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使用 NavigationServer

NavigationServer 即导航服务器。2D 和 3D 版本的 NavigationServer 分别为 NavigationServer2D 和 NavigationServer3D。

2D 和 3D 使用的 NavigationServer 是一样的，NavigationServer3D 是主要服务器。NavigationServer2D 只是一个前端，会进行 2D 位置和 3D 位置的相互转换。因此，完全可以只用 NavigationServer3D 的 API 来实现 2D 导航（就是会有点繁琐）。

与 NavigationServer 通信

To work with the NavigationServer means to prepare parameters for a query that can be sent to the NavigationServer for updates or requesting data.

To reference the internal NavigationServer objects like maps, regions and agents RIDs are used as identification numbers. Every navigation related node in the scene tree has a function that returns the RID for this node.

线程与同步

The NavigationServer does not update every change immediately but waits until the end of the physics frame to synchronize all the changes together.

Waiting for synchronization is required to apply changes to all maps, regions and agents. Synchronization is done because some updates like a recalculation of the entire navigation map are very expensive and require updated data from all other objects. Also the NavigationServer uses a threadpool by default for some functionality like avoidance calculation between agents.

Waiting is not required for most get() functions that only request data from the NavigationServer without making changes. Note that not all data will account for changes made in the same frame. E.g. if an avoidance agent changed the navigation map this frame the agent_get_map() function will still return the old map before the synchronization. The exception to this are nodes that store their values internally before sending the update to the NavigationServer. When a getter on a node is used for a value that was updated in the same frame it will return the already updated value stored on the node.

The NavigationServer is thread-safe as it places all API calls that want to make changes in a queue to be executed in the synchronization phase. Synchronization for the NavigationServer happens in the middle of the physics frame after scene input from scripts and nodes are all done.

备注

The important takeaway is that most NavigationServer changes take effect after the next physics frame and not immediately. This includes all changes made by navigation related nodes in the scene tree or through scripts.

以下函数只会在同步阶段执行：

  • map_set_active()

  • map_set_up()

  • map_set_cell_size()

  • map_set_edge_connection_margin()

  • region_set_map()

  • region_set_transform()

  • region_set_enter_cost()

  • region_set_travel_cost()

  • region_set_navigation_layers()

  • region_set_navigation_mesh()

  • agent_set_map()

  • agent_set_neighbor_dist()

  • agent_set_max_neighbors()

  • agent_set_time_horizon()

  • agent_set_radius()

  • agent_set_max_speed()

  • agent_set_velocity()

  • agent_set_target_velocity()

  • agent_set_position()

  • agent_set_ignore_y()

  • agent_set_callback()

  • free()

2D 和 3D NavigationServer 的区别

NavigationServer2D 和 NavigationServer3D 在各自维度中的功能是等价的，底层使用的相同的 NavigationServer。

Strictly technical a NavigationServer2D is a myth. The NavigationServer2D is a frontend to facilitate conversions of Vector2(x, y) to Vector3(x, 0.0, z) and back for the NavigationServer3D API. 2D uses a flat 3D mesh pathfinding and the NavigationServer2D facilitates the conversions. When a guide uses just NavigationServer without the 2D or 3D suffix it usually works for both servers by exchange Vector2(x, y) with Vector3(x, 0.0, z) or reverse.

Technically it is possible to use the tools for creating navigation meshes in one dimension for the other dimension, e.g. baking a 2D navigation mesh with the 3D NavigationMesh when using flat 3D source geometry or creating 3D flat navigation meshes with the polygon outline draw tools of NavigationRegion2D and NavigationPolygons.

Any RID created with the NavigationServer2D API works on the NavigationServer3D API as well and both 2D and 3D avoidance agents can exist on the same map.

备注

Regions created in 2D and 3D will merge their navigation meshes when placed on the same map and merge conditions apply. The NavigationServer does not discriminate between NavigationRegion2D and NavigationRegion3D nodes as both are regions on the server. By default those nodes register on different navigation maps so this merge can only happen when maps are changed manually e.g. with scripts.

Actors with avoidance enabled will avoid both 2D and 3D avoidance agents when placed on the same map.

警告

自定义的 Godot 构建如果禁用了 3D，则无法使用 NavigationServer2D。

等待同步

At the start of the game, a new scene or procedural navigation changes any path query to a NavigationServer will return empty or wrong.

The navigation map is still empty or not updated at this point. All nodes from the scene tree need to first upload their navigation related data to the NavigationServer. Each added or changed map, region or agent need to be registered with the NavigationServer. Afterward the NavigationServer requires a physics frame for synchronization to update the maps, regions and agents.

One workaround is to make a deferred call to a custom setup function (so all nodes are ready). The setup function makes all the navigation changes, e.g. adding procedural stuff. Afterwards the function waits for the next physics frame before continuing with path queries.

extends Node3D

func _ready():
    # use call deferred to make sure the entire scene tree nodes are setup
    # else await / yield on 'physics_frame' in a _ready() might get stuck
    call_deferred("custom_setup")

func custom_setup():

    # create a new navigation map
    var map: RID = NavigationServer3D.map_create()
    NavigationServer3D.map_set_up(map, Vector3.UP)
    NavigationServer3D.map_set_active(map, true)

    # create a new navigation region and add it to the map
    var region: RID = NavigationServer3D.region_create()
    NavigationServer3D.region_set_transform(region, Transform())
    NavigationServer3D.region_set_map(region, map)

    # create a procedural navigation mesh for the region
    var new_navigation_mesh: NavigationMesh = NavigationMesh.new()
    var vertices: PackedVector3Array = PackedVector3Array([
        Vector3(0,0,0),
        Vector3(9.0,0,0),
        Vector3(0,0,9.0)
    ])
    new_navigation_mesh.set_vertices(vertices)
    var polygon: PackedInt32Array = PackedInt32Array([0, 1, 2])
    new_navigation_mesh.add_polygon(polygon)
    NavigationServer3D.region_set_navigation_mesh(region, new_navigation_mesh)

    # wait for NavigationServer sync to adapt to made changes
    await get_tree().physics_frame

    # query the path from the navigationserver
    var start_position: Vector3 = Vector3(0.1, 0.0, 0.1)
    var target_position: Vector3 = Vector3(1.0, 0.0, 1.0)
    var optimize_path: bool = true

    var path: PackedVector3Array = NavigationServer3D.map_get_path(
        map,
        start_position,
        target_position,
        optimize_path
    )

    print("Found a path!")
    print(path)

服务器避障回调

如果 RVO 避障代理注册了避障回调，NavigationServer 会在 PhysicsServer 同步前发送对应的 velocity_computed 信号。

更多 NavigationAgent 相关的信息见 使用 NavigationAgent。

使用避障的 NavigationAgent 的简化执行顺序如下：

  • 物理帧开始。

  • _physics_process(delta)。

  • NavigationAgent 节点的 set_velocity()。

  • 代理向 NavigationServer 发送速度和位置。

  • NavigationServer 等待同步。

  • NavigationServer 同步并为所有注册的避障代理计算避障速度。

  • NavigationServer 通过信号为每个注册的避障代理发送安全速度向量。

  • 代理收到信号并移动父节点，例如通过 move_and_slide 或 linear_velocity 移动。

  • PhysicsServer 同步。

  • 物理帧结束。

Therefore moving a physicsbody actor in the callback function with the safe velocity is perfectly thread- and physics-safe as all happens inside the same physics frame before the PhysicsServer commits to changes and does its own calculations.