THREE.raycaster : Possible to use it for enemy Ai? - three.js

Question

I've just started learning THREE and have been messing about with the three.js example of controllable MD2 characters to try and fashion it into a 3rd person shooter kind of game. I've been trying to write a simple algorithm for the enemy characters and I'm pretty sure that ray-casting would be ideal.The whole idea is that the enemies should stop rotating once they're facing the player. But Here's the problem that's giving me sleepless nights! :
Let's say, the enemy object is the origin for the ray caster ray. No matter what direction I set for the direction of that ray ( even, for example (1,0,0) - the positive x-axis), the ray's direction is always pointing towards the center of the scene!!!
Please help! haven't been able to find any Example online for this kind of use for the ray caster (apart from collision detection which I really don't need at the moment).

Answer 1

If all you want is for enemies to stop rotating when they are looking at the player, I would consider just checking the direction between them, as it's a lot faster than casting a ray to see if it intersects:
// Assuming `enemy` is a THREE.Mesh
var targetDir = enemy.position.clone().sub(player.position).normalize();
var currentDir = (new THREE.Vector3()).applyMatrix4(enemy.matrixWorld).sub(enemy.position).normalize();
var amountToRotate = currentDir.sub(targetDir);
var offset = amountToRotate.length();
Then rotate each axis no more than the value for that axis in amountToRotate if offset is greater than some threshold.
That said, here is how you use a Raycaster, given the variables above:
var raycaster = new THREE.Raycaster(enemy.position, targetDir);
var intersections = raycaster.intersectObject(player);
Note that if you are running any of the above code in an animation loop, it will create a lot of garbage collection churn because you are constantly creating a bunch of new objects and then immediately throwing them away. A better pattern, which is used a lot in the library itself, is to initialize objects once, copy values to them if you need to, and then use those copies for computation. For example, you could create a function to do your raycasting for you like this:
var isEnemyLookingAtPlayer = (function() {
var raycaster = new THREE.Raycaster();
var pos = new THREE.Vector3();
return function(enemy) {
raycaster.ray.origin.copy(enemy.position);
raycaster.ray.direction.copy(pos.copy(enemy.position).sub(player.position).normalize());
return !!raycaster.intersectObject(player).length;
};
})();