Design philosophy

vgai’s design is shaped by one north star: it should be a great engine for an AI (or a human) to author games in. That yields three priorities.

Determinism — one obvious way

There should be one obvious place and one obvious way to do a thing. The engine avoids configurable indirection in favor of a single, predictable path. The clearest expression of this is phase ordering.

Phase ordering is sacred

Every fixed tick runs systems and GameComponent.update() methods in a fixed order:

#	Phase	What runs
1	input	Sample keyboard / mouse / gamepad.
2	prePhysics	Apply forces/intents to rigid bodies.
3	physics	Step the Rapier world.
4	postPhysics	Read physics back; sync transforms to Object3D; dispatch triggers.
5	gameLogic	General gameplay. Default phase for GameComponents.
6	animation	Advance animation graphs / mixers.
7	preRender	Camera/HUD fixups before drawing.
8	render	Draw the frame.

A component declares its phase with a static field; data flows in one direction through the phases, so you never wonder “did this run before or after physics?”

Don't fight the order

Putting code in the wrong phase is the most common source of one-frame-late bugs. The Manual phase table tells you where new code belongs.

Locality — one place per feature

A feature lives in one place. The scene format, the Zod schema that validates it, and the default values that the editor and runtime share are all single sources of truth in packages/engine/src/scene/. Change the schema once and the editor inspector, JSON-Schema autocomplete, and runtime validation all update together.

Fail-fast validation

Bad data should fail loudly at load time, not silently at frame 10,000. Unknown component names throw when a scene loads; schema parsing rejects malformed fields. npm run validate-scenes checks every scene against the registry before you ship.

The Object3D-as-truth payoff

Because the editor edits the very Object3Ds the runtime uses, two things fall out for free:

• Hot reload of behavior — swap a GameComponent’s code and keep its live state.
• Editor-edits-truth — what you see in the editor is what the game runs.

React is for HUD only

UI is mounted with mountUI(ctx.uiContainer, <Component/>) and is for HUD/overlay only — not gameplay objects. The uiContainer is pointer-events-transparent by default; interactive elements opt back in. (The Visual UI Editor builds on this.)

Next

• Foundations — put the model to work.
• Manual: the game loop & phases — the full phase reference.