Add animation, selection indicator to difficulties

osu.Game/GameModes/Play/BeatmapButton.cs

@@ -16,6 +16,7 @@ using osu.Framework.Graphics.Primitives;
 using OpenTK.Graphics;
 using OpenTK;
 using osu.Game.Graphics;
+using osu.Framework.Graphics.Transformations;
 
 namespace osu.Game.GameModes.Play
 {
@@ -24,14 +25,36 @@ namespace osu.Game.GameModes.Play
         private BeatmapSetInfo beatmapSet;
         private BeatmapInfo beatmap;
 
-        public Action<BeatmapInfo> Selected;
+        public Action<BeatmapInfo> MapSelected;
+        
+        private bool selected;
+
+        public bool Selected
+        {
+            get { return selected; }
+            set
+            {
+                if (selected == value)
+                    return;
+                selected = value;
+                BorderColour = new Color4(
+                    BorderColour.R,
+                    BorderColour.G,
+                    BorderColour.B,
+                    selected ? 255 : 0);
+                GlowRadius = selected ? 3 : 0;
+            }
+        }
 
         public BeatmapButton(BeatmapSetInfo set, BeatmapInfo beatmap)
         {
             this.beatmapSet = set;
             this.beatmap = beatmap;
-            RelativeSizeAxes = Axes.X;
+            Masking = true;
-            Size = new Vector2(1, -1);
+            CornerRadius = 5;
+            BorderThickness = 2;
+            BorderColour = new Color4(221, 255, 255, 0);
+            GlowColour = new Color4(166, 221, 251, 0.75f); // TODO: Get actual color for this
             Children = new Drawable[]
             {
                 new Box
@@ -72,7 +95,7 @@ namespace osu.Game.GameModes.Play
         
         protected override bool OnClick(InputState state)
         {
-            Selected?.Invoke(beatmap);
+            MapSelected?.Invoke(beatmap);
             return true;
         }
     }

osu.Game/GameModes/Play/BeatmapGroup.cs

@@ -60,15 +60,17 @@ namespace osu.Game.GameModes.Play
                     EndTime = Time + 250,
                 });
                 if (collapsed)
-                {
                     topContainer.Remove(difficulties);
-                    setBox.Size = new Vector2(collapsedWidth, -1);
-                }
                 else
-                {
                     topContainer.Add(difficulties);
-                    setBox.Size = new Vector2(1, -1);
+                setBox.ClearTransformations();
-                }
+                setBox.Transforms.Add(new TransformSize(Clock)
+                {
+                    StartValue = new Vector2(collapsed ? 1 : collapsedWidth, -1),
+                    EndValue = new Vector2(collapsed ? collapsedWidth : 1, -1),
+                    StartTime = Time,
+                    EndTime = Time + 200,
+                });
                 setBox.BorderColour = new Color4(
                     setBox.BorderColour.R,
                     setBox.BorderColour.G,
@@ -78,6 +80,27 @@ namespace osu.Game.GameModes.Play
             }
         }
         
+        private void updateSelected(BeatmapInfo map)
+        {
+            int selected = BeatmapSet.Beatmaps.IndexOf(map);
+            var buttons = difficulties.Children.ToList();
+            for (int i = 0; i < buttons.Count; i++)
+            {
+                var button = buttons[i] as BeatmapButton;
+                float targetWidth = 1 - Math.Abs((selected - i) * 0.025f);
+                targetWidth = MathHelper.Clamp(targetWidth, 0.8f, 1);
+                button.Transforms.Add(new TransformSize(Clock)
+                {
+                    StartValue = new Vector2(button.Size.X, -1),
+                    EndValue = new Vector2(targetWidth, -1),
+                    StartTime = Time,
+                    EndTime = Time + 100,
+                });
+                button.Selected = selected == i;
+            }
+            BeatmapSelected?.Invoke(BeatmapSet, map);
+        }
+
         public BeatmapGroup(BeatmapSetInfo beatmapSet, BeatmapResourceStore beatmapStore, TextureStore resources)
         {
             BeatmapSet = beatmapSet;
@@ -85,6 +108,7 @@ namespace osu.Game.GameModes.Play
             Alpha = collapsedAlpha;
             RelativeSizeAxes = Axes.X;
             Size = new Vector2(1, -1);
+            float difficultyWidth = 1;
             Children = new[]
             {
                 topContainer = new FlowContainer
@@ -109,11 +133,23 @@ namespace osu.Game.GameModes.Play
                 RelativeSizeAxes = Axes.X,
                 Size = new Vector2(1, -1),
                 Margin = new MarginPadding { Top = 5 },
-                Padding = new MarginPadding { Left = 25 },
+                Padding = new MarginPadding { Left = 75 },
                 Spacing = new Vector2(0, 5),
                 Direction = FlowDirection.VerticalOnly,
                 Children = this.BeatmapSet.Beatmaps.Select(
-                    b => new BeatmapButton(this.BeatmapSet, b) { Selected = beatmap => BeatmapSelected?.Invoke(beatmapSet, beatmap) })
+                    b => {
+                        float width = difficultyWidth;
+                        if (difficultyWidth > 0.8f) difficultyWidth -= 0.025f;
+                        return new BeatmapButton(this.BeatmapSet, b)
+                        {
+                            MapSelected = beatmap => updateSelected(beatmap),
+                            Selected = width == 1,
+                            Anchor = Anchor.TopRight,
+                            Origin = Anchor.TopRight,
+                            RelativeSizeAxes = Axes.X,
+                            Size = new Vector2(width, -1),
+                        };
+                    })
             };
             collapsed = true;
         }

osu.Game/GameModes/Play/PlaySongSelect.cs

@@ -80,7 +80,7 @@ namespace osu.Game.GameModes.Play
                 {
                     RelativeSizeAxes = Axes.Both,
                     Size = new Vector2(1),
-                    Padding = new MarginPadding { Right = scrollWidth - 100 },
+                    Padding = new MarginPadding { Right = scrollWidth - 200 },
                     Children = new[]
                     {
                         new Box