Amnesia-like object moving?

Questions & Answers
1

Hi.

I ran into a few problems with Unity’s DragRigidbody script. First off, I would like the object being dragged to move faster, I’d like the object to always move as the player moves, and to rotate with the player, so it is always in the view.

Here is my modified DragRigidbody script that I’d like to add these features to:

    var damper = 5.0;
var drag = 10.0;
var angularDrag = 5.0;
var distance = 0.2;
var throwForce = 5.5;
var attachToCenterOfMass = false;
var isPressed = false;

static var springJoint : SpringJoint;

function Update ()
{
	// Make sure the user pressed the mouse down
	if (!Input.GetButtonDown ("Fire1"))
		return;
	if (Input.GetButtonDown ("Fire1")) {
		isPressed = true;
		Debug.Log("isPressed = true;");
	}

	var mainCamera = FindCamera();
		
	// We need to actually hit an object
	var hit : RaycastHit;
	if (!Physics.Raycast(mainCamera.ScreenPointToRay(Input.mousePosition),  hit, Mathf.Infinity))
		return;
	// We need to hit a rigidbody that is not kinematic
	if (!hit.rigidbody || hit.rigidbody.isKinematic)
		return;
	
	if (!springJoint)
	{
		var go = new GameObject("Rigidbody dragger");
		var body : Rigidbody = go.AddComponent ("Rigidbody") as Rigidbody;
		springJoint = go.AddComponent ("SpringJoint");
		body.isKinematic = true;
	}
	
	springJoint.transform.position = hit.point;
	if (attachToCenterOfMass)
	{
		var anchor = transform.TransformDirection(hit.rigidbody.centerOfMass) + hit.rigidbody.transform.position;
		anchor = springJoint.transform.InverseTransformPoint(anchor);
		springJoint.anchor = anchor;
	}
	else
	{
		springJoint.anchor = Vector3.zero;
	}
	
	springJoint.spring = spring;
	springJoint.damper = damper;
	springJoint.maxDistance = distance;
	springJoint.connectedBody = hit.rigidbody;
	
	StartCoroutine ("DragObject", hit.distance);
}

function DragObject (distance : float)
{
	var oldDrag = springJoint.connectedBody.drag;
	var oldAngularDrag = springJoint.connectedBody.angularDrag;
	springJoint.connectedBody.drag = drag;
	springJoint.connectedBody.angularDrag = angularDrag;
	var mainCamera = FindCamera();
	while (isPressed) //(Input.GetButton ("Fire1"))
	{
		var ray = mainCamera.ScreenPointToRay (Input.mousePosition);
		springJoint.transform.position = ray.GetPoint(distance);
		yield;
		while (Input.GetButtonDown("Fire2")) {
		springJoint.rigidbody.MovePosition(transform.position + transform.forward * throwForce);
		yield WaitForSeconds(0.01);
		isPressed = false;
		Debug.Log("Thrown? DragRigidbody.js");
		}
	}
	
	
	if (springJoint.connectedBody)
	{
		springJoint.connectedBody.drag = oldDrag;
		springJoint.connectedBody.angularDrag = oldAngularDrag;
		springJoint.connectedBody = null;
	}
}

function FindCamera ()
{
	if (camera)
		return camera;
	else
		return Camera.main;
}

If you could help me, I would greatly appreciate it!

Thanks!

2

I’m not sure what kind of setup you have, a 3D firstperson view or a 2D side scrolling view, but if you don’t like the springy nature of joints, you could simply parent the object to your player. That way it moves along with the player without any delay and it rotates with the player.

edit
Well in this case just reduce the drag / damper value of the DragScript. That would make the dragging more responsive. But be careful, the spring joint will be more springy then.

The rotation have to be handled manually i guess. Just save the rotation of the object relative to your player. I guess this could be done by multiplying the objects rotation (quaternion) with the inverse of your players quaternion. No you just need to do the reverse in the coroutine with the stored rotation to get the objets rotation.

Another way would be a temporary empty parent gameobject which is rotated like the player.

I haven’t tested those things, but it should work.