发射射线

发射射线

简介

游戏开发中最常见的任务之一是发射射线(或自定义形状的对象)并检查其击中的内容。这可以产生复杂的行为，如AI等。本教程将介绍如何在2D和3D中执行此操作。

Godot将所有低级游戏信息存储在服务器中，而场景只是一个前端。因此，发射射线通常是较低级别的任务。对于简单的射线发射，使用 RayCast 和 RayCast2D 节点就可以了，因为它们将每一帧都返回射线投射的结果。

但是，很多时候，射线投射应该是一个更具交互性的过程，因此必须存在通过代码执行此操作的方法。

空间

In the physics world, Godot stores all the low level collision and physics information in a space. The current 2d space (for 2D Physics) can be obtained by accessing CanvasItem.get_world_2d().space. For 3D, it’s Spatial.get_world().space.

结果空间 RID 可在3D的 PhysicsServer 和2D的 Physics2DServer 中。

获取空间

Godot physics runs by default in the same thread as game logic, but may be set to run on a separate thread to work more efficiently. Due to this, the only time accessing space is safe is during the Node._physics_process() callback. Accessing it from outside this function may result in an error due to space being locked.

要对物理空间执行查询，必须使用 Physics2DDirectSpaceState 和 PhysicsDirectSpaceState 。

在2D中使用以下代码:

GDscript

func _physics_process(delta):
    var space_rid = get_world_2d().space
    var space_state = Physics2DServer.space_get_direct_state(space_rid)

public override void _PhysicsProcess(float delta)
{
    var spaceRid = GetWorld2d().Space;
    var spaceState = Physics2DServer.SpaceGetDirectState(spaceRid);
}

或者更直接:

GDScript

func _physics_process(delta):
    var space_state = get_world_2d().direct_space_state

public override void _PhysicsProcess(float delta)
{
    var spaceState = GetWorld2d().DirectSpaceState;
}

在3D中:

GDScript

func _physics_process(delta):
    var space_state = get_world().direct_space_state

public override void _PhysicsProcess(float delta)
{
    var spaceState = GetWorld().DirectSpaceState;
}

Raycast查询

For performing a 2D raycast query, the method Physics2DDirectSpaceState.intersect_ray() may be used. For example:

GDScript

func _physics_process(delta):
    var space_state = get_world_2d().direct_space_state
    # use global coordinates, not local to node
    var result = space_state.intersect_ray(Vector2(0, 0), Vector2(50, 100))

public override void _PhysicsProcess(float delta)
{
    var spaceState = GetWorld2d().DirectSpaceState;
    // use global coordinates, not local to node
    var result = spaceState.IntersectRay(new Vector2(), new Vector2(50, 100));
}

The result is a dictionary. If the ray didn’t hit anything, the dictionary will be empty. If it did hit something, it will contain collision information:

GDScript

if result:
    print("Hit at point: ", result.position)

if (result.Count > 0)
    GD.Print("Hit at point: ", result["position"]);

发生碰撞时， result 字典包含以下数据:

{
   position: Vector2 # point in world space for collision
   normal: Vector2 # normal in world space for collision
   collider: Object # Object collided or null (if unassociated)
   collider_id: ObjectID # Object it collided against
   rid: RID # RID it collided against
   shape: int # shape index of collider
   metadata: Variant() # metadata of collider
}

使用Vector3坐标，数据在3D空间中类似。

碰撞异常

光线投射的常见用例是使角色能够收集有关其周围世界的数据。这个问题的一个问题是同一个角色有一个对撞机，因此光线只会检测其父对手，如下图所示:

为了避免自相交， intersect_ray() 函数可以采用可选的第三个参数，这是一个异常数组。这是如何从KinematicBody2D或任何其他碰撞对象节点使用它的示例:

GDScript

extends KinematicBody2D
func _physics_process(delta):
    var space_state = get_world_2d().direct_space_state
    var result = space_state.intersect_ray(global_position, enemy_position, [self])

class Body : KinematicBody2D
{
    public override void _PhysicsProcess(float delta)
    {
        var spaceState = GetWorld2d().DirectSpaceState;
        var result = spaceState.IntersectRay(globalPosition, enemyPosition, new object[] { this });
    }
}

例外数组可以包含对象或RID。

碰撞遮罩

虽然例外方法适用于排除父体，但如果需要大型和/或动态的例外列表，则会变得非常不方便。在这种情况下，使用碰撞层/遮罩系统要高效得多。

The optional fourth argument for intersect_ray() is a collision mask. For example, to use the same mask as the parent body, use the collision_mask member variable:

GDScript

extends KinematicBody2D
func _physics_process(delta):
    var space_state = get_world().direct_space_state
    var result = space_state.intersect_ray(global_position, enemy_position,
                            [self], collision_mask)

class Body : KinematicBody2D
{
    public override void _PhysicsProcess(float delta)
    {
        var spaceState = GetWorld2d().DirectSpaceState;
        var result = spaceState.IntersectRay(globalPosition, enemyPosition,
                        new object[] { this }, CollisionMask);
    }
}

See Code example for details on how to set the collision mask.

来自屏幕的3D射线投射

Casting a ray from screen to 3D physics space is useful for object picking. There is not much need to do this because CollisionObject has an “input_event” signal that will let you know when it was clicked, but in case there is any desire to do it manually, here’s how.

要从屏幕投射光线，您需要 Camera 节点。相机``可以是两种投影模式:透视和正交。因此，必须获得射线原点和方向。这是因为 ``origin 在正交模式下改变，而 normal 在透视模式下改变:

要使用相机获取它，可以使用以下代码:

GDScript

const ray_length = 1000
func _input(event):
    if event is InputEventMouseButton and event.pressed and event.button_index == 1:
          var camera = $Camera
          var from = camera.project_ray_origin(event.position)
          var to = from + camera.project_ray_normal(event.position) * ray_length

private const float rayLength = 1000;
public override void _Input(InputEvent @event)
{
    if (@event is InputEventMouseButton eventMouseButton && eventMouseButton.Pressed && eventMouseButton.ButtonIndex == 1)
    {
        var camera = (Camera)GetNode("Camera");
        var from = camera.ProjectRayOrigin(eventMouseButton.Position);
        var to = from + camera.ProjectRayNormal(eventMouseButton.Position) * rayLength;
    }
}

请记住，在 _input() 期间，空格可能被锁定，所以实际上这个查询应该在 _physics_process() 中运行。