Ray-casting

Einführung

Eine der häufigsten Aufgaben in der Spieleentwicklung besteht darin, einen (Licht-) Strahl (oder ein benutzerdefiniertes Objekt) zu werfen und zu überprüfen, was darauf trifft. Dies ermöglicht komplexe Verhaltensweisen, KI usw. In dieser Anleitung wird erklärt, wie dies in 2D und 3D funktioniert.

Godot speichert alle Low-Level-Spielinformationen auf Servern, während die Szene nur ein Frontend ist. Daher ist das Ray-Casting (Strahlenwerfen) im Allgemeinen eine untergeordnete Aufgabe. Bei einfachen Raycasts funktionieren Nodes wie RayCast und RayCast2D, da sie jedem Frame das Ergebnis eines Raycasts zurückgeben.

In vielen Fällen muss Raycasting jedoch ein interaktiverer Prozess sein, sodass eine Möglichkeit vorhanden sein muss, dies per Code zu tun.

Raum

In der Physikwelt speichert Godot alle Kollisions- und Physikinformationen auf niedriger Ebene in einem Raum. Der aktuelle 2D-Raum (für 2D-Physik) kann durch Zugriff auf Folgendes abgerufen werden CanvasItem.get_world_2d().space. Für 3D ist es Spatial.get_world().space.

The resulting space RID can be used in PhysicsServer and Physics2DServer respectively for 3D and 2D.

Accessing space

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.

To perform queries into physics space, the Physics2DDirectSpaceState and PhysicsDirectSpaceState must be used.

Verwenden Sie den folgenden Code in 2D:

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);
}

Oder direkter:

func _physics_process(delta):
    var space_state = get_world_2d().direct_space_state
public override void _PhysicsProcess(float delta)
{
    var spaceState = GetWorld2d().DirectSpaceState;
}

Und in 3D:

func _physics_process(delta):
    var space_state = get_world().direct_space_state
public override void _PhysicsProcess(float delta)
{
    var spaceState = GetWorld().DirectSpaceState;
}

Raycast-Abfrage

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

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:

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

The result dictionary when a collision occurs contains the following data:

{
   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
}

Die Daten sind im 3D-Raum unter Verwendung von Vector3-Koordinaten ähnlich.

Kollisionsausnahmen

Ein häufiger Anwendungsfall für das Ray-Casting besteht darin, einem Charakter das Sammeln von Daten über die Welt um ihn herum zu ermöglichen. Ein Problem dabei ist, dass dasselbe Zeichen einen Kollider hat, sodass der Strahl nur den Kollider seines Elternteils erkennt, wie in der folgenden Abbildung gezeigt:

../../_images/raycast_falsepositive.png

To avoid self-intersection, the intersect_ray() function can take an optional third parameter which is an array of exceptions. This is an example of how to use it from a KinematicBody2D or any other collision object node:

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 });
    }
}

The exceptions array can contain objects or RIDs.

Kollisionsmaske

Während die Ausnahmemethode zum Ausschließen des übergeordneten Körpers gut funktioniert, ist es sehr unpraktisch, wenn Sie eine große oder dynamische Liste von Ausnahmen benötigen. In diesem Fall ist es viel effizienter, das Kollisionsschichten- bzw. Maskensystem zu verwenden.

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:

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 Beispiel for details on how to set the collision mask.

3D-Raycasting vom Bildschirm

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.

To cast a ray from the screen, you need a Camera node. A Camera can be in two projection modes: perspective and orthogonal. Because of this, both the ray origin and direction must be obtained. This is because origin changes in orthogonal mode, while normal changes in perspective mode:

../../_images/raycast_projection.png

To obtain it using a camera, the following code can be used:

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;
    }
}

Remember that during _input(), the space may be locked, so in practice this query should be run in _physics_process().