Not getting expected results from state.get_contact_impulse() function

amityadav381 · July 13, 2024, 10:53am

Godot Version

Godot Engine v4.2.2.stable.official.15073afe3

Question

I’m trying to access the impulse vector, when two RigidBody2D objects colloid.
For this I wrote this in my RigidBody2D gdscript:

The problem is, when there’s a collision and I see the print “APPLIED IMPULSE”, I always get 0 for state.get_contact_impulse(0)
why is that? I’m expecting it to be printed for each colliding object and display the impulse applied to them because of the collision.

There are only two objects of type RigidBody2D, names pen_fighter, and pen_fighter2. I’m attaching the log I see for this code when these two objects colloid:

state.get_contact_count() = 1
get_colliding_bodies =[]
state.get_contact_count() = 1
get_colliding_bodies =[pen_fighter2:<RigidBody2D#24930944216>]
state.get_contact_count() = 0
APPLIED IMPULSE = (0, 0)
get_colliding_bodies =[pen_fighter:<RigidBody2D#24880612557>]
state.get_contact_count() = 0
APPLIED IMPULSE = (0, 0)
get_colliding_bodies =[]

michaelgame_dev · July 13, 2024, 3:07pm

I think it could be related to this bug:

github.com/godotengine/godot

PhysicsDirectBodyState3D.get_contact_impulse() returns zero vector on first frame of collision

opened 01:30AM - 18 Feb 23 UTC

krokoschlange

bug topic:physics

### Godot version v4.0.rc2.official [d2699dc7a] ### System information Endeav…ourOS, Vulkan ### Issue description Calling the `get_contact_impulse()` method on the PhysicsDirectState3D object provided in the `_integrate_forces()` method of `RigidBody3D` returns `Vector3.ZERO` for contacts that were created in the current frame. I would expect this method to return the impulse applied to the rigidbody by the contact, even during the first frame. This becomes an issue particularly with bouncy objects as they often only have one frame of contact which results in no impulse being reported at all. I dug a bit in the physics code and it seems that the contacts of a rigidbody are not updated after `pre_solve` in `GodotBodyPair3D` ran which seems suspicious. ### Steps to reproduce 1. set up a scene with a rigidbody with a collider and something it can collide with (I tested both rigidbodies and staticbodies for this) 2. Turn on `contact_monitor` and set `max_contacts_reported` to a reasonable value 3. Add a script to the rigidbody that implements `_integrate_forces()` and call `state.get_contact_impulse()`, for example print all impulses for all contacts 4. Observe that during the first frame after a new contact is created a zero vector is returned. This is more obvious when a physics material with bounciness 1.0 is added to the rigidbody. ### Minimal reproduction project [impulse_test.zip](https://github.com/godotengine/godot/files/10772643/impulse_test.zip)

amityadav381 · July 13, 2024, 5:09pm

I read up some documentation and saw changing below value could help:
physics-tick-per-second from 60 to 240
max physics steps per second from 8 to 32
I was able to see some impuls values. But those values are not as I expected.

dooferino · January 2, 2025, 10:35pm

Hi @amityadav381 , did you manage to figure out this topic?

amityadav381 · May 25, 2025, 7:10am

Hi @dooferino I changed my solution to not include this approach.
here’s the complete game I made.