How to create a heat seeker

Questions & Answers
1

I am making a 2D tower defense game with unity. I have seen heat seeker type rockets in Kindom Rush that moves around the screen and goes to the target. Really nice effect.

Can anyone give me some direction how to create this type of movement?

2

Hey could not really find the rocket you are mentioning in Kingdom Rush.
Nonetheless we can try.

So first your rocket has a starting point, either a rocket launcher or outside the screen.
Then it has a target point. For now let’s consider the target point to be where you clicked.

So we need to move the object from start to target. You can use Translate or Rigidbody, this is up to you.

Now the purpose is to seek for “heat”, I would think this is mainly a way to make the difference between a character and the environment.
In our case, we will consider that you have a list of potential target, if this is based on heat, then a fire will be on that list, which allows the player to lure the rocket for instance.

You could at a certain frequency, check for the closest item from the list, you could use a sorted list to spare the hassle of ordering.
Then, you check if the distance between the rocket and the closest item is small enough to be considered. This range is up to you. If within range, then you change the target for that new target and translate your rocket towards that new target.

At first it will not look good because your rocket will suddenly change direction so you can work it out with some force principle to get the movement in a curve.

3

It appears from the brief video glimpses, that the projectile heads straight up, levels off at some arbitrary vector than seeks the target. Here is a bit of sample code. To test start with a new scene. Put this script on a game object with a Rigidbody component, with gravity turned off, and with a ‘y’ value of zero. In the inspector initialize ‘target’ to another object in the scene and hit play:

#pragma strict

var target : Transform;
var upHeight = 0.5;
var turnSpeed = 100.0; // Degrees per second

private var initialDirection = Vector3.forward;
private var velocity = 3.0;

function Start() {
	initialDirection = Quaternion.AngleAxis(Random.Range(0.0, 360.0), Vector3.up) * initialDirection;
	transform.rotation = Quaternion.LookRotation(Vector3.up);
	rigidbody.velocity = Vector3.up * velocity;
	
	// Head up for a set distance
	while (transform.position.y < upHeight) {
		yield;
	}
	
	// Level off to an arbitrary vector
	var q = Quaternion.LookRotation(initialDirection);
	while (transform.rotation != q) {
		transform.rotation = Quaternion.RotateTowards(transform.rotation, q, Time.deltaTime * turnSpeed);
		rigidbody.velocity = transform.forward * velocity;
		yield; 
	}
	
	// Seek the target
	q = Quaternion.LookRotation(target.position - transform.position);
	while (transform.rotation != q) {
		rigidbody.velocity = transform.forward * velocity;
		transform.rotation = Quaternion.RotateTowards(transform.rotation, q, Time.deltaTime * turnSpeed);
		q = Quaternion.LookRotation(target.position - transform.position);
		yield; 
	}	
}

function OnCollisionEnter() {
	Debug.Log("Boom");
	Destroy(gameObject);
}

Note this code assumes an object in which the front is facing positive ‘z’ when the rotation is (0,0,0) (or an object like a sphere that has no explicit front).