Distance object generator should output a secondary pattern

In osu!stable, only the hitobjects which ended at the distance object's EndTime would be considered for further pattern generation.

Previously this generator was group _all_ objects including those that don't end at the object's EndTime, resulting in incorrect hitobject count for further pattern generation.

osu.Game.Rulesets.Mania/Beatmaps/ManiaBeatmapConverter.cs

@@ -119,10 +119,13 @@ namespace osu.Game.Rulesets.Mania.Beatmaps
         {
             var generator = new SpecificBeatmapPatternGenerator(Random, original, beatmap, lastPattern, originalBeatmap);
 
-            Pattern newPattern = generator.Generate();
-            lastPattern = newPattern;
+            foreach (var newPattern in generator.Generate())
+            {
+                lastPattern = newPattern;
 
-            return newPattern.HitObjects;
+                foreach (var obj in newPattern.HitObjects)
+                    yield return obj;
+            }
         }
 
         /// <summary>
@@ -167,14 +170,17 @@ namespace osu.Game.Rulesets.Mania.Beatmaps
             }
 
             if (conversion == null)
-                return null;
+                yield break;
 
-            Pattern newPattern = conversion.Generate();
+            foreach (var newPattern in conversion.Generate())
+            {
+                lastPattern = conversion is EndTimeObjectPatternGenerator ? lastPattern : newPattern;
+                lastStair = (conversion as HitObjectPatternGenerator)?.StairType ?? lastStair;
 
-            lastPattern = conversion is EndTimeObjectPatternGenerator ? lastPattern : newPattern;
-            lastStair = (conversion as HitObjectPatternGenerator)?.StairType ?? lastStair;
+                foreach (var obj in newPattern.HitObjects)
+                    yield return obj;
 
-            return newPattern.HitObjects;
+            }
         }
 
         /// <summary>
@@ -187,7 +193,12 @@ namespace osu.Game.Rulesets.Mania.Beatmaps
             {
             }
 
-            public override Pattern Generate()
+            public override IEnumerable<Pattern> Generate()
+            {
+                yield return generate();
+            }
+
+            private Pattern generate()
             {
                 var endTimeData = HitObject as IHasEndTime;
                 var positionData = HitObject as IHasXPosition;

osu.Game.Rulesets.Mania/Beatmaps/Patterns/Legacy/DistanceObjectPatternGenerator.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using osu.Framework.MathUtils;
 using osu.Game.Audio;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Mania.MathUtils;
@@ -57,7 +58,30 @@ namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns.Legacy
             SegmentDuration = (EndTime - HitObject.StartTime) / spanCount;
         }
 
-        public override Pattern Generate()
+        public override IEnumerable<Pattern> Generate()
+        {
+            var originalPattern = generate();
+
+            // We need to split the intermediate pattern into two new patterns:
+            // 1. A pattern containing all objects that do not end at our EndTime.
+            // 2. A pattern containing all objects that end at our EndTime. This will be used for further pattern generation.
+            var intermediatePattern = new Pattern();
+            var endTimePattern = new Pattern();
+
+            foreach (var obj in originalPattern.HitObjects)
+            {
+                if (!Precision.AlmostEquals(EndTime, (obj as IHasEndTime)?.EndTime ?? obj.StartTime))
+                    intermediatePattern.Add(obj);
+                else
+                    endTimePattern.Add(obj);
+            }
+
+
+            yield return intermediatePattern;
+            yield return endTimePattern;
+        }
+
+        private Pattern generate()
         {
             if (TotalColumns == 1)
             {

osu.Game.Rulesets.Mania/Beatmaps/Patterns/Legacy/EndTimeObjectPatternGenerator.cs

@@ -24,7 +24,12 @@ namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns.Legacy
             endTime = endtimeData?.EndTime ?? 0;
         }
 
-        public override Pattern Generate()
+        public override IEnumerable<Pattern> Generate()
+        {
+            yield return generate();
+        }
+
+        private Pattern generate()
         {
             var pattern = new Pattern();
 

osu.Game.Rulesets.Mania/Beatmaps/Patterns/Legacy/HitObjectPatternGenerator.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using OpenTK;
 using osu.Game.Audio;
@@ -87,7 +88,12 @@ namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns.Legacy
             }
         }
 
-        public override Pattern Generate()
+        public override IEnumerable<Pattern> Generate()
+        {
+            yield return generate();
+        }
+
+        private Pattern generate()
         {
             var pattern = new Pattern();
 

osu.Game.Rulesets.Mania/Beatmaps/Patterns/PatternGenerator.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
 using System;
+using System.Collections.Generic;
 using osu.Game.Rulesets.Objects;
 
 namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns
@@ -42,9 +43,9 @@ namespace osu.Game.Rulesets.Mania.Beatmaps.Patterns
         }
 
         /// <summary>
-        /// Generates the pattern for <see cref="HitObject"/>, filled with hit objects.
+        /// Generates the patterns for <see cref="HitObject"/>, each filled with hit objects.
         /// </summary>
-        /// <returns>The <see cref="Pattern"/> containing the hit objects.</returns>
-        public abstract Pattern Generate();
+        /// <returns>The <see cref="Pattern"/>s containing the hit objects.</returns>
+        public abstract IEnumerable<Pattern> Generate();
     }
 }