Add doc comments and cleanup code a bit.

src/Avalonia.Visuals/Media/Drawing.cs

@@ -1,11 +1,19 @@
-using Avalonia.Platform;
-
-namespace Avalonia.Media
+namespace Avalonia.Media
 {
+    /// <summary>
+    /// Abstract class that describes a 2-D drawing.
+    /// </summary>
     public abstract class Drawing : AvaloniaObject
     {
+        /// <summary>
+        /// Draws this drawing to the given <see cref="DrawingContext"/>.
+        /// </summary>
+        /// <param name="context">The drawing context.</param>
         public abstract void Draw(DrawingContext context);
 
+        /// <summary>
+        /// Gets the drawing's bounding rectangle.
+        /// </summary>
         public abstract Rect GetBounds();
     }
 }

src/Avalonia.Visuals/Media/GeometryDrawing.cs

@@ -3,14 +3,36 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Media
 {
+    /// <summary>
+    /// Represents a drawing operation that combines 
+    /// a geometry with and brush and/or pen to produce rendered content.
+    /// </summary>
     public class GeometryDrawing : Drawing
     {
         // Adding the Pen's stroke thickness here could yield wrong results due to transforms.
         private static readonly IPen s_boundsPen = new ImmutablePen(Colors.Black.ToUint32(), 0);
-    
+
+        /// <summary>
+        /// Defines the <see cref="Geometry"/> property.
+        /// </summary>
         public static readonly StyledProperty<Geometry> GeometryProperty =
             AvaloniaProperty.Register<GeometryDrawing, Geometry>(nameof(Geometry));
 
+        /// <summary>
+        /// Defines the <see cref="Brush"/> property.
+        /// </summary>
+        public static readonly StyledProperty<IBrush> BrushProperty =
+            AvaloniaProperty.Register<GeometryDrawing, IBrush>(nameof(Brush), Brushes.Transparent);
+
+        /// <summary>
+        /// Defines the <see cref="Pen"/> property.
+        /// </summary>
+        public static readonly StyledProperty<Pen> PenProperty =
+            AvaloniaProperty.Register<GeometryDrawing, Pen>(nameof(Pen));
+
+        /// <summary>
+        /// Gets or sets the <see cref="Avalonia.Media.Geometry"/> that describes the shape of this <see cref="GeometryDrawing"/>.
+        /// </summary>
         [Content]
         public Geometry Geometry
         {
@@ -18,18 +40,18 @@ namespace Avalonia.Media
             set => SetValue(GeometryProperty, value);
         }
 
-        public static readonly StyledProperty<IBrush> BrushProperty =
-            AvaloniaProperty.Register<GeometryDrawing, IBrush>(nameof(Brush), Brushes.Transparent);
-
+        /// <summary>
+        /// Gets or sets the <see cref="Avalonia.Media.IBrush"/> used to fill the interior of the shape described by this <see cref="GeometryDrawing"/>.
+        /// </summary>
         public IBrush Brush
         {
             get => GetValue(BrushProperty);
             set => SetValue(BrushProperty, value);
         }
 
-        public static readonly StyledProperty<Pen> PenProperty =
-            AvaloniaProperty.Register<GeometryDrawing, Pen>(nameof(Pen));
-
+        /// <summary>
+        /// Gets or sets the <see cref="Avalonia.Media.IPen"/> used to stroke this <see cref="GeometryDrawing"/>.
+        /// </summary>
         public IPen Pen
         {
             get => GetValue(PenProperty);
@@ -46,7 +68,7 @@ namespace Avalonia.Media
 
         public override Rect GetBounds()
         {
-            return Geometry?.GetRenderBounds(s_boundsPen) ?? new Rect();
+            return Geometry?.GetRenderBounds(s_boundsPen) ?? Rect.Empty;
         }
     }
 }