Add basic custom data directory support

osu.Game/Configuration/StorageConfigManager.cs

@@ -0,0 +1,30 @@
+// 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 osu.Framework.Configuration;
+using osu.Framework.Platform;
+
+namespace osu.Game.Configuration
+{
+    public class StorageConfigManager : IniConfigManager<StorageConfig>
+    {
+        protected override string Filename => "storage.ini";
+
+        public StorageConfigManager(Storage storage)
+            : base(storage)
+        {
+        }
+
+        protected override void InitialiseDefaults()
+        {
+            base.InitialiseDefaults();
+
+            Set(StorageConfig.FullPath, string.Empty);
+        }
+    }
+
+    public enum StorageConfig
+    {
+        FullPath,
+    }
+}

osu.Game/OsuGameBase.cs

@@ -132,6 +132,8 @@ namespace osu.Game
 
             dependencies.Cache(contextFactory = new DatabaseContextFactory(Storage));
 
+            dependencies.CacheAs(Storage);
+
             var largeStore = new LargeTextureStore(Host.CreateTextureLoaderStore(new NamespacedResourceStore<byte[]>(Resources, @"Textures")));
             largeStore.AddStore(Host.CreateTextureLoaderStore(new OnlineStore()));
             dependencies.Cache(largeStore);
@@ -300,8 +302,13 @@ namespace osu.Game
         {
             base.SetHost(host);
 
-            if (Storage == null)
-                Storage = host.Storage;
+            var storageConfig = new StorageConfigManager(host.Storage);
+
+            var customStoragePath = storageConfig.Get<string>(StorageConfig.FullPath);
+
+            Storage = !string.IsNullOrEmpty(customStoragePath)
+                ? new CustomStorage(customStoragePath, host)
+                : host.Storage;
 
             if (LocalConfig == null)
                 LocalConfig = new OsuConfigManager(Storage);
@@ -353,5 +360,17 @@ namespace osu.Game
                 public override bool ChangeFocusOnClick => false;
             }
         }
+
+        /// <summary>
+        /// A storage pointing to an absolute location specified by the user to store game data files.
+        /// </summary>
+        private class CustomStorage : NativeStorage
+        {
+            public CustomStorage(string fullPath, GameHost host)
+                : base(string.Empty, host)
+            {
+                BasePath = fullPath;
+            }
+        }
     }
 }