RigidBody2D inconsistent response to apply_impulse

Question

I'm seeing inconsistent rotation behavior using apply_impulse() to a RigidBody2D. Using this simple code:

extends RigidBody2D

func _ready():
    set_process_input(true)
    apply_impulse(Vector2(-10, 0), Vector2(0, -200))

func _input(event):
    if event.is_action_pressed("ui_select"):
        apply_impulse(Vector2(-10, 0), Vector2(0, -200))

As you can see, the apply_impulse() has an offset, so the body should rotate in response. However, when the scene is run, the body does move upward but without any rotation. The same apply_impulse() when run from the _input() function does result in rotation.

I noticed this because I had similar inconsistent rotation response when using apply_impulse() in other functions. Anyone run across this before?

Comments

How much is the angular damp? maybe is nullifying the impulse on fixed process.

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No angular damp. And the impulse applied by _input()doesn't get damped at all. Even with damping, you'd think there'd be some rotation, but it's exactly 0.

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And the shape is not a circle? I have noticed something weird (like no change on initial rotation) with bouncing circles but didn't tested much.

Answer 1

Problem may be that you put the apply_impulse in _ready()

I experienced oddities when working with 3D Physics and not letting it "settle down" at least some fractions of a second directly after scene start. (Usually I give it 0.1sec). Can be that this is similar in 2D.

You can use a one-time timer or a counter (add up deltas) in fixedprocess for delaying the initial impulse.

For example:

extends RigidBody2D

var initialWait = 0.1

func _ready():
    set_process_input(true)
    set_fixed_process(true) 

func _fixed_process(delta):
    if initialWait>0:
        initialWait=initialWait-delta
        return

    set_fixed_process(false)

    apply_impulse(Vector2(-10, 0), Vector2(0, -200))

func _input(event):
    if event.is_action_pressed("ui_select"):
        apply_impulse(Vector2(-10, 0), Vector2(0, -200))

Comments

I thought of this, but the _ready() example was just to demonstrate the problem. It also occurs when the impulse is applied in another function called during the game.

Answer 2

Wait one frame to get rid of the problem with apply_torque_impulse

Example for instantiating a spinning axe:

export var axe_scene: PackedScene
const IMPULSE = 300
const TORQUE  = 100000

func throw_axe():
    var axe = axe_scene.instance() as RigidBody2D
    get_tree().get_root().add_child(axe)
    axe.position = global_position
    axe.apply_central_impulse(IMPULSE)
    yield (get_tree(),"idle_frame")
    axe.apply_torque_impulse(TORQUE)

Comments

This has worked for me. Thanks!

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I found this bug today. My work around is to use call_deferred().

extends RigidBody2D

export var impulse: Vector2 = Vector2(100, -300)
export var torque: float = 200


func _ready() -> void:
    call_deferred("apply_impulse", impulse)
    call_deferred("apply_torque_impulse", torque)