Changing a joint length - player input

gitborg

New to Godot and the forum so hi everyone.

I've been trying to change the length of a 2d joint, but haven't had much luck so far.

The plan is that when up is pushed the distance between two assigned nodes decreases and when down is pressed increases.


var grooveJ

func _ready():
	grooveJ = get_node('/root/Node2D/grooveJ')
	print(grooveJ.length)
	pass 

func _process(_delta):
	if Input.is_action_pressed("ui_up"):
		grooveJ.initial_offset -= 1
		print(grooveJ.initial_offset)
	if Input.is_action_pressed("ui_down"):
		grooveJ.initial_offset += 1
		print(grooveJ.initial_offset)
	pass

On running my code there is a static body node assigned and a rigid body that swings, but the increase or decrease in length although it prints has no effect on the distance between the two nodes. I've also tried with 'length', also spring and pin (although pin has * no obvious distance control).

Is there are well known way to do this kind of thing that I've not been able to find?

Thanks in advance for any responses.

Saitodepaula

I have never used 2D joints, but I've done lots of experiments with 3D joints. One thing I've learned is to try many different values for the joints parameters, specially ones not supposed to be used.

So, you are setting the initial-offset, that, according to the docs, have a default value of 25. What if you set it to 100? 1.000? And what about 0 or negative values?
In physics (and joints) everything depends on the mass of the bodies. What is the mass of your rigid body? Maybe your rigid body is just to heavy for the joint to have any effect (that's why I said above to test absurd values).
Have you tested to change the length?
Have you tested to add/subtract higher values when you press up/down? Like 50 or 100? Or even more...
In 3D, I noticed I get better results when the joint and the bodies joined by the joint doesn't have a child/parent relationship, for example, making the joint be a child of the static body is not good. I have to make the 2 bodies and the joint all be child of another node.