Merge pull request #33615 from bdach/slider-encode-decode-instability

Fix lack of slider encode-decode stability due to truncating control point coordinates on decode

Author: smoogipoo

osu.Game.Tests/Beatmaps/Formats/LegacyBeatmapEncoderTest.cs

@@ -211,6 +211,31 @@ public void TestOnlyEightComboColoursEncoded()
             Assert.That(decodedAfterEncode.skin.Configuration.CustomComboColours, Has.Count.EqualTo(8));
         }
 
+        [Test]
+        public void TestEncodeStabilityOfSliderWithFractionalCoordinates()
+        {
+            Slider originalSlider = new Slider
+            {
+                Position = new Vector2(0.6f),
+                Path = new SliderPath(new[]
+                {
+                    new PathControlPoint(Vector2.Zero, PathType.PERFECT_CURVE),
+                    new PathControlPoint(new Vector2(25.6f, 78.4f)),
+                    new PathControlPoint(new Vector2(55.8f, 34.2f)),
+                })
+            };
+            var beatmap = new Beatmap
+            {
+                HitObjects = { originalSlider }
+            };
+
+            var encoded = encodeToLegacy((beatmap, new TestLegacySkin(beatmaps_resource_store, string.Empty)));
+            var decodedAfterEncode = decodeFromLegacy(encoded, string.Empty, version: LegacyBeatmapEncoder.FIRST_LAZER_VERSION);
+            var decodedSlider = (Slider)decodedAfterEncode.beatmap.HitObjects[0];
+            Assert.That(decodedSlider.Path.ControlPoints.Select(p => p.Position),
+                Is.EquivalentTo(originalSlider.Path.ControlPoints.Select(p => p.Position)));
+        }
+
         private bool areComboColoursEqual(IHasComboColours a, IHasComboColours b)
         {
             // equal to null, no need to SequenceEqual
@@ -233,11 +258,11 @@ private void sort(IBeatmap beatmap)
             }
         }
 
-        private (IBeatmap beatmap, TestLegacySkin skin) decodeFromLegacy(Stream stream, string name)
+        private (IBeatmap beatmap, TestLegacySkin skin) decodeFromLegacy(Stream stream, string name, int version = LegacyDecoder<Beatmap>.LATEST_VERSION)
         {
             using (var reader = new LineBufferedReader(stream))
             {
-                var beatmap = new LegacyBeatmapDecoder { ApplyOffsets = false }.Decode(reader);
+                var beatmap = new LegacyBeatmapDecoder(version) { ApplyOffsets = false }.Decode(reader);
                 var beatmapSkin = new TestLegacySkin(beatmaps_resource_store, name);
                 stream.Seek(0, SeekOrigin.Begin);
                 beatmapSkin.Configuration = new LegacySkinDecoder().Decode(reader);

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

@@ -335,11 +335,14 @@ private PathControlPoint[] convertPathString(string pointString, Vector2 offset)
                 ArrayPool<(PathType, int)>.Shared.Return(segmentsBuffer);
             }
 
-            static Vector2 readPoint(string value, Vector2 startPos)
+            Vector2 readPoint(string value, Vector2 startPos)
             {
                 string[] vertexSplit = value.Split(':');
 
-                Vector2 pos = new Vector2((int)Parsing.ParseDouble(vertexSplit[0], Parsing.MAX_COORDINATE_VALUE), (int)Parsing.ParseDouble(vertexSplit[1], Parsing.MAX_COORDINATE_VALUE)) - startPos;
+                Vector2 pos = formatVersion >= LegacyBeatmapEncoder.FIRST_LAZER_VERSION
+                    ? new Vector2(Parsing.ParseFloat(vertexSplit[0], Parsing.MAX_COORDINATE_VALUE), Parsing.ParseFloat(vertexSplit[1], Parsing.MAX_COORDINATE_VALUE))
+                    : new Vector2((int)Parsing.ParseFloat(vertexSplit[0], Parsing.MAX_COORDINATE_VALUE), (int)Parsing.ParseFloat(vertexSplit[1], Parsing.MAX_COORDINATE_VALUE));
+                pos -= startPos;
                 return pos;
             }
         }