Why does delta time make things go so slowly?

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:bust_in_silhouette: Asked By Millard

So, i have a simple kinematic 2d character with this code

extends KinematicBody2D

export var direction = Vector2(0,0)
export var walk_speed = 200
export var jump_speed = -400
export var gravity = 200

func _ready():

func _physics_process(delta):

    direction.y += gravity * delta
    direction.x = 0

    if Input.is_action_pressed("left"):
	    direction.x -= walk_speed
    if Input.is_action_pressed("right"):
	    direction.x += walk_speed
    if Input.is_action_just_pressed("jump"):
	    direction.y = jump_speed

    var movement = move_and_slide(direction, Vector2(0,-1))

And it works well, but it isn’t consistent (obviously) so in my move and slide function, i added:

var movement = move_and_slide(direction * delta, Vector2(0,-1)

The only problem is that it causes my character to move very slowly. I tried increasing the jump_speed and walk_speed variables, which works somewhat, but it seems like they would need to be big numbers to move correctly and i would rather deal with smaller variables.

So, is there a way to fix this, or do i have to multiply my variables by a hundred?

Also, out of curiosity, why does multiplying it with delta cause this?

:bust_in_silhouette: Reply From: Kanor

You’re absolutely right! And the hundreds is actually the right place for those velocity values. Let me explain:

move_and_slide is a method that factors delta internally. So your code is basically multiplying by delta twice. Just remove the delta and move_and_slide will make it consistent. :slight_smile:


Unlike in move_and_collide, you should not multiply it by delta — the physics engine handles applying the velocity.

thanks to both Kanor and exuln! I had no idea that move and slide already factors delta. Nice. Unsure which answer to select as best though. I guess i’ll choose Kanors since it was first, although exulns was helpful as well. Thanks again! :smiley:

Millard | 2020-09-22 03:29

:bust_in_silhouette: Reply From: exuin

Have you taken a look at the KinematicBody2d tutorial?
From the official tutorials:

The delta parameter in the _process() function refers to the frame length - the amount of time that the previous frame took to complete. Using this value ensures that your movement will remain consistent even if the frame rate changes.

move_and_slide() automatically calculates frame-based movement using delta. Do not multiply your velocity vector by delta before passing it to move_and_slide().

So the reason your character moves slower when you multiple the movement vector by delta in the move_and_slide() function is because delta is less than one, so multiplying the movement vector by it reduces the length of the vector. The move_and_slide() method is consistent already since it multiples by delta automatically.

The speed that you multiple the movement vector by is in pixels/second. I don’t think you need to multiple the variable by 100, since the character would then be moving 20,000 pixels every second, which is bigger than anyone’s computer screen.