Ensure SliderCurve is assigned Calculated before used.

osu.Game.Modes.Osu/Objects/OsuHitObjectParser.cs

@@ -29,8 +29,6 @@ public override HitObject Parse(string text)
                     result = new HitCircle();
                     break;
                 case HitObjectType.Slider:
-                    Slider s = new Slider();
-
                     CurveTypes curveType = CurveTypes.Catmull;
                     int repeatCount = 0;
                     double length = 0;
@@ -79,18 +77,13 @@ public override HitObject Parse(string text)
                     if (split.Length > 7)
                         length = Convert.ToDouble(split[7], CultureInfo.InvariantCulture);
 
-                    s.RepeatCount = repeatCount;
-
-                    s.Curve = new SliderCurve
+                    result = new Slider
                     {
                         ControlPoints = points,
                         Length = length,
-                        CurveType = curveType
+                        CurveType = curveType,
+                        RepeatCount = repeatCount
                     };
-
-                    s.Curve.Calculate();
-
-                    result = s;
                     break;
                 case HitObjectType.Spinner:
                     result = new Spinner();
@@ -101,7 +94,8 @@ public override HitObject Parse(string text)
             }
             result.Position = new Vector2(int.Parse(split[0]), int.Parse(split[1]));
             result.StartTime = double.Parse(split[2]);
-            result.Sample = new HitSampleInfo {
+            result.Sample = new HitSampleInfo
+            {
                 Type = (SampleType)int.Parse(split[4]),
                 Set = SampleSet.Soft,
             };

osu.Game.Modes.Osu/Objects/Slider.cs

@@ -1,6 +1,7 @@
 // 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;
 using osu.Game.Beatmaps;
 using OpenTK;
 
@@ -19,11 +20,28 @@ public override int StackHeight
             set
             {
                 stackHeight = value;
-                if (Curve != null)
-                    Curve.Offset = StackOffset;
+                Curve.Offset = StackOffset;
             }
         }
 
+        public List<Vector2> ControlPoints
+        {
+            get { return Curve.ControlPoints; }
+            set { Curve.ControlPoints = value; }
+        }
+
+        public double Length
+        {
+            get { return Curve.Length; }
+            set { Curve.Length = value; }
+        }
+
+        public CurveTypes CurveType
+        {
+            get { return Curve.CurveType; }
+            set { Curve.CurveType = value; }
+        }
+
         public double Velocity;
 
         public override void SetDefaultsFromBeatmap(Beatmap beatmap)
@@ -35,7 +53,7 @@ public override void SetDefaultsFromBeatmap(Beatmap beatmap)
 
         public int RepeatCount;
 
-        public SliderCurve Curve;
+        internal readonly SliderCurve Curve = new SliderCurve();
     }
 
     public enum CurveTypes

osu.Game.Modes.Osu/Objects/SliderCurve.cs

@@ -172,6 +172,9 @@ private Vector2 interpolateVertices(int i, double d)
         /// <param name="p1">End progress. Ranges from 0 (beginning of the slider) to 1 (end of the slider).</param>
         public void GetPathToProgress(List<Vector2> path, double p0, double p1)
         {
+            if (calculatedPath.Count == 0 && ControlPoints.Count > 0)
+                Calculate();
+
             double d0 = progressToDistance(p0);
             double d1 = progressToDistance(p1);
 
@@ -196,6 +199,9 @@ public void GetPathToProgress(List<Vector2> path, double p0, double p1)
         /// <returns></returns>
         public Vector2 PositionAt(double progress)
         {
+            if (calculatedPath.Count == 0 && ControlPoints.Count > 0)
+                Calculate();
+
             double d = progressToDistance(progress);
             return interpolateVertices(indexOfDistance(d), d) + Offset;
         }