XNA Series – Modular AI

First Thing we need to do is to turn towards our target. Which may be an object, an agent or just some arbitrary location, like a waypoint on a track. Then no matter why we need to turn, we have a way to do a targeted turn. For the sake of flexibility, we will add a turnSpeed to the method so that depending on the call we can determine how fast we will turn.

public void TurnTowards(Vector2D target, float turnSpeed){
           Vector2 difference = target-position;
           float objectRotation = (float)Math.Atan2(difference.Y, difference.X);
           float deltaRotation = MathHelper.WrapAngle(objectRotation - rotation);
           rotation += MathHelper.Clamp(deltaRotation, -turnSpeed, turnSpeed);
}

and then we want to be able to move forward. So we create a move forward method. 

public void MoveForward(float speed)
       {
           position.X += (float)Math.Cos(rotation)*speed;
           position.Y += (float)Math.Sin(rotation)*speed;
       }

where we determine what to add to our current location by getting a unit circle offset from us based on our rotation and then multiply it by our speed.

Now that we have these 2 behaviors, we can construct a Seek method, where we turn towards our target at our turnspeed and then move towards our target using our speed.

public void Seek(Vector2 target, float speed, float turnSpeed)
{
    TurnTowards(target, turnSpeed);
    Move(speed);
}

So with this in our Update method if we had to GameObjects that implemented this Seek method we could call

a.Seek(b.position,2f, 0.02f);

To set our a object seeking b. But like I said, we don’t have to stop there, there are other things we can do with these methods. Check back next time and I’ll talk about how we can make our objects follow a path that we add to by mouse clicking. (Code for this and the next project will be in the next post).