From 9259aa94f10897d044e590ad61e0aa6e5506bf7a Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Tue, 24 May 2022 11:47:42 +0900
Subject: [PATCH] Fix Catmull slider parsing with duplicate initial point

---
 .../Formats/LegacyBeatmapDecoderTest.cs       | 19 +++++++++++++++++++
 ...catmull-duplicate-initial-controlpoint.osu |  2 ++
 .../Objects/Legacy/ConvertHitObjectParser.cs  |  6 ++++--
 3 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 osu.Game.Tests/Resources/catmull-duplicate-initial-controlpoint.osu

diff --git a/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs b/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
index 89baaf228d..e2d9910b82 100644
--- a/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
+++ b/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
@@ -898,5 +898,24 @@ namespace osu.Game.Tests.Beatmaps.Formats
                 Assert.That(controlPoints[3].Type, Is.Null);
             }
         }
+
+        [Test]
+        public void TestLegacyDuplicateInitialCatmullPointIsMerged()
+        {
+            var decoder = new LegacyBeatmapDecoder { ApplyOffsets = false };
+
+            using (var resStream = TestResources.OpenResource("catmull-duplicate-initial-controlpoint.osu"))
+            using (var stream = new LineBufferedReader(resStream))
+            {
+                var decoded = decoder.Decode(stream);
+                var controlPoints = ((IHasPath)decoded.HitObjects[0]).Path.ControlPoints;
+
+                Assert.That(controlPoints.Count, Is.EqualTo(4));
+                Assert.That(controlPoints[0].Type, Is.EqualTo(PathType.Catmull));
+                Assert.That(controlPoints[0].Position, Is.EqualTo(Vector2.Zero));
+                Assert.That(controlPoints[1].Type, Is.Null);
+                Assert.That(controlPoints[1].Position, Is.Not.EqualTo(Vector2.Zero));
+            }
+        }
     }
 }
diff --git a/osu.Game.Tests/Resources/catmull-duplicate-initial-controlpoint.osu b/osu.Game.Tests/Resources/catmull-duplicate-initial-controlpoint.osu
new file mode 100644
index 0000000000..7062229eed
--- /dev/null
+++ b/osu.Game.Tests/Resources/catmull-duplicate-initial-controlpoint.osu
@@ -0,0 +1,2 @@
+[HitObjects]
+200,304,23875,6,0,C|200:304|288:304|288:208|352:208,1,260,8|0
\ No newline at end of file
diff --git a/osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs b/osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs
index 7cf68a2df7..d3d1196eae 100644
--- a/osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs
+++ b/osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs
@@ -340,8 +340,10 @@ namespace osu.Game.Rulesets.Objects.Legacy
                 if (vertices[endIndex].Position != vertices[endIndex - 1].Position)
                     continue;
 
-                // Adjacent legacy Catmull segments should be treated as a single segment.
-                if (FormatVersion < LegacyBeatmapEncoder.FIRST_LAZER_VERSION && type == PathType.Catmull)
+                // Legacy Catmull sliders don't support multiple segments, so adjacent Catmull segments should be treated as a single one.
+                // Importantly, this is not applied to the first control point, which may duplicate the slider path's position
+                // resulting in a duplicate (0,0) control point in the resultant list.
+                if (type == PathType.Catmull && endIndex > 1 && FormatVersion < LegacyBeatmapEncoder.FIRST_LAZER_VERSION)
                     continue;
 
                 // The last control point of each segment is not allowed to start a new implicit segment.