How to redirect a force?

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Emax

I am using a RigidBody3D when it falls I want to redirect the force of gravity (linear_velocity.y) in another direction.
For example as soon as the body touches the floor before the physics engine reset the vertical speed I want to assign it to another axis. How can I do it?

I've tried with this, but it doesn't work

func _integrate_forces(state):
	for contactIndex in state.get_contact_count():
		var normal: Vector3 = state.get_contact_local_normal(contactIndex);
		if normal == Vector3.UP:
			if linear_velocity.y > 0:
				linear_velocity.x += linear_velocity.y;

DaveTheCoder

Emax if normal == Vector3.UP:

It's very unlikely that normal will be exactly the same as Vector3.UP, since their components are floats. There may be other problems with the code, but that sticks out.

Emax

DaveTheCoder You are right but the code is simplified to explain the problem
Take this code as example:

func _integrate_forces(state):
	if state.get_contact_count() > 0:
		print(linear_velocity.y);

even if the body falls from an height this will print 0.
I think the _integrate_forces functions is called after the physics engine process

Pixophir

What @DaveTheCoder said. We should regard it as a mistake to do floating point comparisons for equality, at least inside of physics. Godot has a bunch of almost-equal functions (or is_equal_approx()).

Emax I think the _integrate_forces functions is called after the physics engine process

https://docs.godotengine.org/en/latest/tutorials/physics/physics_introduction.html?highlight=_integrate_forces()

Quote:

Note that we are not setting the linear_velocity or angular_velocity properties directly, but rather applying forces (thrust and torque) to the body and letting the physics engine calculate the resulting movement.

_integrate_forces() is used instead of _physics_process(). In it, one adds forces to the body, and the physics engine calculates the movement.

Emax

Pixophir move_and_slide doesn't exist for rigid bodies. The problem is not the dection of the floor, the problem is that whenever a contact is recorded the vertical force is already gone.

Let's say my scene is configured like this:

The body has attached this script:

func _integrate_forces(state):
	if get_contact_count() > 0:
		print("from _integrate_forces: ", linear_velocity.y);

func _physics_process(delta):
	if get_contact_count() > 0:
		print("from _physics_process: ", linear_velocity.y);

At the exact moment when the body touches the floor (when the contact is recorded) the linear_velocity is already 0, in fact this code prints:

from _integrate_forces: 0
from _physics_process: 0

So I cannot redirect the force in another direction because it's cleared before my code runs.
Maybe I should save the linear velocity at each frame and use it after the contact has been recorded, but it doesn't seem like the right way.

Emax

Solved! in the PhysicsDirectBodyState3D provided in the "_integrate_forces" function for every contact there is get_contact_collider_velocity_at_position that returns the velocity before the contact!