手动更改场景

Sometimes it helps to have more control over how you swap scenes around. A Viewport's child nodes will render to the image it generates. This holds true even for nodes outside of the "current" scene. Autoloads fall into this category, and also scenes which you instantiate and add to the tree at runtime:

var simultaneous_scene = preload("res://levels/level2.tscn").instantiate()

func _add_a_scene_manually():
    # This is like autoloading the scene, only
    # it happens after already loading the main scene.
    get_tree().root.add_child(simultaneous_scene)

public Node simultaneousScene;

public MyClass()
{
    simultaneousScene = ResourceLoader.Load<PackedScene>("res://levels/level2.tscn").Instantiate();
}

public void _AddASceneManually()
{
    // This is like autoloading the scene, only
    // it happens after already loading the main scene.
    GetTree().Root.AddChild(simultaneousScene);
}

To complete the cycle and swap out the new scene with the old one, you have a choice to make. Many strategies exist for removing a scene from view of the Viewport. The tradeoffs involve balancing operation speed and memory consumption, as well as balancing data access and integrity.

Delete the existing scene. SceneTree.change_scene_to_file() and SceneTree.change_scene_to_packed() will delete the current scene immediately. You can also delete the main scene. Assuming the root node's name is "Main", you could do get_node("/root/Main").free() to delete the whole scene.
- 卸载内存.
  好处: RAM不再拖累自重.
  
  坏处: 回到那个场景现在更加昂贵, 因为它必须再次加载回内存(需要时间和内存). 如果不久就回来是不必要的.
  
  坏处: 无法再访问该场景的数据. 如果不久就使用这些数据就不成问题了.
  
  注意: 通过将一个或多个节点重新附加到不同的场景, 甚至直接将其重新附加到 SceneTree, 可以将数据保存在即将删除的场景中.
- 处理停止.
  Pro: No nodes means no processing, physics processing, or input handling. The CPU is available to work on the new scene's contents.
  
  坏处: 这些节点的处理和输入处理不再运行. 如果不需要使用更新的数据, 则不成问题.
Hide the existing scene. By changing the visibility or collision detection of the nodes, you can hide the entire node sub-tree from the player's perspective.
- 记忆仍然存在.
  Pro: You can still access the data if needed.
  
  好处: 无需再移动任何节点来保存数据.
  
  Con: More data is being kept in memory, which will be become a problem on memory-sensitive platforms like web or mobile.
- 处理继续.
  Pro: Data continues to receive processing updates, so the scene will keep any data within it that relies on delta time or frame data updated.
  
  Pro: 节点仍然是组的成员(因为组属于 SceneTree).
  
  Con: The CPU's attention is now divided between both scenes. Too much load could result in low frame rates. You should be sure to test performance as you go to ensure the target platform can support the load from this approach.
Remove the existing scene from the tree. Assign a variable to the existing scene's root node. Then use Node.remove_child(Node) to detach the entire scene from the tree.
- Memory still exists (similar pros/cons as hiding it from view).
- Processing stops (similar pros/cons as deleting it completely).
- Pro: This variation of "hiding" it is much easier to show/hide. Rather than potentially keeping track of multiple changes to the scene, you only need to call the add/remove_child methods. This is similar to disabling game objects in other engines.
- 坏处：与仅从视图中隐藏它不同，如果场景中包含的数据依赖于时间增量、输入、分组或其他通过访问 SceneTree 才能得到的数据，则它将变为陈旧。

There are also cases where you may wish to have many scenes present at the same time, such as adding your own singleton at runtime, or preserving a scene's data between scene changes (adding the scene to the root node).

get_tree().root.add_child(scene)

GetTree().Root.AddChild(scene);

Another case may be displaying multiple scenes at the same time using SubViewportContainers. This is optimal for rendering different content in different parts of the screen (e.g. minimaps, split-screen multiplayer).

Each option will have cases where it is best appropriate, so you must examine the effects of each approach, and determine what path best fits your unique situation.