Collider returns an Object. no access to .Name

[nathanjwtx]

Godot version:
3.1 Mono
Windows 10, i5, GTX1050

Trying to convert the following into C#:
var collision = get_slide_collision(idx) if collision.collider.name == 'Danger':

KinematicCollision2D collision = GetSlideCollision(i);

Doing collison.Collider doesn't expose the name property.

[mysticfall]

I had a discussion with @nathanjwtx on Discord about this issue and to clarify, it is about the binding for KinematicCollision2D.Collider having Object as its return type, which better be changed for something more specific for convenience.

[neikeq]

This property is defined in PhysicsBody and PhysicsBody2D. Looking at the source, it seems the type can't be nothing other than CollisionObject and CollisionObject2D. @reduz, can we update the signature of these methods to reflect this?

[akien-mga]

I think the collider can be TileMap or GridMap too, no? That's why #24739 and related issues are problematic.

[Reneator]

I think the collider can be TileMap or GridMap too, no? That's why #24739 and related issues are problematic.

Wouldn't then just clarifying the different return-types in the documentation improve these misconceptions?

[neikeq]

@akien-mga At least for the collider property in PhysicsBody and PhysicsBody2D I don't see anything other than CollisionObject and CollisionObject2D being set.

[akien-mga]

@neikeq What property do you mean? I don't see any collider property in PhysicsBody2D.

But I can confirm that KinematicCollision2D.collider can be a TileMap:

extends KinematicBody2D
var vel = Vector2(0, 10)
func _physics_process(delta):
	var col = move_and_collide(vel)
	if col:
		print(col.collider)  # prints [TileMap:1162] on collision

[mysticfall]

Maybe we can introduce a common interface like ICollidable?

[neikeq]

@akien-mga My mistake, the classes are KinematicCollision and KinematicCollision2D.

[akien-mga]

My mistake, the classes are KinematicCollision and KinematicCollision2D.

@neikeq So yeah, I can confirm that collider can be something different from a CollisionObject2D as per

godot/scene/2d/physics_body_2d.cpp

Lines 1549 to 1560 in c26f0c9

	Object *KinematicCollision2D::get_collider() const {
	if (collision.collider) {
	return ObjectDB::get_instance(collision.collider);
	}
	return NULL;
	}
	ObjectID KinematicCollision2D::get_collider_id() const {
	return collision.collider;
	}

I guess you thought it's a CollisionObject2D due to the cast for collider_shape?

godot/scene/2d/physics_body_2d.cpp

Lines 1561 to 1573 in c26f0c9

	Object *KinematicCollision2D::get_collider_shape() const {
	Object *collider = get_collider();
	if (collider) {
	CollisionObject2D *obj2d = Object::cast_to<CollisionObject2D>(collider);
	if (obj2d) {
	uint32_t ownerid = obj2d->shape_find_owner(collision.collider_shape);
	return obj2d->shape_owner_get_owner(ownerid);
	}
	}
	return NULL;
	}

I can confirm that in the case of TileMap, it can't retrieve the shape:

extends KinematicBody2D
var vel = Vector2(0, 10)
func _physics_process(delta):
	var col = move_and_collide(vel)
	if col:
		print(col.collider)  # prints [TileMap:1162]
		print(col.collider_shape)  # prints [Object:null]

We could probably make collider return Node2D or Spatial instead of Object, which should solve this issue (not the other ones regarding expecting a CollisionObject2D and getting a TileMap, but that's a broader issue).

[neikeq]

I followed all the code paths that assigned collision.collider until I found something typed. I must have missed something.

Edit: Just checked again. Yes, I missed some usages... 😑

[eka]

I bumped into this when trying to translate some GDScript code to C#.
I there an alternative to get the Name of the collider object right now?

Update:

I was able to circumvent this, casting to Node as

if (((Node)collision.Collider).Name == "Name")

[Zylann]

You should be able to cast Collider to Node, or Spatial or Node2D, since that's the lowest common denominator in classes used for this field, at least in core Godot.
I bind this field to my HTerrain and VoxelTerrain plugin nodes for collisions with them as well. Although, it should be said that the API that allows binding an object to a collider does not require any particular constraint on the type of his object, so in theory, following the current API, Collider could be of any Object type, even if so far these types happen to be nodes: https://docs.godotengine.org/en/stable/classes/class_physicsserver.html#class-physicsserver-method-body-attach-object-instance-id the reason being that the server's API may not know anything about scene tree stuff because it's abstract and should remain that way, so it's all a convention. You could imagine this object being a Tile non-node class for example. Objects don't necessarily have a name so forcing an interface is not possible.