Generating sprite objects and destroying them after they are out of bounds

[sweptica]

I have a fixed orthographic camera for my 2D game with a scrolling background and I want to spawn my sprites randomly outside the camera bounds and have them move inside and out of the camera and get destroyed. Currently I’m using the script below but its generating a lot of sprites within the camera bounds and not working as intended. I cant point out where i’m going wrong?

[33778-screenshot+2014-10-17+01.03.22.jpg|33778]

Random Sprite Generation Code:

	public Vector2 speed = new Vector2(10,10);

	//Moving direction
	public Vector2 direction = new Vector2(-1,0);

	private Vector2 movement;

	public int numToSpawn;

	private Vector3 position;

	float CameraHeight;

	float CameraWidth;

	int spawned = 0;

	public bool spawn;

	void Start () 
	{

		CameraHeight = Camera.main.camera.orthographicSize;

		CameraWidth = CameraHeight * Screen.width/Screen.height;

	}

	void Update () 
	{
 
		movement = new Vector2(speed.x * direction.x, speed.y * direction.y);

		if(spawn)
		{
			position = new Vector3(Random.Range(-0.5f,0), Random.Range(0f,CameraHeight),0f);
			Instantiate(gameObject,position,transform.rotation);
			spawned++;
		}	
	}

	void FixedUpdate()
	{
		rigidbody2D.velocity = movement;

	}


	//Checking Collision property
	void OnTriggerEnter2D(Collider2D col)
	{
		EffectsScript effects =  gameObject.GetComponent<EffectsScript>();
		if(effects.IsColorise)
		{
			effects.RandomColorise();
			
		}
		if(effects.IsMelody)
		{
			effects.Melody();
		}
	}

[DocMcShot]

@sweptica

I think the reason you are getting a bunch of object created is because your instantiating your game objects in the Update() method. Consider making a spawn function and then Invoking it in your start method. Something like:

void Spawn()
{
    if(spawn)
    {
    Instantiate(gameObject,spawnPosition,transform.rotation);
    spawned++;
    }
    Invoke("Spawn", Random.Range(1, 5);
}

Then in your start method call your spawn function.

void Start()
{
//Other stuff you want to do in your start method.

Spawn();
}

As far as a workable solution for spawning the stuff off the screen, I would use some of the functions of the Camera class. Personally I would use ViewportToWorldPoint(). I made some helper functions for a game that found the four corners of the screen, like this:

Vector3 lowerLeftCorner;
Vector3 lowerRightCornter;
Vector3 upperLeftCorner;
Vector3 upperRightCorner;

lowerLeftCorner = mainCam.ViewportToWorldPoint(new Vector3(0f, 0f, 0f));
lowerRightCorner = mainCam.ViewportToWorldPoint(new Vector3(1f, 0f, 0f));
upperLeftCorner = mainCam.ViewportToWorldPoint(new Vector3(0f,1f,0f));
upperLeftCorner = mainCam.ViewportToWorldPoint(new Vector3(1f,1f,0f));

Then to instantiate the gameObject off the screen I did this (I only instantiated gameObjects on the left and bottom of the screen):

//Gets half of the gameObject's width and height so that it can be used to control spawning
    float objWidthOffset = gameObject.renderer.bounds.extents.x;
    float objHeightOffset = gameObject.renderer.bounds.extents.y;

//Spawn object right below bottom of screen.
    Vector3 spawnPosition = new Vector3 (Random.Range(lowerLeftCorner.x + objWidthOffset, lowerRightCorner.x - objWidthOffset), lowerLeftCorner.y - objHeightOffset, 0.0f);

Then you just use the spawnPosition variable in your Instantiate function. Hopefully this helps some. If not, feel free to ask questions