Implement a three-state menu item

osu.Game/Graphics/UserInterface/ThreeStateMenuItem.cs

@@ -0,0 +1,53 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using osu.Framework.Graphics.Sprites;
+
+namespace osu.Game.Graphics.UserInterface
+{
+    public class ThreeStateMenuItem : StatefulMenuItem<ThreeStates>
+    {
+        public ThreeStateMenuItem(string text, MenuItemType type = MenuItemType.Standard)
+            : base(text, type, getNextState)
+        {
+        }
+
+        public override IconUsage? GetIconForState(ThreeStates state)
+        {
+            switch (state)
+            {
+                case ThreeStates.Indeterminate:
+                    return FontAwesome.Regular.Circle;
+
+                case ThreeStates.Enabled:
+                    return FontAwesome.Solid.Check;
+            }
+
+            return null;
+        }
+
+        private static ThreeStates getNextState(ThreeStates state)
+        {
+            switch (state)
+            {
+                case ThreeStates.Disabled:
+                    return ThreeStates.Enabled;
+
+                case ThreeStates.Indeterminate:
+                    return ThreeStates.Enabled;
+
+                case ThreeStates.Enabled:
+                    return ThreeStates.Disabled;
+            }
+
+            return ThreeStates.Disabled;
+        }
+    }
+
+    public enum ThreeStates
+    {
+        Disabled,
+        Indeterminate,
+        Enabled
+    }
+}