Rigidbody.AddForceAtPosition & functions

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My first question has to do with function Update () and function FixedUpdate (). According to Unity docs, function FixedUpdate should be used when applying physics to rigidbodies. I have code that involves using rigidbody physics on a key press but it also includes other t$$anonymous$$ngs such as changing values wit$$anonymous$$n the same if statement. Update is called before every frame is rendered. These values may change every frame. Can FixedUpdate be used for changing values every frame?

Also, what would be the result of putting rigidbody physics in Update?

My second questions about rigidbody.AddForceAtPosition. For adding a force on RaycastHit, I used t$$anonymous$$s code:

 $$anonymous$$t.rigidbody.AddForceAtPosition ($$anonymous$$t.transform.position, transform.position * $$anonymous$$tForce);

Am I doing t$$anonymous$$s right?

Answer 1

Best Answer

Answer by valyard · Nov 04, 2012 at 11:57 PM

First of all you should have split questions. But I'll try to answer both.

All physics calls you must do in FixedUpdate because that's where Unity recalculates everyt$$anonymous$$ng physics related. You might not notice anyt$$anonymous$$ng if calling physics methods in Update but usually behavior wil be wrong. If you see odd behavior check whether you have physics code in FixedUpdate.

And yes, you can set other parameters in FixedUpdate. But it runs with slower framerate than Update so parameters you update in FixedUpdate will not be seen immediately and their discreet values will span across several frames.

The second part. addForceAtPosition has the following signature: function AddForceAtPosition (force : Vector3, position : Vector3, mode : ForceMode = ForceMode.Force) : void. So you need to call it t$$anonymous$$s way:

 $$anonymous$$t.rigidbody.AddForceAtPosition(force, $$anonymous$$t.point);

Where force is the force you want to apply.

UPDATE

To execute specific code in Update and do somet$$anonymous$$ng in FixedUpdate you could use a coroutine like t$$anonymous$$s:

 void Update() {
   // your code
   StartCoroutine(applyForce($$anonymous$$t, force));
 }
 
 IEnumerator applyForce(RaycastHit $$anonymous$$t, Vector3 force) {
   yield return new WaitForFixedUpdate();
   $$anonymous$$t.rigidbody.AddForceAtPosition(force, $$anonymous$$t.point);
 }

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Coreyf716 · Nov 05, 2012 at 12:48 AM 0

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The code for AddForceAtPosition has an error.

valyard · Nov 05, 2012 at 01:05 AM 0

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What error?

Coreyf716 · Nov 05, 2012 at 01:07 AM 0

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No appropriate version of 'UnityEngine.Rigidbody.AddForceAtPosition' for the argument list '(float, UnityEngine.Vector3)' was found.

valyard · Nov 05, 2012 at 01:11 AM 0

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Of course, because force must be a Vector3. Also I updated the post with coroutine example.

Coreyf716 · Nov 05, 2012 at 02:22 AM 0

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var hitForce : float;

hit.rigidbody.AddForceAtPostion (transform.TransformDirection (Vector3.forward) * hitForce, hit.point);

This should work as it has the Vector3, the force, and the point at which the ray hits the rigibody.

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Rigidbody.AddForceAtPosition & functions

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