Not able to place an Area (with CollisionShape) between 2 points

RBogdy

Hello everyone,

I have a test level, with 3 objects in a group. I want to know if one of them passes between the other 2 when I apply an impulse to it. Since this is in 3D and I don't master linear algebra, I thought that a simple way to achieve this would be to create an Area between the 2 objects, give it a Collision shape and test if the moving objects collides with that area.

I create the Areas' CollisionShape (which is a ConvexPolygonShape made out of 4 points) through code, by getting the global_transform.origin of the objects I want it to be spawned between.

I am able to created the collision shape, but I'm not able to place the Area where it should be (from obj1 origin to obj2 origin with the proper size and rotation)

Bellow you can see the code that I came up with

extends Area

onready var test_objects= get_tree().get_nodes_in_group("TestObjects")
onready var collision_polygon = get_child(0).get_shape()

func generate_area_between_objects(object_to_be_moved):
	var index = test_objects.find(object_to_be_moved)
	if index == 0:
		collision_polygon.set_points([Vector3(test_objects[1].global_transform.origin.x, test_objects[1].global_transform.origin.y + 5, test_objects[1].global_transform.origin.z),
							      Vector3(test_objects[2].global_transform.origin.x, test_objects[2].global_transform.origin.y + 5, test_objects[2].global_transform.origin.z),
							      Vector3(test_objects[2].global_transform.origin.x, test_objects[2].global_transform.origin.y - 5, test_objects[2].global_transform.origin.z),
							      Vector3(test_objects[1].global_transform.origin.x, test_objects[1].global_transform.origin.y - 5, test_objects[1].global_transform.origin.z)])
		var mid = (test_objects[2].global_transform.origin + test_objects[1].global_transform.origin) / 2
		var direction = test_objects[2].global_transform.origin.direction_to(test_objects[1].global_transform.origin)
		global_transform.origin = direction
	if index == 1:
		collision_polygon.set_points([Vector3(test_objects[0].global_transform.origin.x, test_objects[0].global_transform.origin.y + 5, test_objects[0].global_transform.origin.z),
							       Vector3(test_objects[2].global_transform.origin.x, test_objects[2].global_transform.origin.y + 5, test_objects[2].global_transform.origin.z),
							       Vector3(test_objects[2].global_transform.origin.x, test_objects[2].global_transform.origin.y - 5, test_objects[2].global_transform.origin.z),
							       Vector3(test_objects[0].global_transform.origin.x, test_objects[0].global_transform.origin.y - 5, test_objects[0].global_transform.origin.z)])
		var mid = (test_objects[2].global_transform.origin + test_objects[0].global_transform.origin) / 2
		var direction = test_objects[2].global_transform.origin.direction_to(test_objects[0].global_transform.origin)
		global_transform.origin = direction
	if index == 2:
		collision_polygon.set_points([Vector3(test_objects[0].global_transform.origin.x, test_objects[0].global_transform.origin.y + 5, test_objects[0].global_transform.origin.z),
							       Vector3(test_objects[1].global_transform.origin.x, test_objects[1].global_transform.origin.y + 5, test_objects[1].global_transform.origin.z),
							       Vector3(test_objects[1].global_transform.origin.x, test_objects[1].global_transform.origin.y - 5, test_objects[1].global_transform.origin.z),
							       Vector3(test_objects[0].global_transform.origin.x, test_objects[0].global_transform.origin.y - 5, test_objects[0].global_transform.origin.z)])
		var mid = (test_objects[1].global_transform.origin + test_objects[0].global_transform.origin) /2 
		var direction = test_objects[1].global_transform.origin.direction_to(test_objects[0].global_transform.origin)
		global_transform.origin = direction

As you can see, I'm setting the Areas' global_transform.origin to the direction, because strangely enough that gives me the result that is the closest to what I'm trying to achieve, however it's not actually on point.
Setting the origin to the mid point between the 2 objects places the Area very far from where it should be.

I appreciate any help related to how I can properly place this Area or any other advice on how you can detect an object passing between 2 others in 3D - I though about eliminating the Y component and doing it in X and Z only, but can't figure that out either 🙁

Kojack

I haven't used manual collision polygons yet, but my guess based on the code: if the points are using the global transforms of the objects, then the polygon is already in the global space and the origin should be 0,0,0.
The reason direction almost works would be because it would be a normalised vector (a length of 1), so close to 0,0,0.

cybereality

The Godot Geometry class has many useful functions so you don't have to code them yourself.

https://docs.godotengine.org/en/stable/classes/class_geometry.html

I would advise thinking about the issue differently. For example, you can draw a line of the path of the projectile, and then test the closest point from the 2 other objects. If you did this in 1D (one axis) then one direction would be positive and the other negative, then you know the projectile passed between (if it were outside then the numbers would either be both positive or both negative).

You can also simplify the projectile as a sphere, that has a radius equal to slightly larger than the distance between the two other objects. If both the objects collide with the sphere, then you have a case where it is in between. There are many ways to do this, you don't need to write any math yourself.

fire7side

There are some good explanations for placing and moving objects here:
http://codetuto.com/2016/01/godot-engine-movement-and-rotation-basics/

RBogdy

Thank you all for your responses.
@Kojack you were right, setting the Transform to Vector3.Zero places the Area right where it should be
@cybereality your notes are great and a good start to think about the problem differently