Vehicle Despawn System

Overview

The Vehicle Despawn System removes NPC vehicles within a specified radius. This is used during bus teleportation to prevent collisions.

How It Works

The system uses a two-phase approach:

1. Mark Phase: Vehicles within radius are flagged for removal
2. Despawn Phase: Flagged vehicles are destroyed in the next FixedUpdate()

System Flow

Game Code (TestTrafficRemovingNpc)
    ↓
TrafficManager.RemoveVehiclesInRadius()
    ↓
NPCVehicleSimulator.RemoveVehiclesInRadius()
    ↓
NPCVehicleInternalState (ShouldDespawn = true)
    ↓
TrafficManager.FixedUpdate() → Despawn()

Usage

Basic Implementation

using AWSIM.TrafficSimulation;
using UnityEngine;

public class TestTrafficRemovingNpc : MonoBehaviour
{
    [SerializeField] TrafficManager trafficManager;
    [SerializeField] Transform centerTransform;
    [SerializeField] float radius;
    [SerializeField] KeyCode RemoveKey = KeyCode.R;

    private void FixedUpdate()
    {
        if (Input.GetKeyDown(RemoveKey))
        {
            trafficManager.RemoveVehiclesInRadius(centerTransform, radius);
        }
    }
}

Component Setup

Inspector Parameters: - Traffic Manager: Reference to the TrafficManager in the scene - Center Transform: The center point for vehicle removal (typically the bus transform) - Radius: Distance in meters from center point - Remove Key: Keyboard key to trigger removal (default: R)

API Reference

RemoveVehiclesInRadius

Method: TrafficManager.RemoveVehiclesInRadius()

Parameters: - center (Transform) - Center point of removal area - radius (float) - Radius in meters

Returns: int - Number of vehicles marked for removal

Implementation Details

Distance Calculation

The system uses squared distance (sqrMagnitude) for performance:

float sqrDistance = (vehiclePosition - center.position).sqrMagnitude;
if (sqrDistance <= radius * radius)
{
    vehicleState.ShouldDespawn = true;
}

Despawn Timing

Vehicles are not destroyed immediately. Destruction occurs in the next FixedUpdate() cycle (typically ~0.02 seconds later).

Testing

1. Add TestTrafficRemovingNpc component to any GameObject
2. Assign the TrafficManager reference from the scene
3. Set the center transform (bus or target location)
4. Configure the radius (recommended: 20-30m)
5. Enter Play mode and press R key to test removal

Performance Notes

• Time Complexity: O(n) where n is the number of active vehicles
• Optimization: Uses squared distance to avoid expensive square root calculations
• Recommended Radius: 20-30m for bus spawning

Common Issues

Vehicles still visible after pressing the key - Wait one FixedUpdate() cycle. Destruction is deferred, not immediate.

Nothing happens when pressing the key - Verify TrafficManager reference is assigned in Inspector - Check that vehicles exist within the specified radius - Ensure the key code matches your input

Performance drops when removing vehicles - Reduce the radius value - Avoid calling the function every frame

Notes

• The test component uses FixedUpdate() with Input.GetKeyDown() for testing purposes
• In production, call RemoveVehiclesInRadius() before teleporting or spawning buses
• Vehicles marked for despawn remain in the scene until next physics update

---

Related: Traffic Spawning System, Bus Teleportation System