HDDE: A Zero-Allocation Hierarchical Utility Architecture

A high-performance, purely data-oriented (ECS/SoA based) game AI engine written in Rust, designed to be seamlessly embedded into game engines via a C-API.

🧠 Architecture Overview

This engine implements a Hierarchical Distributed Decision Engine (HDDE). It replaces traditional monolithic AI controllers (like Behavior Trees) with a 7-stage data pipeline running across flat arrays (Struct of Arrays).

graph TD
    subgraph HDDE Engine
    A[Ingestion] --> B[Decay]
    B --> C[Needs A-Life]
    C --> D[Candidates Gen]
    D --> E[Utility Evaluation]
    E --> F[Commit Decision]
    F --> G[Propagation & Comms]
    G -.-> A
    end
    
    subgraph Game Engine
    S[Sensors] -->|Raw Perception| A
    F -->|Chosen Action| M[Anim & Movement]
    end

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Key Features

• 🚀 Zero Allocations: All data is stored in pre-allocated static-size arrays (SoARegistry). No runtime heap allocations occur during the core update loop.
• 🧩 Data-Oriented (SoA): Maximum CPU cache efficiency. Everything runs on tightly packed arrays.
• ⚖️ Utility AI: Replaces complex behavior trees with multiplicative considerations, providing smooth, unscripted emergent behaviors.
• 📡 Hierarchical Propagation: Bottom-up status reporting and top-down intent directives with simulated communication latency.
• 🧬 A-Life Needs System: Agents have internal needs (hunger, fatigue, curiosity, self-preservation) that naturally decay and affect their tactical utility scores over time, enabling offline open-world simulation.

🛠️ Building and Running

Ensure you have Rust installed.

# Compile the engine
cargo build --release

# Run the hierarchy simulation example
cargo run --example hdde_simulation

🎮 The C-API (Coming Soon)

A lightweight FFI interface designed for Unity and Unreal Engine integrations. Exposes a simple hdde_engine_tick() and hdde_engine_push_events() without bridging complex data types, preserving the zero-allocation philosophy.

📝 License

This project is licensed under the MIT License - see the LICENSE file for details.