What is the best way to Push or Pull an Object?

Question

Hello,

I am currently trying to get a working script for pulling and pushing objects in a 2D game.I have heard there are several ways to do this. At first I was using the script found in the documentation, but I realized it only works for pushing objects and not pulling towards you. Then I came across making your character the parent of your game object. The following is my script atm.

 function OnControllerColliderHit (hit : ControllerColliderHit) {
 
 var body : Transform = hit.transform;
 
 if(body.gameObject.name == "Crate"){
       if (Input.GetButton("Action")){
       body.transform.parent = transform;
       body.rigidbody.isKinematic = true;
        }
       else {
       body.transform.parent = null;
       body.rigidbody.isKinematic = false;
       }
 }
 }

I am having problems using this though. First of all, If I collide with the gameobject and then press the action button, (Hence my velocity is zero), my character will not be able to move at all. On the other hand if I hold the action button and collide with the gameobject at a velocity it will start moving with my character. Second, If I jump on my gameobject and click the action button, it will become the child of my character following his movements. How can I avoid this from happening since the character should only be pulling/pushing if he is on the left or right of the gameobject and not on top of it.

I have also read that you can do this by creating a joint that will attach the game object and the character together. I am wondering though if the joint method could be used if I am not using rigidbody as my controller. Currently I am using The platform input controller script along with the character motor.

Any Help is appreciated. Thank you very much.

Answer 1

Two parts: how to know what to pull, and then pulling it. There might be a few ways to say "I want to pull this." For example, clicking on a crate. But, to go with what you have, bumping a crate selects it. The standard trick is to have a variable, maybe thingToPull which will be set on a bump, and will be nothing (null) if we aren't pulling anything.

Then, once we have thingToPull (no matter how we got it,) we can have Update move it around.

I'm using C#. Finding out what they want to pull, using your first script modified:

 Transform thingToPull; // null if nothing, else a link to some pullable crate

 void OnControllerColliderHit(ControllerColliderHit hit) {
   if(hit.transform.name=="Crate") // NOTE: tags checking may be better
     thingToPull = hit.transform;
 }

Then the player's Update can drag it towards you. Notice I'm being cute here in a few ways. You lose it if it gets beyond 50 meters; it stops when it gets within 3 meters, and it gets pulled harder as you get further away.

 if(thingToPull!=null) {
   Vector3 D = transform.position - thingToPull; // line from crate to player
   float dist = D.magnitude;
   Vector3 pullDir = D.normalized; // short blue arrow from crate to player

   if(dist>50) thingToPull=null; // lose tracking if too far
   else if(dist>3) { // don't pull if too close

     // this is the same math to apply fake gravity. 10 = normal gravity
     float pullF = 10;

     // for fun, pull a little bit more if further away:
     // (so, random, optional junk):
     float pullForDist = (dist-3)/2.0f;
     if(pullForDist>20) pullForDist=20;
     pullF += pullForDist;

     // Now apply to pull force, using standard meters/sec converted
     //    into meters/frame:
     thingToPull.rigidbody.velocity += pullDir*(pullF * Time.deltaTime);
   }
 }

At the end, it just adds to velocity. Lots of guys prefer an AddForce. 10 might be a little high for the pull, but it helps to use numbers that are too big when testing, so you can see it's working.

What is the best way to Push or Pull an Object?

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