Optimization

This page covers some practical optimization techniques for Udon.

SlowUpdate Pattern

Sometimes you’ll have a behavior with an Update() loop like:

using UdonSharp;
using UnityEngine;

public class SomeBehavior : UdonSharpBehaviour
{
    void Update()
    {
        Debug.Log("doing something expensive");
    }
}

Update() is unfortunately slow. Even if it looks simple, Udon runs ~1000x slower than the equivalent C# code.

For periodic tasks that don’t need frame-perfect timing, you can use the “SlowUpdate” pattern instead:

using UdonSharp;
using UnityEngine;

public class GameTimer : UdonSharpBehaviour
{
    private bool slowUpdateScheduled = false;
    private float slowUpdateRate = 1f; // once a second

    public void SlowUpdate()
    {
        Debug.Log("doing something expensive");
        if (slowUpdateScheduled)
        {
            SendCustomEventDelayedSeconds(nameof(SlowUpdate), slowUpdateRate);
        }
    }

    // bookkeeping:

    void Start()
    {
        // Start the slow update cycle
        if (!slowUpdateScheduled)
        {
            slowUpdateScheduled = true;
            SendCustomEventDelayedSeconds(nameof(SlowUpdate), slowUpdateRate);
        }
    }

    void OnEnable()
    {
        // Resume slow updates when re-enabled
        if (!slowUpdateScheduled)
        {
            slowUpdateScheduled = true;
            SendCustomEventDelayedSeconds(nameof(SlowUpdate), slowUpdateRate);
        }
    }

    void OnDisable()
    {
        // Stop scheduling new updates when disabled
        slowUpdateScheduled = false;
    }

}

Now instead of running every frame, this runs once per second, whenever the behavior’s gameObject is enabled.

Owner-Only Updates

For networked behaviors, often only the owner needs to run the slow update:

void OnEnable()
{
    if (Networking.IsOwner(gameObject) && !slowUpdateScheduled)
    {
        slowUpdateScheduled = true;
        SendCustomEventDelayedSeconds(nameof(SlowUpdate), 1f);
    }
}

public override void OnOwnershipTransferred(VRCPlayerApi player)
{
    // New owner should start slow updates
    if (Networking.IsOwner(gameObject) && !slowUpdateScheduled)
    {
        slowUpdateScheduled = true;
        SendCustomEventDelayedSeconds(nameof(SlowUpdate), 0.1f);
    }
    else
    {
        // No longer owner, stop slow updates
        slowUpdateScheduled = false;
    }
}