fix :

1. Add space before {, before Duration, and after 1000
2. How about just ManiaStage?
3. This is really just Columns.Count, you're not saving much with this extra variable here.

osu.Game.Rulesets.Mania/UI/ManiaStage.cs

@@ -0,0 +1,213 @@
+// Copyright (c) 2007-2018 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.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
+using osu.Game.Graphics;
+using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.UI.Scrolling;
+using OpenTK;
+using OpenTK.Graphics;
+
+namespace osu.Game.Rulesets.Mania.UI
+{
+    /// <summary>
+    /// A collection of <see cref="Column"/>s.
+    /// </summary>
+    internal class ManiaStage : ScrollingPlayfield
+    {
+        public const float HIT_TARGET_POSITION = 50;
+
+        private SpecialColumnPosition specialColumnPosition;
+
+        /// <summary>
+        /// The style to use for the special column.
+        /// </summary>
+        public SpecialColumnPosition SpecialColumnPosition
+        {
+            get { return specialColumnPosition; }
+            set
+            {
+                if (IsLoaded)
+                    throw new InvalidOperationException($"Setting {nameof(SpecialColumnPosition)} after the playfield is loaded requires re-creating the playfield.");
+                specialColumnPosition = value;
+            }
+        }
+
+        public IEnumerable<Column> Columns => columns.Children;
+        private readonly FillFlowContainer<Column> columns;
+
+        protected override Container<Drawable> Content => content;
+        private readonly Container<Drawable> content;
+
+        public Container<DrawableManiaJudgement> Judgements => judgements;
+        private readonly Container<DrawableManiaJudgement> judgements;
+
+        private readonly Container topLevelContainer;
+
+        private List<Color4> normalColumnColours = new List<Color4>();
+        private Color4 specialColumnColour;
+
+        public ManiaStage()
+            : base(ScrollingDirection.Up)
+        {
+            Name = "Playfield elements";
+            Anchor = Anchor.TopCentre;
+            Origin = Anchor.TopCentre;
+            //RelativeSizeAxes = Axes.Y;
+            //AutoSizeAxes = Axes.X;
+            InternalChildren = new Drawable[]
+            {
+                new Container
+                {
+                    Anchor = Anchor.TopCentre,
+                    Origin = Anchor.TopCentre,
+                    RelativeSizeAxes = Axes.Y,
+                    AutoSizeAxes = Axes.X,
+                    Children = new Drawable[]
+                    {
+                        new Container
+                        {
+                            Name = "Columns mask",
+                            RelativeSizeAxes = Axes.Y,
+                            AutoSizeAxes = Axes.X,
+                            Masking = true,
+                            Children = new Drawable[]
+                            {
+                                new Box
+                                {
+                                    Name = "Background",
+                                    RelativeSizeAxes = Axes.Both,
+                                    Colour = new Color4(0, 0, 0, 0.8f)
+                                },
+                                columns = new FillFlowContainer<Column>
+                                {
+                                    Name = "Columns",
+                                    RelativeSizeAxes = Axes.Y,
+                                    AutoSizeAxes = Axes.X,
+                                    Direction = FillDirection.Horizontal,
+                                    Padding = new MarginPadding { Left = 1, Right = 1 },
+                                    Spacing = new Vector2(1, 0)
+                                },
+                            }
+                        },
+                        new Container
+                        {
+                            Name = "Barlines mask",
+                            Anchor = Anchor.TopCentre,
+                            Origin = Anchor.TopCentre,
+                            RelativeSizeAxes = Axes.Y,
+                            Width = 1366, // Bar lines should only be masked on the vertical axis
+                            BypassAutoSizeAxes = Axes.Both,
+                            Masking = true,
+                            Child = content = new Container
+                            {
+                                Name = "Bar lines",
+                                Anchor = Anchor.TopCentre,
+                                Origin = Anchor.TopCentre,
+                                RelativeSizeAxes = Axes.Y,
+                                Padding = new MarginPadding { Top = HIT_TARGET_POSITION }
+                            }
+                        },
+                        judgements = new Container<DrawableManiaJudgement>
+                        {
+                            Anchor = Anchor.TopCentre,
+                            Origin = Anchor.Centre,
+                            AutoSizeAxes = Axes.Both,
+                            Y = HIT_TARGET_POSITION + 150,
+                            BypassAutoSizeAxes = Axes.Both
+                        },
+                        topLevelContainer = new Container { RelativeSizeAxes = Axes.Both }
+                    }
+                }
+            };
+        }
+
+        /// <summary>
+        /// Whether the column index is a special column for this playfield.
+        /// </summary>
+        /// <param name="column">The 0-based column index.</param>
+        /// <returns>Whether the column is a special column.</returns>
+        private bool isSpecialColumn(int column)
+        {
+            switch (SpecialColumnPosition)
+            {
+                default:
+                case SpecialColumnPosition.Normal:
+                    return columns.Count % 2 == 1 && column == columns.Count / 2;
+                case SpecialColumnPosition.Left:
+                    return column == 0;
+                case SpecialColumnPosition.Right:
+                    return column == columns.Count - 1;
+            }
+        }
+
+        public void AddColumn(Column c)
+        {
+            c.VisibleTimeRange.BindTo(VisibleTimeRange);
+            topLevelContainer.Add(c.TopLevelContainer.CreateProxy());
+            columns.Add(c);
+
+            Margin = new MarginPadding
+            {
+                Left = columns.Count * HIT_TARGET_POSITION / 2,
+                Right = columns.Count * HIT_TARGET_POSITION / 2,
+            };
+        }
+
+        public void AddJudgement(Judgement judgement)
+        {
+            judgements.Clear();
+            judgements.Add(new DrawableManiaJudgement(judgement)
+            {
+                Anchor = Anchor.Centre,
+                Origin = Anchor.Centre,
+            });
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(OsuColour colours)
+        {
+            normalColumnColours = new List<Color4>
+            {
+                colours.RedDark,
+                colours.GreenDark
+            };
+
+            specialColumnColour = colours.BlueDark;
+
+            // Set the special column + colour + key
+            foreach (var column in Columns)
+            {
+                if (!column.IsSpecial)
+                    continue;
+
+                column.AccentColour = specialColumnColour;
+            }
+
+            var nonSpecialColumns = Columns.Where(c => !c.IsSpecial).ToList();
+
+            // We'll set the colours of the non-special columns in a separate loop, because the non-special
+            // column colours are mirrored across their centre and special styles mess with this
+            for (int i = 0; i < Math.Ceiling(nonSpecialColumns.Count / 2f); i++)
+            {
+                Color4 colour = normalColumnColours[i % normalColumnColours.Count];
+                nonSpecialColumns[i].AccentColour = colour;
+                nonSpecialColumns[nonSpecialColumns.Count - 1 - i].AccentColour = colour;
+            }
+        }
+
+
+        protected override void Update()
+        {
+            // Due to masking differences, it is not possible to get the width of the columns container automatically
+            // While masking on effectively only the Y-axis, so we need to set the width of the bar line container manually
+            content.Width = columns.Width;
+        }
+    }
+}