Swarming

New Feature: the player has a swarm that acts as a shield and can also be used to attack the enemy. I've been tasked to program this swarm behavior that has two states: protect and attack. In protect, the swarm will move around the player acting as a shield. The swarm is still vunerable to fire from both the enemy and the player, so if the player wished to fire at the enemy they risk the chance of destroying their shield. Attack is where each member of the swarm will latch onto the nearest enemy and attack them.

To implement this, I needed to brush up my boid skills. Boids are the simulation of a group of objects that act as a swarm or flock. They follow three simple rules: seperation, alignment, and cohesion. Seperation assures that each member of the swarm doesn't collide with another. Alignment is that they steer towards their target (which can be a leader or the average heading of the nearest flocks). Cohesion is where they steer to move towards the average position of the swarm. For this algorithm, the swarm doesn't act alone, they base their movements off a target creating a leader-follower paradigm. Boids are incredibly difficult to get right, and require fine-tuning to get right. Each rule produces a vector of where they must move, the sum of the vectors will produce their true trajectory. When creating the boids for this game, I ran into problems getting the boids to act in a fluid manner.

The big problem I ran into is when the swarm gets close to the player, then they should circle around the player acting as a shield. In order to get the trajectory to circle around the player, I figured it would just be the tangent of the cirlce they would make. The tangent is just the perpendicular line of the radius vector. The radius vector is easily obtained by the taking the difference between the two objects position vectors and rotating it 90 degrees to get the tangent. When I ran the code, the swarm would form a circle around the player, but they wouldn't move. Only playing with the degrees of rotation did I find that by rotating the radius vector by 45 degrees, they would move in an elliptical manner around the player which makes sense. This gets me the results I'm after, but I'm still confused why rotating 90 degrees doesn't get me the result I wanted. However, for prototype, its good enough and that's what I'll take. I need to move on to creating enemy classes (which I'll cover next week).