How To avoid random spawn to spawn at previously spawned object position so that they do not overlap

Questions & Answers
1

This code randomly spawns objects and then destroy them after some wait. what I want to do is to make sure the random spawned object is not spawned at previously spawned object such as it spawns above it. How may I do that?

public IEnumerator Spawn () {
    		yield return new WaitForSeconds (2.0f);
    		counting = true;
    		while (timeLeft > 0 && gameOver==false)
    		{
    			GameObject ball = balls [Random.Range (0, balls.Length)];
    
    			Vector3 spawnPosition = new Vector3 ( Random.Range (-maxWidth, maxWidth), Random.Range (-maxHeight, maxHeight), 0.0f);
    
    			Quaternion spawnRotation = Quaternion.identity;
    
    			GameObject ballClone = (GameObject) Instantiate (ball, spawnPosition, spawnRotation);
    			StartCoroutine (DestroyAfterWait (ballClone));
    			yield return new WaitForSeconds (Random.Range (1.0f, 2.0f));
    
    		}
    		//yield return new WaitForSeconds (2.0f);
    		GameOver ();
    
    	
    	}
2

Put the Balls in a List and check if the spawnPosition is closer to it than the size of the ball.


    using System.Collections.Generic;
    private List<GameObject> spawnedBalls = new List<GameObject>();
    
    public IEnumerator Spawn () {
    yield return new WaitForSeconds (2.0f);
    counting = true;
    while (timeLeft > 0 && gameOver==false)
    {
    
    MakeClean();
    Vector spawnPosition = GetSpawnPosition();
    
    if(spawnPosition != Vector3.zero)
    {
    	Quaternion spawnRotation = Quaternion.identity;
    	GameObject ballClone = (GameObject) Instantiate (ball, spawnPosition, spawnRotation);
    	spawnedPositions.Add(ballClone);
    
    	StartCoroutine (DestroyAfterWait (ballClone));
    }
    
    yield return new WaitForSeconds (Random.Range (1.0f, 2.0f));
    }
    //yield return new WaitForSeconds (2.0f);
    GameOver ();
    }
    
    
    void MakeClean()
    {
    	while(!CleanUpList())
    	{
    		CleanUpList();
    	}
    }
    
    bool CleanUpList()
    {
    	foreach(GameObject ball in spawnedBalls)
    	{
    		if(ball != null)
    			continue;
    		else
    		{
    			spawnedBalls.Remove(ball);
    			return false;
    		}
    	}
    	return true;
    }
    
    Vector3 GetSpawnPosition()
    {
    	GameObject ball = balls [Random.Range (0, balls.Length)];
    	Vector3 spawnPosition = new Vector3 ( Random.Range (-maxWidth, maxWidth), Random.Range (-maxHeight, maxHeight), 0.0f);
    	
    	float sizeOfBall = 1.0f;
    	foreach(GameObject ball in spawnedBalls)
    	{
    		if(Vector3.Distance(ball.transform.position, spawnPosition) <= sizeOfBall)
    		{
    			return Vector3.zero;
    		}
    	}
    	
    	return spawnPosition;
    }

Code is untested but i hope you get the idea. I noticed comparing Vectors is much faster than using Physics in large projects so i started to use this approach more often in my projects. (That was in Unity4, not sure about U5). So GetSpawnPosition either returns Vector3.zero or if the position was fine a valid Vector3.