Pathfinding With NavMesh: Getting Started
Characters in a game often need to navigate around obstacles in the level. Because this is such a common situation in games, Unity provides a built-in pathfinding solution, called NavMesh. In this tutorial, you’ll implement point-and-click movement using NavMesh. By Joseph Hocking.
Characters in a game often must find their way around obstacles. Think about baddies trying to follow the player in a maze. The technical term for this problem is pathfinding. This is where the computer needs to calculate a path for the characters to move along. Because this situation arises often in games, Unity provides a built-in pathfinding solution, called NavMesh.
In this tutorial, you’ll learn:
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- Pathfinding approaches that games use
- How to use NavMesh, Unity’s pathfinding tech
- Ways to tweak or customize NavMesh navigation
To get some hands-on practice, you’ll implement point-and-click movement using Unity’s NavMesh pathfinding. Download the project files at the top or bottom of this tutorial by clicking the Download Materials button. The sample project uses Unity 2020.1.17 and provides a sample scene, so you can concentrate on the pathfinding functionality.
Pathfinding in Games
AI characters in games often must find the best path to take to reach their destination. You can choose from several algorithms for pathfinding, but A* is a great choice in all but a few specialized situations.
A* (or A-star)
The A* algorithm is commonly employed for pathfinding in all sorts of computing environments — it’s not specific to Unity. There’s even an A* article on this site, which discusses the algorithm in the context of iOS development. For a deeper look, this article offers an illustrated, interactive guide to the algorithm. This one explains the steps independent of any particular tech stack.
This tutorial won’t explain A* in detail right here because, well, you can read those excellent explanations. Instead, it’s right on to Unity’s pathfinding approach!
Navigation Meshes
The A* articles mentioned earlier discuss pathfinding on a grid of squares, but the algorithm does not require a map like that. A* can work with other shapes, too! All the algorithm needs is a graph of connected nodes, and a grid of squares is merely one such graph. You can even use A* with maps of the real world: The intersections of roads are nodes, and roads are the connections between nodes.
Games often represent the pathfinding graph with a mesh. That is, just like a 3D model, the graph used for pathfinding can be represented with vertices connected by edges. A mesh like this is called a Navigation Mesh, so Unity’s tech for this has the abbreviated name NavMesh.
Unity has basic NavMesh functionality built-in, but it provides more robust mesh generation and pathfinding through an open-source project called NavMesh Components. When you set up your own projects, you can download these components from that GitHub repository. But they are already included in the starter project. Now, it’s time to go over how to use these components!
Getting Started
To get the hang of using NavMesh components, you’ll develop a simple demo of point-and-click movement. The character will move to the spot clicked on, just like a point-and-click adventure game. With the power of NavMesh, the character will even know how to get around obstacles.
Your character needs a scene to run around in and some obstacles to navigate around. Fortunately, the starter project provides these. Navigate to Assets/RW/Scenes and open SampleScene. This scene simply has a bunch of blocks for the walls and floor, along with a capsule to represent the player.
With the level set up to navigate around, you already have what you need to build the navigation mesh!
Generating the NavMesh
First, create an empty GameObject and name it NavMesh. The navigation mesh will be generated from and attached to this object. Now, add a NavMeshSurface component to this object. In the Inspector, there are now a bunch of navigation settings, as well as a couple of buttons for managing the mesh generation.
That’s it — you’re ready to create your first mesh! Click Bake, and Unity generates a navigation mesh using the default settings.
Your first baked mesh!
Your first baked mesh!
Understanding NavMeshSurface
What happened? The underlying code is quite complex, but the broad steps aren’t hard to understand. NavMeshSurface first decides which way is up, using its own GameObject’s rotation. It then identifies the surfaces in the scene facing that direction. (In this case, they’re all flat, but NavMeshSurface also works with terrain and other irregular meshes.)
The NavMesh system then must determine what parts of each surface are walkable. Game characters come in all shapes and sizes. The areas that are walkable by a little cat character, for example, would be different from those walkable by a human or a giant robot. This is where the diagram at the top of NavMeshSurface comes in.
It might look like notes from math class, but these are your NavMesh agent settings.
It might look like notes from math class, but these are your NavMesh agent settings.
The diagram illustrates the properties of the particular kind of agent that will walk on this mesh, such as its radius and height. (You can access these settings in the Agent Type dropdown if you like, but they are not needed for this tutorial.)
The NavMesh system uses these settings to identify where this agent could go. When the system finds an area that is flat, wide and tall enough for this kind of agent, it marks that area as walkable. Then, it generates a flat navigation mesh — the blue areas that just appeared in the scene.
Now that you’ve baked a mesh, it’s time to look more closely at the result. The default settings work pretty well, but there are always things to tweak.
Tuning the NavMesh with Layers
First of all, there’s a hole in the mesh surrounding the player. By default, everything in the scene is considered a potential obstacle to navigate around. You need to explicitly tell NavMeshSurface not to include the player as an obstacle.
NavMeshSurface has a dropdown menu called Include Layers. If you de-select a layer in that dropdown, the mesh generation system ignores the objects on that layer. Follow these steps to put the player on a new layer and then exclude that layer from the mesh:
- Select the Player GameObject in the Hierarchy.
- In the Layer dropdown, select Add Layer.
- In the layer management view that appears, type the name Player in the first available row.
- Select the player again. Using the Layer dropdown, change its layer to the newly created Player layer. (For an additional challenge, say “player layer” to yourself five times fast.)
- A popup appears, asking whether to assign child objects to that layer as well. Choose Yes, change children.
- Select NavMesh.
- In the Inspector, open the Include Layers dropdown and click Player to de-select it.
Create and then assign a layer for the player from this dropdown.
Create and then assign a layer for the player from this dropdown.
Now, Unity will understand that the player isn’t part of the scenery. Click Bake to regenerate the navigation mesh. No more hole!