Scene Management and Game Flow

# CHAPTER 12

Scene Management and Game Flow #

1. Introduction #

2. Learning Objectives #

• Understand what a Unity Scene is and how to manage multiple scenes.

• Add scenes to the Build Settings index.

• Use SceneManager.LoadScene() to transition between levels.

• Create a functional Main Menu with "Play" and "Quit" buttons.

• Implement a Pause system using Time.timeScale.

3. Scenes and Build Settings #

• You might have a MainMenu scene, a Level01 scene, and a Level02 scene.

• Before Unity can switch between them, it needs a master list.

1. 1. Go to File -> Build Settings.

1. 2. Open your Project window and drag your scene files into the Scenes In Build box.

1. 3. The order matters! The scene at index 0 (the top of the list) is the one that loads automatically when the player launches the actual .exe game.

4. Loading Scenes with C# #

using UnityEngine;
using UnityEngine.SceneManagement; // REQUIRED!

public class LevelManager : MonoBehaviour
{
    public void LoadNextLevel()
    {
        // Load the scene by its exact string name
        SceneManager.LoadScene("Level_02");
        
        // OR load by its index number in the Build Settings
        // SceneManager.LoadScene(1);
    }

    public void RestartCurrentLevel()
    {
        // A neat trick to reload whatever scene is currently active!
        SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
    }
}

5. Building a Main Menu #

1. 1. Create a new Scene (Ctrl+N) and save it as MainMenu.

1. 2. Add a UI Canvas and two Buttons: "Start Game" and "Quit".

1. 3. Create a MainMenuManager script.

1. 4. Hook the "Start Game" button to a function that calls SceneManager.LoadScene("Level_01").

1. 5. Hook the "Quit" button to a function that calls Application.Quit(). *(Note: Quit only works in the built .exe game, it does nothing when playing inside the Unity Editor).*

6. Pausing the Game (TimeScale) #

• Time.timeScale = 1f; (Normal speed).

• Time.timeScale = 0.5f; (Matrix-style slow motion).

• Time.timeScale = 0f; (Completely frozen).

public GameObject pauseMenuUI; // The Canvas panel containing the menu
private bool isPaused = false;

void Update()
{
    if (Input.GetKeyDown(KeyCode.Escape))
    {
        if (isPaused) ResumeGame();
        else PauseGame();
    }
}

public void PauseGame()
{
    pauseMenuUI.SetActive(true); // Show the menu graphics
    Time.timeScale = 0f;         // Freeze the game physics/movement
    isPaused = true;
}

public void ResumeGame()
{
    pauseMenuUI.SetActive(false); // Hide the menu
    Time.timeScale = 1f;          // Unfreeze the game!
    isPaused = false;
}

7. Visual Learning: Game Flow Architecture #

               [ Application Launched ]
                         |
           (Loads Build Index 0 Automatically)
                         v
                  [ Main Menu Scene ]
                         |
       (Player clicks "Start" -> LoadScene(1))
                         v
                  [ Level 01 Scene ]
                    /            \
       (Player hits Escape)    (Player reaches door)
             /                        \
    [ Pause Menu UI ]          (LoadScene(2))
    (TimeScale = 0)                   v
                              [ Level 02 Scene ]

8. Best Practices #

• DontDestroyOnLoad: Normally, when you load a new scene, Unity deletes absolutely everything from the old scene. If you have an AudioSource playing background music, the music will awkwardly restart. You can attach a simple script to your MusicManager containing DontDestroyOnLoad(gameObject);. This magical function tells Unity to carry the object over into the new scene without destroying it, ensuring uninterrupted music!

9. Common Mistakes #

• Restarting a Paused Game: A player dies while the game is paused (TimeScale = 0), and they click "Restart Level". The level reloads, but nothing moves! The game is completely frozen! TimeScale is a global setting that persists across scenes. If you set it to 0, you MUST remember to set Time.timeScale = 1f; inside the Start() method of your LevelManager so the game always unfreezes on a fresh load.

10. Mini Project: The Portal #

1. 1. Ensure you have Level01 and Level02 added to your Build Settings.

1. 2. In Level_01, create a glowing Cylinder and check Is Trigger on its collider.

1. 3. Attach this script to the Cylinder:

using UnityEngine;
using UnityEngine.SceneManagement;

public class LevelPortal : MonoBehaviour
{
    public string nextLevelName; // Type "Level_02" in the Inspector

    void OnTriggerEnter(Collider other)
    {
        if (other.CompareTag("Player"))
        {
            Debug.Log("Teleporting to next level!");
            SceneManager.LoadScene(nextLevelName);
        }
    }
}

1. 4. Walk your player into the cylinder and watch the scene seamlessly transition!

11. Practice Exercises #

1. 1. What menu window must you open to add your scenes into a master index list before they can be loaded via script?

1. 2. What C# variable controls the global speed of physics, animations, and Time.deltaTime, allowing you to pause the game?

12. MCQs with Answers #

13. Interview Questions #

• Q: Walk me through the exact pipeline required to transition from a MainMenu scene to a Level_01 scene when a UI button is clicked.

• Q: Explain how Time.timeScale works in Unity. Provide an example of a severe game-breaking bug that can occur if timeScale is not managed properly across scene transitions.

• Q: What is the purpose of the DontDestroyOnLoad method? Provide a scenario where its usage is critical for a smooth player experience.

14. FAQs #

15. Summary #

16. Next Chapter Recommendation #