Jitter when colliding a corner (KinematicBody2D and CollisionShape2D)

[pc9098]

Godot version

v3.4.4-stable_win64

System information

Windows 10, i5-9600K, RTX 2060, 16GB RAM, GLES3

Issue description

``When I move my 2D character to any corner shape it jitters.

My player is: a KinematicBody2D with a Sprite and a CollisionShape2D (it happens in any shape: rectangle, capsule, circle, ...).
My player has a script attached.
The walls are: a StaticBody2D with a CollisionPolygon2D.

Godot_v3.2022-08-20.16-35-11-47.mp4

extends KinematicBody2D

var vel = Vector2.ZERO

const MAX_SPD = 80

func _physics_process(delta):
	var input_vector = Vector2.ZERO
	input_vector.x = Input.get_action_strength("ui_right") - Input.get_action_strength("ui_left")
	input_vector.y = Input.get_action_strength("ui_down") - Input.get_action_strength("ui_up")
	input_vector = input_vector.normalized()
	
	vel = input_vector * MAX_SPD
	
	vel = move_and_slide(vel)

The prints on the wall:

"before(-80, 0)
after(6.303683, 7.879045)
Falsefloor
Truewall

before(-80, 0)
after(6.29903, -31.520666)
Falsefloor
Truewall

before(-80, 0)
after(-3.076349, 15.385308)
Falsefloor
Truewall"

etc

The prints on the floor:

"before(0, 80)
after(28.24184, -7.050445)
Falsefloor
Truewall

before(0, 80)
after(-18.827187, 4.720105)
Falsefloor
Truewall

before(0, 80)
after(-7.062556, -7.058139)
Falsefloor
Truewall"

etc

This bug only happens with a corner, but not a single wall

Steps to reproduce

Make the same scene as I did with the same script, and just collide with a corner-like (not a wall but 2 walls making a corner!)

Minimal reproduction project

p2.zip

[Calinou]

This is likely an issue with your code, rather than the physics engine. In other words, your player is "flip-flopping" endlessly between two walls due to the instant acceleration and lack of friction.

Try ignoring movement if it's smaller than a certain amount, or implement some kind of movement acceleration/friction.

[pc9098]

I knew with acceleration it can be "fixed" (not really fixed but making the jittering so little that the screen can't show it), but I'd rather have a solution which implied pushing the character to the right place (right above the corner) instead of some units in the above

[Hiiamwilliam]

My understanding is that when you slide in those corners you always end up entering one wall then pushed away into the other wall. This is why it jitters. If this is the actual reason, there is no bug here.

Do you want an easy way of "fixing" this jitter? Instead of move_and_slide with default parameters, decrease max_slides to 2:

vel = move_and_slide(vel, Vector2.ZERO, false, 2)

This will likely have negative consequences if your game has moving platforms and other KinematicBody interactions, but it does stop this specific jittering.