Tower Defender - Part 4

Tower placement on defined “Ground” layer

The purpose of the blog is to document my journey in building a simple Tower Defense game. In this forth part I show how to Place the Tower over a specified area (ground layer).

The following Unity / C# features will be covered:

• Physics Raycast
• Layermask
• Input System

Explain logic for the tower placement script

This script will initiate a tower at the position of the mouse cursor if the cursor is above specified Layer (ground).

Variables defined at the start:

• A prefab UI reference to assign the tower game object that will be initiated at mouse click.
• A layer mask UI reference to assign specify what the ground is.

The Update method:

• The mouse pointer position is stored in a variable “ray”.
• The variable “RaycastHit” is storing information about the object that is hit.
• The IF statement is checking if the mouse is hitting the “groundLayer”.
• The following IF statement is checking if there is a Tower at the mouse location and if not it initiates one. (But doesn’t place it on the ground yet)
• If the mouse button is clicked on a ground layer, a Tower will be initiated. If the mouse is hoovering away from the “Ground” layer the floating Tower will be destroyed.

Custom Function - PlaceTower:

• This function will initiate a Tower prefab and replaces the hoovering current tower with a new tower.

Custom Function - DestroyTower:

• This function will destroy the Tower game object.

The complete C# code for the the tower placement script

using UnityEngine;
using UnityEngine.InputSystem;

public class TowerPlacement : MonoBehaviour
{
    [SerializeField] private GameObject towerPrefab;
    [SerializeField] private LayerMask groundLayer;

    private GameObject currentTower;

    private void Update()
    {
        HandleTowerPlacement();
    }

    private void HandleTowerPlacement()
    {
        Ray ray = Camera.main.ScreenPointToRay(Mouse.current.position.ReadValue());
        RaycastHit hitInfo;

        if (Physics.Raycast(ray, out hitInfo, Mathf.Infinity, groundLayer))
        {
            if (currentTower == null)
            {
                currentTower = Instantiate(towerPrefab, hitInfo.point, Quaternion.identity);
            }
            else
            {
                currentTower.transform.position = hitInfo.point;
            }

            if (Mouse.current.leftButton.wasPressedThisFrame)
            {
                PlaceTower(hitInfo.point);
            }
        }
        else
        {
            DestroyTower();
        }
    }

    private void PlaceTower(Vector3 position)
    {
        if (currentTower == null)
        {
            return;
        }

        GameObject newTower Instantiate(towerPrefab, position, Quaternion.identity);
        currentTower = newTower;
    }

    private void DestroyTower()
    {
        if (currentTower != null)
        {
            Destroy(currentTower);
            currentTower = null;
        }
    }
}

Game preview