How is Scene.isLoaded determined? - unity3d

Question

I cannot find anything in docs that breaks down the scene loading process and how the Scene.isLoaded property is determined.
I need to mock large scene loading and cannot find a way to delay a scene's loading. It would be useful to understand the flow especially when needing to load external assets in the scene and only mark the scene as loaded via code.

Answer 1

You should have a look at SceneManager.LoadSceneAsync and especially allowSceneActivation which allows you to do exactly that: Delay a scenes loading and e.g. display a loading screen meanwhile.
Example from the docs:
// This script lets you load a Scene asynchronously.
// It uses an asyncOperation to calculate the progress and outputs
// the current progress to Text (could also be used to make progress bars).
// Attach this script to a GameObject
// Create a Button (Create>UI>Button) and a Text GameObject (Create>UI>Text)
// and attach them both to the Inspector of your GameObject
//In Play Mode, press your Button to load the Scene, and the Text
// changes depending on progress. Press the space key to activate the Scene.
//Note: The progress may look like it goes straight to 100% if your Scene doesn’t have a lot to load.
using System.Collections;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;
public class AsyncOperationProgressExample : MonoBehaviour
{
public Text m_Text;
public Button m_Button;
void Start()
{
//Call the LoadButton() function when the user clicks this Button
m_Button.onClick.AddListener(LoadButton);
}
void LoadButton()
{
//Start loading the Scene asynchronously and output the progress bar
StartCoroutine(LoadScene());
}
IEnumerator LoadScene()
{
yield return null;
//Begin to load the Scene you specify
AsyncOperation asyncOperation = SceneManager.LoadSceneAsync("Scene3");
//Don't let the Scene activate until you allow it to
asyncOperation.allowSceneActivation = false;
Debug.Log("Pro :" + asyncOperation.progress);
//When the load is still in progress, output the Text and progress bar
while (!asyncOperation.isDone)
{
//Output the current progress
m_Text.text = "Loading progress: " + (asyncOperation.progress * 100) + "%";
// Check if the load has finished
if (asyncOperation.progress >= 0.9f)
{
//Change the Text to show the Scene is ready
m_Text.text = "Press the space bar to continue";
//Wait to you press the space key to activate the Scene
if (Input.GetKeyDown(KeyCode.Space))
//Activate the Scene
asyncOperation.allowSceneActivation = true;
}
yield return null;
}
}
}
Also checkout sceneLoaded: as stated in the docs
Add a delegate to this to get notifications when a Scene has loaded.
This happens after the scene has been loaded and afaik after the Awake calls finished. You can easily test this by using a script like
public class Test : MonoBehaviour
{
private void Awake()
{
Debug.Log("Awake");
SceneManager.sceneLoaded += OnSceneLoaded;
}
private void OnSceneLoaded(Scene scene, LoadSceneMode mode)
{
Debug.Log("OnSceneLoaded");
}
}
You will see both the
Awake
OnSceneLoaded
debugs in the console meaning that Awake was called before OnSceneLoaded.
→ At this moment I would also expect the Scene.isLoaded to be set to true.