Allow rearranging playlist tracks

osu.Game/Overlays/Music/PlaylistItem.cs

@@ -8,6 +8,7 @@ using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Sprites;
+using osu.Framework.Input;
 using osu.Framework.Localisation;
 using osu.Game.Beatmaps;
 using osu.Game.Graphics;
@@ -28,6 +29,7 @@ namespace osu.Game.Overlays.Music
         private IEnumerable<SpriteText> titleSprites;
         private UnicodeBindableString titleBind;
         private UnicodeBindableString artistBind;
+        private FillFlowContainer<PlaylistItem> Playlist;
 
         public readonly BeatmapSetInfo BeatmapSetInfo;
 
@@ -48,8 +50,9 @@ namespace osu.Game.Overlays.Music
             }
         }
 
-        public PlaylistItem(BeatmapSetInfo setInfo)
+        public PlaylistItem(FillFlowContainer<PlaylistItem> playlist, BeatmapSetInfo setInfo)
         {
+            Playlist = playlist;
             BeatmapSetInfo = setInfo;
 
             RelativeSizeAxes = Axes.X;
@@ -132,6 +135,44 @@ namespace osu.Game.Overlays.Music
             return true;
         }
 
+        protected override bool OnDragStart(InputState state)
+        {
+            return true;
+        }
+
+        // Maybe render some ghost text
+        protected override bool OnDrag(InputState state)
+        {
+            return true;
+        }
+
+        private int clamp(int value, int min, int max)
+        {
+            return (value <= min) ? min : (value >= max) ? max : value;
+        }
+
+        protected override bool OnDragEnd(InputState state)
+        {
+            int src = (int) Depth;
+            int dst = clamp((int) ((state.Mouse.Position.Y - Parent.DrawPosition.Y) / Height), 0, Playlist.Count - 1);
+
+            if (src == dst)
+                return true;
+
+            if (src < dst)
+            {
+                for (int i = src + 1; i <= dst; i++)
+                    Playlist.ChangeChildDepth(Playlist[i], i - 1);
+            }
+            else
+            {
+                for (int i = dst; i < src; i++)
+                    Playlist.ChangeChildDepth(Playlist[i], i + 1);
+            }
+            Playlist.ChangeChildDepth(this, dst);
+            return true;
+        }
+
         public string[] FilterTerms { get; private set; }
 
         private bool matching = true;

osu.Game/Overlays/Music/PlaylistList.cs

@@ -19,7 +19,7 @@ namespace osu.Game.Overlays.Music
         {
             set
             {
-                items.Children = value.Select(item => new PlaylistItem(item) { OnSelect = itemSelected }).ToList();
+                items.Children = value.Select((item, index) => new PlaylistItem(items, item) { OnSelect = itemSelected, Depth = index }).ToList();
             }
         }
 
@@ -75,7 +75,7 @@ namespace osu.Game.Overlays.Music
 
         public void AddBeatmapSet(BeatmapSetInfo beatmapSet)
         {
-            items.Add(new PlaylistItem(beatmapSet) { OnSelect = itemSelected });
+            items.Add(new PlaylistItem(items, beatmapSet) { OnSelect = itemSelected, Depth = items.Count });
         }
 
         public void RemoveBeatmapSet(BeatmapSetInfo beatmapSet)
@@ -96,6 +96,9 @@ namespace osu.Game.Overlays.Music
                 }
             }
 
+            // Compare with reversed ChildID and Depth
+            protected override int Compare(Drawable x, Drawable y) => base.Compare(y, x);
+
             public IEnumerable<IFilterable> FilterableChildren => Children;
 
             public ItemSearchContainer()