From dd902441b098983802cb1bbda3fae0ad8c86fa5f Mon Sep 17 00:00:00 2001
From: Leon Gebler <leon.gebler@gebler-online.de>
Date: Mon, 5 Apr 2021 17:21:45 +0200
Subject: [PATCH] Add tests for consecutive perfect-curve segments

---
 .../Formats/LegacyBeatmapDecoderTest.cs       | 30 +++++++++++++++++++
 .../Resources/multi-segment-slider.osu        |  7 +++++
 .../Beatmaps/Formats/LegacyBeatmapEncoder.cs  |  2 +-
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs b/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
index fb18be3ae1..0f82492e51 100644
--- a/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
+++ b/osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapDecoderTest.cs
@@ -740,6 +740,36 @@ public void TestMultiSegmentSliders()
                 Assert.That(fifth.ControlPoints[5].Type.Value, Is.EqualTo(PathType.Bezier));
                 Assert.That(fifth.ControlPoints[6].Position.Value, Is.EqualTo(new Vector2(5, 5)));
                 Assert.That(fifth.ControlPoints[6].Type.Value, Is.EqualTo(null));
+
+                // Implicit perfect-curve multi-segment(Should convert to bezier to match stable)
+                var sixth = ((IHasPath)decoded.HitObjects[5]).Path;
+
+                Assert.That(sixth.ControlPoints[0].Position.Value, Is.EqualTo(Vector2.Zero));
+                Assert.That(sixth.ControlPoints[0].Type.Value == PathType.Bezier);
+                Assert.That(sixth.ControlPoints[1].Position.Value, Is.EqualTo(new Vector2(75, 145)));
+                Assert.That(sixth.ControlPoints[1].Type.Value == null);
+                Assert.That(sixth.ControlPoints[2].Position.Value, Is.EqualTo(new Vector2(170, 75)));
+
+                Assert.That(sixth.ControlPoints[2].Type.Value == PathType.Bezier);
+                Assert.That(sixth.ControlPoints[3].Position.Value, Is.EqualTo(new Vector2(300, 145)));
+                Assert.That(sixth.ControlPoints[3].Type.Value == null);
+                Assert.That(sixth.ControlPoints[4].Position.Value, Is.EqualTo(new Vector2(410, 20)));
+                Assert.That(sixth.ControlPoints[4].Type.Value == null);
+
+                // Explicit perfect-curve multi-segment(Should not convert to bezier)
+                var seventh = ((IHasPath)decoded.HitObjects[6]).Path;
+
+                Assert.That(seventh.ControlPoints[0].Position.Value, Is.EqualTo(Vector2.Zero));
+                Assert.That(seventh.ControlPoints[0].Type.Value == PathType.PerfectCurve);
+                Assert.That(seventh.ControlPoints[1].Position.Value, Is.EqualTo(new Vector2(75, 145)));
+                Assert.That(seventh.ControlPoints[1].Type.Value == null);
+                Assert.That(seventh.ControlPoints[2].Position.Value, Is.EqualTo(new Vector2(170, 75)));
+
+                Assert.That(seventh.ControlPoints[2].Type.Value == PathType.PerfectCurve);
+                Assert.That(seventh.ControlPoints[3].Position.Value, Is.EqualTo(new Vector2(300, 145)));
+                Assert.That(seventh.ControlPoints[3].Type.Value == null);
+                Assert.That(seventh.ControlPoints[4].Position.Value, Is.EqualTo(new Vector2(410, 20)));
+                Assert.That(seventh.ControlPoints[4].Type.Value == null);
             }
         }
     }
diff --git a/osu.Game.Tests/Resources/multi-segment-slider.osu b/osu.Game.Tests/Resources/multi-segment-slider.osu
index cc86710067..135132e35c 100644
--- a/osu.Game.Tests/Resources/multi-segment-slider.osu
+++ b/osu.Game.Tests/Resources/multi-segment-slider.osu
@@ -15,3 +15,10 @@ osu file format v128
 
 // Last control point in segment duplicated
 0,0,5000,2,0,B|1:1|2:2|3:3|3:3|B|4:4|5:5,2,200
+
+// Implicit perfect-curve multi-segment (Should convert to bezier to match stable)
+0,0,6000,2,0,P|75:145|170:75|170:75|300:145|410:20,1,475,0:0:0:0:
+
+// Explicit perfect-curve multi-segment (Should not convert to bezier)
+0,0,7000,2,0,P|75:145|P|170:75|300:145|410:20,1,650,0:0:0:0:
+
diff --git a/osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs b/osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs
index 0bb1aa873f..da44b96ed3 100644
--- a/osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs
+++ b/osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs
@@ -333,7 +333,7 @@ private void addPathData(TextWriter writer, IHasPath pathData, Vector2 position)
 
                     // Explicit segments have a new format in which the type is injected into the middle of the control point string.
                     // To preserve compatibility with osu-stable as much as possible, explicit segments with the same type are converted to use implicit segments by duplicating the control point.
-                    // One exception are consecutive perfect curves, which aren't supported in osu-stable
+                    // One exception are consecutive perfect curves, which aren't supported in osu!stable and can lead to decoding issues if encoded as implicit segments
                     bool needsExplicitSegment = point.Type.Value != lastType || point.Type.Value == PathType.PerfectCurve;
 
                     // Another exception to this is when the last two control points of the last segment were duplicated. This is not a scenario supported by osu!stable.