Fix up combo colours + a few nullrefs.

osu.Game.Modes.Osu/Beatmaps/OsuBeatmapConverter.cs

@@ -9,6 +9,7 @@ using osu.Game.Modes.Osu.Objects.Drawables;
 using System.Collections.Generic;
 using osu.Game.Modes.Objects.Types;
 using OpenTK.Graphics;
+using System.Linq;
 
 namespace osu.Game.Modes.Osu.Beatmaps
 {
@@ -16,12 +17,25 @@ namespace osu.Game.Modes.Osu.Beatmaps
     {
         public Beatmap<OsuHitObject> Convert(Beatmap original)
         {
+            List<OsuHitObject> converted = convertHitObjects(original.HitObjects, original.BeatmapInfo?.StackLeniency ?? 0.7f);
+
+            converted.ForEach(c => c.SetDefaultsFromBeatmap(original));
+
             return new Beatmap<OsuHitObject>(original)
             {
-                HitObjects = convertHitObjects(original.HitObjects, original.BeatmapInfo?.StackLeniency ?? 0.7f)
+                HitObjects = converted
             };
         }
 
+        private List<OsuHitObject> convertHitObjects(List<HitObject> hitObjects, float stackLeniency)
+        {
+            List<OsuHitObject> converted = hitObjects.Select(h => convertHitObject(h)).ToList();
+
+            updateStacking(converted, stackLeniency);
+
+            return converted;
+        }
+
         private OsuHitObject convertHitObject(HitObject original)
         {
             IHasCurve curveData = original as IHasCurve;
@@ -82,28 +96,6 @@ namespace osu.Game.Modes.Osu.Beatmaps
             };
         }
 
-        private List<OsuHitObject> convertHitObjects(List<HitObject> hitObjects, float stackLeniency)
-        {
-            List<OsuHitObject> converted = new List<OsuHitObject>();
-
-            int combo = 0;
-            foreach (HitObject h in hitObjects)
-            {
-                OsuHitObject c = convertHitObject(h);
-
-                if (c.NewCombo)
-                    combo = 0;
-
-                c.ComboIndex = combo++;
-
-                converted.Add(c);
-            }
-
-            updateStacking(converted, stackLeniency);
-
-            return converted;
-        }
-
         private void updateStacking(List<OsuHitObject> hitObjects, float stackLeniency, int startIndex = 0, int endIndex = -1)
         {
             if (endIndex == -1)

osu.Game/Beatmaps/Formats/BeatmapDecoder.cs

@@ -44,7 +44,25 @@ namespace osu.Game.Beatmaps.Formats
 
         public virtual Beatmap Process(Beatmap beatmap)
         {
-            ApplyColours(beatmap);
+            int comboIndex = 0;
+            int colourIndex = 0;
+
+            foreach (var obj in beatmap.HitObjects)
+            {
+                HitObjectWithCombo comboObject = obj as HitObjectWithCombo;
+
+                if (comboObject == null || comboObject.NewCombo)
+                {
+                    comboIndex = 0;
+                    colourIndex = (colourIndex + 1) % beatmap.ComboColors.Count;
+                }
+
+                if (comboObject != null)
+                {
+                    comboObject.ComboIndex = comboIndex++;
+                    comboObject.ComboColour = beatmap.ComboColors[colourIndex];
+                }
+            }
 
             return beatmap;
         }
@@ -55,7 +73,12 @@ namespace osu.Game.Beatmaps.Formats
             {
                 HitObjects = new List<HitObject>(),
                 ControlPoints = new List<ControlPoint>(),
-                ComboColors = new List<Color4>(),
+                ComboColors = new List<Color4> {
+                    new Color4(17, 136, 170, 255),
+                    new Color4(102, 136, 0, 255),
+                    new Color4(204, 102, 0, 255),
+                    new Color4(121, 9, 13, 255),
+                },
                 BeatmapInfo = new BeatmapInfo
                 {
                     Metadata = new BeatmapMetadata(),
@@ -66,30 +89,5 @@ namespace osu.Game.Beatmaps.Formats
             return beatmap;
         }
         protected abstract void ParseFile(TextReader stream, Beatmap beatmap);
-
-        public virtual void ApplyColours(Beatmap b)
-        {
-            List<Color4> colours = b.ComboColors ?? new List<Color4> {
-                new Color4(17, 136, 170, 255),
-                new Color4(102, 136, 0, 255),
-                new Color4(204, 102, 0, 255),
-                new Color4(121, 9, 13, 255),
-            };
-
-            if (colours.Count == 0) return;
-
-            int i = -1;
-
-            foreach (HitObject h in b.HitObjects)
-            {
-                IHasCombo ihc = h as IHasCombo;
-
-                if (ihc == null)
-                    continue;
-
-                if (ihc.NewCombo || i == -1) i = (i + 1) % colours.Count;
-                ihc.ComboColour = colours[i];
-            }
-        }
     }
 }

osu.Game/Beatmaps/Formats/OsuLegacyDecoder.cs

@@ -10,6 +10,7 @@ using osu.Game.Beatmaps.Samples;
 using osu.Game.Beatmaps.Timing;
 using osu.Game.Modes;
 using osu.Game.Modes.Objects;
+using osu.Game.Modes.Objects.Types;
 
 namespace osu.Game.Beatmaps.Formats
 {
@@ -212,14 +213,23 @@ namespace osu.Game.Beatmaps.Formats
                 beatmap.ControlPoints.Add(cp);
         }
 
-        private void handleColours(Beatmap beatmap, string key, string val)
+        private void handleColours(Beatmap beatmap, string key, string val, ref bool hasCustomColours)
         {
             string[] split = val.Split(',');
+
             if (split.Length != 3)
                 throw new InvalidOperationException($@"Color specified in incorrect format (should be R,G,B): {val}");
+
             byte r, g, b;
             if (!byte.TryParse(split[0], out r) || !byte.TryParse(split[1], out g) || !byte.TryParse(split[2], out b))
                 throw new InvalidOperationException(@"Color must be specified with 8-bit integer components");
+
+            if (!hasCustomColours)
+            {
+                beatmap.ComboColors.Clear();
+                hasCustomColours = true;
+            }
+
             // Note: the combo index specified in the beatmap is discarded
             if (key.StartsWith(@"Combo"))
             {
@@ -237,6 +247,8 @@ namespace osu.Game.Beatmaps.Formats
         {
             HitObjectParser parser = null;
 
+            bool hasCustomColours = false;
+
             var section = Section.None;
             while (true)
             {
@@ -283,16 +295,14 @@ namespace osu.Game.Beatmaps.Formats
                         handleTimingPoints(beatmap, val);
                         break;
                     case Section.Colours:
-                        handleColours(beatmap, key, val);
+                        handleColours(beatmap, key, val, ref hasCustomColours);
                         break;
                     case Section.HitObjects:
                         var obj = parser?.Parse(val);
 
                         if (obj != null)
-                        {
-                            obj.SetDefaultsFromBeatmap(beatmap);
                             beatmap.HitObjects.Add(obj);
-                        }
+
                         break;
                 }
             }

osu.Game/Modes/Objects/Hit.cs

@@ -7,12 +7,8 @@ using OpenTK.Graphics;
 
 namespace osu.Game.Modes.Objects
 {
-    internal class Hit : HitObject, IHasPosition, IHasCombo
+    internal class Hit : HitObjectWithCombo, IHasPosition
     {
         public Vector2 Position { get; set; }
-        public Color4 ComboColour { get; set; }
-
-        public bool NewCombo { get; set; }
-        public int ComboIndex { get; set; }
     }
 }

osu.Game/Modes/Objects/HitObjectWithCombo.cs

@@ -0,0 +1,18 @@
+using osu.Game.Modes.Objects.Types;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using OpenTK.Graphics;
+using osu.Game.Beatmaps;
+
+namespace osu.Game.Modes.Objects
+{
+    internal class HitObjectWithCombo : HitObject, IHasCombo
+    {
+        public Color4 ComboColour { get; set; }
+        public bool NewCombo { get; set; }
+        public int ComboIndex { get; set; }
+    }
+}

osu.Game/Modes/Objects/Slider.cs

@@ -8,18 +8,14 @@ using OpenTK.Graphics;
 
 namespace osu.Game.Modes.Objects
 {
-    internal class Slider : HitObject, IHasCurve, IHasDistance, IHasPosition, IHasCombo, IHasRepeats
+    internal class Slider : HitObjectWithCombo, IHasCurve, IHasPosition, IHasDistance, IHasRepeats
     {
         public List<Vector2> ControlPoints { get; set; }
         public CurveType CurveType { get; set; }
 
-        public double Distance { get; set; }
-
         public Vector2 Position { get; set; }
 
-        public Color4 ComboColour { get; set; }
+        public double Distance { get; set; }
-        public bool NewCombo { get; set; }
-        public int ComboIndex { get; set; }
 
         public int RepeatCount { get; set; }
     }

osu.Game/Modes/Objects/Types/IHasCombo.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Modes.Objects.Types
         /// <summary>
         /// The colour of this HitObject in the combo.
         /// </summary>
-        Color4 ComboColour { get; set; }
+        Color4 ComboColour { get; }
 
         /// <summary>
         /// Whether the HitObject starts a new combo.

osu.Game/osu.Game.csproj

@@ -94,6 +94,7 @@
     <Compile Include="Modes\Mods\IApplicableMod.cs" />
     <Compile Include="Modes\Mods\ModType.cs" />
     <Compile Include="Modes\Objects\Hit.cs" />
+    <Compile Include="Modes\Objects\HitObjectWithCombo.cs" />
     <Compile Include="Modes\Objects\IHitObjectConverter.cs" />
     <Compile Include="Modes\Objects\LegacyHitObjectParser.cs" />
     <Compile Include="Modes\Objects\Slider.cs" />