Architecture

Technical architecture of frond.

Layer Structure

frond/
├── core/                    # Pure Rust, no engine deps
│   ├── frond-spatial/       # Quadtree, BVH, spatial hash
│   ├── frond-pathfinding/   # A*, flow fields, nav mesh
│   └── frond-math/          # Kinematic helpers, curves
│
├── bindings/                # Engine-specific adapters
│   ├── frond-godot/         # GDExtension
│   ├── frond-bevy/          # Bevy systems/components
│   ├── frond-unity/         # NativePlugin + C# wrapper
│   └── frond-love/          # Lua FFI for Love2D
│
├── scripting/               # Game logic in engine-native languages
│   ├── frond-gdscript/      # GDScript library
│   ├── frond-lua/           # Lua patterns (Love2D, etc.)
│   └── frond-csharp/        # C# patterns (Unity)
│
└── docs/                    # Universal patterns, language-agnostic

What Lives Where

Layer	Contents	Why
core/	Spatial, pathfinding, math	Perf-critical, complex algorithms, called 1000s/frame
bindings/	Engine glue	Thin adapters to expose core to each engine
scripting/	FSM, stats, inventory, timing, damage	Game logic, moddable, rapid iteration
docs/	Camera, coyote time, patterns	Universal knowledge, any language

Rule of thumb: If modders should be able to change it, it's scripting. If it needs to be fast, it's core.

Core Dependencies

• glam - Math types (shared by Bevy, macroquad, rend3, others)
• serde - Serialization for config files
• thiserror - Error handling

Engine Targets

Engine	Binding	Scripting	Status
Godot	GDExtension	GDScript	First target
Bevy	bevy_ecs	(Rust)	Planned
Unity	NativePlugin	C#	Planned
Love2D	Lua FFI	Lua	Planned

Godot Integration

GDScript (scripting/)

Game logic lives in GDScript for moddability:

# FSM for movement states
extends Node
var fsm = preload("res://addons/frond/fsm.gd").new()

func _ready():
    fsm.add_state("idle")
    fsm.add_state("run")
    fsm.set_initial("idle")

GDExtension (bindings/)

Performance-critical code in Rust, exposed to GDScript:

// bindings/frond-godot/src/lib.rs
use godot::prelude::*;

#[derive(GodotClass)]
#[class(base=Node)]
struct SpatialIndex { ... }

#[godot_api]
impl SpatialIndex {
    #[func]
    fn query_radius(&self, center: Vector2, radius: f32) -> Array<i64> { ... }
}

Headless Testing

Test without the editor:

godot --headless --script res://tests/test_fsm.gd --quit

Configuration

Tunable parameters live in asset files, not code.

// movement.ron
MovementConfig(
    jump_force: 15.0,
    gravity: 40.0,
    slide_decay: 0.95,
)

Load via serde in Rust or ConfigFile in GDScript.