Add a way to adjust the conversion process with mods

osu.Game/Rulesets/Mods/IApplicableToBeatmapConverter.cs

@@ -0,0 +1,22 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Objects;
+
+namespace osu.Game.Rulesets.Mods
+{
+    /// <summary>
+    /// Interface for a <see cref="Mod"/> that applies changes to a <see cref="BeatmapConverter{TObject}"/>.
+    /// </summary>
+    /// <typeparam name="TObject">The type of converted <see cref="HitObject"/>.</typeparam>
+    public interface IApplicableToBeatmapConverter<TObject>
+        where TObject : HitObject
+    {
+        /// <summary>
+        /// Applies this <see cref="Mod"/> to a <see cref="BeatmapConverter{TObject}"/>.
+        /// </summary>
+        /// <param name="beatmapConverter">The <see cref="BeatmapConverter{TObject}"/> to apply to.</param>
+        void ApplyToBeatmapConverter(BeatmapConverter<TObject> beatmapConverter);
+    }
+}

osu.Game/Rulesets/UI/RulesetContainer.cs

@@ -176,6 +176,10 @@ namespace osu.Game.Rulesets.UI
             if (!converter.CanConvert(workingBeatmap.Beatmap))
                 throw new BeatmapInvalidForRulesetException($"{nameof(Beatmap)} can not be converted for the current ruleset (converter: {converter}).");
 
+            // Apply conversion adjustments before converting
+            foreach (var mod in Mods.OfType<IApplicableToBeatmapConverter<TObject>>())
+                mod.ApplyToBeatmapConverter(converter);
+
             // Convert the beatmap
             Beatmap = converter.Convert(workingBeatmap.Beatmap);
 

osu.Game/osu.Game.csproj

@@ -313,6 +313,7 @@
     <Compile Include="Overlays\Settings\Sections\Maintenance\DeleteAllBeatmapsDialog.cs" />
     <Compile Include="Rulesets\Mods\IApplicableFailOverride.cs" />
     <Compile Include="Rulesets\Mods\IApplicableMod.cs" />
+    <Compile Include="Rulesets\Mods\IApplicableToBeatmapConverter.cs" />
     <Compile Include="Rulesets\Mods\IApplicableToDrawableHitObject.cs" />
     <Compile Include="Screens\Select\ImportFromStablePopup.cs" />
     <Compile Include="Overlays\Settings\SettingsButton.cs" />