Inaccurate Collision Box problem

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1

Godot Version

Godot_v4.6.3-stable_linux.x86_64

Question

I created a small script that tests for box-collision and than draw a box - green if no collision is found, red if a collision is detected, but the results are sometimes inaccurate.

In the image, the center is a wall so the box should always be red.

collision_test
collision_test1073×609 30.7 KB

collision_test4
collision_test41073×609 29.4 KB

collision_test3
collision_test31073×609 28.8 KB

		debug_multimesh_solid.instance_count = 1
		var pos = debugMeshPosition
		var transform = Transform3D(global_basis, pos)
		debug_multimesh_solid.set_instance_transform(0, transform)
		debug_multimesh_solid.set_instance_color(0, Color.BLUE)
		
		var space := get_world_3d().direct_space_state
		var collision_box = SphereShape3D.new()
		
		
		
		var params := PhysicsShapeQueryParameters3D.new()
		params.shape = collision_box
		params.transform = transform
		params.collide_with_bodies = true
		params.collide_with_areas = false
		params.collision_mask = 0x7fffffff
		
		var result := space.collide_shape(params, 1)
		if result.size() != 0:
			debug_multimesh_solid.set_instance_color(0, Color.RED)
		else:
			debug_multimesh_solid.set_instance_color(0, Color.GREEN)

That is the code to check the collision.

extends Node3D
@export var wireframe: Shader


var debugMeshPosition = Vector3()



var debug_multimesh_solid: MultiMesh = null

func debug_multimesh_solid_init():
	var mm := MultiMeshInstance3D.new()
	
	var box := BoxMesh.new()
	var mat := StandardMaterial3D.new()
		
	mat.vertex_color_use_as_albedo = true
	
	box.material = mat
	debug_multimesh_solid = MultiMesh.new()
	debug_multimesh_solid.use_colors = true
	debug_multimesh_solid.instance_count = 0
	
	
	debug_multimesh_solid.transform_format = MultiMesh.TRANSFORM_3D
	debug_multimesh_solid.mesh = box
	
	
	mm.multimesh = debug_multimesh_solid
	add_child(mm)


func debug_multimesh_update():	
	if true:
		debug_multimesh_solid.instance_count = 1
		var pos = debugMeshPosition
		var transform = Transform3D(global_basis, pos)
		debug_multimesh_solid.set_instance_transform(0, transform)
		debug_multimesh_solid.set_instance_color(0, Color.BLUE)
		
		var space := get_world_3d().direct_space_state
		var collision_box = SphereShape3D.new()
		
		
		
		var params := PhysicsShapeQueryParameters3D.new()
		params.shape = collision_box
		params.transform = transform
		params.collide_with_bodies = true
		params.collide_with_areas = false
		params.collision_mask = 0x7fffffff
		
		var result := space.collide_shape(params, 1)
		if result.size() != 0:
			debug_multimesh_solid.set_instance_color(0, Color.RED)
		else:
			debug_multimesh_solid.set_instance_color(0, Color.GREEN)
		



func _unhandled_input(event):
	if event is InputEventKey:
		var distance = 0.1
		if event.keycode == KEY_UP and event.pressed:
			debugMeshPosition.z += distance
		if event.keycode == KEY_DOWN and event.pressed:
			debugMeshPosition.z -= distance
		if event.keycode == KEY_LEFT and event.pressed:
			debugMeshPosition.x += distance
		if event.keycode == KEY_RIGHT and event.pressed:
			debugMeshPosition.x -= distance	
		if event.keycode == KEY_PAGEUP and event.pressed:
			debugMeshPosition.y += distance
		if event.keycode == KEY_PAGEDOWN and event.pressed:
			debugMeshPosition.y -= distance

# Called when the node enters the scene tree for the first time.
func _ready() -> void:
	debug_multimesh_solid_init()
	pass # Replace with function body.


# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(delta: float) -> void:
	debug_multimesh_update()
	pass

This is the whole code for my test. It is added to the root Node3D Node.
It allows you to move the Box with the KEY_UP … and KEY_PAGEUP Keys.

Thank you for your time :slight_smile:

2

You do not appear to be using any CollisionObject3D objects. I suggest fixing that, or showing us where they are in your hierarchy.

3

You’re right. The walls are just collision-enabled with static collisions.
But shouldnt space.collide_shape or space.intersect_shape still work for it?

4

Depends on where you’re calling it from. You are trying to get low-level access to the physics engine, so I suggest you read up on how to use it. You haven’t provided enough code to tell if you are using it correctly.

5

But I have posted the whole code?
Just create a new project, add some CSGBox3D with collision enabled and add the code (the second) to root Node3D.

It will automatically render the Collision-Box with green or red and you can move it around with the cursor keys.

Just remove the
@export var wireframe: Shader
that is not needed.

6

You attached two scripts, and the first one is not complete.

7

The first is just a snippet from the second that contains collision test and the rendering so you do not need to read all of it.

I have now tested something else:
Before I just used CSGBox3D with Use Collision enabled. If I use a StaticBody3D with CSGBox3d and a CollisionShape with the same size as the CSGBox3D instead it works.

So It seems UseCollision is buggy or at least behaves weird when using it with CSGBox3d.

8

That’s because you should not be using a CSGBox3D. The only thing they should be used for is creating MeshInstance3D objects. They are horribly inefficient. But there was no indication in your code that you were using one so I couldn’t tell you that.