Mouse input lag causes line rendering jitter

Questions & Answers
1

I have

  1. a 2D sprite that moves with a rigidbody2d,
  2. mouse input that provides a location in world space,
  3. a line renderer that draws a line between the sprite and mouse point.

When my sprite moves, the line jitters badly. I’ve attached a gif.

https://giphy.com/gifs/l3q2xdNZjKrlRlYu4

This is the simplest project that reproduces this error. Code sample below:

void Update() {
    var moveInput = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));

    var rawMousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
    lookPosition = new Vector3(rawMousePosition.x, rawMousePosition.y, 0);

    lineRenderer.SetPosition(0, transform.position);
    lineRenderer.SetPosition(1, lookPosition);
}

void FixedUpdate() {
    rigidBody2d.velocity = moveInput.normalized * moveSpeed;
}

Moving the sprite directly using it’s transform, the line doesn’t jitter, but the line still noticeably lags behind the mouse point.

https://giphy.com/gifs/l3q2Qwi29hWeSkG5y

void Update() {
    var moveInput = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));
    transform.Translate(moveInput * moveSpeed * Time.deltaTime);

    var rawMousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
    lookPosition = new Vector3(rawMousePosition.x, rawMousePosition.y, 0);

    lineRenderer.SetPosition(0, transform.position);
    lineRenderer.SetPosition(1, lookPosition);
}

I can accept the line lagging behind the mouse point in the 2nd scenario; my question is how do I prevent the jitter in the 1st scenario, given that I’m moving rigidbodies in my 2D project?

2

It most likely has to do with the update order. You’re probably updating the line position before the rigidbody updates the position. That would give you the jitter. Try moving your line update code to LateUpdate(); Read here for more info.