From 16d4544ff9b4ca72fcd0899c9cd56a1a92f91246 Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Fri, 1 Apr 2022 17:06:37 +0900
Subject: [PATCH] Prevent reloads when playlist item order changes

---
 osu.Game/Online/Rooms/PlaylistItem.cs         |  6 ++++--
 .../Match/Playlist/MultiplayerPlaylist.cs     | 20 +++++++++++++++++--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/osu.Game/Online/Rooms/PlaylistItem.cs b/osu.Game/Online/Rooms/PlaylistItem.cs
index f696362cbb..a56851cfe6 100644
--- a/osu.Game/Online/Rooms/PlaylistItem.cs
+++ b/osu.Game/Online/Rooms/PlaylistItem.cs
@@ -11,6 +11,7 @@ using osu.Framework.Bindables;
 using osu.Game.Beatmaps;
 using osu.Game.Online.API;
 using osu.Game.Online.API.Requests.Responses;
+using osu.Game.Utils;
 
 namespace osu.Game.Online.Rooms
 {
@@ -101,13 +102,13 @@ namespace osu.Game.Online.Rooms
 
         #endregion
 
-        public PlaylistItem With(IBeatmapInfo beatmap) => new PlaylistItem(beatmap)
+        public PlaylistItem With(Optional<IBeatmapInfo> beatmap = default, Optional<ushort?> playlistOrder = default) => new PlaylistItem(beatmap.GetOr(Beatmap))
         {
             ID = ID,
             OwnerID = OwnerID,
             RulesetID = RulesetID,
             Expired = Expired,
-            PlaylistOrder = PlaylistOrder,
+            PlaylistOrder = playlistOrder.GetOr(PlaylistOrder),
             PlayedAt = PlayedAt,
             AllowedMods = AllowedMods,
             RequiredMods = RequiredMods,
@@ -119,6 +120,7 @@ namespace osu.Game.Online.Rooms
                && Beatmap.OnlineID == other.Beatmap.OnlineID
                && RulesetID == other.RulesetID
                && Expired == other.Expired
+               && PlaylistOrder == other.PlaylistOrder
                && AllowedMods.SequenceEqual(other.AllowedMods)
                && RequiredMods.SequenceEqual(other.RequiredMods);
     }
diff --git a/osu.Game/Screens/OnlinePlay/Multiplayer/Match/Playlist/MultiplayerPlaylist.cs b/osu.Game/Screens/OnlinePlay/Multiplayer/Match/Playlist/MultiplayerPlaylist.cs
index 879a21e7c1..41f548a630 100644
--- a/osu.Game/Screens/OnlinePlay/Multiplayer/Match/Playlist/MultiplayerPlaylist.cs
+++ b/osu.Game/Screens/OnlinePlay/Multiplayer/Match/Playlist/MultiplayerPlaylist.cs
@@ -117,8 +117,24 @@ namespace osu.Game.Screens.OnlinePlay.Multiplayer.Match.Playlist
         {
             base.PlaylistItemChanged(item);
 
-            removeItemFromLists(item.ID);
-            addItemToLists(item);
+            var newApiItem = Playlist.SingleOrDefault(i => i.ID == item.ID);
+            var existingApiItemInQueue = queueList.Items.SingleOrDefault(i => i.ID == item.ID);
+
+            // Test if the only change between the two playlist items is the order.
+            if (newApiItem != null && existingApiItemInQueue != null && existingApiItemInQueue.With(playlistOrder: newApiItem.PlaylistOrder).Equals(newApiItem))
+            {
+                // Set the new playlist order directly without refreshing the DrawablePlaylistItem.
+                existingApiItemInQueue.PlaylistOrder = newApiItem.PlaylistOrder;
+
+                // The following isn't really required, but is here for safety and explicitness.
+                // MultiplayerQueueList internally binds to changes in Playlist to invalidate its own layout, which is mutated on every playlist operation.
+                queueList.Invalidate();
+            }
+            else
+            {
+                removeItemFromLists(item.ID);
+                addItemToLists(item);
+            }
         }
 
         private void addItemToLists(MultiplayerPlaylistItem item)