How to make enemy AI move side to side on platform

Phaser 3
1

I’m trying to make a simple enemy AI where the enemy (animated sprite) moves side to side on the ground but gets faster over time, capping at a max speed .

I’ve followed the official “get started with your first game” tutorial for the platformer and I’m stuck on how to make my enemy move on its own (without player input).

2

Something like

if (enemy.x < LEFT && enemy.body.velocity.x < 0) {
  enemy.setVelocityX(speed);
  if (speed < MAX) speed += INC;
} else if (enemy.x > RIGHT && enemy.body.velocity.x > 0) {
  enemy.setVelocityX(-speed);
  if (speed < MAX) speed += INC;
}
1 Like
3

Thanks for the logic samme! That should be able to do it.

A few questions, would I put this code inside the update () or the create()?

Also, how can I get an animation to play on the enemy while it moves? I am currently using the following method to give the enemy animations. I need them to play whenever the enemy moves though:

“this.anims.create({
key: ‘left’,
frames: this.anims.generateFrameNumbers(‘dude’, { start: 0, end: 3 }),
frameRate: 10,
repeat: -1
});”

4

Put it in update() because it needs to run each frame.

Animations can be something like

if (enemy.body.velocity.x < 0) {
  enemy.anims.play('left', true);
} else if (enemy.body.velocity.x > 0) {
  enemy.anims.play('right', true);
} else {
  player.anims.play('turn');
}
1 Like
5

Ok perfect thanks.

One thing I’ve noticed though is that your solution doesn’t work at 60 fps but works fine at 30.

6

Doesn’t work how?

7

Basically the enemy won’t move. I ended up simplifying the logic by just saying (after giving the enemy some initial velocity):

function update() { 
//START ENEMY LOGIC
if (baddie.x == RIGHT){
  baddie.setVelocityX(-baddiespeed);
  if (baddiespeed < MAXSPEED){
    baddiespeed += baddiespeedstep;
  } 
}
else if (baddie.x == LEFT){
  baddie.setVelocityX(baddiespeed);
  if (baddiespeed < MAXSPEED){
    baddiespeed += baddiespeedstep;
  } 
}

}

8

Mine doesn’t prevent the enemy from stopping, but if you want that you can do

if (enemy.x < LEFT && enemy.body.velocity.x <= 0) {
  enemy.setVelocityX(speed); // etc.
} else if (enemy.x > RIGHT && enemy.body.velocity.x >= 0) {
  enemy.setVelocityX(-speed); // etc.
}
1 Like