Add gradient brushes.

Dashboard.Drawing/Brush.cs

@@ -14,26 +14,36 @@ namespace Dashboard.Drawing
     {
     }
 
-    public readonly struct SolidBrush : IBrush
+    public readonly struct SolidBrush(Color Color) : IBrush
     {
         public IDrawExtension Kind { get; } = SolidBrushExtension.Instance;
-        public Color Color { get; }
-
-        public SolidBrush(Color color)
-        {
-            Color = color;
-        }
-
         public override int GetHashCode()
         {
             return HashCode.Combine(Kind, Color);
         }
     }
 
+    public readonly struct GradientBrush(Gradient Gradient) : IBrush
+    {
+        public IDrawExtension Kind { get; } = GradientBrushExtension.Instance;
+
+        public override int GetHashCode()
+        {
+            return HashCode.Combine(Kind, Gradient);
+        }
+    }
+
     public class SolidBrushExtension : DrawExtension
     {
         private SolidBrushExtension() : base("DB_Brush_solid", new[] { BrushExtension.Instance }) { }
 
         public static readonly SolidBrushExtension Instance = new SolidBrushExtension();
     }
+
+    public class GradientBrushExtension : DrawExtension
+    {
+        private GradientBrushExtension() : base("DB_Brush_gradient", new[] { BrushExtension.Instance }) { }
+
+        public static readonly GradientBrushExtension Instance = new GradientBrushExtension();
+    }
 }