Add further abstraction to Sliders/IHasCurve.

osu.Game/Modes/Objects/CurvedHitObject.cs

@@ -0,0 +1,46 @@
+using osu.Game.Modes.Objects.Types;
+using System.Collections.Generic;
+using OpenTK;
+
+namespace osu.Game.Modes.Objects
+{
+    public class CurvedHitObject : HitObject, IHasCurve
+    {
+        public SliderCurve Curve { get; } = new SliderCurve();
+
+        public int RepeatCount { get; set; } = 1;
+
+        public double EndTime => 0;
+        public double Duration => 0;
+
+        public List<Vector2> ControlPoints
+        {
+            get { return Curve.ControlPoints; }
+            set { Curve.ControlPoints = value; }
+        }
+
+        public CurveType CurveType
+        {
+            get { return Curve.CurveType; }
+            set { Curve.CurveType = value; }
+        }
+
+        public double Distance
+        {
+            get { return Curve.Distance; }
+            set { Curve.Distance = value; }
+        }
+
+        public Vector2 PositionAt(double progress) => Curve.PositionAt(ProgressAt(progress));
+
+        public double ProgressAt(double progress)
+        {
+            var p = progress * RepeatCount % 1;
+            if (RepeatAt(progress) % 2 == 1)
+                p = 1 - p;
+            return p;
+        }
+
+        public int RepeatAt(double progress) => (int)(progress * RepeatCount);
+    }
+}