Rename Frame to FillContainer.

Voile/Source/UI/Containers/FillContainer.cs

@@ -0,0 +1,61 @@
+using Voile.Rendering;
+
+namespace Voile.UI.Containers;
+
+/// <summary>
+/// A special container that occupies the entire available size of the parent. <br />
+/// Usually used as a root element for the UI system.
+/// </summary>
+public class FillContainer : Container
+{
+    public FillContainer()
+    {
+
+    }
+
+    public FillContainer(Rect minimumSize) : base(minimumSize)
+    {
+
+    }
+
+    public override void Arrange()
+    {
+
+    }
+
+    public override void Render(RenderSystem renderer, Style style)
+    {
+        base.Render(renderer, style);
+
+        Rect parentSize;
+
+        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();
+
+        if (Size == _lastParentSize) return;
+
+        Size = _lastParentSize;
+    }
+
+    private Rect _lastParentSize = Rect.Zero;
+}