Building a 3D Tower Defense Game — Wave Spawner

In this article, we’ll be looking at creating a simple wave spawning system. The first thing I want to do is to create an empty GameObject called “GameManager” and create a C# script for it called “WaveSpawner”.

Wave Spawner

We need to get a reference to the enemy prefab, the spawn position, time between waves, wave count, and how many waves we need to spawn.

 [SerializeField] private GameObject _enemyPrefab;
 [SerializeField] private GameObject _spawnPos;

 [SerializeField] private float _timeBetweenWaves = 5f;
 [SerializeField] private float _countdown = 2f;
 private int _waveIndex = 0;
 private int _maxWave = 5;

I want it to spawn only 5 waves. The first wave should be spawned after 2 seconds, and each subsequent wave should be spawned after 5 seconds. Since we need to execute the spawning after each interval, this would be good use case for a Coroutine.

void Update()
{
    if (_countdown <= 0f)
    {
        StartCoroutine(SpawnWave());
        _countdown = _timeBetweenWaves;
    }
    if (_waveIndex < _maxWave)
    {
        _countdown -= Time.deltaTime;
    } 
}

Now let’s create the logic for the SpawnWave fucntion.

IEnumerator SpawnWave()
{
    _waveIndex++;
    Instantiate(_enemyPrefab, _spawnPos.transform.position, Quaternion.identity);
    yield return null;
}

So each time the SpawnWave function is executed, the _waveIndex variable is incremented by 1 and a new enemy will be spawned using the Instantiate method.

Wave UI

I also created a canvas GameObject for the UI, which will inform the player about the current wave they are on and display the countdown between waves.

Let’s create a C# script for the canvas.

using UnityEngine;
using UnityEngine.UI;
using TMPro;

public class GamePlayUI : MonoBehaviour
{
    [SerializeField] TMP_Text _waveText;
    [SerializeField] TMP_Text _timeText;
    private int _maxWave = 5;

    public void UpdateWaveText(int waveIndex)
    {
        _waveText.text = "Wave " + waveIndex + "/" + _maxWave;
    }

    public void UpdateTimeText(float time)
    {
        _timeText.text = "Incoming Wave In " + string.Format("{0:0.00}", time);
    }
}

And here’s the full code for the Wave Spawner with the UI elements incorporated:

using UnityEngine;
using System.Collections;

public class WaveSpawner : MonoBehaviour
{
    [SerializeField] private GameObject _enemyPrefab;
    [SerializeField] private GameObject _spawnPos;

    [SerializeField] private float _timeBetweenWaves = 5f;
    [SerializeField] private float _countdown = 2f;
    private int _waveIndex = 0;
    private int _maxWave = 5;

    [SerializeField] private GamePlayUI _gamePlayUI;

    void Start()
    {
        _gamePlayUI.UpdateWaveText(_waveIndex + 1);
    }

    void Update()
    {
        if (_countdown <= 0f)
        {
            StartCoroutine(SpawnWave());
            _countdown = _timeBetweenWaves;
        }
        if (_waveIndex < _maxWave)
        {
            _countdown -= Time.deltaTime;
            _gamePlayUI.UpdateTimeText(_countdown);
        } 
    }

    IEnumerator SpawnWave()
    {
        _waveIndex++;
        if (_waveIndex > 1)
        {
            _gamePlayUI.UpdateWaveText(_waveIndex);
        }
        Instantiate(_enemyPrefab, _spawnPos.transform.position, Quaternion.identity);
        yield return null;
    }

}

And here’s the result: