Processing diagram (game loop)

[berarma]

I've made a basic main loop diagram by looking at the code. I'd be willing to improve it and adding it to the documentation, but I don't know where or how. For now, I'd like to make sure it's correct and complete.

I needed to know the order things happen inside the Godot engine to better write code for it. I don't think there's something similar in the documentation. There are some pages that give some information but not the whole picture:

• https://docs.godotengine.org/en/stable/tutorials/scripting/scene_tree.html
• https://docs.godotengine.org/en/stable/tutorials/best_practices/godot_notifications.html
• https://docs.godotengine.org/en/stable/tutorials/scripting/idle_and_physics_processing.html
• https://docs.godotengine.org/en/stable/tutorials/inputs/inputevent.html

Please, add any I may have missed, also corrections and suggestions.

Related issues: #9204 #5492

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Processing diagram for Godot 4

MainLoop is the scene tree object. In the default configuration it's an SceneTree object.

It may lack some platform specific information.

• Call MainLoop._initialize().
  • Call DisplayServer::process_events(). Processes window manager events including input.
  • Process joystick/gamepad events.
  • Physics processing step (run as many times as needed).
    • Flush input buffered events when agile_event_flushing is true (Android only).
    • Call NOTIFICATION_TRANSFORM_CHANGED on nodes and update physics objects transforms.
    • Call MainLoop._physics_process().
    • Send signal SceneTree.physics_frame.
    • Process object picking.
    • Call _physics_process() in the scene nodes.
    • Flush unique calls to groups.
    • Process timers in physics processing mode.
    • Process tweens in physics processing mode.
    • Call NOTIFICATION_TRANSFORM_CHANGED on nodes and update physics objects transforms.
    • Process queue_delete()/queue_free() calls.
    • Process deferred calls.
    • Physics server step.
  • Flush input buffered events when agile_event_flushing is true (Android only).
  • Idle processing step.
    • Call MainLoop._process().
    • Automatic polling of MultiplayerAPI.
    • Call NOTIFICATION_TRANSFORM_CHANGED on nodes and update physics objects transforms.
    • Call _process() in the scene nodes.
    • Flush unique calls to groups.
    • Call NOTIFICATION_TRANSFORM_CHANGED on nodes and update physics objects transforms.
    • Process queue_delete()/queue_free() calls.
    • Change scene if requested. If changed, emit scene_changed signal (Godot 4.5+).
    • Process timers in idle processing mode.
    • Process tweens in idle processing mode.
    • Call NOTIFICATION_TRANSFORM_CHANGED on nodes and update physics objects transforms.
    • Process deferred calls.
  • Rendering. Emits signals RenderingServer.frame_pre_draw and RenderingServer.frame_post_draw.
  • Audio update.
  • Debugger iteration.
  • Flush input buffered events when agile_event_flushing is false (Android only).
  • Add frame to MovieWriter if used.
  • Optional frame delay to achieve target fps.
• Call MainLoop._finalize().

[berarma]

Related: #9204.

[berarma]

Additional information: #5492

[libardia]

Thank you. I needed to know this for my situation but nowhere was as thorough as I needed, except this fabulous post.