如何检查2d统一的垂直速度？

Question

I am trying to animate my sprite when my vertical velocity is less than 0 (moving downwards). How do you do it?

if (VERTICALVELOCITY < 0) {
animator.SetFloat("IsFalling", true);
}

Try to change VERTICALVELOCITY and maybe help with the code. Also, should I do it in Void Update or FixedUpdate?

Answer 1

If you're using a rigibody you may do this:

public class CheckSpeed : MonoBehaviour
{
    private Rigidbody2D rb2D;

    void Start() => rb2D = GetComponent<Rigidbody2D>();

    private float GetVerticalSpeed() => rb2D.velocity.y;
}

Your code will become:

if (GetVerticalSpeed() < 0) {
animator.SetFloat("IsFalling", true);
}

Since this is related to an animation I would set it to LateUpdate.

Answer 2

Do you have a rigidbody on that gameobject? Then it's easy.

private Rigidbody rb;

Start()
{
    rb = getComponent<Rigidbody>();
}

Update ()
{
    if(rb.velocity.y < 0)
    {
        // do your stuff
    }
}

Otherwise, you need to log the y-position every frame.

float ypos_lastframe = 0;

Start()
{
    ypos_lastframe = transform.position.y;
}

Update()
{
    if(transform.position.y < ypos_lastframe)
    {
       // do your stuff
    }
    // important to do this assignment AFTER the check above.
    ypos_lastframe = transform.position.y;
}