Scripting a prefab to duplicate itself within a fixed radius

Question

I'm trying to do something very simple with JavaScript, but cobbling together a script from the samples in the reference documentation isn't working for me at all.

I have a cylinder prefab, and all I want it to do is duplicate itself in a random position, within a certain radius. That cylinder would then also duplicate itself, etc, into infinity. Idealy, I'd also like to be able to adjust the number of duplicates that are instantiated.

I guess the first thing to do is to make the cylinder duplicate itself at all. This is all I have so far:

 var cylinder : GameObject;

function Update () {

 yield WaitForSeconds (3);
 cylinder = Instantiate(transform.position, transform.rotation);

}

Basically, I don't understand the syntax for 'Instantiate'.

Answer 1

Here's how you can work with instantiation:

 var myPrefab : GameObject;
 Instantiate(myPrefab, Vector3.zero, Quaternion.identity);

In the script above we instantiate a predefined object which is set to the variable myPrefab in the Inspector. The position is 0 on world-XYZ and the rotation is unchanged.

 var myPrefab : GameObject;
 var myGameObject = Instantiate(myPrefab, Vector3.zero, Quaternion.identity);

In this script we reference the prefab instantiation to myGameObject. The object will still instantiate as normal but will be able to be easily modified directly and referenced to. For instance:

 myGameObject.name = "Instantiated Prefab";

You always define like this: Instantiate(the object to spawn, the position, the rotation);

To instantiate something at a random position try this out:

 var rndX : int = Random.Range(-10, 10);
 var rndY : int = Random.Range(-10, 10);
 var rndZ : int = Random.Range(-10, 10);
 Instantiate(myPrefab, transform.position+Vector3(rndX, rndY, rndZ), Quaternion.identity);

Keep in mind that transform.position means the scripts current transform's position in world-space.

Answer 2

Working version of your code, because explaining it is harder than demonstrating-

var circleRadius : float; var waitTime : float;

function Start()
{
    StartCoroutine(WaitAndDuplicate());
}

function WaitAndDuplicate()
{
    while(true)
    {
        yield WaitForSeconds(waitTime);
        var randomOffset : Vector3 = Random.insideUnitCircle * circleRadius;
        randomOffset = Vector3(randomOffset.x, randomOffset.z, randomOffset.y);
        Instantiate(gameObject, transform.position + randomOffset, transform.rotation);
    }
}

Add this script to the gameObject you want turned into a serious grey-goo scenario, and watch your GPU melt!

Instantiate takes 3 things- an original, a location, and a rotation. It copies the original, and puts it where you tell it to with the other two parts! As for the circle thing, Random.insideUnitCircle is a nice way of making random offsets in 2D- I had to rotate it back to the normal plane (in which x and z are the main coordinates and y is height, a decision I may never understand), so that it would spread out instead of up and down.

If you want your object to spawn anywhere in space (not just in a circle), replace

Random.insideUnitCircle

with

Random.insideUnitSphere

still multiplying this with the desired maximum radius (so that it is not just a number between Vector3.zero and one in any direction).

Scripting a prefab to duplicate itself within a fixed radius

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