Add "Mirror" mod

osu.Game.Rulesets.Osu/Mods/OsuModMirror.cs

@@ -0,0 +1,35 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Linq;
+using osu.Framework.Extensions.IEnumerableExtensions;
+using osu.Game.Rulesets.Mods;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Rulesets.Osu.Objects;
+using osu.Game.Rulesets.Osu.UI;
+using osuTK;
+
+namespace osu.Game.Rulesets.Osu.Mods
+{
+    public class OsuModMirror : ModMirror, IApplicableToHitObject
+    {
+        public void ApplyToHitObject(HitObject hitObject)
+        {
+            var osuObject = (OsuHitObject)hitObject;
+
+            osuObject.Position = new Vector2(OsuPlayfield.BASE_SIZE.X - osuObject.X, osuObject.Position.Y);
+
+            if (!(hitObject is Slider slider))
+                return;
+
+            slider.NestedHitObjects.OfType<SliderTick>().ForEach(h => h.Position = new Vector2(OsuPlayfield.BASE_SIZE.X - h.Position.X, h.Position.Y));
+            slider.NestedHitObjects.OfType<SliderRepeat>().ForEach(h => h.Position = new Vector2(OsuPlayfield.BASE_SIZE.X - h.Position.X, h.Position.Y));
+
+            var controlPoints = slider.Path.ControlPoints.Select(p => new PathControlPoint(p.Position.Value, p.Type.Value)).ToArray();
+            foreach (var point in controlPoints)
+                point.Position.Value = new Vector2(-point.Position.Value.X, point.Position.Value.Y);
+
+            slider.Path = new SliderPath(controlPoints, slider.Path.ExpectedDistance.Value);
+        }
+    }
+}

osu.Game.Rulesets.Osu/OsuRuleset.cs

@@ -166,6 +166,7 @@ public override IEnumerable<Mod> GetModsFor(ModType type)
                         new OsuModDifficultyAdjust(),
                         new OsuModClassic(),
                         new OsuModRandom(),
+                        new OsuModMirror(),
                     };
 
                 case ModType.Automation:

osu.Game/Rulesets/Mods/ModMirror.cs

@@ -0,0 +1,14 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+namespace osu.Game.Rulesets.Mods
+{
+    public abstract class ModMirror : Mod
+    {
+        public override string Name => "Mirror";
+        public override string Acronym => "MR";
+        public override ModType Type => ModType.Conversion;
+        public override string Description => "Flips the beatmap horizontally.";
+		public override double ScoreMultiplier => 1;
+    }
+}