Implement note placement

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

@@ -21,6 +21,11 @@ namespace osu.Game.Rulesets.Mania.UI
         private const float column_width = 45;
         private const float special_column_width = 70;
 
+        /// <summary>
+        /// The index of this column as part of the whole playfield.
+        /// </summary>
+        public readonly int Index;
+
         public readonly Bindable<ManiaAction> Action = new Bindable<ManiaAction>();
 
         private readonly ColumnBackground background;
@@ -30,8 +35,10 @@ namespace osu.Game.Rulesets.Mania.UI
         internal readonly Container TopLevelContainer;
         private readonly Container explosionContainer;
 
-        public Column()
+        public Column(int index)
         {
+            Index = index;
+
             RelativeSizeAxes = Axes.Y;
             Width = column_width;
 

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

@@ -54,6 +54,33 @@ namespace osu.Game.Rulesets.Mania.UI
 
         public void Add(BarLine barline) => stages.ForEach(s => s.Add(barline));
 
+        /// <summary>
+        /// Retrieves a column from a screen-space position.
+        /// </summary>
+        /// <param name="screenSpacePosition">The screen-space position.</param>
+        /// <returns>The column which the <paramref name="screenSpacePosition"/> lies in.</returns>
+        public Column GetColumnByPosition(Vector2 screenSpacePosition)
+        {
+            Column found = null;
+
+            foreach (var stage in stages)
+            {
+                foreach (var column in stage.Columns)
+                {
+                    if (column.ReceivePositionalInputAt(screenSpacePosition))
+                    {
+                        found = column;
+                        break;
+                    }
+                }
+
+                if (found != null)
+                    break;
+            }
+
+            return found;
+        }
+
         private ManiaStage getStageByColumn(int column)
         {
             int sum = 0;

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

@@ -123,7 +123,7 @@ namespace osu.Game.Rulesets.Mania.UI
             for (int i = 0; i < definition.Columns; i++)
             {
                 var isSpecial = definition.IsSpecialColumn(i);
-                var column = new Column
+                var column = new Column(firstColumnIndex + i)
                 {
                     IsSpecial = isSpecial,
                     Action = { Value = isSpecial ? specialColumnStartAction++ : normalColumnStartAction++ }