AUMSS/Runtime/PickupMovementFixer.cs

using UdonSharp;
using UnityEngine;
using VRC.SDK3.Components;
using VRC.SDKBase;

[UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)]
[DisallowMultipleComponent]
[AddComponentMenu("Artyom Scripting System/Pickup Following Mover Fix")]
public class PickupMovementFixer : UdonSharpBehaviour
{
    public GameObject targetObject;  // The object to follow

    private int pickupLayer = 13;  // The layer assigned to pickup objects
    private Collider triggerCollider;
    private Vector3 previousTargetPosition;
    private Vector3 targetVelocity;
    private bool carrying; // While the target moves, and for one frame after it stops
    private bool ready;

    private void Start()
    {
        triggerCollider = GetComponent<Collider>();
        if (triggerCollider == null || !triggerCollider.isTrigger)
        {
            Debug.LogError("[AUMSS] Pickup Following Mover Fix: Collider must be set as a trigger.");
        }
        if (targetObject == null)
        {
            Debug.LogError("[AUMSS] Pickup Following Mover Fix: Target Object isn't assigned.");
            enabled = false;
            return;
        }
        previousTargetPosition = targetObject.transform.position;
        ready = true;
    }

    // LateUpdate runs after Update scripts and Animators have moved the target this frame,
    // so the movement measured here matches this frame's deltaTime
    private void LateUpdate()
    {
        if (!ready) return; // Not set up (enabled = false only takes effect next frame)
        Vector3 currentTargetPosition = targetObject.transform.position;
        Vector3 newVelocity = (currentTargetPosition - previousTargetPosition) / Time.deltaTime;
        previousTargetPosition = currentTargetPosition;

        // A still target leaves the pickups to their own physics, so they can fall and slide.
        // The frame it stops still applies (zero), so the pickups stop with it instead of sliding off.
        bool moving = newVelocity.sqrMagnitude > 0.0001f;
        carrying = moving || targetVelocity.sqrMagnitude > 0.0001f;
        targetVelocity = newVelocity;
    }

    private void OnTriggerEnter(Collider other)
    {
        Carry(other);
    }

    private void OnTriggerStay(Collider other)
    {
        Carry(other);
    }

    private void Carry(Collider other)
    {
        if (!ready || !carrying || other == null || other.gameObject.layer != pickupLayer) return;
        VRC_Pickup pickup = other.GetComponent<VRC_Pickup>();
        if (pickup == null || pickup.IsHeld) return;
        // A synced pickup is moved by its owner; anyone else setting its velocity just fights the sync
        if (other.GetComponent<VRCObjectSync>() != null && !Networking.IsOwner(other.gameObject)) return;

        Rigidbody pickupRigidbody = other.GetComponent<Rigidbody>();
        if (pickupRigidbody != null)
        {
            pickupRigidbody.velocity = targetVelocity;
        }
    }
}