Add basic structure for new rotation handler

osu.Game/Screens/Edit/Compose/Components/SelectionHandler.cs

@@ -55,6 +55,8 @@ namespace osu.Game.Screens.Edit.Compose.Components
         [Resolved(CanBeNull = true)]
         protected IEditorChangeHandler ChangeHandler { get; private set; }
 
+        protected SelectionRotationHandler RotationHandler { get; private set; }
+
         protected SelectionHandler()
         {
             selectedBlueprints = new List<SelectionBlueprint<T>>();
@@ -66,6 +68,8 @@ namespace osu.Game.Screens.Edit.Compose.Components
         [BackgroundDependencyLoader]
         private void load()
         {
+            RotationHandler = CreateRotationHandler();
+
             InternalChild = SelectionBox = CreateSelectionBox();
 
             SelectedItems.CollectionChanged += (_, _) =>
@@ -132,6 +136,11 @@ namespace osu.Game.Screens.Edit.Compose.Components
         /// <returns>Whether any items could be rotated.</returns>
         public virtual bool HandleRotation(float angle) => false;
 
+        /// <summary>
+        /// Creates the handler to use for rotation operations.
+        /// </summary>
+        public virtual SelectionRotationHandler CreateRotationHandler() => new SelectionRotationHandler();
+
         /// <summary>
         /// Handles the selected items being scaled.
         /// </summary>

osu.Game/Screens/Edit/Compose/Components/SelectionRotationHandler.cs

@@ -0,0 +1,31 @@
+// 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.Bindables;
+using osuTK;
+
+namespace osu.Game.Screens.Edit.Compose.Components
+{
+    /// <summary>
+    /// Base handler for editor rotation operations.
+    /// </summary>
+    public class SelectionRotationHandler
+    {
+        /// <summary>
+        /// Whether the rotation can currently be performed.
+        /// </summary>
+        public Bindable<bool> CanRotate { get; private set; } = new BindableBool();
+
+        public virtual void Begin()
+        {
+        }
+
+        public virtual void Update(float rotation, Vector2 origin)
+        {
+        }
+
+        public virtual void Commit()
+        {
+        }
+    }
+}