better-tee/Assets/Packages/Mirror/Examples/Lobby/Scripts/NetworkLobbyManagerExt.cs

using UnityEngine;
using UnityEngine.Rendering;

namespace Mirror.Examples.NetworkLobby
{
    public class NetworkLobbyManagerExt : NetworkLobbyManager
    {
        /// <summary>
        /// Called just after GamePlayer object is instantiated and just before it replaces LobbyPlayer object.
        /// This is the ideal point to pass any data like player name, credentials, tokens, colors, etc.
        /// into the GamePlayer object as it is about to enter the Online scene.
        /// </summary>
        /// <param name="lobbyPlayer"></param>
        /// <param name="gamePlayer"></param>
        /// <returns>true unless some code in here decides it needs to abort the replacement</returns>
        public override bool OnLobbyServerSceneLoadedForPlayer(GameObject lobbyPlayer, GameObject gamePlayer)
        {
            PlayerController player = gamePlayer.GetComponent<PlayerController>();
            player.index = lobbyPlayer.GetComponent<NetworkLobbyPlayer>().index;
            player.playerColor = Random.ColorHSV(0f, 1f, 1f, 1f, 0.5f, 1f);
            return true;
        }

        /*
            This code below is to demonstrate how to do a Start button that only appears for the Host player
            showStartButton is a local bool that's needed because OnLobbyServerPlayersReady is only fired when
            all players are ready, but if a player cancels their ready state there's no callback to set it back to false
            Therefore, allPlayersReady is used in combination with showStartButton to show/hide the Start button correctly.
            Setting showStartButton false when the button is pressed hides it in the game scene since NetworkLobbyManager
            is set as DontDestroyOnLoad = true.
        */

        bool showStartButton;

        public override void OnLobbyServerPlayersReady()
        {
            // calling the base method calls ServerChangeScene as soon as all players are in Ready state.
            if (isHeadless)
                base.OnLobbyServerPlayersReady();
            else
                showStartButton = true;
        }

        public override void OnGUI()
        {
            base.OnGUI();

            if (allPlayersReady && showStartButton && GUI.Button(new Rect(150, 300, 120, 20), "START GAME"))
            {
                // set to false to hide it in the game scene
                showStartButton = false;

                ServerChangeScene(GameplayScene);
            }
        }
    }
}