From 3c2d8cad0acbbdc5374dacaf0392931f86b665f2 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 12 Mar 2019 17:32:40 +0900
Subject: [PATCH] Add better async logic for ScreenWithBeatmapBackground

---
 .../Backgrounds/BackgroundScreenBeatmap.cs    | 28 ++++++++++++-------
 .../Play/ScreenWithBeatmapBackground.cs       |  2 +-
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/osu.Game/Screens/Backgrounds/BackgroundScreenBeatmap.cs b/osu.Game/Screens/Backgrounds/BackgroundScreenBeatmap.cs
index d7aa095440..54ce005469 100644
--- a/osu.Game/Screens/Backgrounds/BackgroundScreenBeatmap.cs
+++ b/osu.Game/Screens/Backgrounds/BackgroundScreenBeatmap.cs
@@ -1,6 +1,7 @@
 // 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.Threading;
 using osu.Framework.Allocation;
 using osu.Framework.Bindables;
 using osu.Framework.Graphics;
@@ -36,9 +37,13 @@ namespace osu.Game.Screens.Backgrounds
         [BackgroundDependencyLoader]
         private void load()
         {
-            backgroundLoaded(new BeatmapBackground(beatmap));
+            var background = new BeatmapBackground(beatmap);
+            LoadComponent(background);
+            switchBackground(background);
         }
 
+        private CancellationTokenSource cancellationSource;
+
         public WorkingBeatmap Beatmap
         {
             get => beatmap;
@@ -49,14 +54,18 @@ namespace osu.Game.Screens.Backgrounds
 
                 beatmap = value;
 
-                // load will be completed in async load.
-                if (LoadState < LoadState.Ready) return;
+                Schedule(() =>
+                {
+                    if ((Background as BeatmapBackground)?.Beatmap == beatmap)
+                        return;
 
-                Schedule(() => { LoadComponentAsync(new BeatmapBackground(beatmap), b => Schedule(() => backgroundLoaded(b))); });
+                    cancellationSource?.Cancel();
+                    LoadComponentAsync(new BeatmapBackground(beatmap), switchBackground, (cancellationSource = new CancellationTokenSource()).Token);
+                });
             }
         }
 
-        private void backgroundLoaded(BeatmapBackground b)
+        private void switchBackground(BeatmapBackground b)
         {
             float newDepth = 0;
             if (Background != null)
@@ -75,25 +84,24 @@ namespace osu.Game.Screens.Backgrounds
 
         public override bool Equals(BackgroundScreen other)
         {
-            var otherBeatmapBackground = other as BackgroundScreenBeatmap;
-            if (otherBeatmapBackground == null) return false;
+            if (!(other is BackgroundScreenBeatmap otherBeatmapBackground)) return false;
 
             return base.Equals(other) && beatmap == otherBeatmapBackground.Beatmap;
         }
 
         protected class BeatmapBackground : Background
         {
-            private readonly WorkingBeatmap beatmap;
+            public readonly WorkingBeatmap Beatmap;
 
             public BeatmapBackground(WorkingBeatmap beatmap)
             {
-                this.beatmap = beatmap;
+                Beatmap = beatmap;
             }
 
             [BackgroundDependencyLoader]
             private void load(TextureStore textures)
             {
-                Sprite.Texture = beatmap?.Background ?? textures.Get(@"Backgrounds/bg1");
+                Sprite.Texture = Beatmap?.Background ?? textures.Get(@"Backgrounds/bg1");
             }
         }
     }
diff --git a/osu.Game/Screens/Play/ScreenWithBeatmapBackground.cs b/osu.Game/Screens/Play/ScreenWithBeatmapBackground.cs
index 328aa1d18e..3aabceaaef 100644
--- a/osu.Game/Screens/Play/ScreenWithBeatmapBackground.cs
+++ b/osu.Game/Screens/Play/ScreenWithBeatmapBackground.cs
@@ -55,7 +55,7 @@ namespace osu.Game.Screens.Play
         /// Called when background elements require updates, usually due to a user changing a setting.
         /// </summary>
         /// <param name="userChange"></param>
-        protected virtual void UpdateBackgroundElements()
+        protected void UpdateBackgroundElements()
         {
             if (!this.IsCurrentScreen()) return;