The Sentry is your basic cannon fodder enemy. It can be in any of three states:
private int state;
private final int MOVING_TO_PLAYER = 0;
private final int SHOOTING = 1;
private final int COOLDOWN = 2;
When in the MOVING_TO_PLAYER state, the Sentry will simply try to get closer to the player. Once it reaches a certain proximity, it will move on to the SHOOTING state. Here, it will stop moving and fire a bullet. Then it will move into the COOLDOWN state where it will wait for some time. I have to find the edges in this FSM, meaning I have to find which states can transition to which other states.
MOVING_TO_PLAYER transitions to SHOOTING, SHOOTING transitions to COOLDOWN, and COOLDOWN can either go back to MOVING_TO_PLAYER or SHOOTING. So here's our list of edges for the graph:
MOVING_TO_PLAYER --> SHOOTING : if within range
SHOOTING --> COOLDOWN
COOLDOWN --> MOVING_TO_PLAYER : if out of range
COOLDOWN --> SHOOTING : if within range
Now coding the Sentry's AI is simple.
if(state == MOVING_TO_PLAYER) {
if(player.getx() < x) {
left = true;
right = false;
}
else if(player.getx() > x) {
left = false;
right = true;
}
if(Math.abs(player.getx() - x) < range) {
state == SHOOTING;
}
}
else if(state == SHOOTING) {
left = right = false;
GameObjectFactory.createBullet(...);
state = COOLDOWN;
}
else if(state == COOLDOWN) {
timer++;
if(timer > time) {
timer = 0;
if(Math.abs(player.getx() - x) < range) {
state = SHOOTING;
}
else {
state = MOVING_TO_PLAYER;
}
}
}
This is an easy way to give your NPCs some behavior. State based AI is simple to implement and can be effective.
