How can I animate a physics-enabled Skeleton2D?

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1

Godot Version

4.5 unstable, with PRs: 1, 2, but that shouldn’t be relevant.

Question

Though I’m a beginner to Godot, I’ve jumped right in and decided to mess with the experimental PhysicalBone2D nodes. While I have found plain ragdoll mode entertaining, I would like a way to animate it, while the physics are active.

The three relevant options I am currently aware of are:

  • Full ragdoll. No predetermined artistic control.
  • Entirely non-physical. No ragdoll physics.
  • Mixed. Some parts ragdoll, others not.

None of these are what I want. I want to have a physics-enabled bone attract toward a specific position, sort of like the muscles are moving it there. And I want to be able to have this follow a whole predetermined (or algorithmical, if I need to) animation.

Is this possible, with the current state of this? Or is it not yet there?

Thank you!

2

I’ve not tested it but PhysicalBone2D extends RigidBody2D so you should be able to “control” it by applying forces or impulses or by overriding the RigidBody2D._integrate_forces() function and controlling the state directly.

Here’s an example that show how to control a platformer character by overriding _integrate_forces() godot-demo-projects/2d/physics_platformer/player/player.gd at master · godotengine/godot-demo-projects · GitHub

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Thank you!

Trying to get this solution to work, though, I can’t seem to get it working quite right..

muscular_physical_bone_2d.gd

extends PhysicalBone2D

@export var force_position: Vector2
@export var target_position: Vector2
@export_range(0, 1) var strength: float = 1.0
@export_range(0, 1) var tenseness: float = 0.5

func _integrate_forces(state: PhysicsDirectBodyState2D) -> void:
	var parent_transform_inverse = get_parent().global_transform.affine_inverse()
	var global_force_position: Vector2 = force_position * global_transform.affine_inverse()
	var velocity_at_force: Vector2 = state.get_velocity_at_local_position(force_position)

	var force: Vector2 = (target_position * parent_transform_inverse - global_force_position - velocity_at_force * tenseness) * strength

	state.apply_force(force, global_force_position - position)

    # To preserve Newton's third law of motion:
	get_parent().apply_force(-force, global_force_position - get_parent().position)
  • force_position: the position the force is exerted, in the PhysicalBone2D’s local space.
  • target_position: the position to bring the force position to, but in the parent’s local space.
  • strength: a factor of how much this affects things.
  • tenseness: how much this accounts for already present motion, to minimize wobbling.

(Should be easy to animate something like this, using Godot’s built-in animation system.)

Configuring this, the skeleton just seems to go crazy! Do you have any idea what I might be doing wrong?

Minimal Reproducible Project (hosted on Proton Drive)

Edit: Added video of problem (from MRP):