Scenes and Nodes

Services

Almost everything engine-side is a Service - a singleton fetched by name with fb.get_service(name) rather than imported directly. A project's entry point registers the ones it needs (files, renderer, graphics, window, scene_manager, ...) once, at startup, in dependency order - see Getting Started for a working example. A service can declare dependencies on other service names; registering it before those dependencies are up warns rather than failing outright.

Scenes

A Scene is a self-contained root of the node tree - a level, a menu, whatever one fb.set_scene(name) should swap to as a unit. Add scenes up front with fb.add_scene(...) and switch between already-added scenes with fb.set_scene(name); a scene's on_initialize() is where it builds its own node tree (self.add(...)) the first time it's added.

Nodes

Every object in a scene - sprites, cameras, colliders, tilemaps - is a Node in a plain parent/child tree rooted at the scene. Node2D/Node3D add a Transform/Transform3 (position, rotation, scale) and a world_transform that composes with the parent's, so a child's transform is always relative to its parent's, all the way up to the scene root.

Lifecycle hooks a node overrides:

Hook	Called
on_initialize()	Once, when the node is added to an initialized parent/scene
on_update()	Every frame, during the update phase
on_draw()	Every frame, during the draw phase (2D nodes only - 3D rendering goes through the active GraphicsPipeline instead)

A node can require a specific parent type (parental_requirement) or specific child types (requirements) - both just warn, rather than prevent construction, if unmet.

Cameras

Camera2D and Camera3D are nodes like any other (added to the tree, positioned via the normal transform) whose only job is producing view_matrix/proj_matrix for whichever pipeline reads scene.camera - set scene.camera = my_camera after adding it, or nothing draws.

Update order

Per-frame work runs in fixed phases (see UpdatePhase): EARLY, PHYSICS, UPDATE, DRAW, LATE. A node's own on_update() runs in the UPDATE phase; a service (or anything else) that needs to hook a specific phase directly calls fb.register_service_update(phase, callback). LATE in particular runs after the active GraphicsPipeline's own DRAW- phase render, which is the hook point for anything that needs to post-process or overlay on top of a finished frame.