Merge pull request #1697 from peppy/song-select-state-simplification

Rewrite BeatmapCarousel with ModelView implementation

osu-framework

@@ -1 +1 @@
-Subproject commit fc6de01ad6045544991bf278316c9eed8ea01ef1
+Subproject commit 5da6990a8e68dea852495950996e1362a293dbd5

osu.Game.Tests/Visual/TestCaseBeatmapCarousel.cs

@@ -0,0 +1,342 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using osu.Framework.Allocation;
+using osu.Framework.Extensions;
+using osu.Framework.Graphics;
+using osu.Game.Beatmaps;
+using osu.Game.Configuration;
+using osu.Game.Screens.Select;
+using osu.Game.Screens.Select.Carousel;
+using osu.Game.Screens.Select.Filter;
+
+namespace osu.Game.Tests.Visual
+{
+    internal class TestCaseBeatmapCarousel : OsuTestCase
+    {
+        private TestBeatmapCarousel carousel;
+
+        public override IReadOnlyList<Type> RequiredTypes => new[]
+        {
+            typeof(CarouselItem),
+            typeof(CarouselGroup),
+            typeof(CarouselGroupEagerSelect),
+            typeof(CarouselBeatmap),
+            typeof(CarouselBeatmapSet),
+
+            typeof(DrawableCarouselItem),
+            typeof(CarouselItemState),
+
+            typeof(DrawableCarouselBeatmap),
+            typeof(DrawableCarouselBeatmapSet),
+        };
+
+
+        private readonly Stack<BeatmapSetInfo> selectedSets = new Stack<BeatmapSetInfo>();
+
+        private BeatmapInfo currentSelection;
+
+        private const int set_count = 5;
+
+        [BackgroundDependencyLoader]
+        private void load()
+        {
+            Add(carousel = new TestBeatmapCarousel
+            {
+                RelativeSizeAxes = Axes.Both,
+            });
+
+            List<BeatmapSetInfo> beatmapSets = new List<BeatmapSetInfo>();
+
+            for (int i = 1; i <= set_count; i++)
+                beatmapSets.Add(createTestBeatmapSet(i));
+
+            carousel.SelectionChanged = s => currentSelection = s;
+
+            AddStep("Load Beatmaps", () => { carousel.BeatmapSets = beatmapSets; });
+
+            AddUntilStep(() => carousel.BeatmapSets.Any(), "Wait for load");
+
+            testTraversal();
+            testFiltering();
+            testRandom();
+            testAddRemove();
+            testSorting();
+
+            testRemoveAll();
+        }
+
+        private void ensureRandomFetchSuccess() =>
+            AddAssert("ensure prev random fetch worked", () => selectedSets.Peek() == carousel.SelectedBeatmapSet);
+
+        private void checkSelected(int set, int? diff = null) =>
+            AddAssert($"selected is set{set}{(diff.HasValue ? $" diff{diff.Value}" : "")}", () =>
+            {
+                if (diff != null)
+                    return carousel.SelectedBeatmap == carousel.BeatmapSets.Skip(set - 1).First().Beatmaps.Skip(diff.Value - 1).First();
+
+                return carousel.BeatmapSets.Skip(set - 1).First().Beatmaps.Contains(carousel.SelectedBeatmap);
+            });
+
+        private void setSelected(int set, int diff) =>
+            AddStep($"select set{set} diff{diff}", () =>
+                carousel.SelectBeatmap(carousel.BeatmapSets.Skip(set - 1).First().Beatmaps.Skip(diff - 1).First()));
+
+        private void advanceSelection(bool diff, int direction = 1, int count = 1)
+        {
+            if (count == 1)
+                AddStep($"select {(direction > 0 ? "next" : "prev")} {(diff ? "diff" : "set")}", () =>
+                    carousel.SelectNext(direction, !diff));
+            else
+            {
+                AddRepeatStep($"select {(direction > 0 ? "next" : "prev")} {(diff ? "diff" : "set")}", () =>
+                    carousel.SelectNext(direction, !diff), count);
+            }
+        }
+
+        private void checkVisibleItemCount(bool diff, int count) =>
+            AddAssert($"{count} {(diff ? "diffs" : "sets")} visible", () =>
+                carousel.Items.Count(s => (diff ? s.Item is CarouselBeatmap : s.Item is CarouselBeatmapSet) && s.Item.Visible) == count);
+
+        private void nextRandom() =>
+            AddStep("select random next", () =>
+            {
+                carousel.RandomAlgorithm.Value = RandomSelectAlgorithm.RandomPermutation;
+
+                if (!selectedSets.Any() && carousel.SelectedBeatmap != null)
+                    selectedSets.Push(carousel.SelectedBeatmapSet);
+
+                carousel.SelectNextRandom();
+                selectedSets.Push(carousel.SelectedBeatmapSet);
+            });
+
+        private void ensureRandomDidntRepeat() =>
+            AddAssert("ensure no repeats", () => selectedSets.Distinct().Count() == selectedSets.Count);
+
+        private void prevRandom() => AddStep("select random last", () =>
+        {
+            carousel.SelectPreviousRandom();
+            selectedSets.Pop();
+        });
+
+        /// <summary>
+        /// Test keyboard traversal
+        /// </summary>
+        private void testTraversal()
+        {
+            advanceSelection(direction: 1, diff: false);
+            checkSelected(1, 1);
+
+            advanceSelection(direction: 1, diff: true);
+            checkSelected(1, 2);
+
+            advanceSelection(direction: -1, diff: false);
+            checkSelected(set_count, 1);
+
+            advanceSelection(direction: -1, diff: true);
+            checkSelected(set_count - 1, 3);
+
+            advanceSelection(diff: false);
+            advanceSelection(diff: false);
+            checkSelected(1, 2);
+
+            advanceSelection(direction: -1, diff: true);
+            advanceSelection(direction: -1, diff: true);
+            checkSelected(set_count, 3);
+        }
+
+        /// <summary>
+        /// Test filtering
+        /// </summary>
+        private void testFiltering()
+        {
+            // basic filtering
+
+            setSelected(1, 1);
+
+            AddStep("Filter", () => carousel.Filter(new FilterCriteria { SearchText = "set #3!" }, false));
+            checkVisibleItemCount(diff: false, count: 1);
+            checkVisibleItemCount(diff: true, count: 3);
+            checkSelected(3, 1);
+
+            advanceSelection(diff: true, count: 4);
+            checkSelected(3, 2);
+
+            AddStep("Un-filter (debounce)", () => carousel.Filter(new FilterCriteria()));
+            AddUntilStep(() => !carousel.PendingFilterTask, "Wait for debounce");
+            checkVisibleItemCount(diff: false, count: set_count);
+            checkVisibleItemCount(diff: true, count: 3);
+
+            // test filtering some difficulties (and keeping current beatmap set selected).
+
+            setSelected(1, 2);
+            AddStep("Filter some difficulties", () => carousel.Filter(new FilterCriteria { SearchText = "Normal" }, false));
+            checkSelected(1, 1);
+
+            AddStep("Un-filter", () => carousel.Filter(new FilterCriteria(), false));
+            checkSelected(1, 1);
+
+            AddStep("Filter all", () => carousel.Filter(new FilterCriteria { SearchText = "Dingo" }, false));
+
+            checkVisibleItemCount(false, 0);
+            checkVisibleItemCount(true, 0);
+            AddAssert("Selection is null", () => currentSelection == null);
+
+            AddStep("Un-filter", () => carousel.Filter(new FilterCriteria(), false));
+
+            AddAssert("Selection is non-null", () => currentSelection != null);
+        }
+
+        /// <summary>
+        /// Test random non-repeating algorithm
+        /// </summary>
+        private void testRandom()
+        {
+            setSelected(1, 1);
+
+            nextRandom();
+            ensureRandomDidntRepeat();
+            nextRandom();
+            ensureRandomDidntRepeat();
+            nextRandom();
+            ensureRandomDidntRepeat();
+
+            prevRandom();
+            ensureRandomFetchSuccess();
+            prevRandom();
+            ensureRandomFetchSuccess();
+
+            nextRandom();
+            ensureRandomDidntRepeat();
+            nextRandom();
+            ensureRandomDidntRepeat();
+
+            nextRandom();
+            AddAssert("ensure repeat", () => selectedSets.Contains(carousel.SelectedBeatmapSet));
+        }
+
+        /// <summary>
+        /// Test adding and removing beatmap sets
+        /// </summary>
+        private void testAddRemove()
+        {
+            AddStep("Add new set", () => carousel.UpdateBeatmapSet(createTestBeatmapSet(set_count + 1)));
+            AddStep("Add new set", () => carousel.UpdateBeatmapSet(createTestBeatmapSet(set_count + 2)));
+
+            checkVisibleItemCount(false, set_count + 2);
+
+            AddStep("Remove set", () => carousel.RemoveBeatmapSet(createTestBeatmapSet(set_count + 2)));
+
+            checkVisibleItemCount(false, set_count + 1);
+
+            setSelected(set_count + 1, 1);
+
+            AddStep("Remove set", () => carousel.RemoveBeatmapSet(createTestBeatmapSet(set_count + 1)));
+
+            checkVisibleItemCount(false, set_count);
+
+            checkSelected(set_count);
+        }
+
+        /// <summary>
+        /// Test sorting
+        /// </summary>
+        private void testSorting()
+        {
+            AddStep("Sort by author", () => carousel.Filter(new FilterCriteria { Sort = SortMode.Author }, false));
+            AddAssert("Check zzzzz is at bottom", () => carousel.BeatmapSets.Last().Metadata.AuthorString == "zzzzz");
+            AddStep("Sort by artist", () => carousel.Filter(new FilterCriteria { Sort = SortMode.Artist }, false));
+            AddAssert($"Check #{set_count} is at bottom", () => carousel.BeatmapSets.Last().Metadata.Title.EndsWith($"#{set_count}!"));
+        }
+
+        private void testRemoveAll()
+        {
+            setSelected(2, 1);
+            AddAssert("Selection is non-null", () => currentSelection != null);
+
+            AddStep("Remove selected", () => carousel.RemoveBeatmapSet(carousel.SelectedBeatmapSet));
+            checkSelected(2);
+
+            AddStep("Remove first", () => carousel.RemoveBeatmapSet(carousel.BeatmapSets.First()));
+            AddStep("Remove first", () => carousel.RemoveBeatmapSet(carousel.BeatmapSets.First()));
+            checkSelected(1);
+
+            AddUntilStep(() =>
+            {
+                if (!carousel.BeatmapSets.Any()) return true;
+
+                carousel.RemoveBeatmapSet(carousel.BeatmapSets.Last());
+                return false;
+            }, "Remove all");
+
+            AddAssert("Selection is null", () => currentSelection == null);
+        }
+
+
+        private BeatmapSetInfo createTestBeatmapSet(int i)
+        {
+            return new BeatmapSetInfo
+            {
+                ID = i,
+                OnlineBeatmapSetID = i,
+                Hash = new MemoryStream(Encoding.UTF8.GetBytes(Guid.NewGuid().ToString())).ComputeMD5Hash(),
+                Metadata = new BeatmapMetadata
+                {
+                    OnlineBeatmapSetID = i,
+                    // Create random metadata, then we can check if sorting works based on these
+                    Artist = $"peppy{i.ToString().PadLeft(6, '0')}",
+                    Title = $"test set #{i}!",
+                    AuthorString = string.Concat(Enumerable.Repeat((char)('z' - Math.Min(25, i - 1)), 5))
+                },
+                Beatmaps = new List<BeatmapInfo>(new[]
+                {
+                    new BeatmapInfo
+                    {
+                        OnlineBeatmapID = i * 10,
+                        Path = "normal.osu",
+                        Version = "Normal",
+                        StarDifficulty = 2,
+                        BaseDifficulty = new BeatmapDifficulty
+                        {
+                            OverallDifficulty = 3.5f,
+                        }
+                    },
+                    new BeatmapInfo
+                    {
+                        OnlineBeatmapID = i * 10 + 1,
+                        Path = "hard.osu",
+                        Version = "Hard",
+                        StarDifficulty = 5,
+                        BaseDifficulty = new BeatmapDifficulty
+                        {
+                            OverallDifficulty = 5,
+                        }
+                    },
+                    new BeatmapInfo
+                    {
+                        OnlineBeatmapID = i * 10 + 2,
+                        Path = "insane.osu",
+                        Version = "Insane",
+                        StarDifficulty = 6,
+                        BaseDifficulty = new BeatmapDifficulty
+                        {
+                            OverallDifficulty = 7,
+                        }
+                    },
+                }),
+            };
+        }
+
+        private class TestBeatmapCarousel : BeatmapCarousel
+        {
+            public new List<DrawableCarouselItem> Items => base.Items;
+
+            public bool PendingFilterTask => FilterTask != null;
+        }
+    }
+}

osu.Game.Tests/Visual/TestCasePlaySongSelect.cs

@@ -13,6 +13,7 @@
 using osu.Game.Database;
 using osu.Game.Rulesets;
 using osu.Game.Screens.Select;
+using osu.Game.Screens.Select.Carousel;
 using osu.Game.Screens.Select.Filter;
 using osu.Game.Tests.Platform;
 
@@ -26,10 +27,28 @@ internal class TestCasePlaySongSelect : OsuTestCase
 
         private DependencyContainer dependencies;
 
+        public override IReadOnlyList<Type> RequiredTypes => new[]
+        {
+            typeof(SongSelect),
+            typeof(BeatmapCarousel),
+
+            typeof(CarouselItem),
+            typeof(CarouselGroup),
+            typeof(CarouselGroupEagerSelect),
+            typeof(CarouselBeatmap),
+            typeof(CarouselBeatmapSet),
+
+            typeof(DrawableCarouselItem),
+            typeof(CarouselItemState),
+
+            typeof(DrawableCarouselBeatmap),
+            typeof(DrawableCarouselBeatmapSet),
+        };
+
         protected override IReadOnlyDependencyContainer CreateLocalDependencies(IReadOnlyDependencyContainer parent) => dependencies = new DependencyContainer(parent);
 
         [BackgroundDependencyLoader]
-        private void load()
+        private void load(BeatmapManager baseManager)
         {
             PlaySongSelect songSelect;
 
@@ -43,7 +62,10 @@ private void load()
                 Func<OsuDbContext> contextFactory = () => context;
 
                 dependencies.Cache(rulesets = new RulesetStore(contextFactory));
-                dependencies.Cache(manager = new BeatmapManager(storage, contextFactory, rulesets, null));
+                dependencies.Cache(manager = new BeatmapManager(storage, contextFactory, rulesets, null)
+                {
+                    DefaultBeatmap = baseManager.GetWorkingBeatmap(null)
+                });
 
                 for (int i = 0; i < 100; i += 10)
                     manager.Import(createTestBeatmapSet(i));

osu.Game.Tests/osu.Game.Tests.csproj

@@ -88,6 +88,7 @@
     <Compile Include="Beatmaps\IO\ImportBeatmapTest.cs" />
     <Compile Include="Resources\Resource.cs" />
     <Compile Include="Beatmaps\Formats\LegacyBeatmapDecoderTest.cs" />
+    <Compile Include="Visual\TestCaseBeatmapCarousel.cs" />
     <Compile Include="Visual\TestCaseBeatmapDetailArea.cs" />
     <Compile Include="Visual\TestCaseBeatmapDetails.cs" />
     <Compile Include="Visual\TestCaseBeatmapInfoWedge.cs" />

osu.Game/Beatmaps/BeatmapInfo.cs

@@ -118,6 +118,8 @@ public string StoredBookmarks
         [JsonProperty("difficulty_rating")]
         public double StarDifficulty { get; set; }
 
+        public override string ToString() => $"{Metadata} [{Version}]";
+
         public bool Equals(BeatmapInfo other)
         {
             if (ID == 0 || other?.ID == 0)

osu.Game/Beatmaps/BeatmapManager.cs

@@ -374,12 +374,9 @@ private void undelete(BeatmapStore beatmaps, FileStore files, BeatmapSetInfo bea
         /// <returns>A <see cref="WorkingBeatmap"/> instance correlating to the provided <see cref="BeatmapInfo"/>.</returns>
         public WorkingBeatmap GetWorkingBeatmap(BeatmapInfo beatmapInfo, WorkingBeatmap previous = null)
         {
-            if (beatmapInfo == null || beatmapInfo == DefaultBeatmap?.BeatmapInfo)
+            if (beatmapInfo?.BeatmapSet == null || beatmapInfo == DefaultBeatmap?.BeatmapInfo)
                 return DefaultBeatmap;
 
-            if (beatmapInfo.BeatmapSet == null)
-                throw new InvalidOperationException($@"Beatmap set {beatmapInfo.BeatmapSetInfoID} is not in the local database.");
-
             if (beatmapInfo.Metadata == null)
                 beatmapInfo.Metadata = beatmapInfo.BeatmapSet.Metadata;
 

osu.Game/Beatmaps/BeatmapMetadata.cs

@@ -57,6 +57,8 @@ public string AuthorString
         public string AudioFile { get; set; }
         public string BackgroundFile { get; set; }
 
+        public override string ToString() => $"{Artist} - {Title} ({Author})";
+
         public string[] SearchableTerms => new[]
         {
             Author?.Username,

osu.Game/Beatmaps/BeatmapSetInfo.cs

@@ -33,6 +33,8 @@ public class BeatmapSetInfo : IHasPrimaryKey
 
         public List<BeatmapSetFileInfo> Files { get; set; }
 
+        public override string ToString() => Metadata.ToString();
+
         public bool Protected { get; set; }
     }
 }

osu.Game/Beatmaps/Drawables/BeatmapGroup.cs

@@ -1,147 +0,0 @@
-// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
-// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
-
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using osu.Framework;
-using osu.Framework.Graphics;
-
-namespace osu.Game.Beatmaps.Drawables
-{
-    public class BeatmapGroup : IStateful<BeatmapGroupState>
-    {
-        public event Action<BeatmapGroupState> StateChanged;
-
-        public BeatmapPanel SelectedPanel;
-
-        /// <summary>
-        /// Fires when one of our difficulties was selected. Will fire on first expand.
-        /// </summary>
-        public Action<BeatmapGroup, BeatmapPanel> SelectionChanged;
-
-        /// <summary>
-        /// Fires when one of our difficulties is clicked when already selected. Should start playing the map.
-        /// </summary>
-        public Action<BeatmapInfo> StartRequested;
-
-        public Action<BeatmapSetInfo> DeleteRequested;
-
-        public Action<BeatmapSetInfo> RestoreHiddenRequested;
-
-        public Action<BeatmapInfo> HideDifficultyRequested;
-
-        public Action<BeatmapInfo> EditRequested;
-
-        public BeatmapSetHeader Header;
-
-        public List<BeatmapPanel> BeatmapPanels;
-
-        public BeatmapSetInfo BeatmapSet;
-
-        private BeatmapGroupState state;
-
-        public BeatmapGroupState State
-        {
-            get { return state; }
-            set
-            {
-                state = value;
-                UpdateState();
-                StateChanged?.Invoke(state);
-            }
-        }
-
-        public void UpdateState()
-        {
-            switch (state)
-            {
-                case BeatmapGroupState.Expanded:
-                    Header.State = PanelSelectedState.Selected;
-                    foreach (BeatmapPanel panel in BeatmapPanels)
-                        if (panel == SelectedPanel)
-                            panel.State = PanelSelectedState.Selected;
-                        else if (panel.Filtered)
-                            panel.State = PanelSelectedState.Hidden;
-                        else
-                            panel.State = PanelSelectedState.NotSelected;
-                    break;
-                case BeatmapGroupState.Collapsed:
-                    Header.State = PanelSelectedState.NotSelected;
-                    foreach (BeatmapPanel panel in BeatmapPanels)
-                        panel.State = PanelSelectedState.Hidden;
-                    break;
-                case BeatmapGroupState.Hidden:
-                    Header.State = PanelSelectedState.Hidden;
-                    foreach (BeatmapPanel panel in BeatmapPanels)
-                        panel.State = PanelSelectedState.Hidden;
-                    break;
-            }
-        }
-
-        public BeatmapGroup(BeatmapSetInfo beatmapSet, BeatmapManager manager)
-        {
-            if (beatmapSet == null)
-                throw new ArgumentNullException(nameof(beatmapSet));
-            if (manager == null)
-                throw new ArgumentNullException(nameof(manager));
-
-            BeatmapSet = beatmapSet;
-            WorkingBeatmap beatmap = manager.GetWorkingBeatmap(BeatmapSet.Beatmaps.FirstOrDefault());
-
-            Header = new BeatmapSetHeader(beatmap)
-            {
-                GainedSelection = headerGainedSelection,
-                DeleteRequested = b => DeleteRequested(b),
-                RestoreHiddenRequested = b => RestoreHiddenRequested(b),
-                RelativeSizeAxes = Axes.X,
-            };
-
-            BeatmapPanels = BeatmapSet.Beatmaps.Where(b => !b.Hidden).OrderBy(b => b.RulesetID).ThenBy(b => b.StarDifficulty).Select(b => new BeatmapPanel(b)
-            {
-                Alpha = 0,
-                GainedSelection = panelGainedSelection,
-                HideRequested = p => HideDifficultyRequested?.Invoke(p),
-                StartRequested = p => StartRequested?.Invoke(p.Beatmap),
-                EditRequested = p => EditRequested?.Invoke(p.Beatmap),
-                RelativeSizeAxes = Axes.X,
-            }).ToList();
-
-            Header.AddDifficultyIcons(BeatmapPanels);
-        }
-
-
-        private void headerGainedSelection(BeatmapSetHeader panel)
-        {
-            State = BeatmapGroupState.Expanded;
-
-            //we want to make sure one of our children is selected in the case none have been selected yet.
-            if (SelectedPanel == null)
-                BeatmapPanels.First(p => !p.Filtered).State = PanelSelectedState.Selected;
-        }
-
-        private void panelGainedSelection(BeatmapPanel panel)
-        {
-            try
-            {
-                if (SelectedPanel == panel) return;
-
-                if (SelectedPanel != null)
-                    SelectedPanel.State = PanelSelectedState.NotSelected;
-                SelectedPanel = panel;
-            }
-            finally
-            {
-                State = BeatmapGroupState.Expanded;
-                SelectionChanged?.Invoke(this, SelectedPanel);
-            }
-        }
-    }
-
-    public enum BeatmapGroupState
-    {
-        Collapsed,
-        Expanded,
-        Hidden,
-    }
-}

osu.Game/Configuration/OsuConfigManager.cs

@@ -20,7 +20,7 @@ protected override void InitialiseDefaults()
             Set(OsuSetting.DisplayStarsMinimum, 0.0, 0, 10, 0.1);
             Set(OsuSetting.DisplayStarsMaximum, 10.0, 0, 10, 0.1);
 
-            Set(OsuSetting.SelectionRandomType, SelectionRandomType.RandomPermutation);
+            Set(OsuSetting.RandomSelectAlgorithm, RandomSelectAlgorithm.RandomPermutation);
 
             Set(OsuSetting.ChatDisplayHeight, ChatOverlay.DEFAULT_HEIGHT, 0.2, 1);
 
@@ -108,7 +108,7 @@ public enum OsuSetting
         SaveUsername,
         DisplayStarsMinimum,
         DisplayStarsMaximum,
-        SelectionRandomType,
+        RandomSelectAlgorithm,
         SnakingInSliders,
         SnakingOutSliders,
         ShowFpsDisplay,

osu.Game/Configuration/RandomSelectAlgorithm.cs

@@ -5,11 +5,11 @@
 
 namespace osu.Game.Configuration
 {
-   public enum SelectionRandomType
+   public enum RandomSelectAlgorithm
     {
         [Description("Never repeat")]
         RandomPermutation,
         [Description("Random")]
         Random
     }
-}
+}

osu.Game/Graphics/SpriteIcon.cs

@@ -15,14 +15,19 @@ namespace osu.Game.Graphics
 {
     public class SpriteIcon : CompositeDrawable
     {
-        private readonly Sprite spriteShadow;
-        private readonly Sprite spriteMain;
+        private Sprite spriteShadow;
+        private Sprite spriteMain;
 
         private Cached layout = new Cached();
-        private readonly Container shadowVisibility;
+        private Container shadowVisibility;
 
-        public SpriteIcon()
+        private FontStore store;
+
+        [BackgroundDependencyLoader]
+        private void load(FontStore store)
         {
+            this.store = store;
+
             InternalChildren = new Drawable[]
             {
                 shadowVisibility = new Container
@@ -39,7 +44,7 @@ public SpriteIcon()
                         Y = 2,
                         Colour = new Color4(0f, 0f, 0f, 0.2f),
                     },
-                    Alpha = 0,
+                    Alpha = shadow ? 1 : 0,
                 },
                 spriteMain = new Sprite
                 {
@@ -49,14 +54,7 @@ public SpriteIcon()
                     FillMode = FillMode.Fit
                 },
             };
-        }
 
-        private FontStore store;
-
-        [BackgroundDependencyLoader]
-        private void load(FontStore store)
-        {
-            this.store = store;
             updateTexture();
         }
 
@@ -105,12 +103,15 @@ protected override void Update()
             }
         }
 
+        private bool shadow;
         public bool Shadow
         {
-            get { return spriteShadow.IsPresent; }
+            get { return shadow; }
             set
             {
-                shadowVisibility.Alpha = value ? 1 : 0;
+                shadow = value;
+                if (shadowVisibility != null)
+                    shadowVisibility.Alpha = value ? 1 : 0;
             }
         }
 

osu.Game/Graphics/UserInterface/StarCounter.cs

@@ -6,6 +6,7 @@
 using osu.Framework.Graphics.Containers;
 using osu.Framework.MathUtils;
 using System;
+using System.Linq;
 
 namespace osu.Game.Graphics.UserInterface
 {
@@ -72,16 +73,9 @@ public StarCounter(int starCount = 10)
                     AutoSizeAxes = Axes.Both,
                     Direction = FillDirection.Horizontal,
                     Spacing = new Vector2(star_spacing),
+                    ChildrenEnumerable = Enumerable.Range(0, StarCount).Select(i => new Star { Alpha = minStarAlpha })
                 }
             };
-
-            for (int i = 0; i < StarCount; i++)
-            {
-                stars.Add(new Star
-                {
-                    Alpha = minStarAlpha,
-                });
-            }
         }
 
         protected override void LoadComplete()
@@ -147,15 +141,12 @@ public Star()
             {
                 Size = new Vector2(star_size);
 
-                Children = new[]
+                Child = Icon = new SpriteIcon
                 {
-                    Icon = new SpriteIcon
-                    {
-                        Size = new Vector2(star_size),
-                        Icon = FontAwesome.fa_star,
-                        Anchor = Anchor.Centre,
-                        Origin = Anchor.Centre,
-                    }
+                    Size = new Vector2(star_size),
+                    Icon = FontAwesome.fa_star,
+                    Anchor = Anchor.Centre,
+                    Origin = Anchor.Centre,
                 };
             }
         }

osu.Game/Overlays/Settings/Sections/Gameplay/SongSelectSettings.cs

@@ -34,10 +34,10 @@ private void load(OsuConfigManager config)
                     Bindable = config.GetBindable<double>(OsuSetting.DisplayStarsMaximum),
                     KeyboardStep = 1f
                 },
-                new SettingsEnumDropdown<SelectionRandomType>
+                new SettingsEnumDropdown<RandomSelectAlgorithm>
                 {
-                    LabelText = "Random beatmap selection",
-                    Bindable = config.GetBindable<SelectionRandomType>(OsuSetting.SelectionRandomType),
+                    LabelText = "Random selection algorithm",
+                    Bindable = config.GetBindable<RandomSelectAlgorithm>(OsuSetting.RandomSelectAlgorithm),
                 }
             };
         }

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -7,7 +7,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using osu.Game.Beatmaps.Drawables;
 using osu.Game.Configuration;
 using osu.Framework.Input;
 using OpenTK.Input;
@@ -15,169 +14,166 @@
 using System.Diagnostics;
 using System.Threading.Tasks;
 using osu.Framework.Allocation;
+using osu.Framework.Caching;
 using osu.Framework.Threading;
 using osu.Framework.Configuration;
+using osu.Framework.Extensions.IEnumerableExtensions;
 using osu.Game.Beatmaps;
 using osu.Game.Graphics.Containers;
 using osu.Game.Graphics.Cursor;
+using osu.Game.Screens.Select.Carousel;
 
 namespace osu.Game.Screens.Select
 {
     public class BeatmapCarousel : OsuScrollContainer
     {
-        public BeatmapInfo SelectedBeatmap => selectedPanel?.Beatmap;
+        /// <summary>
+        /// Triggered when the <see cref="BeatmapSets"/> loaded change and are completely loaded.
+        /// </summary>
+        public Action BeatmapSetsChanged;
+
+        /// <summary>
+        /// The currently selected beatmap.
+        /// </summary>
+        public BeatmapInfo SelectedBeatmap => selectedBeatmap?.Beatmap;
+
+        private CarouselBeatmap selectedBeatmap => selectedBeatmapSet?.Beatmaps.FirstOrDefault(s => s.State == CarouselItemState.Selected);
+
+        /// <summary>
+        /// The currently selected beatmap set.
+        /// </summary>
+        public BeatmapSetInfo SelectedBeatmapSet => selectedBeatmapSet?.BeatmapSet;
+
+        private CarouselBeatmapSet selectedBeatmapSet;
+
+        /// <summary>
+        /// Raised when the <see cref="SelectedBeatmap"/> is changed.
+        /// </summary>
+        public Action<BeatmapInfo> SelectionChanged;
 
         public override bool HandleInput => AllowSelection;
 
-        public Action BeatmapsChanged;
+        private IEnumerable<CarouselBeatmapSet> beatmapSets => root.Children.OfType<CarouselBeatmapSet>();
 
-        public IEnumerable<BeatmapSetInfo> Beatmaps
+        public IEnumerable<BeatmapSetInfo> BeatmapSets
         {
-            get { return groups.Select(g => g.BeatmapSet); }
+            get { return beatmapSets.Select(g => g.BeatmapSet); }
             set
             {
-                scrollableContent.Clear(false);
-                panels.Clear();
-                groups.Clear();
-
-                List<BeatmapGroup> newGroups = null;
+                CarouselGroup newRoot = new CarouselGroupEagerSelect();
 
                 Task.Run(() =>
                 {
-                    newGroups = value.Select(createGroup).Where(g => g != null).ToList();
-                    criteria.Filter(newGroups);
-                }).ContinueWith(t =>
-                {
-                    Schedule(() =>
-                    {
-                        foreach (var g in newGroups)
-                            addGroup(g);
+                    value.Select(createCarouselSet).Where(g => g != null).ForEach(newRoot.AddChild);
+                    newRoot.Filter(activeCriteria);
 
-                        computeYPositions();
-                        BeatmapsChanged?.Invoke();
-                    });
-                });
+                    // preload drawables as the ctor overhead is quite high currently.
+                    var _ = newRoot.Drawables;
+                }).ContinueWith(_ => Schedule(() =>
+                {
+                    root = newRoot;
+                    scrollableContent.Clear(false);
+                    itemsCache.Invalidate();
+                    scrollPositionCache.Invalidate();
+                    BeatmapSetsChanged?.Invoke();
+                }));
             }
         }
 
         private readonly List<float> yPositions = new List<float>();
+        private Cached itemsCache = new Cached();
+        private Cached scrollPositionCache = new Cached();
 
-        /// <summary>
-        /// Required for now unfortunately.
-        /// </summary>
-        private BeatmapManager manager;
+        private readonly Container<DrawableCarouselItem> scrollableContent;
 
-        private readonly Container<Panel> scrollableContent;
+        public Bindable<RandomSelectAlgorithm> RandomAlgorithm = new Bindable<RandomSelectAlgorithm>();
+        private readonly List<CarouselBeatmapSet> previouslyVisitedRandomSets = new List<CarouselBeatmapSet>();
+        private readonly Stack<CarouselBeatmap> randomSelectedBeatmaps = new Stack<CarouselBeatmap>();
 
-        private readonly List<BeatmapGroup> groups = new List<BeatmapGroup>();
-
-        private Bindable<SelectionRandomType> randomType;
-        private readonly List<BeatmapGroup> seenGroups = new List<BeatmapGroup>();
-
-        private readonly List<Panel> panels = new List<Panel>();
-
-        private readonly Stack<KeyValuePair<BeatmapGroup, BeatmapPanel>> randomSelectedBeatmaps = new Stack<KeyValuePair<BeatmapGroup, BeatmapPanel>>();
-
-        private BeatmapGroup selectedGroup;
-        private BeatmapPanel selectedPanel;
+        protected List<DrawableCarouselItem> Items = new List<DrawableCarouselItem>();
+        private CarouselGroup root = new CarouselGroupEagerSelect();
 
         public BeatmapCarousel()
         {
-            Add(new OsuContextMenuContainer
+            Child = new OsuContextMenuContainer
             {
                 RelativeSizeAxes = Axes.X,
                 AutoSizeAxes = Axes.Y,
-                Child = scrollableContent = new Container<Panel>
+                Child = scrollableContent = new Container<DrawableCarouselItem>
                 {
                     RelativeSizeAxes = Axes.X,
                 }
-            });
+            };
         }
 
-        public void RemoveBeatmap(BeatmapSetInfo beatmapSet)
+        [BackgroundDependencyLoader(permitNulls: true)]
+        private void load(OsuConfigManager config)
         {
-            Schedule(() => removeGroup(groups.Find(b => b.BeatmapSet.ID == beatmapSet.ID)));
+            config.BindWith(OsuSetting.RandomSelectAlgorithm, RandomAlgorithm);
+        }
+
+        public void RemoveBeatmapSet(BeatmapSetInfo beatmapSet)
+        {
+            Schedule(() =>
+            {
+                var existingSet = beatmapSets.FirstOrDefault(b => b.BeatmapSet.ID == beatmapSet.ID);
+
+                if (existingSet == null)
+                    return;
+
+                root.RemoveChild(existingSet);
+                itemsCache.Invalidate();
+            });
         }
 
         public void UpdateBeatmapSet(BeatmapSetInfo beatmapSet)
         {
-            // todo: this method should be smarter as to not recreate panels that haven't changed, etc.
-            var oldGroup = groups.Find(b => b.BeatmapSet.ID == beatmapSet.ID);
-
-            var newGroup = createGroup(beatmapSet);
-
-            int index = groups.IndexOf(oldGroup);
-            if (index >= 0)
-                groups.RemoveAt(index);
-
-            if (newGroup != null)
+            Schedule(() =>
             {
-                if (index >= 0)
-                    groups.Insert(index, newGroup);
-                else
-                    addGroup(newGroup);
-            }
+                CarouselBeatmapSet existingSet = beatmapSets.FirstOrDefault(b => b.BeatmapSet.ID == beatmapSet.ID);
 
-            bool hadSelection = selectedGroup == oldGroup;
+                bool hadSelection = existingSet?.State?.Value == CarouselItemState.Selected;
 
-            if (hadSelection && newGroup == null)
-                selectedGroup = null;
+                var newSet = createCarouselSet(beatmapSet);
 
-            Filter(null, false);
+                if (existingSet != null)
+                    root.RemoveChild(existingSet);
 
-            //check if we can/need to maintain our current selection.
-            if (hadSelection && newGroup != null)
-            {
-                var newSelection =
-                    newGroup.BeatmapPanels.Find(p => p.Beatmap.ID == selectedPanel?.Beatmap.ID);
+                if (newSet == null)
+                {
+                    itemsCache.Invalidate();
+                    SelectNext();
+                    return;
+                }
 
-                if (newSelection == null && oldGroup != null && selectedPanel != null)
-                    newSelection = newGroup.BeatmapPanels[Math.Min(newGroup.BeatmapPanels.Count - 1, oldGroup.BeatmapPanels.IndexOf(selectedPanel))];
+                root.AddChild(newSet);
 
-                selectGroup(newGroup, newSelection);
-            }
+                applyActiveCriteria(false, false);
+
+                //check if we can/need to maintain our current selection.
+                if (hadSelection)
+                    select((CarouselItem)newSet.Beatmaps.FirstOrDefault(b => b.Beatmap.ID == selectedBeatmap?.Beatmap.ID) ?? newSet);
+
+                itemsCache.Invalidate();
+            });
         }
 
-        public void SelectBeatmap(BeatmapInfo beatmap, bool animated = true)
+        public void SelectBeatmap(BeatmapInfo beatmap)
         {
-            if (beatmap == null || beatmap.Hidden)
-            {
-                SelectNext();
+            if (beatmap?.Hidden != false)
                 return;
-            }
 
-            if (beatmap == SelectedBeatmap) return;
-
-            foreach (BeatmapGroup group in groups)
+            foreach (CarouselBeatmapSet group in beatmapSets)
             {
-                var panel = group.BeatmapPanels.FirstOrDefault(p => p.Beatmap.Equals(beatmap));
-                if (panel != null)
+                var item = group.Beatmaps.FirstOrDefault(p => p.Beatmap.Equals(beatmap));
+                if (item != null)
                 {
-                    selectGroup(group, panel, animated);
+                    select(item);
                     return;
                 }
             }
         }
 
-        public Action<BeatmapInfo> SelectionChanged;
-
-        public Action StartRequested;
-
-        public Action<BeatmapSetInfo> DeleteRequested;
-
-        public Action<BeatmapSetInfo> RestoreRequested;
-
-        public Action<BeatmapInfo> EditRequested;
-
-        public Action<BeatmapInfo> HideDifficultyRequested;
-
-        private void selectNullBeatmap()
-        {
-            selectedGroup = null;
-            selectedPanel = null;
-            SelectionChanged?.Invoke(null);
-        }
-
         /// <summary>
         /// Increment selection in the carousel in a chosen direction.
         /// </summary>
@@ -185,331 +181,137 @@ private void selectNullBeatmap()
         /// <param name="skipDifficulties">Whether to skip individual difficulties and only increment over full groups.</param>
         public void SelectNext(int direction = 1, bool skipDifficulties = true)
         {
-            // todo: we may want to refactor and remove this as an optimisation in the future.
-            if (groups.All(g => g.State == BeatmapGroupState.Hidden))
-            {
-                selectNullBeatmap();
-                return;
-            }
-
-            int originalIndex = Math.Max(0, groups.IndexOf(selectedGroup));
+            int originalIndex = Items.IndexOf(selectedBeatmap?.Drawables.First());
             int currentIndex = originalIndex;
 
             // local function to increment the index in the required direction, wrapping over extremities.
-            int incrementIndex() => currentIndex = (currentIndex + direction + groups.Count) % groups.Count;
+            int incrementIndex() => currentIndex = (currentIndex + direction + Items.Count) % Items.Count;
 
-            // in the case we are skipping difficulties, we want to increment the index once before starting to find out new target
-            // (we don't care about the currently selected group).
-            if (skipDifficulties)
-                incrementIndex();
-
-            do
+            while (incrementIndex() != originalIndex)
             {
-                var group = groups[currentIndex];
+                var item = Items[currentIndex].Item;
 
-                if (group.State == BeatmapGroupState.Hidden) continue;
+                if (item.Filtered || item.State == CarouselItemState.Selected) continue;
 
-                // we are only interested in non-filtered panels.
-                IEnumerable<BeatmapPanel> validPanels = group.BeatmapPanels.Where(p => !p.Filtered);
-
-                // if we are considering difficulties, we need to do a few extrea steps.
-                if (!skipDifficulties)
+                switch (item)
                 {
-                    // we want to reverse the panel order if we are searching backwards.
-                    if (direction < 0)
-                        validPanels = validPanels.Reverse();
-
-                    // if we are currently on the selected panel, let's try to find a valid difficulty before leaving to the next group.
-                    // the first valid difficulty is found by skipping to the selected panel and then one further.
-                    if (currentIndex == originalIndex)
-                        validPanels = validPanels.SkipWhile(p => p != selectedPanel).Skip(1);
+                    case CarouselBeatmap beatmap:
+                        if (skipDifficulties) continue;
+                        select(beatmap);
+                        return;
+                    case CarouselBeatmapSet set:
+                        if (skipDifficulties)
+                            select(set);
+                        else
+                            select(direction > 0 ? set.Beatmaps.First(b => !b.Filtered) : set.Beatmaps.Last(b => !b.Filtered));
+                        return;
                 }
-
-                var next = validPanels.FirstOrDefault();
-
-                // at this point, we can perform the selection change if we have a valid new target, else continue to increment in the specified direction.
-                if (next != null)
-                {
-                    selectGroup(group, next);
-                    return;
-                }
-            } while (incrementIndex() != originalIndex);
+            }
         }
 
-        private IEnumerable<BeatmapGroup> getVisibleGroups() => groups.Where(selectGroup => selectGroup.State != BeatmapGroupState.Hidden);
-
         public void SelectNextRandom()
         {
-            if (groups.Count == 0)
+            var visible = beatmapSets.Where(s => !s.Filtered).ToList();
+            if (!visible.Any())
                 return;
 
-            var visibleGroups = getVisibleGroups();
-            if (!visibleGroups.Any())
-                return;
-
-            if (selectedGroup != null)
-                randomSelectedBeatmaps.Push(new KeyValuePair<BeatmapGroup, BeatmapPanel>(selectedGroup, selectedGroup.SelectedPanel));
-
-            BeatmapGroup group;
-
-            if (randomType == SelectionRandomType.RandomPermutation)
+            if (selectedBeatmap != null)
             {
-                var notSeenGroups = visibleGroups.Except(seenGroups);
-                if (!notSeenGroups.Any())
+                randomSelectedBeatmaps.Push(selectedBeatmap);
+
+                // when performing a random, we want to add the current set to the previously visited list
+                // else the user may be "randomised" to the existing selection.
+                if (previouslyVisitedRandomSets.LastOrDefault() != selectedBeatmapSet)
+                    previouslyVisitedRandomSets.Add(selectedBeatmapSet);
+            }
+
+            CarouselBeatmapSet set;
+
+            if (RandomAlgorithm == RandomSelectAlgorithm.RandomPermutation)
+            {
+                var notYetVisitedSets = visible.Except(previouslyVisitedRandomSets).ToList();
+                if (!notYetVisitedSets.Any())
                 {
-                    seenGroups.Clear();
-                    notSeenGroups = visibleGroups;
+                    previouslyVisitedRandomSets.Clear();
+                    notYetVisitedSets = visible;
                 }
 
-                group = notSeenGroups.ElementAt(RNG.Next(notSeenGroups.Count()));
-                seenGroups.Add(group);
+                set = notYetVisitedSets.ElementAt(RNG.Next(notYetVisitedSets.Count));
+                previouslyVisitedRandomSets.Add(set);
             }
             else
-                group = visibleGroups.ElementAt(RNG.Next(visibleGroups.Count()));
+                set = visible.ElementAt(RNG.Next(visible.Count));
 
-            BeatmapPanel panel = group.BeatmapPanels[RNG.Next(group.BeatmapPanels.Count)];
-
-            selectGroup(group, panel);
+            select(set.Beatmaps.Skip(RNG.Next(set.Beatmaps.Count())).FirstOrDefault());
         }
 
         public void SelectPreviousRandom()
         {
-            if (!randomSelectedBeatmaps.Any())
-                return;
-
-            var visibleGroups = getVisibleGroups();
-            if (!visibleGroups.Any())
-                return;
-
             while (randomSelectedBeatmaps.Any())
             {
-                var beatmapCoordinates = randomSelectedBeatmaps.Pop();
-                var group = beatmapCoordinates.Key;
-                if (visibleGroups.Contains(group))
+                var beatmap = randomSelectedBeatmaps.Pop();
+
+                if (!beatmap.Filtered)
                 {
-                    selectGroup(group, beatmapCoordinates.Value);
+                    if (RandomAlgorithm == RandomSelectAlgorithm.RandomPermutation)
+                        previouslyVisitedRandomSets.Remove(selectedBeatmapSet);
+                    select(beatmap);
                     break;
                 }
             }
         }
 
-        private FilterCriteria criteria = new FilterCriteria();
+        private void select(CarouselItem item)
+        {
+            if (item == null) return;
+            item.State.Value = CarouselItemState.Selected;
+        }
 
-        private ScheduledDelegate filterTask;
+        private FilterCriteria activeCriteria = new FilterCriteria();
+
+        protected ScheduledDelegate FilterTask;
 
         public bool AllowSelection = true;
 
-        public void FlushPendingFilters()
+        public void FlushPendingFilterOperations()
         {
-            if (filterTask?.Completed == false)
-                Filter(null, false);
+            if (FilterTask?.Completed == false)
+                applyActiveCriteria(false, false);
         }
 
-        public void Filter(FilterCriteria newCriteria = null, bool debounce = true)
+        public void Filter(FilterCriteria newCriteria, bool debounce = true)
         {
             if (newCriteria != null)
-                criteria = newCriteria;
+                activeCriteria = newCriteria;
 
-            Action perform = delegate
+            applyActiveCriteria(debounce, true);
+        }
+
+        private void applyActiveCriteria(bool debounce, bool scroll)
+        {
+            if (root.Children.Any() != true) return;
+
+            void perform()
             {
-                filterTask = null;
+                FilterTask = null;
 
-                criteria.Filter(groups);
+                root.Filter(activeCriteria);
+                itemsCache.Invalidate();
+                if (scroll) scrollPositionCache.Invalidate();
+            }
 
-                var filtered = new List<BeatmapGroup>(groups);
-
-                scrollableContent.Clear(false);
-                panels.Clear();
-                groups.Clear();
-
-                foreach (var g in filtered)
-                    addGroup(g);
-
-                computeYPositions();
-
-                selectedGroup?.UpdateState();
-
-                if (selectedGroup == null || selectedGroup.State == BeatmapGroupState.Hidden)
-                    SelectNext();
-                else
-                    selectGroup(selectedGroup, selectedPanel);
-            };
-
-            filterTask?.Cancel();
-            filterTask = null;
+            FilterTask?.Cancel();
+            FilterTask = null;
 
             if (debounce)
-                filterTask = Scheduler.AddDelayed(perform, 250);
+                FilterTask = Scheduler.AddDelayed(perform, 250);
             else
                 perform();
         }
 
-        public void ScrollToSelected(bool animated = true)
-        {
-            float selectedY = computeYPositions(animated);
-            ScrollTo(selectedY, animated);
-        }
+        private float? scrollTarget;
 
-        private BeatmapGroup createGroup(BeatmapSetInfo beatmapSet)
-        {
-            if (beatmapSet.Beatmaps.All(b => b.Hidden))
-                return null;
-
-            foreach (var b in beatmapSet.Beatmaps)
-            {
-                if (b.Metadata == null)
-                    b.Metadata = beatmapSet.Metadata;
-            }
-
-            return new BeatmapGroup(beatmapSet, manager)
-            {
-                SelectionChanged = (g, p) => selectGroup(g, p),
-                StartRequested = b => StartRequested?.Invoke(),
-                DeleteRequested = b => DeleteRequested?.Invoke(b),
-                RestoreHiddenRequested = s => RestoreRequested?.Invoke(s),
-                EditRequested = b => EditRequested?.Invoke(b),
-                HideDifficultyRequested = b => HideDifficultyRequested?.Invoke(b),
-                State = BeatmapGroupState.Collapsed
-            };
-        }
-
-        [BackgroundDependencyLoader(permitNulls: true)]
-        private void load(BeatmapManager manager, OsuConfigManager config)
-        {
-            this.manager = manager;
-
-            randomType = config.GetBindable<SelectionRandomType>(OsuSetting.SelectionRandomType);
-        }
-
-        private void addGroup(BeatmapGroup group)
-        {
-            // prevent duplicates by concurrent independent actions trying to add a group
-            if (groups.Any(g => g.BeatmapSet.ID == group.BeatmapSet.ID))
-                return;
-
-            groups.Add(group);
-            panels.Add(group.Header);
-            panels.AddRange(group.BeatmapPanels);
-        }
-
-        private void removeGroup(BeatmapGroup group)
-        {
-            if (group == null)
-                return;
-
-            if (selectedGroup == group)
-            {
-                if (getVisibleGroups().Count() == 1)
-                    selectNullBeatmap();
-                else
-                    SelectNext();
-            }
-
-            groups.Remove(group);
-            panels.Remove(group.Header);
-            foreach (var p in group.BeatmapPanels)
-                panels.Remove(p);
-
-            scrollableContent.Remove(group.Header);
-            scrollableContent.RemoveRange(group.BeatmapPanels);
-
-            computeYPositions();
-        }
-
-        /// <summary>
-        /// Computes the target Y positions for every panel in the carousel.
-        /// </summary>
-        /// <returns>The Y position of the currently selected panel.</returns>
-        private float computeYPositions(bool animated = true)
-        {
-            yPositions.Clear();
-
-            float currentY = DrawHeight / 2;
-            float selectedY = currentY;
-
-            foreach (BeatmapGroup group in groups)
-            {
-                movePanel(group.Header, group.State != BeatmapGroupState.Hidden, animated, ref currentY);
-
-                if (group.State == BeatmapGroupState.Expanded)
-                {
-                    group.Header.MoveToX(-100, 500, Easing.OutExpo);
-                    var headerY = group.Header.Position.Y;
-
-                    foreach (BeatmapPanel panel in group.BeatmapPanels)
-                    {
-                        if (panel == selectedPanel)
-                            selectedY = currentY + panel.DrawHeight / 2 - DrawHeight / 2;
-
-                        panel.MoveToX(-50, 500, Easing.OutExpo);
-
-                        bool isHidden = panel.State == PanelSelectedState.Hidden;
-
-                        //on first display we want to begin hidden under our group's header.
-                        if (isHidden || panel.Alpha == 0)
-                            panel.MoveToY(headerY);
-
-                        movePanel(panel, !isHidden, animated, ref currentY);
-                    }
-                }
-                else
-                {
-                    group.Header.MoveToX(0, 500, Easing.OutExpo);
-
-                    foreach (BeatmapPanel panel in group.BeatmapPanels)
-                    {
-                        panel.MoveToX(0, 500, Easing.OutExpo);
-                        movePanel(panel, false, animated, ref currentY);
-                    }
-                }
-            }
-
-            currentY += DrawHeight / 2;
-            scrollableContent.Height = currentY;
-
-            return selectedY;
-        }
-
-        private void movePanel(Panel panel, bool advance, bool animated, ref float currentY)
-        {
-            yPositions.Add(currentY);
-            panel.MoveToY(currentY, animated ? 750 : 0, Easing.OutExpo);
-
-            if (advance)
-                currentY += panel.DrawHeight + 5;
-        }
-
-        private void selectGroup(BeatmapGroup group, BeatmapPanel panel = null, bool animated = true)
-        {
-            try
-            {
-                if (panel == null || panel.Filtered == true)
-                    panel = group.BeatmapPanels.First(p => !p.Filtered);
-
-                if (selectedPanel == panel) return;
-
-                Trace.Assert(group.BeatmapPanels.Contains(panel), @"Selected panel must be in provided group");
-
-                if (selectedGroup != null && selectedGroup != group && selectedGroup.State != BeatmapGroupState.Hidden)
-                    selectedGroup.State = BeatmapGroupState.Collapsed;
-
-                group.State = BeatmapGroupState.Expanded;
-                group.SelectedPanel = panel;
-
-                panel.State = PanelSelectedState.Selected;
-
-                if (selectedPanel == panel) return;
-
-                selectedPanel = panel;
-                selectedGroup = group;
-
-                SelectionChanged?.Invoke(panel.Beatmap);
-            }
-            finally
-            {
-                ScrollToSelected(animated);
-            }
-        }
+        public void ScrollToSelected() => scrollPositionCache.Invalidate();
 
         protected override bool OnKeyDown(InputState state, KeyDownEventArgs args)
         {
@@ -545,68 +347,185 @@ protected override void Update()
         {
             base.Update();
 
+            if (!itemsCache.IsValid)
+                updateItems();
+
+            if (!scrollPositionCache.IsValid)
+                updateScrollPosition();
+
             float drawHeight = DrawHeight;
 
-            // Remove all panels that should no longer be on-screen
-            scrollableContent.RemoveAll(delegate(Panel p)
-            {
-                float panelPosY = p.Position.Y;
-                bool remove = panelPosY < Current - p.DrawHeight || panelPosY > Current + drawHeight || !p.IsPresent;
-                return remove;
-            });
+            // Remove all items that should no longer be on-screen
+            scrollableContent.RemoveAll(p => p.Y < Current - p.DrawHeight || p.Y > Current + drawHeight || !p.IsPresent);
 
-            // Find index range of all panels that should be on-screen
-            Trace.Assert(panels.Count == yPositions.Count);
+            // Find index range of all items that should be on-screen
+            Trace.Assert(Items.Count == yPositions.Count);
 
-            int firstIndex = yPositions.BinarySearch(Current - Panel.MAX_HEIGHT);
+            int firstIndex = yPositions.BinarySearch(Current - DrawableCarouselItem.MAX_HEIGHT);
             if (firstIndex < 0) firstIndex = ~firstIndex;
             int lastIndex = yPositions.BinarySearch(Current + drawHeight);
-            if (lastIndex < 0)
-            {
-                lastIndex = ~lastIndex;
+            if (lastIndex < 0) lastIndex = ~lastIndex;
 
-                // Add the first panel of the last visible beatmap group to preload its data.
-                if (lastIndex != 0 && panels[lastIndex - 1] is BeatmapSetHeader)
-                    lastIndex++;
-            }
+            int notVisibleCount = 0;
 
-            // Add those panels within the previously found index range that should be displayed.
+            // Add those items within the previously found index range that should be displayed.
             for (int i = firstIndex; i < lastIndex; ++i)
             {
-                Panel panel = panels[i];
-                if (panel.State == PanelSelectedState.Hidden)
+                DrawableCarouselItem item = Items[i];
+
+                if (!item.Item.Visible)
+                {
+                    if (!item.IsPresent)
+                        notVisibleCount++;
                     continue;
+                }
 
                 // Only add if we're not already part of the content.
-                if (!scrollableContent.Contains(panel))
+                if (!scrollableContent.Contains(item))
                 {
-                    // Makes sure headers are always _below_ panels,
+                    // Makes sure headers are always _below_ items,
                     // and depth flows downward.
-                    panel.Depth = i + (panel is BeatmapSetHeader ? panels.Count : 0);
+                    item.Depth = i + (item is DrawableCarouselBeatmapSet ? -Items.Count : 0);
 
-                    switch (panel.LoadState)
+                    switch (item.LoadState)
                     {
                         case LoadState.NotLoaded:
-                            LoadComponentAsync(panel);
+                            LoadComponentAsync(item);
                             break;
                         case LoadState.Loading:
                             break;
                         default:
-                            scrollableContent.Add(panel);
+                            scrollableContent.Add(item);
                             break;
                     }
                 }
             }
 
-            // Update externally controlled state of currently visible panels
+            // this is not actually useful right now, but once we have groups may well be.
+            if (notVisibleCount > 50)
+                itemsCache.Invalidate();
+
+            // Update externally controlled state of currently visible items
             // (e.g. x-offset and opacity).
             float halfHeight = drawHeight / 2;
-            foreach (Panel p in scrollableContent.Children)
-                updatePanel(p, halfHeight);
+            foreach (DrawableCarouselItem p in scrollableContent.Children)
+                updateItem(p, halfHeight);
+        }
+
+        private CarouselBeatmapSet createCarouselSet(BeatmapSetInfo beatmapSet)
+        {
+            if (beatmapSet.Beatmaps.All(b => b.Hidden))
+                return null;
+
+            // todo: remove the need for this.
+            foreach (var b in beatmapSet.Beatmaps)
+            {
+                if (b.Metadata == null)
+                    b.Metadata = beatmapSet.Metadata;
+            }
+
+            var set = new CarouselBeatmapSet(beatmapSet);
+
+            foreach (var c in set.Beatmaps)
+            {
+                c.State.ValueChanged += v =>
+                {
+                    if (v == CarouselItemState.Selected)
+                    {
+                        selectedBeatmapSet = set;
+                        SelectionChanged?.Invoke(c.Beatmap);
+
+                        itemsCache.Invalidate();
+                        scrollPositionCache.Invalidate();
+                    }
+                };
+            }
+
+            return set;
         }
 
         /// <summary>
-        /// Computes the x-offset of currently visible panels. Makes the carousel appear round.
+        /// Computes the target Y positions for every item in the carousel.
+        /// </summary>
+        /// <returns>The Y position of the currently selected item.</returns>
+        private void updateItems()
+        {
+            Items = root.Drawables.ToList();
+
+            yPositions.Clear();
+
+            float currentY = DrawHeight / 2;
+            DrawableCarouselBeatmapSet lastSet = null;
+
+            scrollTarget = null;
+
+            foreach (DrawableCarouselItem d in Items)
+            {
+                if (d.IsPresent)
+                {
+                    switch (d)
+                    {
+                        case DrawableCarouselBeatmapSet set:
+                            lastSet = set;
+
+                            set.MoveToX(set.Item.State == CarouselItemState.Selected ? -100 : 0, 500, Easing.OutExpo);
+                            set.MoveToY(currentY, 750, Easing.OutExpo);
+                            break;
+                        case DrawableCarouselBeatmap beatmap:
+                            if (beatmap.Item.State.Value == CarouselItemState.Selected)
+                                scrollTarget = currentY + beatmap.DrawHeight / 2 - DrawHeight / 2;
+
+                            void performMove(float y, float? startY = null)
+                            {
+                                if (startY != null) beatmap.MoveTo(new Vector2(0, startY.Value));
+                                beatmap.MoveToX(beatmap.Item.State == CarouselItemState.Selected ? -50 : 0, 500, Easing.OutExpo);
+                                beatmap.MoveToY(y, 750, Easing.OutExpo);
+                            }
+
+                            Debug.Assert(lastSet != null);
+
+                            float? setY = null;
+                            if (!d.IsLoaded || beatmap.Alpha == 0) // can't use IsPresent due to DrawableCarouselItem override.
+                                setY = lastSet.Y + lastSet.DrawHeight + 5;
+
+                            if (d.IsLoaded)
+                                performMove(currentY, setY);
+                            else
+                            {
+                                float y = currentY;
+                                d.OnLoadComplete = _ => performMove(y, setY);
+                            }
+
+                            break;
+                    }
+                }
+
+                yPositions.Add(currentY);
+
+                if (d.Item.Visible)
+                    currentY += d.DrawHeight + 5;
+            }
+
+            currentY += DrawHeight / 2;
+            scrollableContent.Height = currentY;
+
+            if (selectedBeatmapSet != null && selectedBeatmapSet.State.Value != CarouselItemState.Selected)
+            {
+                selectedBeatmapSet = null;
+                SelectionChanged?.Invoke(null);
+            }
+
+            itemsCache.Validate();
+        }
+
+        private void updateScrollPosition()
+        {
+            if (scrollTarget != null) ScrollTo(scrollTarget.Value);
+            scrollPositionCache.Validate();
+        }
+
+        /// <summary>
+        /// Computes the x-offset of currently visible items. Makes the carousel appear round.
         /// </summary>
         /// <param name="dist">
         /// Vertical distance from the center of the carousel container
@@ -624,20 +543,20 @@ private static float offsetX(float dist, float halfHeight)
         }
 
         /// <summary>
-        /// Update a panel's x position and multiplicative alpha based on its y position and
+        /// Update a item's x position and multiplicative alpha based on its y position and
         /// the current scroll position.
         /// </summary>
-        /// <param name="p">The panel to be updated.</param>
+        /// <param name="p">The item to be updated.</param>
         /// <param name="halfHeight">Half the draw height of the carousel container.</param>
-        private void updatePanel(Panel p, float halfHeight)
+        private void updateItem(DrawableCarouselItem p, float halfHeight)
         {
             var height = p.IsPresent ? p.DrawHeight : 0;
 
-            float panelDrawY = p.Position.Y - Current + height / 2;
-            float dist = Math.Abs(1f - panelDrawY / halfHeight);
+            float itemDrawY = p.Position.Y - Current + height / 2;
+            float dist = Math.Abs(1f - itemDrawY / halfHeight);
 
             // Setting the origin position serves as an additive position on top of potential
-            // local transformation we may want to apply (e.g. when a panel gets selected, we
+            // local transformation we may want to apply (e.g. when a item gets selected, we
             // may want to smoothly transform it leftwards.)
             p.OriginPosition = new Vector2(-offsetX(dist, halfHeight), 0);
 

osu.Game/Screens/Select/Carousel/CarouselBeatmap.cs

@@ -0,0 +1,55 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Linq;
+using osu.Game.Beatmaps;
+using osu.Game.Screens.Select.Filter;
+
+namespace osu.Game.Screens.Select.Carousel
+{
+    public class CarouselBeatmap : CarouselItem
+    {
+        public readonly BeatmapInfo Beatmap;
+
+        public CarouselBeatmap(BeatmapInfo beatmap)
+        {
+            Beatmap = beatmap;
+            State.Value = CarouselItemState.Collapsed;
+        }
+
+        protected override DrawableCarouselItem CreateDrawableRepresentation() => new DrawableCarouselBeatmap(this);
+
+        public override void Filter(FilterCriteria criteria)
+        {
+            base.Filter(criteria);
+
+            bool match = criteria.Ruleset == null || Beatmap.RulesetID == criteria.Ruleset.ID || Beatmap.RulesetID == 0 && criteria.Ruleset.ID > 0 && criteria.AllowConvertedBeatmaps;
+
+            if (!string.IsNullOrEmpty(criteria.SearchText))
+                match &=
+                    Beatmap.Metadata.SearchableTerms.Any(term => term.IndexOf(criteria.SearchText, StringComparison.InvariantCultureIgnoreCase) >= 0) ||
+                    Beatmap.Version.IndexOf(criteria.SearchText, StringComparison.InvariantCultureIgnoreCase) >= 0;
+
+            Filtered.Value = !match;
+        }
+
+        public override int CompareTo(FilterCriteria criteria, CarouselItem other)
+        {
+            if (!(other is CarouselBeatmap otherBeatmap))
+                return base.CompareTo(criteria, other);
+
+            switch (criteria.Sort)
+            {
+                default:
+                case SortMode.Difficulty:
+                    var ruleset = Beatmap.RulesetID.CompareTo(otherBeatmap.Beatmap.RulesetID);
+                    if (ruleset != 0) return ruleset;
+
+                    return Beatmap.StarDifficulty.CompareTo(otherBeatmap.Beatmap.StarDifficulty);
+            }
+        }
+
+        public override string ToString() => Beatmap.ToString();
+    }
+}

osu.Game/Screens/Select/Carousel/CarouselBeatmapSet.cs

@@ -0,0 +1,58 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Game.Beatmaps;
+using osu.Game.Screens.Select.Filter;
+
+namespace osu.Game.Screens.Select.Carousel
+{
+    public class CarouselBeatmapSet : CarouselGroupEagerSelect
+    {
+        public IEnumerable<CarouselBeatmap> Beatmaps => InternalChildren.OfType<CarouselBeatmap>();
+
+        public BeatmapSetInfo BeatmapSet;
+
+        public CarouselBeatmapSet(BeatmapSetInfo beatmapSet)
+        {
+            BeatmapSet = beatmapSet ?? throw new ArgumentNullException(nameof(beatmapSet));
+
+            beatmapSet.Beatmaps
+                      .Where(b => !b.Hidden)
+                      .Select(b => new CarouselBeatmap(b))
+                      .ForEach(AddChild);
+        }
+
+        protected override DrawableCarouselItem CreateDrawableRepresentation() => new DrawableCarouselBeatmapSet(this);
+
+        public override int CompareTo(FilterCriteria criteria, CarouselItem other)
+        {
+            if (!(other is CarouselBeatmapSet otherSet))
+                return base.CompareTo(criteria, other);
+
+            switch (criteria.Sort)
+            {
+                default:
+                case SortMode.Artist:
+                    return string.Compare(BeatmapSet.Metadata.Artist, otherSet.BeatmapSet.Metadata.Artist, StringComparison.InvariantCultureIgnoreCase);
+                case SortMode.Title:
+                    return string.Compare(BeatmapSet.Metadata.Title, otherSet.BeatmapSet.Metadata.Title, StringComparison.InvariantCultureIgnoreCase);
+                case SortMode.Author:
+                    return string.Compare(BeatmapSet.Metadata.Author.Username, otherSet.BeatmapSet.Metadata.Author.Username, StringComparison.InvariantCultureIgnoreCase);
+                case SortMode.Difficulty:
+                    return BeatmapSet.MaxStarDifficulty.CompareTo(otherSet.BeatmapSet.MaxStarDifficulty);
+            }
+        }
+
+        public override void Filter(FilterCriteria criteria)
+        {
+            base.Filter(criteria);
+            Filtered.Value = InternalChildren.All(i => i.Filtered);
+        }
+
+        public override string ToString() => BeatmapSet.ToString();
+    }
+}

osu.Game/Screens/Select/Carousel/CarouselGroup.cs

@@ -0,0 +1,91 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System.Collections.Generic;
+
+namespace osu.Game.Screens.Select.Carousel
+{
+    /// <summary>
+    /// A group which ensures only one child is selected.
+    /// </summary>
+    public class CarouselGroup : CarouselItem
+    {
+        private readonly List<CarouselItem> items;
+
+        protected override DrawableCarouselItem CreateDrawableRepresentation() => null;
+
+        public IReadOnlyList<CarouselItem> Children => InternalChildren;
+
+        protected List<CarouselItem> InternalChildren = new List<CarouselItem>();
+
+        public override List<DrawableCarouselItem> Drawables
+        {
+            get
+            {
+                var drawables = base.Drawables;
+                foreach (var c in InternalChildren)
+                    drawables.AddRange(c.Drawables);
+                return drawables;
+            }
+        }
+
+        public virtual void RemoveChild(CarouselItem i)
+        {
+            InternalChildren.Remove(i);
+
+            // it's important we do the deselection after removing, so any further actions based on
+            // State.ValueChanged make decisions post-removal.
+            i.State.Value = CarouselItemState.Collapsed;
+        }
+
+        public virtual void AddChild(CarouselItem i)
+        {
+            i.State.ValueChanged += v => ChildItemStateChanged(i, v);
+            InternalChildren.Add(i);
+        }
+
+        public CarouselGroup(List<CarouselItem> items = null)
+        {
+            if (items != null) InternalChildren = items;
+
+            State.ValueChanged += v =>
+            {
+                switch (v)
+                {
+                    case CarouselItemState.Collapsed:
+                    case CarouselItemState.NotSelected:
+                        InternalChildren.ForEach(c => c.State.Value = CarouselItemState.Collapsed);
+                        break;
+                    case CarouselItemState.Selected:
+                        InternalChildren.ForEach(c =>
+                        {
+                            if (c.State == CarouselItemState.Collapsed) c.State.Value = CarouselItemState.NotSelected;
+                        });
+                        break;
+                }
+            };
+        }
+
+        public override void Filter(FilterCriteria criteria)
+        {
+            base.Filter(criteria);
+            InternalChildren.Sort((x, y) => x.CompareTo(criteria, y));
+            InternalChildren.ForEach(c => c.Filter(criteria));
+        }
+
+        protected virtual void ChildItemStateChanged(CarouselItem item, CarouselItemState value)
+        {
+            // ensure we are the only item selected
+            if (value == CarouselItemState.Selected)
+            {
+                foreach (var b in InternalChildren)
+                {
+                    if (item == b) continue;
+                    b.State.Value = CarouselItemState.NotSelected;
+                }
+
+                State.Value = CarouselItemState.Selected;
+            }
+        }
+    }
+}

osu.Game/Screens/Select/Carousel/CarouselGroupEagerSelect.cs

@@ -0,0 +1,104 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Linq;
+
+namespace osu.Game.Screens.Select.Carousel
+{
+    /// <summary>
+    /// A group which ensures at least one child is selected (if the group itself is selected).
+    /// </summary>
+    public class CarouselGroupEagerSelect : CarouselGroup
+    {
+        public CarouselGroupEagerSelect()
+        {
+            State.ValueChanged += v =>
+            {
+                if (v == CarouselItemState.Selected)
+                    attemptSelection();
+            };
+        }
+
+        /// <summary>
+        /// We need to keep track of the index for cases where the selection is removed but we want to select a new item based on its old location.
+        /// </summary>
+        private int lastSelectedIndex;
+
+        private CarouselItem lastSelected;
+
+        /// <summary>
+        /// To avoid overhead during filter operations, we don't attempt any selections until after all
+        /// children have been filtered. This bool will be true during the base <see cref="Filter(FilterCriteria)"/>
+        /// operation.
+        /// </summary>
+        private bool filteringChildren;
+
+        public override void Filter(FilterCriteria criteria)
+        {
+            filteringChildren = true;
+            base.Filter(criteria);
+            filteringChildren = false;
+
+            attemptSelection();
+        }
+
+        public override void RemoveChild(CarouselItem i)
+        {
+            base.RemoveChild(i);
+
+            if (i != lastSelected)
+                updateSelectedIndex();
+        }
+
+        public override void AddChild(CarouselItem i)
+        {
+            base.AddChild(i);
+            attemptSelection();
+        }
+
+        protected override void ChildItemStateChanged(CarouselItem item, CarouselItemState value)
+        {
+            base.ChildItemStateChanged(item, value);
+
+            switch (value)
+            {
+                case CarouselItemState.Selected:
+                    updateSelected(item);
+                    break;
+                case CarouselItemState.NotSelected:
+                case CarouselItemState.Collapsed:
+                    attemptSelection();
+                    break;
+            }
+        }
+
+        private void attemptSelection()
+        {
+            if (filteringChildren) return;
+
+            // we only perform eager selection if we are a currently selected group.
+            if (State != CarouselItemState.Selected) return;
+
+            // we only perform eager selection if none of our children are in a selected state already.
+            if (Children.Any(i => i.State == CarouselItemState.Selected)) return;
+
+            CarouselItem nextToSelect =
+                Children.Skip(lastSelectedIndex).FirstOrDefault(i => !i.Filtered) ??
+                Children.Reverse().Skip(InternalChildren.Count - lastSelectedIndex).FirstOrDefault(i => !i.Filtered);
+
+            if (nextToSelect != null)
+                nextToSelect.State.Value = CarouselItemState.Selected;
+            else
+                updateSelected(null);
+        }
+
+        private void updateSelected(CarouselItem newSelection)
+        {
+            lastSelected = newSelection;
+            updateSelectedIndex();
+        }
+
+        private void updateSelectedIndex() => lastSelectedIndex = lastSelected == null ? 0 : Math.Max(0, InternalChildren.IndexOf(lastSelected));
+    }
+}

osu.Game/Screens/Select/Carousel/CarouselItem.cs

@@ -0,0 +1,62 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+using System.Collections.Generic;
+using osu.Framework.Configuration;
+
+namespace osu.Game.Screens.Select.Carousel
+{
+    public abstract class CarouselItem
+    {
+        public readonly BindableBool Filtered = new BindableBool();
+
+        public readonly Bindable<CarouselItemState> State = new Bindable<CarouselItemState>(CarouselItemState.NotSelected);
+
+        /// <summary>
+        /// This item is not in a hidden state.
+        /// </summary>
+        public bool Visible => State.Value != CarouselItemState.Collapsed && !Filtered;
+
+        public virtual List<DrawableCarouselItem> Drawables
+        {
+            get
+            {
+                var items = new List<DrawableCarouselItem>();
+
+                var self = drawableRepresentation.Value;
+                if (self?.IsPresent == true) items.Add(self);
+
+                return items;
+            }
+        }
+
+        protected CarouselItem()
+        {
+            drawableRepresentation = new Lazy<DrawableCarouselItem>(CreateDrawableRepresentation);
+
+            Filtered.ValueChanged += v =>
+            {
+                if (v && State == CarouselItemState.Selected)
+                    State.Value = CarouselItemState.NotSelected;
+            };
+        }
+
+        private readonly Lazy<DrawableCarouselItem> drawableRepresentation;
+
+        protected abstract DrawableCarouselItem CreateDrawableRepresentation();
+
+        public virtual void Filter(FilterCriteria criteria)
+        {
+        }
+
+        public virtual int CompareTo(FilterCriteria criteria, CarouselItem other) => GetHashCode().CompareTo(other.GetHashCode());
+    }
+
+    public enum CarouselItemState
+    {
+        Collapsed,
+        NotSelected,
+        Selected,
+    }
+}

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmap.cs

@@ -2,85 +2,56 @@
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
 using System;
-using osu.Framework.Configuration;
+using osu.Framework.Allocation;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Colour;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Cursor;
+using osu.Framework.Graphics.Shapes;
 using osu.Framework.Graphics.Sprites;
+using osu.Framework.Graphics.UserInterface;
+using osu.Framework.Input;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Drawables;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Backgrounds;
+using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
 using OpenTK;
 using OpenTK.Graphics;
-using osu.Framework.Input;
-using osu.Game.Graphics.Sprites;
-using osu.Framework.Graphics.Shapes;
-using osu.Framework.Graphics.UserInterface;
 
-namespace osu.Game.Beatmaps.Drawables
+namespace osu.Game.Screens.Select.Carousel
 {
-    public class BeatmapPanel : Panel, IHasContextMenu
+    public class DrawableCarouselBeatmap : DrawableCarouselItem, IHasContextMenu
     {
-        public BeatmapInfo Beatmap;
-        private readonly Sprite background;
+        private readonly BeatmapInfo beatmap;
 
-        public Action<BeatmapPanel> GainedSelection;
-        public Action<BeatmapPanel> StartRequested;
-        public Action<BeatmapPanel> EditRequested;
-        public Action<BeatmapInfo> HideRequested;
+        private Sprite background;
 
-        private readonly Triangles triangles;
-        private readonly StarCounter starCounter;
+        private Action<BeatmapInfo> startRequested;
+        private Action<BeatmapInfo> editRequested;
+        private Action<BeatmapInfo> hideRequested;
 
-        protected override void Selected()
+        private Triangles triangles;
+        private StarCounter starCounter;
+
+        public DrawableCarouselBeatmap(CarouselBeatmap panel) : base(panel)
         {
-            base.Selected();
-
-            GainedSelection?.Invoke(this);
-
-            background.Colour = ColourInfo.GradientVertical(
-                new Color4(20, 43, 51, 255),
-                new Color4(40, 86, 102, 255));
-
-            triangles.Colour = Color4.White;
-        }
-
-        protected override void Deselected()
-        {
-            base.Deselected();
-
-            background.Colour = new Color4(20, 43, 51, 255);
-            triangles.Colour = OsuColour.Gray(0.5f);
-        }
-
-        protected override bool OnClick(InputState state)
-        {
-            if (State == PanelSelectedState.Selected)
-                StartRequested?.Invoke(this);
-
-            return base.OnClick(state);
-        }
-
-        public BindableBool Filtered = new BindableBool();
-
-        protected override void ApplyState(PanelSelectedState last = PanelSelectedState.Hidden)
-        {
-            if (!IsLoaded) return;
-
-            base.ApplyState(last);
-
-            if (last == PanelSelectedState.Hidden && State != last)
-                starCounter.ReplayAnimation();
-        }
-
-        public BeatmapPanel(BeatmapInfo beatmap)
-        {
-            if (beatmap == null)
-                throw new ArgumentNullException(nameof(beatmap));
-
-            Beatmap = beatmap;
+            beatmap = panel.Beatmap;
             Height *= 0.60f;
+        }
+
+        [BackgroundDependencyLoader(true)]
+        private void load(SongSelect songSelect, BeatmapManager manager)
+        {
+            if (songSelect != null)
+            {
+                startRequested = songSelect.Start;
+                editRequested = songSelect.Edit;
+            }
+
+            if (manager != null)
+                hideRequested = manager.Hide;
 
             Children = new Drawable[]
             {
@@ -160,11 +131,46 @@ public BeatmapPanel(BeatmapInfo beatmap)
             };
         }
 
+        protected override void Selected()
+        {
+            base.Selected();
+
+            background.Colour = ColourInfo.GradientVertical(
+                new Color4(20, 43, 51, 255),
+                new Color4(40, 86, 102, 255));
+
+            triangles.Colour = Color4.White;
+        }
+
+        protected override void Deselected()
+        {
+            base.Deselected();
+
+            background.Colour = new Color4(20, 43, 51, 255);
+            triangles.Colour = OsuColour.Gray(0.5f);
+        }
+
+        protected override bool OnClick(InputState state)
+        {
+            if (Item.State == CarouselItemState.Selected)
+                startRequested?.Invoke(beatmap);
+
+            return base.OnClick(state);
+        }
+
+        protected override void ApplyState()
+        {
+            if (Item.State.Value != CarouselItemState.Collapsed && Alpha == 0)
+                starCounter.ReplayAnimation();
+
+            base.ApplyState();
+        }
+
         public MenuItem[] ContextMenuItems => new MenuItem[]
         {
-            new OsuMenuItem("Play", MenuItemType.Highlighted, () => StartRequested?.Invoke(this)),
-            new OsuMenuItem("Edit", MenuItemType.Standard, () => EditRequested?.Invoke(this)),
-            new OsuMenuItem("Hide", MenuItemType.Destructive, () => HideRequested?.Invoke(Beatmap)),
+            new OsuMenuItem("Play", MenuItemType.Highlighted, () => startRequested?.Invoke(beatmap)),
+            new OsuMenuItem("Edit", MenuItemType.Standard, () => editRequested?.Invoke(beatmap)),
+            new OsuMenuItem("Hide", MenuItemType.Destructive, () => hideRequested?.Invoke(beatmap)),
         };
     }
 }

osu.Game/Screens/Select/Carousel/DrawableCarouselBeatmapSet.cs

@@ -4,68 +4,57 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using OpenTK;
-using OpenTK.Graphics;
 using osu.Framework.Allocation;
 using osu.Framework.Configuration;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Colour;
 using osu.Framework.Graphics.Containers;
 using osu.Framework.Graphics.Cursor;
-using osu.Framework.Localisation;
-using osu.Game.Graphics.Sprites;
 using osu.Framework.Graphics.Shapes;
 using osu.Framework.Graphics.UserInterface;
+using osu.Framework.Localisation;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.Drawables;
+using osu.Game.Graphics.Sprites;
 using osu.Game.Graphics.UserInterface;
+using OpenTK;
+using OpenTK.Graphics;
 
-namespace osu.Game.Beatmaps.Drawables
+namespace osu.Game.Screens.Select.Carousel
 {
-    public class BeatmapSetHeader : Panel, IHasContextMenu
+    public class DrawableCarouselBeatmapSet : DrawableCarouselItem, IHasContextMenu
     {
-        public Action<BeatmapSetHeader> GainedSelection;
+        private Action<BeatmapSetInfo> deleteRequested;
+        private Action<BeatmapSetInfo> restoreHiddenRequested;
 
-        public Action<BeatmapSetInfo> DeleteRequested;
-
-        public Action<BeatmapSetInfo> RestoreHiddenRequested;
-
-        private readonly WorkingBeatmap beatmap;
+        private readonly BeatmapSetInfo beatmapSet;
 
         private readonly FillFlowContainer difficultyIcons;
 
-        public BeatmapSetHeader(WorkingBeatmap beatmap)
+        public DrawableCarouselBeatmapSet(CarouselBeatmapSet set)
+            : base(set)
         {
-            if (beatmap == null)
-                throw new ArgumentNullException(nameof(beatmap));
-
-            this.beatmap = beatmap;
-
-            difficultyIcons = new FillFlowContainer
-            {
-                Margin = new MarginPadding { Top = 5 },
-                AutoSizeAxes = Axes.Both,
-            };
-        }
-
-        protected override void Selected()
-        {
-            base.Selected();
-            GainedSelection?.Invoke(this);
+            beatmapSet = set.BeatmapSet;
         }
 
         [BackgroundDependencyLoader]
-        private void load(LocalisationEngine localisation)
+        private void load(LocalisationEngine localisation, BeatmapManager manager)
         {
             if (localisation == null)
                 throw new ArgumentNullException(nameof(localisation));
 
+            restoreHiddenRequested = s => s.Beatmaps.ForEach(manager.Restore);
+            deleteRequested = manager.Delete;
+
             Children = new Drawable[]
             {
                 new DelayedLoadWrapper(
-                    new PanelBackground(beatmap)
+                    new PanelBackground(manager.GetWorkingBeatmap(beatmapSet.Beatmaps.FirstOrDefault()))
                     {
                         RelativeSizeAxes = Axes.Both,
-                        OnLoadComplete = d => d.FadeInFromZero(400, Easing.Out),
-                    }, 300),
+                        OnLoadComplete = d => d.FadeInFromZero(1000, Easing.OutQuint),
+                    }, 300
+                ),
                 new FillFlowContainer
                 {
                     Direction = FillDirection.Vertical,
@@ -76,23 +65,46 @@ private void load(LocalisationEngine localisation)
                         new OsuSpriteText
                         {
                             Font = @"Exo2.0-BoldItalic",
-                            Current = localisation.GetUnicodePreference(beatmap.Metadata.TitleUnicode, beatmap.Metadata.Title),
+                            Current = localisation.GetUnicodePreference(beatmapSet.Metadata.TitleUnicode, beatmapSet.Metadata.Title),
                             TextSize = 22,
                             Shadow = true,
                         },
                         new OsuSpriteText
                         {
                             Font = @"Exo2.0-SemiBoldItalic",
-                            Current = localisation.GetUnicodePreference(beatmap.Metadata.ArtistUnicode, beatmap.Metadata.Artist),
+                            Current = localisation.GetUnicodePreference(beatmapSet.Metadata.ArtistUnicode, beatmapSet.Metadata.Artist),
                             TextSize = 17,
                             Shadow = true,
                         },
-                        difficultyIcons
+                        new FillFlowContainer<FilterableDifficultyIcon>
+                        {
+                            Margin = new MarginPadding { Top = 5 },
+                            AutoSizeAxes = Axes.Both,
+                            Children = ((CarouselBeatmapSet)Item).Beatmaps.Select(b => new FilterableDifficultyIcon(b)).ToList()
+                        }
                     }
                 }
             };
         }
 
+        public MenuItem[] ContextMenuItems
+        {
+            get
+            {
+                List<MenuItem> items = new List<MenuItem>();
+
+                if (Item.State == CarouselItemState.NotSelected)
+                    items.Add(new OsuMenuItem("Expand", MenuItemType.Highlighted, () => Item.State.Value = CarouselItemState.Selected));
+
+                if (beatmapSet.Beatmaps.Any(b => b.Hidden))
+                    items.Add(new OsuMenuItem("Restore all hidden", MenuItemType.Standard, () => restoreHiddenRequested?.Invoke(beatmapSet)));
+
+                items.Add(new OsuMenuItem("Delete", MenuItemType.Destructive, () => deleteRequested?.Invoke(beatmapSet)));
+
+                return items.ToArray();
+            }
+        }
+
         private class PanelBackground : BufferedContainer
         {
             public PanelBackground(WorkingBeatmap working)
@@ -129,22 +141,19 @@ public PanelBackground(WorkingBeatmap working)
                             new Box
                             {
                                 RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(
-                                    Color4.Black, new Color4(0f, 0f, 0f, 0.9f)),
+                                Colour = ColourInfo.GradientHorizontal(Color4.Black, new Color4(0f, 0f, 0f, 0.9f)),
                                 Width = 0.05f,
                             },
                             new Box
                             {
                                 RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(
-                                    new Color4(0f, 0f, 0f, 0.9f), new Color4(0f, 0f, 0f, 0.1f)),
+                                Colour = ColourInfo.GradientHorizontal(new Color4(0f, 0f, 0f, 0.9f), new Color4(0f, 0f, 0f, 0.1f)),
                                 Width = 0.2f,
                             },
                             new Box
                             {
                                 RelativeSizeAxes = Axes.Both,
-                                Colour = ColourInfo.GradientHorizontal(
-                                    new Color4(0f, 0f, 0f, 0.1f), new Color4(0, 0, 0, 0)),
+                                Colour = ColourInfo.GradientHorizontal(new Color4(0f, 0f, 0f, 0.1f), new Color4(0, 0, 0, 0)),
                                 Width = 0.05f,
                             },
                         }
@@ -153,41 +162,15 @@ public PanelBackground(WorkingBeatmap working)
             }
         }
 
-        public void AddDifficultyIcons(IEnumerable<BeatmapPanel> panels)
-        {
-            if (panels == null)
-                throw new ArgumentNullException(nameof(panels));
-
-            difficultyIcons.AddRange(panels.Select(p => new FilterableDifficultyIcon(p)));
-        }
-
-        public MenuItem[] ContextMenuItems
-        {
-            get
-            {
-                List<MenuItem> items = new List<MenuItem>();
-
-                if (State == PanelSelectedState.NotSelected)
-                    items.Add(new OsuMenuItem("Expand", MenuItemType.Highlighted, () => State = PanelSelectedState.Selected));
-
-                if (beatmap.BeatmapSetInfo.Beatmaps.Any(b => b.Hidden))
-                    items.Add(new OsuMenuItem("Restore all hidden", MenuItemType.Standard, () => RestoreHiddenRequested?.Invoke(beatmap.BeatmapSetInfo)));
-
-                items.Add(new OsuMenuItem("Delete", MenuItemType.Destructive, () => DeleteRequested?.Invoke(beatmap.BeatmapSetInfo)));
-
-                return items.ToArray();
-            }
-        }
-
         public class FilterableDifficultyIcon : DifficultyIcon
         {
             private readonly BindableBool filtered = new BindableBool();
 
-            public FilterableDifficultyIcon(BeatmapPanel panel)
-                : base(panel.Beatmap)
+            public FilterableDifficultyIcon(CarouselBeatmap item)
+                : base(item.Beatmap)
             {
-                filtered.BindTo(panel.Filtered);
-                filtered.ValueChanged += v => this.FadeTo(v ? 0.1f : 1, 100);
+                filtered.BindTo(item.Filtered);
+                filtered.ValueChanged += v => Schedule(() => this.FadeTo(v ? 0.1f : 1, 100));
                 filtered.TriggerChange();
             }
         }

osu.Game/Screens/Select/Carousel/DrawableCarouselItem.cs

@@ -1,45 +1,53 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using System;
-using osu.Framework;
+using osu.Framework.Allocation;
 using osu.Framework.Audio;
 using osu.Framework.Audio.Sample;
-using osu.Framework.Allocation;
+using osu.Framework.Extensions.Color4Extensions;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
 using osu.Framework.Input;
+using osu.Framework.MathUtils;
+using osu.Game.Graphics;
 using OpenTK;
 using OpenTK.Graphics;
-using osu.Framework.Extensions.Color4Extensions;
-using osu.Framework.MathUtils;
-using osu.Framework.Graphics.Shapes;
-using osu.Game.Graphics;
 
-namespace osu.Game.Beatmaps.Drawables
+namespace osu.Game.Screens.Select.Carousel
 {
-    public class Panel : Container, IStateful<PanelSelectedState>
+    public abstract class DrawableCarouselItem : Container
     {
         public const float MAX_HEIGHT = 80;
 
-        public event Action<PanelSelectedState> StateChanged;
-
         public override bool RemoveWhenNotAlive => false;
 
-        private readonly Container nestedContainer;
+        public override bool IsPresent => base.IsPresent || Item.Visible;
 
-        private readonly Container borderContainer;
+        public readonly CarouselItem Item;
 
-        private readonly Box hoverLayer;
+        private Container nestedContainer;
+        private Container borderContainer;
+
+        private Box hoverLayer;
 
         protected override Container<Drawable> Content => nestedContainer;
 
-        protected Panel()
+        protected DrawableCarouselItem(CarouselItem item)
         {
+            Item = item;
+
             Height = MAX_HEIGHT;
             RelativeSizeAxes = Axes.X;
+            Alpha = 0;
+        }
 
-            AddInternal(borderContainer = new Container
+        private SampleChannel sampleHover;
+
+        [BackgroundDependencyLoader]
+        private void load(AudioManager audio, OsuColour colours)
+        {
+            InternalChild = borderContainer = new Container
             {
                 RelativeSizeAxes = Axes.Both,
                 Masking = true,
@@ -58,16 +66,8 @@ protected Panel()
                         Blending = BlendingMode.Additive,
                     },
                 }
-            });
+            };
 
-            Alpha = 0;
-        }
-
-        private SampleChannel sampleHover;
-
-        [BackgroundDependencyLoader]
-        private void load(AudioManager audio, OsuColour colours)
-        {
             sampleHover = audio.Sample.Get($@"SongSelect/song-ping-variation-{RNG.Next(1, 5)}");
             hoverLayer.Colour = colours.Blue.Opacity(0.1f);
         }
@@ -86,60 +86,41 @@ protected override void OnHoverLost(InputState state)
             base.OnHoverLost(state);
         }
 
-        public void SetMultiplicativeAlpha(float alpha)
-        {
-            borderContainer.Alpha = alpha;
-        }
+        public void SetMultiplicativeAlpha(float alpha) => borderContainer.Alpha = alpha;
 
         protected override void LoadComplete()
         {
             base.LoadComplete();
+
             ApplyState();
+            Item.Filtered.ValueChanged += _ => Schedule(ApplyState);
+            Item.State.ValueChanged += _ => Schedule(ApplyState);
         }
 
-        protected virtual void ApplyState(PanelSelectedState last = PanelSelectedState.Hidden)
+        protected virtual void ApplyState()
         {
             if (!IsLoaded) return;
 
-            switch (state)
+            switch (Item.State.Value)
             {
-                case PanelSelectedState.Hidden:
-                case PanelSelectedState.NotSelected:
+                case CarouselItemState.NotSelected:
                     Deselected();
                     break;
-                case PanelSelectedState.Selected:
+                case CarouselItemState.Selected:
                     Selected();
                     break;
             }
 
-            if (state == PanelSelectedState.Hidden)
+            if (!Item.Visible)
                 this.FadeOut(300, Easing.OutQuint);
             else
                 this.FadeIn(250);
         }
 
-        private PanelSelectedState state = PanelSelectedState.NotSelected;
-
-        public PanelSelectedState State
-        {
-            get { return state; }
-
-            set
-            {
-                if (state == value)
-                    return;
-
-                var last = state;
-                state = value;
-
-                ApplyState(last);
-
-                StateChanged?.Invoke(State);
-            }
-        }
-
         protected virtual void Selected()
         {
+            Item.State.Value = CarouselItemState.Selected;
+
             borderContainer.BorderThickness = 2.5f;
             borderContainer.EdgeEffect = new EdgeEffectParameters
             {
@@ -152,6 +133,8 @@ protected virtual void Selected()
 
         protected virtual void Deselected()
         {
+            Item.State.Value = CarouselItemState.NotSelected;
+
             borderContainer.BorderThickness = 0;
             borderContainer.EdgeEffect = new EdgeEffectParameters
             {
@@ -164,15 +147,8 @@ protected virtual void Deselected()
 
         protected override bool OnClick(InputState state)
         {
-            State = PanelSelectedState.Selected;
+            Item.State.Value = CarouselItemState.Selected;
             return true;
         }
     }
-
-    public enum PanelSelectedState
-    {
-        Hidden,
-        NotSelected,
-        Selected
-    }
 }

osu.Game/Screens/Select/EditSongSelect.cs

@@ -1,14 +1,12 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using osu.Framework.Input;
-
 namespace osu.Game.Screens.Select
 {
     public class EditSongSelect : SongSelect
     {
         protected override bool ShowFooter => false;
 
-        protected override void OnSelected(InputState state) => Exit();
+        protected override void Start() => Exit();
     }
 }

osu.Game/Screens/Select/FilterCriteria.cs

@@ -1,11 +1,6 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using osu.Game.Beatmaps;
-using osu.Game.Beatmaps.Drawables;
 using osu.Game.Rulesets;
 using osu.Game.Screens.Select.Filter;
 
@@ -18,54 +13,5 @@ public class FilterCriteria
         public string SearchText;
         public RulesetInfo Ruleset;
         public bool AllowConvertedBeatmaps;
-
-        private bool canConvert(BeatmapInfo beatmapInfo) => beatmapInfo.RulesetID == Ruleset.ID || beatmapInfo.RulesetID == 0 && Ruleset.ID > 0 && AllowConvertedBeatmaps;
-
-        public void Filter(List<BeatmapGroup> groups)
-        {
-            foreach (var g in groups)
-            {
-                var set = g.BeatmapSet;
-
-                // we only support converts from osu! mode to other modes for now.
-                // in the future this will have to change, at which point this condition will become a touch more complicated.
-                bool hasCurrentMode = set.Beatmaps.Any(canConvert);
-
-                bool match = hasCurrentMode;
-
-                if (!string.IsNullOrEmpty(SearchText))
-                    match &= set.Metadata.SearchableTerms.Any(term => term.IndexOf(SearchText, StringComparison.InvariantCultureIgnoreCase) >= 0);
-
-                foreach (var panel in g.BeatmapPanels)
-                    panel.Filtered.Value = !canConvert(panel.Beatmap);
-
-                switch (g.State)
-                {
-                    case BeatmapGroupState.Hidden:
-                        if (match) g.State = BeatmapGroupState.Collapsed;
-                        break;
-                    default:
-                        if (!match) g.State = BeatmapGroupState.Hidden;
-                        break;
-                }
-            }
-
-            switch (Sort)
-            {
-                default:
-                case SortMode.Artist:
-                    groups.Sort((x, y) => string.Compare(x.BeatmapSet.Metadata.Artist, y.BeatmapSet.Metadata.Artist, StringComparison.InvariantCultureIgnoreCase));
-                    break;
-                case SortMode.Title:
-                    groups.Sort((x, y) => string.Compare(x.BeatmapSet.Metadata.Title, y.BeatmapSet.Metadata.Title, StringComparison.InvariantCultureIgnoreCase));
-                    break;
-                case SortMode.Author:
-                    groups.Sort((x, y) => string.Compare(x.BeatmapSet.Metadata.Author.Username, y.BeatmapSet.Metadata.Author.Username, StringComparison.InvariantCultureIgnoreCase));
-                    break;
-                case SortMode.Difficulty:
-                    groups.Sort((x, y) => x.BeatmapSet.MaxStarDifficulty.CompareTo(y.BeatmapSet.MaxStarDifficulty));
-                    break;
-            }
-        }
     }
 }

osu.Game/Screens/Select/MatchSongSelect.cs

@@ -1,12 +1,10 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using osu.Framework.Input;
-
 namespace osu.Game.Screens.Select
 {
     public class MatchSongSelect : SongSelect
     {
-        protected override void OnSelected(InputState state) => Exit();
+        protected override void Start() => Exit();
     }
 }

osu.Game/Screens/Select/PlaySongSelect.cs

@@ -8,7 +8,6 @@
 using osu.Framework.Audio.Sample;
 using osu.Framework.Graphics;
 using osu.Framework.Graphics.Containers;
-using osu.Framework.Input;
 using osu.Framework.Screens;
 using osu.Game.Beatmaps;
 using osu.Game.Graphics;
@@ -114,11 +113,12 @@ protected override bool OnExiting(Screen next)
             return false;
         }
 
-        protected override void OnSelected(InputState state)
+        protected override void Start()
         {
             if (player != null) return;
 
-            if (state?.Keyboard.ControlPressed == true)
+            // Ctrl+Enter should start map with autoplay enabled.
+            if (GetContainingInputManager().CurrentState?.Keyboard.ControlPressed == true)
             {
                 var auto = Ruleset.Value.CreateInstance().GetAutoplayMod();
                 var autoType = auto.GetType();

osu.Game/Screens/Select/SongSelect.cs

@@ -27,25 +27,11 @@ namespace osu.Game.Screens.Select
 {
     public abstract class SongSelect : OsuScreen
     {
-        private BeatmapManager beatmaps;
-        protected override BackgroundScreen CreateBackground() => new BackgroundScreenBeatmap();
-
-        private readonly BeatmapCarousel carousel;
-        private DialogOverlay dialogOverlay;
-
         private static readonly Vector2 wedged_container_size = new Vector2(0.5f, 245);
-
+        private static readonly Vector2 background_blur = new Vector2(20);
         private const float left_area_padding = 20;
 
-        private readonly BeatmapInfoWedge beatmapInfoWedge;
-
-        protected Container LeftContent;
-
-        private static readonly Vector2 background_blur = new Vector2(20);
-        private CancellationTokenSource initialAddSetsTask;
-
-        private SampleChannel sampleChangeDifficulty;
-        private SampleChannel sampleChangeBeatmap;
+        public readonly FilterControl FilterControl;
 
         protected virtual bool ShowFooter => true;
 
@@ -65,77 +51,90 @@ public abstract class SongSelect : OsuScreen
         /// </summary>
         protected readonly Container FooterPanels;
 
-        public readonly FilterControl FilterControl;
+        protected override BackgroundScreen CreateBackground() => new BackgroundScreenBeatmap();
+
+        protected Container LeftContent;
+
+        private readonly BeatmapCarousel carousel;
+        private readonly BeatmapInfoWedge beatmapInfoWedge;
+        private DialogOverlay dialogOverlay;
+        private BeatmapManager beatmaps;
+
+        private SampleChannel sampleChangeDifficulty;
+        private SampleChannel sampleChangeBeatmap;
+
+        private CancellationTokenSource initialAddSetsTask;
+
+        private DependencyContainer dependencies;
+        protected override IReadOnlyDependencyContainer CreateLocalDependencies(IReadOnlyDependencyContainer parent) => dependencies = new DependencyContainer(parent);
 
         protected SongSelect()
         {
             const float carousel_width = 640;
             const float filter_height = 100;
 
-            Add(new ParallaxContainer
+            AddRange(new Drawable[]
             {
-                Padding = new MarginPadding { Top = filter_height },
-                ParallaxAmount = 0.005f,
-                RelativeSizeAxes = Axes.Both,
-                Children = new[]
+                new ParallaxContainer
                 {
-                    new WedgeBackground
+                    Padding = new MarginPadding { Top = filter_height },
+                    ParallaxAmount = 0.005f,
+                    RelativeSizeAxes = Axes.Both,
+                    Children = new[]
                     {
-                        RelativeSizeAxes = Axes.Both,
-                        Padding = new MarginPadding { Right = carousel_width * 0.76f },
+                        new WedgeBackground
+                        {
+                            RelativeSizeAxes = Axes.Both,
+                            Padding = new MarginPadding { Right = carousel_width * 0.76f },
+                        }
                     }
-                }
-            });
-            Add(LeftContent = new Container
-            {
-                Origin = Anchor.BottomLeft,
-                Anchor = Anchor.BottomLeft,
-                RelativeSizeAxes = Axes.Both,
-                Size = new Vector2(wedged_container_size.X, 1),
-                Padding = new MarginPadding
-                {
-                    Bottom = 50,
-                    Top = wedged_container_size.Y + left_area_padding,
-                    Left = left_area_padding,
-                    Right = left_area_padding * 2,
-                }
-            });
-            Add(carousel = new BeatmapCarousel
-            {
-                RelativeSizeAxes = Axes.Y,
-                Size = new Vector2(carousel_width, 1),
-                Anchor = Anchor.CentreRight,
-                Origin = Anchor.CentreRight,
-                SelectionChanged = carouselSelectionChanged,
-                BeatmapsChanged = carouselBeatmapsLoaded,
-                DeleteRequested = promptDelete,
-                RestoreRequested = s => { foreach (var b in s.Beatmaps) beatmaps.Restore(b); },
-                EditRequested = editRequested,
-                HideDifficultyRequested = b => beatmaps.Hide(b),
-                StartRequested = () => carouselRaisedStart(),
-            });
-            Add(FilterControl = new FilterControl
-            {
-                RelativeSizeAxes = Axes.X,
-                Height = filter_height,
-                FilterChanged = criteria => filterChanged(criteria),
-                Exit = Exit,
-            });
-            Add(beatmapInfoWedge = new BeatmapInfoWedge
-            {
-                Alpha = 0,
-                Size = wedged_container_size,
-                RelativeSizeAxes = Axes.X,
-                Margin = new MarginPadding
-                {
-                    Top = left_area_padding,
-                    Right = left_area_padding,
                 },
-            });
-            Add(new ResetScrollContainer(() => carousel.ScrollToSelected())
-            {
-                RelativeSizeAxes = Axes.Y,
-                Width = 250,
+                LeftContent = new Container
+                {
+                    Origin = Anchor.BottomLeft,
+                    Anchor = Anchor.BottomLeft,
+                    RelativeSizeAxes = Axes.Both,
+                    Size = new Vector2(wedged_container_size.X, 1),
+                    Padding = new MarginPadding
+                    {
+                        Bottom = 50,
+                        Top = wedged_container_size.Y + left_area_padding,
+                        Left = left_area_padding,
+                        Right = left_area_padding * 2,
+                    }
+                },
+                carousel = new BeatmapCarousel
+                {
+                    RelativeSizeAxes = Axes.Y,
+                    Size = new Vector2(carousel_width, 1),
+                    Anchor = Anchor.CentreRight,
+                    Origin = Anchor.CentreRight,
+                    SelectionChanged = carouselSelectionChanged,
+                    BeatmapSetsChanged = carouselBeatmapsLoaded,
+                },
+                FilterControl = new FilterControl
+                {
+                    RelativeSizeAxes = Axes.X,
+                    Height = filter_height,
+                    FilterChanged = c => carousel.Filter(c),
+                    Exit = Exit,
+                },
+                beatmapInfoWedge = new BeatmapInfoWedge
+                {
+                    Alpha = 0,
+                    Size = wedged_container_size,
+                    RelativeSizeAxes = Axes.X,
+                    Margin = new MarginPadding
+                    {
+                        Top = left_area_padding,
+                        Right = left_area_padding,
+                    },
+                },
+                new ResetScrollContainer(() => carousel.ScrollToSelected())
+                {
+                    RelativeSizeAxes = Axes.Y,
+                    Width = 250,
+                }
             });
 
             if (ShowFooter)
@@ -163,12 +162,14 @@ protected SongSelect()
         [BackgroundDependencyLoader(permitNulls: true)]
         private void load(BeatmapManager beatmaps, AudioManager audio, DialogOverlay dialog, OsuGame osu, OsuColour colours)
         {
+            dependencies.Cache(this);
+
             if (Footer != null)
             {
                 Footer.AddButton(@"random", colours.Green, triggerRandom, Key.F2);
                 Footer.AddButton(@"options", colours.Blue, BeatmapOptions, Key.F3);
 
-                BeatmapOptions.AddButton(@"Delete", @"Beatmap", FontAwesome.fa_trash, colours.Pink, () => promptDelete(Beatmap.Value.BeatmapSetInfo), Key.Number4, float.MaxValue);
+                BeatmapOptions.AddButton(@"Delete", @"Beatmap", FontAwesome.fa_trash, colours.Pink, () => delete(Beatmap.Value.BeatmapSetInfo), Key.Number4, float.MaxValue);
             }
 
             if (this.beatmaps == null)
@@ -189,51 +190,31 @@ private void load(BeatmapManager beatmaps, AudioManager audio, DialogOverlay dia
 
             initialAddSetsTask = new CancellationTokenSource();
 
-            carousel.Beatmaps = this.beatmaps.GetAllUsableBeatmapSets();
-
-            Beatmap.ValueChanged += beatmap_ValueChanged;
+            carousel.BeatmapSets = this.beatmaps.GetAllUsableBeatmapSets();
 
             Beatmap.DisabledChanged += disabled => carousel.AllowSelection = !disabled;
-            carousel.AllowSelection = !Beatmap.Disabled;
+            Beatmap.TriggerChange();
+
+            Beatmap.ValueChanged += b =>
+            {
+                if (IsCurrentScreen)
+                    carousel.SelectBeatmap(b?.BeatmapInfo);
+            };
         }
 
-        private void editRequested(BeatmapInfo beatmap)
+        public void Edit(BeatmapInfo beatmap)
         {
             Beatmap.Value = beatmaps.GetWorkingBeatmap(beatmap, Beatmap);
             Push(new Editor());
         }
 
-        private void onBeatmapRestored(BeatmapInfo beatmap)
-        {
-            Schedule(() =>
-            {
-                var beatmapSet = beatmaps.QueryBeatmapSet(s => s.ID == beatmap.BeatmapSetInfoID);
-                carousel.UpdateBeatmapSet(beatmapSet);
-            });
-        }
-
-        private void onBeatmapHidden(BeatmapInfo beatmap)
-        {
-            Schedule(() =>
-            {
-                var beatmapSet = beatmaps.QueryBeatmapSet(s => s.ID == beatmap.BeatmapSetInfoID);
-                carousel.UpdateBeatmapSet(beatmapSet);
-            });
-        }
-
-        private void carouselBeatmapsLoaded()
-        {
-            if (Beatmap.Value.BeatmapSetInfo?.DeletePending == false)
-                carousel.SelectBeatmap(Beatmap.Value.BeatmapInfo, false);
-            else
-                carousel.SelectNextRandom();
-        }
-
-        private void carouselRaisedStart(InputState state = null)
+        public void Start(BeatmapInfo beatmap)
         {
             // if we have a pending filter operation, we want to run it now.
             // it could change selection (ie. if the ruleset has been changed).
-            carousel.FlushPendingFilters();
+            carousel.FlushPendingFilterOperations();
+
+            carousel.SelectBeatmap(beatmap);
 
             if (selectionChangedDebounce?.Completed == false)
             {
@@ -242,9 +223,14 @@ private void carouselRaisedStart(InputState state = null)
                 selectionChangedDebounce = null;
             }
 
-            OnSelected(state);
+            Start();
         }
 
+        /// <summary>
+        /// Called when a selection is made.
+        /// </summary>
+        protected abstract void Start();
+
         private ScheduledDelegate selectionChangedDebounce;
 
         // We need to keep track of the last selected beatmap ignoring debounce to play the correct selection sounds.
@@ -261,7 +247,7 @@ private void carouselSelectionChanged(BeatmapInfo beatmap)
                 // In these cases, the other component has already loaded the beatmap, so we don't need to do so again.
                 if (beatmap?.Equals(Beatmap.Value.BeatmapInfo) != true)
                 {
-                    bool preview = beatmap?.BeatmapSetInfoID != Beatmap.Value.BeatmapInfo.BeatmapSetInfoID;
+                    bool preview = beatmap?.BeatmapSetInfoID != Beatmap.Value?.BeatmapInfo.BeatmapSetInfoID;
 
                     Beatmap.Value = beatmaps.GetWorkingBeatmap(beatmap, Beatmap);
                     ensurePlayingSelected(preview);
@@ -301,23 +287,11 @@ private void triggerRandom()
                 carousel.SelectNextRandom();
         }
 
-        protected abstract void OnSelected(InputState state);
-
-        private void filterChanged(FilterCriteria criteria, bool debounce = true)
-        {
-            carousel.Filter(criteria, debounce);
-        }
-
-        private void onBeatmapSetAdded(BeatmapSetInfo s) => Schedule(() => carousel.UpdateBeatmapSet(s));
-
-        private void onBeatmapSetRemoved(BeatmapSetInfo s) => Schedule(() => removeBeatmapSet(s));
-
         protected override void OnEntering(Screen last)
         {
             base.OnEntering(last);
 
             Content.FadeInFromZero(250);
-
             FilterControl.Activate();
         }
 
@@ -346,7 +320,7 @@ protected override void LogoArriving(OsuLogo logo, bool resuming)
 
             logo.Action = () =>
             {
-                carouselRaisedStart();
+                Start();
                 return false;
             };
         }
@@ -358,13 +332,6 @@ protected override void LogoExiting(OsuLogo logo)
             logo.FadeOut(logo_transition / 2, Easing.Out);
         }
 
-        private void beatmap_ValueChanged(WorkingBeatmap beatmap)
-        {
-            if (!IsCurrentScreen) return;
-
-            carousel.SelectBeatmap(beatmap?.BeatmapInfo);
-        }
-
         protected override void OnResuming(Screen last)
         {
             if (Beatmap != null && !Beatmap.Value.BeatmapSetInfo.DeletePending)
@@ -425,8 +392,7 @@ protected override void Dispose(bool isDisposing)
         /// <param name="beatmap">The working beatmap.</param>
         protected virtual void UpdateBeatmap(WorkingBeatmap beatmap)
         {
-            var backgroundModeBeatmap = Background as BackgroundScreenBeatmap;
-            if (backgroundModeBeatmap != null)
+            if (Background is BackgroundScreenBeatmap backgroundModeBeatmap)
             {
                 backgroundModeBeatmap.Beatmap = beatmap;
                 backgroundModeBeatmap.BlurTo(background_blur, 750, Easing.OutQuint);
@@ -451,18 +417,22 @@ private void ensurePlayingSelected(bool preview = false)
             }
         }
 
-        private void removeBeatmapSet(BeatmapSetInfo beatmapSet)
+        private void onBeatmapSetAdded(BeatmapSetInfo s) => carousel.UpdateBeatmapSet(s);
+        private void onBeatmapSetRemoved(BeatmapSetInfo s) => carousel.RemoveBeatmapSet(s);
+        private void onBeatmapRestored(BeatmapInfo b) => carousel.UpdateBeatmapSet(beatmaps.QueryBeatmapSet(s => s.ID == b.BeatmapSetInfoID));
+        private void onBeatmapHidden(BeatmapInfo b) => carousel.UpdateBeatmapSet(beatmaps.QueryBeatmapSet(s => s.ID == b.BeatmapSetInfoID));
+
+        private void carouselBeatmapsLoaded()
         {
-            carousel.RemoveBeatmap(beatmapSet);
-            if (carousel.SelectedBeatmap == null)
-                Beatmap.SetDefault();
+            if (Beatmap.Value.BeatmapSetInfo?.DeletePending == false)
+                carousel.SelectBeatmap(Beatmap.Value.BeatmapInfo);
+            else
+                carousel.SelectNextRandom();
         }
 
-        private void promptDelete(BeatmapSetInfo beatmap)
+        private void delete(BeatmapSetInfo beatmap)
         {
-            if (beatmap == null)
-                return;
-
+            if (beatmap == null) return;
             dialogOverlay?.Push(new BeatmapDeleteDialog(beatmap));
         }
 
@@ -474,15 +444,16 @@ protected override bool OnKeyDown(InputState state, KeyDownEventArgs args)
             {
                 case Key.KeypadEnter:
                 case Key.Enter:
-                    carouselRaisedStart(state);
+                    Start();
                     return true;
                 case Key.Delete:
                     if (state.Keyboard.ShiftPressed)
                     {
                         if (!Beatmap.IsDefault)
-                            promptDelete(Beatmap.Value.BeatmapSetInfo);
+                            delete(Beatmap.Value.BeatmapSetInfo);
                         return true;
                     }
+
                     break;
             }
 

osu.Game/Users/User.cs

@@ -136,5 +136,7 @@ public class RankHistoryData
 
         [JsonProperty(@"rankHistory")]
         public RankHistoryData RankHistory;
+
+        public override string ToString() => Username;
     }
 }

osu.Game/osu.Game.csproj

@@ -262,10 +262,7 @@
     <Compile Include="Beatmaps\ControlPoints\TimingControlPoint.cs" />
     <Compile Include="Beatmaps\DifficultyCalculator.cs" />
     <Compile Include="Beatmaps\Drawables\BeatmapBackgroundSprite.cs" />
-    <Compile Include="Beatmaps\Drawables\BeatmapGroup.cs" />
-    <Compile Include="Beatmaps\Drawables\BeatmapPanel.cs" />
     <Compile Include="Beatmaps\Drawables\BeatmapSetCover.cs" />
-    <Compile Include="Beatmaps\Drawables\BeatmapSetHeader.cs" />
     <Compile Include="Beatmaps\Formats\LegacyDecoder.cs" />
     <Compile Include="Beatmaps\Formats\LegacyStoryboardDecoder.cs" />
     <Compile Include="Database\DatabaseContextFactory.cs" />
@@ -316,7 +313,6 @@
     <Compile Include="Rulesets\Mods\IApplicableToScoreProcessor.cs" />
     <Compile Include="Beatmaps\Drawables\DifficultyColouredContainer.cs" />
     <Compile Include="Beatmaps\Drawables\DifficultyIcon.cs" />
-    <Compile Include="Beatmaps\Drawables\Panel.cs" />
     <Compile Include="Beatmaps\DummyWorkingBeatmap.cs" />
     <Compile Include="Beatmaps\Formats\Decoder.cs" />
     <Compile Include="Beatmaps\Formats\LegacyBeatmapDecoder.cs" />
@@ -347,7 +343,7 @@
     <Compile Include="Configuration\ReleaseStream.cs" />
     <Compile Include="Configuration\ScoreMeterType.cs" />
     <Compile Include="Configuration\ScreenshotFormat.cs" />
-    <Compile Include="Configuration\SelectionRandomType.cs" />
+    <Compile Include="Configuration\RandomSelectAlgorithm.cs" />
     <Compile Include="Database\DatabaseBackedStore.cs" />
     <Compile Include="Database\OsuDbContext.cs" />
     <Compile Include="Graphics\Backgrounds\Background.cs" />
@@ -756,6 +752,14 @@
     <Compile Include="Screens\Select\BeatmapDetailAreaTabControl.cs" />
     <Compile Include="Screens\Select\BeatmapDetails.cs" />
     <Compile Include="Screens\Select\BeatmapInfoWedge.cs" />
+    <Compile Include="Screens\Select\Carousel\CarouselBeatmap.cs" />
+    <Compile Include="Screens\Select\Carousel\CarouselBeatmapSet.cs" />
+    <Compile Include="Screens\Select\Carousel\CarouselGroup.cs" />
+    <Compile Include="Screens\Select\Carousel\CarouselGroupEagerSelect.cs" />
+    <Compile Include="Screens\Select\Carousel\CarouselItem.cs" />
+    <Compile Include="Screens\Select\Carousel\DrawableCarouselBeatmap.cs" />
+    <Compile Include="Screens\Select\Carousel\DrawableCarouselBeatmapSet.cs" />
+    <Compile Include="Screens\Select\Carousel\DrawableCarouselItem.cs" />
     <Compile Include="Screens\Select\Details\AdvancedStats.cs" />
     <Compile Include="Screens\Select\Details\FailRetryGraph.cs" />
     <Compile Include="Screens\Select\Details\UserRatings.cs" />
@@ -855,4 +859,4 @@
   <Import Project="$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.osx.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.osx.targets" Condition="Exists('$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.osx.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.osx.targets')" />
   <Import Project="$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.linux.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.linux.targets" Condition="Exists('$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.linux.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.linux.targets')" />
   <Import Project="$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.v110_xp.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.v110_xp.targets" Condition="Exists('$(SolutionDir)\packages\SQLitePCLRaw.lib.e_sqlite3.v110_xp.1.1.8\build\net35\SQLitePCLRaw.lib.e_sqlite3.v110_xp.targets')" />
-</Project>
+</Project>