get; set; }
 }
 
 public interface IParentableElement
 {
+    /// <summary>
+    /// This parentable element's children.
+    /// </summary>
     public IReadOnlyList<IElement> Children { get; }
+    /// <summary>
+    /// Add a child element to this element.
+    /// </summary>
+    /// <param name="child">Child <see cref="IElement"/>.</param>
     public void AddChild(IElement child);
+    /// <summary>
+    /// Remove a child element from this element.
+    /// </summary>
+    /// <param name="child">Child <see cref="IElement"/> to remove.</param>
     public void RemoveChild(IElement child);
 }
 
@@ -27,18 +44,48 @@ public interface IResizeableElement
 
 public interface IUpdatableElement
 {
+    /// <summary>
+    /// Specifies if this element's properties have changed, making it necessary to update it.
+    /// </summary>
+    public bool Dirty { get; }
+    /// <summary>
+    /// Update this element.
+    /// </summary>
     void Update();
+    /// <summary>
+    /// Marks this element as changed, requiring an update.
+    /// </summary>
+    void MarkDirty();
 }
 
 public interface IRenderableElement
 {
+    /// <summary>
+    /// Specifies if this element should be drawn.
+    /// </summary>
     public bool Visible { get; set; }
+    /// <summary>
+    /// Render this element.
+    /// </summary>
+    /// <param name="renderer">Renderer to call draw operations on.</param>
+    /// <param name="style">A style to use to draw this element.</param>
     public void Render(RenderSystem renderer, Style style);
+    /// <summary>
+    /// Draws this element's size bounds.
+    /// </summary>
+    /// <param name="renderer">Renderer to use.</param>
     public void DrawSize(RenderSystem renderer);
 }
 
 public interface IInputElement
 {
+    /// <summary>
+    /// Specifies if this element should ignore inputs.
+    /// </summary>
     public bool IgnoreInput { get; set; }
+    /// <summary>
+    /// Send an input action to this element.
+    /// </summary>
+    /// <param name="action">Input action to send.</param>
     void Input(IInputAction action);
 }

Voile/Source/UI/Widgets/Widget.cs

@@ -22,11 +22,14 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement, IRes
     public Widget(Vector2 position)
     {
         Position = position;
+        Size = MinimumRect;
     }
 
     /// </inheritdoc>
     public abstract Rect MinimumRect { get; }
 
+    public bool Dirty => _isDirty;
+
     /// <summary>
     /// Called when its time to draw this widget.
     /// </summary>
@@ -41,15 +44,22 @@ public abstract class Widget : IElement, IRenderableElement, IInputElement, IRes
 
     public void Update()
     {
+        if (!_isDirty) return;
+        _isDirty = false;
+
         if (Size == Rect.Zero)
         {
             Size = MinimumRect;
         }
     }
 
+    public void MarkDirty() => _isDirty = true;
+
     public void DrawSize(RenderSystem renderer)
     {
         renderer.SetTransform(Position, Vector2.Zero);
         renderer.DrawRectangleOutline(new Vector2(Size.Width, Size.Height), Color.Red, 2.0f);
     }
+
+    private bool _isDirty = true;
 }