---
title: "Navigation Grid and Flow Field"
package: "@phaser-ae/nav"
tier: Free
version: 3.0.0-5
released: 2026-10-14
updated: 2026-10-19
description: "Pathfinding for 2D tile maps and 3D terrain: A-star routes straightened for walkers of any size, and flow fields for hordes heading to one place."
url: https://phaser.io/packs/nav
site: Phaser - https://phaser.io
---

# Navigation Grid and Flow Field

Pathfinding in two tiers: a grid that routes one agent somewhere specific, and a flow field that answers the same
question once for a thousand agents heading to the same place. Both work on a 2D tile map or over 3D terrain, and both
plan for bodies with a size.

## What it does

A **grid** runs A* between two world points and then string-pulls the result, so a route reads as a straight line
wherever it can instead of a staircase of cells. `NavGrid2d` takes a tile map, as an array of walkable cells or a
`blocked(x, y)` test, over world x and y, and returns plain `{ x, y }` points for a top-down game. `NavGrid` samples a
height function over world x and z for a 3D game on terrain, marks cliffs, water and blocked footprints unwalkable and
prefers flat routes. Open or close a cell with `setWalkable` when a door shuts or a crate drops, and the next route goes
round.

A **flow field** floods the whole grid outward from one goal and leaves a direction in every cell. Each follower then
reads `dirAt` where it stands, a single lookup rather than a search, which is how a horde chases the player or a crowd
pours towards an exit.

The part that is easy to get wrong is size. Give a grid, or a single call, a **radius**, and A* refuses gaps narrower
than the body, string pulling keeps a straight leg only where the whole body fits, and a flow field floods only cells
the body can stand in. A 20-unit guard is never sent through a 16-unit gap or routed so close to a door jamb that it
catches, yet it still fits through any gap that is wide enough, exactly. One grid serves guards, a thief and an ogre,
each planned at its own size.

## Features

- **A* with string pulling** — direct routes as world points, or `[]` when there is none, or the nearest reachable point
  with `partial`.
- **2D and 3D grids** — `grid2d` over a tile map in x and y, `grid` over a height function in x and z.
- **Walkers with a size** — a radius per grid or per call, exact against the grid's walls.
- **Flow fields** — one flood per goal, a direction in every cell, sized for the body.
- **Straight-line checks** — `clear` says whether a body can slide straight between two points.
- **Terrain rules** — cliffs by step height, a slope penalty, water below a level and blocked footprints.
- **Weighted flow grids** — `flowGrid` with costly cells, several goals, smooth steering and `canBuild`.
- **Live edits** — open and close cells as doors move, with cached clearance rebuilt only when a cell changes.
- **Off-thread routes** — `pathAsync` plans on a worker and can be cancelled.
- **Headless** — no objects, no drawing, the same in a worker or a test as in a frame.

## Good for

- **Top-down stealth and dungeon games**, where guards of different sizes chase through doors and corridors.
- **Horde and survival games**, where hundreds of enemies flow towards the player through one field.
- **Tower defence**, with weighted cells, several goals and a check that a new tower leaves every spawn a route.
- **3D games on terrain**, where walkers avoid cliffs and water and prefer flat ground.
- **Colony and management sims**, where workers walk between stores and sites.
- **Strategy and tactics**, where units are told where to go and must find their own way.

## Make it yours

A 2D grid takes its columns and rows, the cell size, an origin and a walkable array or a blocked test, or both. A map
whose walls are not whole tiles, a round pillar or a diagonal wall, can be sampled at a finer cell through `blocked`. A
3D grid takes the height function, its size, centre and resolution, a water level, a blocked test, the highest step a
walker can climb and how much slope costs. Every grid takes a default radius, and every query can override it.

Two different uses: a top-down heist where 12-unit guards plan on a 16-unit tile map with `path`, and a smaller thief
plans on the same grid with a 4-unit radius; and a 3D zombie game where one flow field towards the player steers a whole
crowd of 1.2-unit walkers across hilly terrain, round cliffs and out of the water.

## A quick look

A tile map for guards 12 units across, a route, and a door that shuts:

```ts
const map = ['##########', '#....#...#', '#....#...#', '#........#', '##########'];
const grid = game.nav.grid2d({
    cols: map[0].length, rows: map.length, cell: 16,
    walkable: [...map.join('')].map(c => c !== '#'),
    radius: 6,                                     // every guard is a 12-unit disc
});
const route = grid.path(guard, thief);             // [{x, y}, …] clear of every wall by 6
grid.setWalkable(grid.idx(5, 3), false);           // a door shuts; the next path goes round
const field = game.nav.flow(grid, player);         // a horde reads field.dirAt(x, y)
```

## Works with

- `steering` — moves bodies along these routes and fields, with avoidance, flocking and arrival.
- `nav-mesh` — for 3D levels a height grid cannot hold: bridges, arches and a floor above a floor.
- `track` — for authored routes such as rails and circuits rather than searched ones.
- `grid-move` and `grid-walker` — for movement locked to a grid's lanes.
- `jobs` — work yards whose workers walk routes planned here.
- `levelgen` — mazes, dungeons and caves whose tile grids can become the walkable map.

## Good to know

- The 3D grid holds one height per cell, so bridges and overhangs need `nav-mesh`.
- A flow field serves one goal; a second goal is a second field. The weighted flow grid takes several goals but plans
  for points, not bodies.
- Neither knows about moving obstacles: change a cell and plan again, or let `steering`'s avoidance handle what moves.
- A route is clear for the body, but a follower that cuts corners early or swings wide on momentum can still clip a
  wall; turn early only when `clear` says so.
- Walls are whole cells, so curved and diagonal walls need a cell small enough to follow them.

---

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