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Core Concepts

CAT becomes easier to use once six concepts are clear.

Authoring concepts

Part Model

A reusable asset that describes one logical part. It may contain a physics body, connectors, actuators, feature definitions, and source mesh information.

Assembly Asset

An authored arrangement of Part Models and the Relations between their connectors. The asset stores a runtime-ready snapshot used when an Assembly Actor initializes.

Runtime concepts

Part

A runtime instance of a Part Model inside an Assembly. Blueprint accesses it through a CAT Part object.

Connector

A named attachment point on a Part. A connector provides a transform, alignment behavior, constraint settings, and occupancy state.

Relation

The runtime connection between two connector endpoints. Removing or breaking a Relation can split the topology into separate assemblies.

Actuator

A controllable element such as a Motor or Fan. Controllers and gameplay code submit normalized control values to actuators.

The runtime flow

Part Model / Assembly Asset
          ↓
   CAT Assembly Actor
          ↓
 Runtime Assembly State
          ↓
   Physics Projection
          ↓
 Blueprint Objects + Replication

Authoring data and runtime state are different

Edit Part Models and Assembly Assets in the editor. During play, query and change the Assembly State through the Assembly Actor, Assembly Component, and runtime objects.

Control concepts

  • A Control Station identifies the part from which a player controls an assembly.
  • An Assembly Controller translates sustained input into actuator output.
  • A Gameplay Feature handles part-scoped behavior such as firing, activation, or damage reactions.

Use a Controller for continuous physics control. Use Gameplay Feature input for discrete gameplay actions.