[MainLoop] is the abstract base class for a Godot project's game loop. It is inherited by [SceneTree], which is the default game loop implementation used in Godot projects, though it is also possible to write and use one's own [MainLoop] subclass instead of the scene tree.
Upon the application start, a [MainLoop] implementation must be provided to the OS; otherwise, the application will exit. This happens automatically (and a [SceneTree] is created) unless a [MainLoop] [Script] is provided from the command line (with e.g. [code]godot -s my_loop.gd[/code]) or the [member ProjectSettings.application/run/main_loop_type] project setting is overwritten.
Called each physics tick. [param delta] is the logical time between physics ticks in seconds and is equal to [member Engine.time_scale] / [member Engine.physics_ticks_per_second]. Equivalent to [method Node._physics_process].
If implemented, the method must return a boolean value. [code]true[/code] ends the main loop, while [code]false[/code] lets it proceed to the next step.
[b]Note:[/b] [method _physics_process] may be called up to [member Engine.max_physics_steps_per_frame] times per (idle) frame. This step limit may be reached when the engine is suffering performance issues.
[b]Note:[/b] Accumulated [param delta] may diverge from real world seconds.
Called on each idle frame, prior to rendering, and after physics ticks have been processed. [param delta] is the time between frames in seconds. Equivalent to [method Node._process].
If implemented, the method must return a boolean value. [code]true[/code] ends the main loop, while [code]false[/code] lets it proceed to the next frame.
[b]Note:[/b] When the engine is struggling and the frame rate is lowered, [param delta] will increase. When [param delta] is increased, it's capped at a maximum of [member Engine.time_scale] * [member Engine.max_physics_steps_per_frame] / [member Engine.physics_ticks_per_second]. As a result, accumulated [param delta] may not represent real world time.
[b]Note:[/b] When [code]--fixed-fps[/code] is enabled or the engine is running in Movie Maker mode (see [MovieWriter]), process [param delta] will always be the same for every frame, regardless of how much time the frame took to render.
[b]Note:[/b] Frame delta may be post-processed by [member OS.delta_smoothing] if this is enabled for the project.
Notification received when translations may have changed. Can be triggered by the user changing the locale. Can be used to respond to language changes, for example to change the UI strings on the fly. Useful when working with the built-in translation support, like [method Object.tr].
[b]Note:[/b] On iOS, you only have approximately 5 seconds to finish a task started by this signal. If you go over this allotment, iOS will kill the app instead of pausing it.
Notification received from the OS when the application is focused, i.e. when changing the focus from the OS desktop or a thirdparty application to any open window of the Godot instance.
Notification received from the OS when the application is defocused, i.e. when changing the focus from any open window of the Godot instance to the OS desktop or a thirdparty application.
