Add composite managing display of selection box drag handles

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

@@ -0,0 +1,103 @@
+// 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 System.Collections.Generic;
+using System.Linq;
+using JetBrains.Annotations;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+
+namespace osu.Game.Screens.Edit.Compose.Components
+{
+    /// <summary>
+    /// Represents a display composite containing and managing the visibility state of the selection box's drag handles.
+    /// </summary>
+    public class SelectionBoxDragHandleDisplay : CompositeDrawable
+    {
+        private Container<SelectionBoxScaleHandle> scaleHandles;
+        private Container<SelectionBoxRotationHandle> rotationHandles;
+
+        private readonly List<SelectionBoxDragHandle> allDragHandles = new List<SelectionBoxDragHandle>();
+
+        public new MarginPadding Padding
+        {
+            get => base.Padding;
+            set => base.Padding = value;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            InternalChildren = new Drawable[]
+            {
+                scaleHandles = new Container<SelectionBoxScaleHandle>
+                {
+                    RelativeSizeAxes = Axes.Both,
+                },
+                rotationHandles = new Container<SelectionBoxRotationHandle>
+                {
+                    RelativeSizeAxes = Axes.Both,
+                    Padding = new MarginPadding(-12.5f),
+                },
+            };
+        }
+
+        public void AddScaleHandle(SelectionBoxScaleHandle handle)
+        {
+            bindDragHandle(handle);
+            scaleHandles.Add(handle);
+        }
+
+        public void AddRotationHandle(SelectionBoxRotationHandle handle)
+        {
+            handle.Alpha = 0;
+            handle.AlwaysPresent = true;
+
+            bindDragHandle(handle);
+            rotationHandles.Add(handle);
+        }
+
+        private void bindDragHandle(SelectionBoxDragHandle handle)
+        {
+            handle.HoverGained += updateRotationHandlesVisibility;
+            handle.HoverLost += updateRotationHandlesVisibility;
+            handle.OperationStarted += updateRotationHandlesVisibility;
+            handle.OperationEnded += updateRotationHandlesVisibility;
+            allDragHandles.Add(handle);
+        }
+
+        private SelectionBoxRotationHandle displayedRotationHandle;
+        private SelectionBoxDragHandle activeHandle;
+
+        private void updateRotationHandlesVisibility()
+        {
+            if (activeHandle?.InOperation == true || activeHandle?.IsHovered == true)
+                return;
+
+            displayedRotationHandle?.FadeOut(SelectionBoxControl.TRANSFORM_DURATION, Easing.OutQuint);
+            displayedRotationHandle = null;
+
+            activeHandle = allDragHandles.SingleOrDefault(h => h.InOperation);
+            activeHandle ??= allDragHandles.SingleOrDefault(h => h.IsHovered);
+
+            if (activeHandle != null)
+            {
+                displayedRotationHandle = getCorrespondingRotationHandle(activeHandle, rotationHandles);
+                displayedRotationHandle?.FadeIn(SelectionBoxControl.TRANSFORM_DURATION, Easing.OutQuint);
+            }
+        }
+
+        /// <summary>
+        /// Gets the rotation handle corresponding to the given handle.
+        /// </summary>
+        [CanBeNull]
+        private static SelectionBoxRotationHandle getCorrespondingRotationHandle(SelectionBoxDragHandle handle, IEnumerable<SelectionBoxRotationHandle> rotationHandles)
+        {
+            if (handle is SelectionBoxRotationHandle rotationHandle)
+                return rotationHandle;
+
+            return rotationHandles.SingleOrDefault(r => r.Anchor == handle.Anchor);
+        }
+    }
+}