introduce main menu background modes

osu.Game/Graphics/Backgrounds/BeatmapBackground.cs

@@ -0,0 +1,28 @@
+// 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.Allocation;
+using osu.Framework.Graphics.Textures;
+using osu.Game.Beatmaps;
+
+namespace osu.Game.Graphics.Backgrounds
+{
+    public class BeatmapBackground : Background
+    {
+        public readonly WorkingBeatmap Beatmap;
+
+        private readonly string fallbackTextureName;
+
+        public BeatmapBackground(WorkingBeatmap beatmap, string fallbackTextureName = @"Backgrounds/bg1")
+        {
+            Beatmap = beatmap;
+            this.fallbackTextureName = fallbackTextureName;
+        }
+
+        [BackgroundDependencyLoader]
+        private void load(TextureStore textures)
+        {
+            Sprite.Texture = Beatmap?.Background ?? textures.Get(fallbackTextureName);
+        }
+    }
+}