# ants-simulation

GPU-accelerated ant colony simulation. ants navigate via pheromone trails, all computed in GLSL fragment shaders rendered to offscreen textures. uses WebGL2 features (MRT, GLSL3). side-view ant farm with sand/powder physics and material-based world.

## stack

- three.js (0.173) — WebGL2 renderer, render targets, MRT, shader materials
- lil-gui — runtime parameter tweaking
- vite — dev server and build
- biome — lint + format
- bun — runtime, test runner, package manager
- typescript

## commands

- `just check` — lint, typecheck, test (the gate for all work)
- `bun run dev` — start dev server
- `bun run build` — production build to `build/`
- `bun test` — run tests

## architecture

all simulation logic runs on the GPU via ping-pong render targets. no JS-side simulation loop — `Renderer.ts` orchestrates render passes and manages all WebGLRenderTargets.

### render pipeline (per frame)

1. `SandPhysicsScene` — Margolus block CA for sand/powder physics
2. `WorldBlurScene` — diffuse + decay pheromones (3 channels: toHome, toFood, repellent, blocked by solid cells)
3. clear `antsPresenceRenderTarget` (ant-ant spatial queries, stub)
4. `AntsComputeScene` — per-ant state via MRT (writes 2 textures simultaneously), material-aware digging
5. `AntsDiscretizeScene` — maps continuous ant positions to discrete world grid cells
6. `WorldComputeScene` — merges ant deposits into world pheromone grid
7. `ColonyStats` — CPU readback of ant texture, computes aggregate stats (foragerRatio), feeds back as uniforms
8. `DrawScene` — user painting with material palette
9. `ScreenScene` — final composited output with side/top camera views (V to toggle)

### GPU textures

**ant state** — 2 RGBA Float32 textures per ping-pong target (MRT, `count: 2`):
- texture 0: `[pos.x, pos.y, angle, packed(storage << 1 | isCarrying)]`
- texture 1: `[personality, cargoMaterialId, pathIntDx, pathIntDy]`

**world state** — RGBA Float32 (worldSize x worldSize):
- R: material ID (0-255), maps to MaterialRegistry entry
- G: scentToHome
- B: scentToFood
- A: repellent pheromone

**discrete ants** — RGBA UnsignedByte (worldSize x worldSize):
- R: carrying ant scent deposit, G: non-carrying ant scent deposit, B: cell cleared flag, A: 1

**ant presence** — RGBA Float32 (worldSize x worldSize), cleared each frame. stub for future ant-ant spatial interaction.

### material system

`src/materials/` defines a data-driven material registry. adding a new material requires only a registry entry — no shader changes needed.

- `MaterialRegistry` — 6 built-in materials (ids 0-5): air, sand, dirt, rock, food, home
- behavior types: `BEHAVIOR_POWDER` (0), `BEHAVIOR_LIQUID` (1), `BEHAVIOR_GAS` (2), `BEHAVIOR_SOLID` (3)
- each material has: id, name, behavior, density, hardness, angleOfRepose, color
- lookup textures (256x1 Float RGBA) uploaded as uniforms to shaders:
  - properties texture: `[behavior, density, hardness, angleOfRepose]` per row
  - colors texture: `[r, g, b, a]` per row
- material IDs defined in `src/constants.ts` (MAT_AIR through MAT_HOME)

### sand physics

Margolus neighborhood cellular automata runs as the first render pass each frame.

- world is divided into 2x2 blocks; block offset alternates each frame between (0,0) and (1,1)
- within each block, cells with `BEHAVIOR_POWDER` fall downward and slide diagonally, swapping with lighter materials
- physics pass writes back to world ping-pong target before pheromone diffusion runs
- `src/sand/margolus.ts` computes the per-frame block offset (JS side, passed as uniform)

### key files

- `src/Renderer.ts` — render target creation, pass orchestration, MRT setup, colony stats readback
- `src/Config.ts` — simulation parameters (per-channel pheromone configs)
- `src/constants.ts` — material IDs (single source of truth for TS + GLSL)
- `src/ColonyStats.ts` — CPU readback of ant texture for colony-level aggregate stats
- `src/StatsOverlay.ts` — on-screen stats display (cursor position, TPS, colony info)
- `src/materials/types.ts` — Material interface and BehaviorType constants
- `src/materials/registry.ts` — MaterialRegistry with 6 built-in materials
- `src/materials/lookupTexture.ts` — builds GPU lookup textures from registry
- `src/sand/margolus.ts` — Margolus block offset calculation
- `src/scenes/SandPhysicsScene.ts` — sand physics render pass
- `src/shaders/antsCompute.frag` — ant behavior + MRT output (2 render targets via layout qualifiers)
- `src/shaders/worldBlur.frag` — per-channel pheromone diffusion/decay (solid cells block diffusion)
- `src/shaders/world.frag` — material ID preservation + pheromone merging
- `src/shaders/sandPhysics.frag` — Margolus block CA for powder/sand movement

## planning docs

- `REALISM-IDEAS.md` — research-backed features for more realistic ant behavior
- `INFRASTRUCTURE.md` — data structure analysis mapping features to GPU infrastructure layers
- `docs/plans/2026-03-11-ant-farm-sand-physics-design.md` — sand physics design
- `docs/plans/2026-03-11-ant-farm-implementation.md` — ant farm implementation plan

## shader files

in `src/shaders/`. each scene has a matched .vert/.frag pair. loaded as raw strings by the vite glsl plugin in `vite.config.ts`. all shaders use GLSL3 (`#version 300 es` via three.js `glslVersion: THREE.GLSL3`).

## textures

in `public/textures/` — ant.png and food.png sprites.