Implement slider control point deletion

osu.Game.Rulesets.Osu/Edit/Blueprints/Sliders/Components/PathControlPointVisualiser.cs

@@ -2,12 +2,16 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
+using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Input;
 using osu.Framework.Input.Events;
 using osu.Game.Rulesets.Osu.Objects;
+using osu.Game.Screens.Edit.Compose;
 using osuTK;
+using osuTK.Input;
 
 namespace osu.Game.Rulesets.Osu.Edit.Blueprints.Sliders.Components
 {
@@ -20,6 +24,9 @@ namespace osu.Game.Rulesets.Osu.Edit.Blueprints.Sliders.Components
 
         private InputManager inputManager;
 
+        [Resolved(CanBeNull = true)]
+        private IPlacementHandler placementHandler { get; set; }
+
         public PathControlPointVisualiser(Slider slider)
         {
             this.slider = slider;
@@ -70,5 +77,44 @@ namespace osu.Game.Rulesets.Osu.Edit.Blueprints.Sliders.Components
                     piece.IsSelected.Value = piece.Index == index;
             }
         }
+
+        protected override bool OnKeyDown(KeyDownEvent e)
+        {
+            switch (e.Key)
+            {
+                case Key.Delete:
+                    var newControlPoints = new List<Vector2>();
+
+                    foreach (var piece in pieces)
+                    {
+                        if (!piece.IsSelected.Value)
+                            newControlPoints.Add(slider.Path.ControlPoints[piece.Index]);
+                    }
+
+                    // Ensure that there are any points to be deleted
+                    if (newControlPoints.Count == slider.Path.ControlPoints.Length)
+                        return false;
+
+                    // If there are 0 remaining control points, treat the slider as being deleted
+                    if (newControlPoints.Count == 0)
+                    {
+                        placementHandler?.Delete(slider);
+                        return true;
+                    }
+
+                    // Make control points relative
+                    Vector2 first = newControlPoints[0];
+                    for (int i = 0; i < newControlPoints.Count; i++)
+                        newControlPoints[i] = newControlPoints[i] - first;
+
+                    // The slider's position defines the position of the first control point, and all further control points are relative to that point
+                    slider.Position = slider.Position + first;
+                    ControlPointsChanged?.Invoke(newControlPoints.ToArray());
+
+                    return true;
+            }
+
+            return false;
+        }
     }
 }