Fix path control points losing curve type on save/reload or undo

osu.Game.Rulesets.Osu.Tests/Editor/TestSceneSliderChangeStates.cs

@@ -0,0 +1,47 @@
+// Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Linq;
+using NUnit.Framework;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Rulesets.Objects.Types;
+using osu.Game.Rulesets.Osu.Objects;
+using osu.Game.Tests.Beatmaps;
+using osuTK;
+
+namespace osu.Game.Rulesets.Osu.Tests.Editor
+{
+    public partial class TestSceneSliderChangeStates : TestSceneOsuEditor
+    {
+        protected override IBeatmap CreateBeatmap(RulesetInfo ruleset) => new TestBeatmap(ruleset, false);
+
+        [TestCase(SplineType.Catmull)]
+        [TestCase(SplineType.BSpline)]
+        [TestCase(SplineType.Linear)]
+        [TestCase(SplineType.PerfectCurve)]
+        public void TestSliderRetainsCurveTypes(SplineType splineType)
+        {
+            Slider? slider = null;
+            PathType pathType = new PathType(splineType);
+
+            AddStep("add slider", () => EditorBeatmap.Add(slider = new Slider
+            {
+                StartTime = 500,
+                Path = new SliderPath(new[]
+                {
+                    new PathControlPoint(Vector2.Zero, pathType),
+                    new PathControlPoint(new Vector2(200, 0), pathType),
+                })
+            }));
+            AddAssert("slider has correct spline type", () => ((Slider)EditorBeatmap.HitObjects[0]).Path.ControlPoints.All(p => p.Type == pathType));
+            AddStep("remove object", () => EditorBeatmap.Remove(slider));
+            AddAssert("slider removed", () => EditorBeatmap.HitObjects.Count == 0);
+            addUndoSteps();
+            AddAssert("slider not removed", () => EditorBeatmap.HitObjects.Count == 1);
+            AddAssert("slider has correct spline type", () => ((Slider)EditorBeatmap.HitObjects[0]).Path.ControlPoints.All(p => p.Type == pathType));
+        }
+
+        private void addUndoSteps() => AddStep("undo", () => Editor.Undo());
+    }
+}

osu.Game/Beatmaps/Formats/LegacyBeatmapEncoder.cs

@@ -450,7 +450,7 @@ 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 and can lead to decoding issues if encoded as implicit segments
-                    bool needsExplicitSegment = point.Type != lastType || point.Type == PathType.PERFECT_CURVE;
+                    bool needsExplicitSegment = point.Type != lastType || point.Type == PathType.PERFECT_CURVE || i == pathData.Path.ControlPoints.Count - 1;
 
                     // 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.
                     // Lazer does not add implicit segments for the last two control points of _any_ explicit segment, so an explicit segment is forced in order to maintain consistency with the decoder.

osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs

@@ -351,13 +351,19 @@ private IEnumerable<ArraySegment<PathControlPoint>> convertPoints(PathType type,
             {
                 int endPointLength = endPoint == null ? 0 : 1;
 
-                if (vertices.Length + endPointLength != 3)
-                    type = PathType.BEZIER;
-                else if (isLinear(points[0], points[1], endPoint ?? points[2]))
+                if (FormatVersion < LegacyBeatmapEncoder.FIRST_LAZER_VERSION)
                 {
-                    // osu-stable special-cased colinear perfect curves to a linear path
-                    type = PathType.LINEAR;
+                    if (vertices.Length + endPointLength != 3)
+                        type = PathType.BEZIER;
+                    else if (isLinear(points[0], points[1], endPoint ?? points[2]))
+                    {
+                        // osu-stable special-cased colinear perfect curves to a linear path
+                        type = PathType.LINEAR;
+                    }
                 }
+                else if (vertices.Length + endPointLength > 3)
+                    // Lazer supports perfect curves with less than 3 points and colinear points
+                    type = PathType.BEZIER;
             }
 
             // The first control point must have a definite type.