What is delta in _physics_process for?

antoniosos

Usually you multiply physics calculations by delta so the frame rate doesn't change them but since _physics_process already isn't tied to the frame rate I don't see any use for it and when I multiplied by it so that when I mess with the Physics settings the calculations would stay the same the results were different.

xyz

antoniosos _physics_process() runs in sync with physics frames (ticks) which can be set in project settings. So it's not a wise thing for your time dependent code to assume that default 60 ticks per second is set in stone, as you may want to change this rate in the future development. Frame drops can also happen for intense physics simulations, in which case delta won't be 1/physics_ticks for some frames.

antoniosos

xyz
So should function I call in _physics_process look like this
func move(delta): if Input.is_action_pressed("left"): player.velocity.x -= speed * delta if Input.is_action_pressed("right"): player.velocity.x += speed * delta if Input.is_action_just_pressed("jump"): player.velocity.y = jump_strength * delta
or should I not multiply by delta?

xyz

antoniosos No, because you're just assigning a value of velocity. Multiplying it by delta makes no sense physics-wise.

Read up on basics of kinematic motion to understand how the basic motion is modeled with math, and what's the role of (delta) time in it.

GorEldeen

antoniosos you should never use delta with anything that doesn't include calculations

for example:
speed = speed2 * delta
velocity = Vector2(speed, speed2) * delta

this is because you're not doing real-time calculations

instead you can use it in these cases:
speed += speed2 * delta
velocity += Vector2(speed, speed2) * delta

xyz

GorEldeen you should never use delta with anything that doesn't include calculations

What do you mean by "doesn't include calculations". All of your above examples include some calculations.

GorEldeen

xyz sorry, I meant real-time calculations, which happens while the game is running, unlike the calculations that happens only once

xyz

GorEldeen Well delta is only available in real time anyway, and it represents an approximate time "differential" between consecutive frames. It's typically used in calculations that include either numerical integration or approximate derivation of some function/value in respect to time.

An example of numerical integration would be calculating the velocity by integrating acceleration:
velocity += acceleration * delta

And an example of a derivative may be calculating the velocity from the distance travelled in a slice of time:
velocity = (position_current - position_previous) / delta