Unity 2D: Inconsistent jump height in game window

Question

Whenever I start the unity editor and play it in the Game windows, sometimes the object can jump higher sometimes it is just small jump. I didn't change any value in my script nor changed it in inspector window.

It usually happens when I restart the unity editor or having my computer shutdown / restart and reopening the project.

Here are the jump code

void jump() {
     if (isInGround) {
         float currentJumpForce = jumpForce * Mathf.Abs(rigidBody.velocity.x) / 3.53f;
         rigidBody.AddForce(Vector2.up * currentJumpForce);
         animator.SetTrigger("isJump");
     }
}

I place the code inside the FixedUpdate method, for what I have read the physics calculation should be inside FixedUpdate right?

private void FixedUpdate() {
    if (Input.GetKeyDown(KeyCode.UpArrow)) {
        jump();
    }
}

I have read many are having similar problem, but it really doesn't answer this question.

UPDATE:

I forget to explain it in the question. The jumpForce is calculated based on the velocity of the gameObject has. I capped the velocity to certain speed based on this code

void accelerate() {
     if (rigidBody.velocity.x <= maxSpeed) {
         rigidBody.AddForce(Vector2.right * acceletateForce);
     }
}

where maxSpeed is a constant. I know this is probably not the accurate way to cap the velocity, or is it? Maybe this is where it gets messed up?

I just kinda assume the velocity is the capped from the camera movement and the 'display' or the movement of the screen. It seems the same to me.

Answer 1

Physics calculations should indeed be in the FixedUpdate. However, Input should be captured in the Update. This is because the FixedUpdate is called whenever the physics engine updates, while Update is called whenever the screen updates. You can thus have more than one call to FixedUpdate in the frame where the user pressed the key.

There are two options to solve this. First, call the jump function in the Update function, which works, though not entirely correct. Or set a flag in the Update and call the Jump function in FixedUpdate.

See also this