From b0bd39fc4972b46b3577d90feab9aa2a1521e201 Mon Sep 17 00:00:00 2001
From: Dean Herbert <pe@ppy.sh>
Date: Tue, 2 Nov 2021 16:36:28 +0900
Subject: [PATCH] Fix multiplayer room participants display not updating as new
 users join/leave

Can add tests on request, but not sure the code around this area is here
to stay permanently. Should be pretty low risk.

- Closes https://github.com/ppy/osu/issues/14788.
---
 .../Online/Multiplayer/MultiplayerClient.cs    | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/osu.Game/Online/Multiplayer/MultiplayerClient.cs b/osu.Game/Online/Multiplayer/MultiplayerClient.cs
index 28505f6b0e..bf4bb13655 100644
--- a/osu.Game/Online/Multiplayer/MultiplayerClient.cs
+++ b/osu.Game/Online/Multiplayer/MultiplayerClient.cs
@@ -148,6 +148,10 @@ namespace osu.Game.Online.Multiplayer
                 {
                     Room = joinedRoom;
                     APIRoom = room;
+
+                    Debug.Assert(LocalUser != null);
+                    addUserToAPIRoom(LocalUser);
+
                     foreach (var user in joinedRoom.Users)
                         updateUserPlayingState(user.UserID, user.State);
 
@@ -372,6 +376,8 @@ namespace osu.Game.Online.Multiplayer
 
                 Room.Users.Add(user);
 
+                addUserToAPIRoom(user);
+
                 UserJoined?.Invoke(user);
                 RoomUpdated?.Invoke();
             });
@@ -391,6 +397,14 @@ namespace osu.Game.Online.Multiplayer
             return handleUserLeft(user, UserKicked);
         }
 
+        private void addUserToAPIRoom(MultiplayerRoomUser user)
+        {
+            Debug.Assert(APIRoom != null);
+
+            APIRoom.RecentParticipants.Add(user.User);
+            APIRoom.ParticipantCount.Value++;
+        }
+
         private Task handleUserLeft(MultiplayerRoomUser user, Action<MultiplayerRoomUser>? callback)
         {
             if (Room == null)
@@ -404,6 +418,10 @@ namespace osu.Game.Online.Multiplayer
                 Room.Users.Remove(user);
                 PlayingUserIds.Remove(user.UserID);
 
+                Debug.Assert(APIRoom != null);
+                APIRoom.RecentParticipants.RemoveAll(u => u.Id == user.UserID);
+                APIRoom.ParticipantCount.Value--;
+
                 callback?.Invoke(user);
                 RoomUpdated?.Invoke();
             }, false);