Custom RPCs

Why ?

Short answer: Il2Cpp.

Long answer:

Classic Mono syntax to declare an RPC method:

[PunRPC]
public void RPCA_StartGame()
{
    ...
}

With Il2Cpp, we can't use the [PunRPC] Attribute to define our methods as valid RPCs in Photon.
This is due to Il2Cpp handling [PunRPC] as Il2CppSystem.Attribute, which is not a valid System.Attribute that can be applied to methods anymore.

To counter this, we create a custom Attribute [CustomRPC].
Then, we hook into the Photon logic flow to register our custom RPCA_ methods as valid PunRPC methods.

Development

1. Add CustomRPCs.dll as a dependency in your csproj:

   <Reference Include="CustomRPCs">
       <HintPath>Libs\CustomRPCs.dll</HintPath>
   </Reference>

2. Add the [CustomRPC] attribute to your RPCA_ methods.

3. Profit!

Runtime

Add CustomRPCs.dll as a classic Melon mod in Mods/.

At game start, you should see:

Loading Mods...

------------------------------
Melon Assembly loaded: '.\Mods\CustomRPCs.dll'
------------------------------

------------------------------
CustomRPCs vX.X.X
by t1nquen
Assembly: CustomRPCs.dll
------------------------------

Example

The following example creates a [CustomRPC] method RPCA_SetScale(float scale) allowing to change the size of a player on network.

For demo purposes, you can trigger a random scale change on your player by pressing the H key.

using Il2Cpp;
using MelonLoader;
using UnityEngine;
using HarmonyLib;
using Il2CppPhoton.Pun;

using CustomRPCs;

namespace HideNSeek;

[RegisterTypeInIl2Cpp]
public class ScalingTool : MonoBehaviourPun
{
    private Player player;
    void Start() => player = GetComponent<Player>();
    void Update()
    {
        if (player.IsLocalPlayer() && Input.GetKeyDown(KeyCode.H))
            Call_SetScale(Random.Range(0f, 2f));
    }

    /// <summary>
    /// Call `RPCA_SetScale(scale)` on all clients.
    /// </summary>
    /// <param name="scale"></param>
    public void Call_SetScale(float scale)
    {
        player.refs.view.RPC("RPCA_SetScale", RpcTarget.All, scale);
    }

    /// <summary>
    /// Define custom RPCA with [CustomRPC]
    /// so that it is registered to Photon.
    /// </summary>
    /// <param name="scale"></param>
    [CustomRPC]
    public void RPCA_SetScale(float scale)
    {
        player.transform.localScale = new Vector3(scale, scale, scale);
    }
}

[HarmonyPatch]
public static class ComponentAdder
{
    /// <summary>
    /// Add our custom Pun component to all players.
    /// Using a patch ensures that players are actually
    /// defined at the time we add the component(s).
    /// </summary>
    /// <param name="__instance"></param>
    [HarmonyPatch(typeof(Player), nameof(Player.Start))]
    [HarmonyPostfix]
    private static void StartPatch(Player __instance)
    {
        __instance.gameObject.AddComponent<ScalingTool>();
    }
}

Note that the ScalingTool component MUST be added client-side on all Player views for the RPCA to work.
This is done through the ComponentAdder patch.

Since ScalingTool is a custom class, it MUST include the [RegisterTypeInIl2Cpp] attribute before using AddComponent<>().