Architecture

Technology Stack

Component	Technology
Language	Rust
Game engine	Bevy 0.18 (ECS)
Physics	Avian2D
Serialization	serde + serde_json, RON
Noise	noise crate (Perlin FBM)
CLI	clap (derive)

System Execution Order

Systems run in a defined order via GameSet:

Input → Commands → Movement → Fov → Lighting → Barriers → Render

Set	Responsibility
Input	Keyboard, mouse, controller input
Commands	TCP server commands, overseer actions
Movement	Player/unit movement, stairs, terrain sync
Fov	Shadowcasting field of view computation
Lighting	Light source propagation
Barriers	Elevation barrier updates
Render	Tile sprite rendering

Dependencies: Movement runs after Input. Fov runs after Movement. Lighting and Barriers run after Fov. Render runs last.

World Model

WorldMap
  └─ HashMap<i32, Layer>           z-level → Layer
     └─ HashMap<IVec2, Chunk>      chunk pos → Chunk (32×32)
        ├─ Vec<BlockVolume>        dense block storage
        ├─ HashMap<(u8,u8), FloorCoverId>    sparse floor covers
        └─ HashMap<(u8,u8), CeilingCoverId>  sparse ceiling covers

Constants

Constant	Value
`CHUNK_SIZE`	32×32 tiles
`TILE_SIZE_PX`	32.0 pixels
Z range	-100 to +100

Coordinate System

X = East (+) / West (-)
Y = North (+) / South (-)
Z = Vertical levels (up +)
Player at z=N stands on a solid block at z=N-1

Block System

BlockType is a u16 newtype (not an enum) for extensibility — supports up to 65,535 block types.

BlockRegistry uses a flat Vec<Option<BlockProps>> indexed by the u16 ID for O(1) lookup. Block properties include:

blocks_movement — whether the block blocks horizontal movement
supports_standing — whether units can stand on it
vision_transmittance — FOV light pass-through (0.0–1.0)
light_transmittance — lighting pass-through (0.0–1.0)
placeable, mineable — interaction rules
Sprite atlas coordinates and color fallback

Data-Driven Design

Block and item definitions live in RON files, loaded at startup:

assets/blocks.ron — block types, properties, sprite mappings
assets/items.ron — item definitions (id, name, group, stack size)

Atlases: Natural.png (20×22 grid), Civilized.png (24×18 grid), People.png.

No recompilation needed to add or modify blocks and items.

Key Patterns

Dirty Flags

A DirtyFlags resource tracks what needs recomputation:

render_dirty — tile sprites need refresh
lighting_dirty — light values changed
fov_dirty — visibility needs recalculation
barriers_dirty — elevation barriers changed
chunks_generated — new chunks were created

Systems check dirty flags and skip work when nothing changed.

Command System

GameCommand is a serde-tagged enum routed through a CommandQueue. Commands come from:

TCP server (kinswardctl)
Overseer mode UI
Internal game systems

The command executor processes the queue each frame in the Commands system set.

Task System

A global TaskQueue holds Build, Demolish, and Pickup tasks. Tasks are created by overseer commands or zone operations. Idle Colony units automatically pick the nearest pending task.

State Machine

InputMode tracks the current game mode:

Adventure — direct player control
Overseer — RTS-style unit management

Mode switching triggers camera transitions and input handler swaps.

Surface Index

Maps (x, y) columns to walkable z-levels. Used by pathfinding and grounding to determine where units can stand. Rebuilt when blocks change.

Rendering

Tile-based rendering: one Bevy entity per visible tile. Sprites come from 10px-cell texture atlases scaled 3.2× to fill the 32px tile size.

Final tile color formula:

color = base_color × depth_factor × light_value × visibility

Module Layout

Module	Responsibility
`src/world/`	WorldMap, blocks, chunks, layers, surfaces, grounding
`src/commands/`	GameCommand, executor, TCP server, region-map export
`src/render/`	Viewport, sprites, FPS display
`src/fov/`	Shadowcasting FOV, visibility maps
`src/lighting/`	Light propagation
`src/generation/`	Procedural generation, climate pipeline (16 modules)
`src/units/`	Unit components, spawner, possession, movement
`src/overseer/`	RTS mode: camera, selection, commands, pathfinding, tasks
`src/companions/`	Companion behaviors
`src/ui/`	UI animation system
`src/schedule.rs`	GameSet definition and ordering

Binaries

Binary	Purpose
`kinsward`	Main game
`kinswardctl`	CLI debug tool
`worldgen`	Headless world generation