Add method to retrieve legacy score multiplier

osu.Game.Rulesets.Catch/Difficulty/CatchLegacyScoreSimulator.cs

@@ -2,10 +2,13 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Catch.Mods;
 using osu.Game.Rulesets.Catch.Objects;
 using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Types;
 using osu.Game.Rulesets.Scoring;
@@ -137,5 +140,53 @@ namespace osu.Game.Rulesets.Catch.Difficulty
             if (increaseCombo)
                 combo++;
         }
+
+        public double GetLegacyScoreMultiplier(IReadOnlyList<Mod> mods, LegacyBeatmapConversionDifficultyInfo difficulty)
+        {
+            bool scoreV2 = mods.Any(m => m is ModScoreV2);
+
+            double multiplier = 1.0;
+
+            foreach (var mod in mods)
+            {
+                switch (mod)
+                {
+                    case CatchModNoFail:
+                        multiplier *= scoreV2 ? 1.0 : 0.5;
+                        break;
+
+                    case CatchModEasy:
+                        multiplier *= 0.5;
+                        break;
+
+                    case CatchModHalfTime:
+                    case CatchModDaycore:
+                        multiplier *= 0.3;
+                        break;
+
+                    case CatchModHidden:
+                        multiplier *= scoreV2 ? 1.0 : 1.06;
+                        break;
+
+                    case CatchModHardRock:
+                        multiplier *= 1.12;
+                        break;
+
+                    case CatchModDoubleTime:
+                    case CatchModNightcore:
+                        multiplier *= 1.06;
+                        break;
+
+                    case CatchModFlashlight:
+                        multiplier *= 1.12;
+                        break;
+
+                    case CatchModRelax:
+                        return 0;
+                }
+            }
+
+            return multiplier;
+        }
     }
 }

osu.Game.Rulesets.Mania/Difficulty/ManiaLegacyScoreSimulator.cs

@@ -1,7 +1,12 @@
 // 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.Collections.Generic;
+using System.Linq;
 using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Mania.Beatmaps;
+using osu.Game.Rulesets.Mania.Mods;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Scoring.Legacy;
 
 namespace osu.Game.Rulesets.Mania.Difficulty
@@ -12,5 +17,50 @@ namespace osu.Game.Rulesets.Mania.Difficulty
         {
             return new LegacyScoreAttributes { ComboScore = 1000000 };
         }
+
+        public double GetLegacyScoreMultiplier(IReadOnlyList<Mod> mods, LegacyBeatmapConversionDifficultyInfo difficulty)
+        {
+            bool scoreV2 = mods.Any(m => m is ModScoreV2);
+
+            double multiplier = 1.0;
+
+            foreach (var mod in mods)
+            {
+                switch (mod)
+                {
+                    case ManiaModNoFail:
+                        multiplier *= scoreV2 ? 1.0 : 0.5;
+                        break;
+
+                    case ManiaModEasy:
+                        multiplier *= 0.5;
+                        break;
+
+                    case ManiaModHalfTime:
+                    case ManiaModDaycore:
+                        multiplier *= 0.5;
+                        break;
+                }
+            }
+
+            if (new ManiaRuleset().RulesetInfo.Equals(difficulty.SourceRuleset))
+                return multiplier;
+
+            // Apply key mod multipliers.
+
+            int originalColumns = ManiaBeatmapConverter.GetColumnCount(difficulty);
+            int actualColumns = originalColumns;
+
+            actualColumns = mods.OfType<ManiaKeyMod>().SingleOrDefault()?.KeyCount ?? actualColumns;
+            if (mods.Any(m => m is ManiaModDualStages))
+                actualColumns *= 2;
+
+            if (actualColumns > originalColumns)
+                multiplier *= 0.9;
+            else if (actualColumns < originalColumns)
+                multiplier *= 0.9 - 0.04 * (originalColumns - actualColumns);
+
+            return multiplier;
+        }
     }
 }

osu.Game.Rulesets.Osu/Difficulty/OsuLegacyScoreSimulator.cs

@@ -2,11 +2,14 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Types;
+using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Rulesets.Osu.Objects;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Scoring.Legacy;
@@ -174,5 +177,58 @@ namespace osu.Game.Rulesets.Osu.Difficulty
             if (increaseCombo)
                 combo++;
         }
+
+        public double GetLegacyScoreMultiplier(IReadOnlyList<Mod> mods, LegacyBeatmapConversionDifficultyInfo difficulty)
+        {
+            bool scoreV2 = mods.Any(m => m is ModScoreV2);
+
+            double multiplier = 1.0;
+
+            foreach (var mod in mods)
+            {
+                switch (mod)
+                {
+                    case OsuModNoFail:
+                        multiplier *= scoreV2 ? 1.0 : 0.5;
+                        break;
+
+                    case OsuModEasy:
+                        multiplier *= 0.5;
+                        break;
+
+                    case OsuModHalfTime:
+                    case OsuModDaycore:
+                        multiplier *= 0.3;
+                        break;
+
+                    case OsuModHidden:
+                        multiplier *= 1.06;
+                        break;
+
+                    case OsuModHardRock:
+                        multiplier *= scoreV2 ? 1.10 : 1.06;
+                        break;
+
+                    case OsuModDoubleTime:
+                    case OsuModNightcore:
+                        multiplier *= scoreV2 ? 1.20 : 1.12;
+                        break;
+
+                    case OsuModFlashlight:
+                        multiplier *= 1.12;
+                        break;
+
+                    case OsuModSpunOut:
+                        multiplier *= 0.9;
+                        break;
+
+                    case OsuModRelax:
+                    case OsuModAutopilot:
+                        return 0;
+                }
+            }
+
+            return multiplier;
+        }
     }
 }

osu.Game.Rulesets.Taiko/Difficulty/TaikoLegacyScoreSimulator.cs

@@ -2,13 +2,16 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets.Judgements;
+using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Objects;
 using osu.Game.Rulesets.Objects.Types;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Scoring.Legacy;
+using osu.Game.Rulesets.Taiko.Mods;
 using osu.Game.Rulesets.Taiko.Objects;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty
@@ -194,5 +197,47 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             if (increaseCombo)
                 combo++;
         }
+
+        public double GetLegacyScoreMultiplier(IReadOnlyList<Mod> mods, LegacyBeatmapConversionDifficultyInfo difficulty)
+        {
+            bool scoreV2 = mods.Any(m => m is ModScoreV2);
+
+            double multiplier = 1.0;
+
+            foreach (var mod in mods)
+            {
+                switch (mod)
+                {
+                    case TaikoModNoFail:
+                        multiplier *= scoreV2 ? 1.0 : 0.5;
+                        break;
+
+                    case TaikoModEasy:
+                        multiplier *= 0.5;
+                        break;
+
+                    case TaikoModHalfTime:
+                    case TaikoModDaycore:
+                        multiplier *= 0.3;
+                        break;
+
+                    case TaikoModHidden:
+                    case TaikoModHardRock:
+                        multiplier *= 1.06;
+                        break;
+
+                    case TaikoModDoubleTime:
+                    case TaikoModNightcore:
+                    case TaikoModFlashlight:
+                        multiplier *= 1.12;
+                        break;
+
+                    case TaikoModRelax:
+                        return 0;
+                }
+            }
+
+            return multiplier;
+        }
     }
 }

osu.Game/Rulesets/Scoring/Legacy/ILegacyScoreSimulator.cs

@@ -1,7 +1,9 @@
 // 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.Collections.Generic;
 using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Mods;
 
 namespace osu.Game.Rulesets.Scoring.Legacy
 {
@@ -16,5 +18,13 @@ namespace osu.Game.Rulesets.Scoring.Legacy
         /// <param name="workingBeatmap">The working beatmap.</param>
         /// <param name="playableBeatmap">A playable version of the beatmap for the ruleset.</param>
         LegacyScoreAttributes Simulate(IWorkingBeatmap workingBeatmap, IBeatmap playableBeatmap);
+
+        /// <summary>
+        /// Returns the legacy score multiplier for the mods. This is only used during legacy score conversion.
+        /// </summary>
+        /// <param name="mods">The mods.</param>
+        /// <param name="difficulty">Extra difficulty parameters.</param>
+        /// <returns>The legacy multiplier.</returns>
+        double GetLegacyScoreMultiplier(IReadOnlyList<Mod> mods, LegacyBeatmapConversionDifficultyInfo difficulty);
     }
 }