# Systems

Technical references for engine contributors and game programmers who need subsystem behavior, ownership, or performance details. For scene and asset editing without code, start with [Working in the editor](/docs/guides/editor-workflow.md). Prefer [guides/](/docs/guides.md) for task-based instructions.

## Runtime

- [Architecture](/docs/systems/architecture.md)
- [Lifecycle](/docs/systems/lifecycle.md)
- [Frontends and drivers](/docs/systems/frontends-and-drivers.md)
- [Platforms](/docs/systems/platforms.md)
- [Session services](/docs/systems/session-services.md)
- [Scenes and gameplay](/docs/systems/scenes-and-gameplay.md)
- [Actor communication](/docs/systems/entity-messaging.md) — `hi.actors` / `Actors.*`, messages, name-keyed fields
- [Refs](/docs/systems/refs.md)
- [Replication wire version](/docs/systems/replication-wire-version.md) — current hook and codec limits

## Presentation and simulation

- [Coordinate space](/docs/systems/coordinate-space.md) — axes, handedness, euler, cameras, clip depth
- [Rendering](/docs/systems/rendering.md) · [Renderer architecture](/docs/systems/renderer-architecture.md) · [Frame governor](/docs/systems/frame-governor.md) · [Pipeline compilation](/docs/systems/pipeline-compilation.md)
- [Skeletal animation](/docs/systems/animation.md) — skeletons, clips, graphs, layers, events, foot IK, root motion, joint sockets
- [GPU particles](/docs/systems/particles.md)
- [Visual Zones](/docs/systems/visual-zones.md) · [Volumetric media](/docs/systems/volumetric-fog.md)
- [Input](/docs/systems/input.md) · [Audio](/docs/systems/audio.md) · [Physics](/docs/systems/physics.md)
- [Motion Kit](/docs/systems/motion-kit.md) · [Temporal Kit](/docs/systems/temporal-kit.md)
- [UI documents](/docs/systems/ui-documents.md) — data-driven `.ui.json` screens: slots, events, animation, editor

## Assets

- [Assets and Shinra](/docs/systems/assets-and-shinra.md)
- [Prefabs](/docs/systems/prefabs.md)
- [Asset residency](/docs/systems/asset-residency.md)
- [Asset formats](/docs/systems/asset-formats.md)
- [Document schemas](/docs/systems/document-schemas.md) — every authored JSON kind: registry, envelope, rendered JSON Schemas, validation and current versions

## Editor host

- [UI and editor](/docs/systems/ui-and-editor.md) — chrome, command palette, profiler, game `hi.editor` SDK, [Editor MCP](/docs/systems/ui-and-editor.md#agent-mcp-per-project) (editor-only)
- [Editor asset hot reload](/docs/systems/editor-asset-hot-reload.md) — daemon events, render-thread pause, and in-place rebind vs full scene re-instantiation
- [Editor project selector](/docs/systems/editor-project-selector.md)