Proposed: Create a Conceptual Model of VRChat Networking

The Context

In the realm of virtual reality, particularly within VRChat, understanding the networking model is crucial for developers. This proposal aims to create a comprehensive conceptual model of VRChat’s networking system.

The Problem Statement

Developers often struggle with the intricacies of VRChat’s networking, leading to inefficient code and suboptimal user experiences. A clear and concise guide is needed to demystify the process.

Describe How Your Proposal Will Work with Code, Pseudo-Code, Mock-Ups, or Diagrams

Sending Data in VRChat

There are two primary methods to send data in VRChat:

1. Udonsynced Variables:

   • Mark variables as [UdonSynced].
   • Call RequestSerialization() in the script to send a copy of the synced variables to all other clients.
   • Only the owner can call RequestSerialization(), so ensure you call Networking.SetOwner() first.
   • An event called OnDeserialization is triggered when a network packet is received.

2. Network Events:

   • Use SendCustomNetworkEvent() to send an event.
   • Specify a string that matches the name of a function taking no arguments; this function will run upon receiving the event.
   • Choose to send the event either to the owner or all clients.

// Example of Udonsynced variable
[UdonBehaviourSyncMode(BehaviourSyncMode.Manual)]
public class SyncExample : UdonSharpBehaviour
{
    [UdonSynced] private int syncedVariable;

    public void UpdateVariable(int newValue)
    {
        if (Networking.IsOwner(gameObject))
        {
            syncedVariable = newValue;
            RequestSerialization();
        }
    }

    public override void OnDeserialization()
    {
        // Handle deserialized data
    }
}

// Example of Network Event
public class EventExample : UdonSharpBehaviour
{
    public void TriggerEvent()
    {
        SendCustomNetworkEvent(VRC.Udon.Common.Interfaces.NetworkEventTarget.All, "HandleEvent");
    }

    public void HandleEvent()
    {
        // Handle the event
    }
}

The Benefits

• Improved Readability: Clear guidelines enhance the readability of networking code.
• Consistency: Ensures uniformity in how networking tasks are handled across different projects.
• Efficiency: Streamlined processes make it easier for developers to implement networking features quickly.

The Downsides

• Initial Setup Time: Establishing and fine-tuning the mental model requires an initial investment of time and resources.
• Limited Flexibility: Strict adherence to the model may limit creative solutions to unique problems.

The Road Not Taken

Alternative approaches such as manual editing or using different networking models were considered but ultimately impossible as we don’t run VRChat.

The Infrequent Use Case

In scenarios where highly specialized or technical networking solutions are required, additional human oversight may be necessary to ensure accuracy and appropriateness.

In Core and Done by Us

We need to understand how networking models work.

Status

Status: Proposed

Decision Makers

• V-Sekai development team
• Fire
• MMMaellon

Tags

• V-Sekai

Further Reading

1. V-Sekai · GitHub - Official GitHub account for the V-Sekai development community focusing on social VR functionality for the Godot Engine.
2. V-Sekai/v-sekai-game - GitHub page for the V-Sekai open-source project, which brings social VR/VRSNS/metaverse components to the Godot Engine.

AI assistant Aria assisted with this article.

The byte count(s) of every synced variable type in udon

Centauri2442 recorded the byte count(s) of every synced variable type in udon

System Type	maxByte	minByte	variableType	Notes
System.Boolean	2	2	Bool
System.Char	2	2	Char
System.Byte	2	2	Byte
System.SByte	2	2	SByte
System.Int16	4	2	Short	Swaps every other
System.UInt16	4	2	UShort	Swaps every other
System.Int32	8	4	Int	Swaps every other
System.UInt32	8	4	UInt	Swaps every other
System.Int64	12	8	Long	Swaps every other
System.UInt64	12	8	ULong	Swaps every other
System.Single	8	4	Float	Swaps every other
System.Double	12	8	Double	Swaps every other
UnityEngine.Vector2	8	8	Vector2
UnityEngine.Vector3	12	12	Vector3
UnityEngine.Vector4	16	16	Vector4
UnityEngine.Quaternion	16	16	Quaternion
System.String	84	1	String	Null: No serialization | 84 + 1 byte per character, byte size allocated per for (84, 88, 92, etc)
RVCUInt	8	8	RVCUInt
UnityEngine.Color	8	8	Color
UnityEngine.Color32	8	8	Color32
System.BooleanArray	80	80	BooleanArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 4 values (5, 9, 13, etc)
System.CharArray	80	80	CharArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 4 values (5, 9, 13, etc)
System.ByteArray	80	80	ByteArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 4 values (5, 9, 13, etc)
System.SByteArray	80	80	SByteArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 4 values (5, 9, 13, etc)
System.Int16Array	80	80	ShortArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 2 values (3, 5, 7, etc)
System.UInt16Array	80	80	UShortArray	80 + array size in increments of 4 as buffer (80, 84, 88, etc) | Will increase every 2 values (3, 5, 7, etc)
System.Int32Array	80	80	IntArray	80 + array size * 4
System.UInt32Array	80	80	UIntArray	80 + array size * 4
System.Int64Array	80	80	LongArray	80 + array size * 8
System.UInt64Array	80	80	ULongArray	80 + array size * 8
System.SingleArray	80	80	FloatArray	80 + array size * 4
System.DoubleArray	80	80	DoubleArray	80 + array size * 8
UnityEngine.Vector2Array	80	80	Vector2Array	80 + array size * 8
UnityEngine.Vector3Array	80	80	Vector3Array	80 + array size * 12
UnityEngine.Vector4Array	80	80	Vector4Array	80 + array size * 16
UnityEngine.QuaternionArray	80	80	QuaternionArray	80 + array size * 16
System.StringArray	80	80	StringArray	84 + (2, 4, or 8 bytes per character). Size of 0: 84 bytes. Size greater than 0 but with any null values: 0 bytes. Size greater than 0 with all valid strings: 84 + (2, 4, or 8 bytes per character)
RVCUStringArray	80	80	RVCUStringArray	84 + (2, 4, or 8 bytes per character). Size of 0: 84 bytes. Size greater than 0 but with any null values: 0 bytes. Size greater than 0 with all valid strings: 84 + (2, 4, or 8 bytes per character)
UnityEngine.ColorArray	80	80	ColorArray	80 + array size * 16
UnityEngine.Color32Array	80	80	Color32Array	80 + array size * 4

Question: How many UdonSharpBehaviour instances can a server have?

Answer: In VRChat, which uses UdonSharp for scripting, there isn’t a hard limit on the number of UdonSharpBehaviour instances a world (or server instance) can have. However, practical limits are imposed by performance considerations. Each UdonSharpBehaviour consumes memory and processing power, so the total number you can effectively use will depend on the complexity of your scripts and the capabilities of the hardware running the world. It’s essential to optimize your scripts and manage resources efficiently to ensure smooth performance.

Question: Can UdonSharpBehaviour instances communicate with each other?

Answer: Yes, UdonSharpBehaviour instances can communicate with each other. Here are some ways they can interact:

• Custom Network Events: You can send custom network events (with zero parameters) to trigger actions in other UdonSharpBehaviour instances. The receiver won’t know who the sender is, and the action will be performed locally on the UdonSharpBehaviour’s current frame.
• Synced Variables: If you need to send data, it’s better to use synced variables rather than mixing them with network events. When these variables get updated, the OnDeserialization() method will be called. This is a function in UdonSharpBehaviour that you can override to handle any work needed with the updated variables.

Question: How should I represent the entire state in a networked application?

Answer: You typically don’t mix network events with synced variables. If you need to send data, just use synced variables. When the variables get updated, OnDeserialization() will be called. That’s a function in UdonSharpBehaviour that you can override. Do all the work needed with the variables in OnDeserialization.

Question: Does using FieldChangeCallbacks affect performance in space and time?

Answer: There’s an advanced feature called FieldChangeCallbacks that allows for code simplification. Basically, create a C# property with a getter and a setter and specify it as the field change callback. The setter will be called in addition to OnDeserialization when network updates come in. This helps combine the code for local and remote clients in the setter. This is an advanced code-writing optimization for making your code cleaner. No, it does not affect performance in terms of space and time. FieldChangeCallbacks reduces code repetition, thereby simplifying the codebase and making it more maintainable.

Question: How can the order and exact value changes of three variables affect their interpretation in a networked system?

Answer: Assume we calculate the state of the world independently for each frame, without depending on previous frames. This means that while the exact values of the three variables are crucial for determining the current state, the order of changes within the same frame does not affect the final state interpretation at that frame.