GameMaker Studio: Enemy Chase AI Tutorial Video Lecture | Game Maker Tutorial: Build Games from Scratch - Game Development

I gave developers welcome back today
we're gonna be taking our first look
into the exciting world of enemy AI a
very very very popular topic on my
patreon spreadsheet and we're going to
be looking at it in the context of a
platform or at least to begin with and
today we're gonna be starting off super
super simple and we're going to be
building off of the stuff covered in my
state machines tutorial on how to create
an enemy that can have various different
states that are controlled by various
different conditions and can go between
idle and chasing you and like agroed and
like alert or patrolling and all those
different kinds of things but starting
off the day what we're going to do is
going to create something very simple
and I have it on screen here I'm just
going to create a some system whereby we
have our basic platformer and there's a
little red enemy dude over there who's
idle at the moment but when we step into
the dark blue sort of circle he becomes
angry and we'll chase after you until
you move outside of the lighter blue
circle on the outside which is this kind
of Dee aggro range where he just goes
back to idle again okay those circles
are just there to demonstrate the point
they're not really part of the code
we're going to be doing today but they
do demonstrate the kind of ranges so I
just threw them in there as a visual aid
so the starters off I've gone back and
use the code from my basic platform a
tutorial just a little green square I
can move around jump do all super basic
stuff the player doesn't and solve have
a state machine going for him because we
don't don't need that to work with
enemies the enemy itself will have a
state machine that we can control it's
different states at any given time but
we only really need a very basic player
to interact with all our enemies just to
kind of get the point across of what
we're trying to do I've set up a sprite
for our enemy ahead of time but other
than that I don't have anything here I
just have the bat salute barebone basics
of our platform so the first thing we
want to do before we get started making
our enemy is we're going to go to the
creation code of room 0 just this room
I've thrown together here and I'm doing
it in the creation code of this room but
you probably do this in some sort of
initialization object or script that you
recall we're over you know when you
typically initialize like your global
variables and things like that it's very
common to have like an initialize room
or an initialized object or script or
whatever that you call at the very
beginning of your game to just kind of
declare things that are common to the
whole game and that's where we would
also call our enumerators and we're
going to make an enumerator in the
creation code of this room just so it's
made at the very start of the game and
I'll call it enum e underscore state now
if you haven't watched my other tutorial
on state machines I highly recommend you
do it's not impossible for you to follow
along with this video if you haven't
watched that but it'll understand it'll
help you understand the sort of the
basics of what it is I'm doing with
things like States and what it means
like swap between states if you have a
basic understanding of code you might
just be able to follow along anyway and
kind of pick it up as you go along which
is great but I do highly recommend you
watch that video as well but what I'm
doing here is I'm creating an enumerator
for the different states our enemies can
be and just to make it easier for us to
control our enemy state at any given
time rather than setting a variable
called state to 0 or 1 or 2 we're going
to set it the East eight dot idle for
our it will state and chase for a chase
state ok those the only two states we're
going to have just to begin with anyone
have an idle state where an enemy just
chills out doesn't really do anything
will obey physics and everything but
otherwise doesn't do anything else and a
chase state but to allow them to chase
after the player when the meat gets too
close
ok doing this means instead of me having
the right state equals 1 for idle a in
our enemy object for example or state
equals 2 what I can now do is write
state equals e underscore state standing
for enemy enemy and score state just an
easy way of doing it
dot idle for example and then that will
probably I think it equals one anyway by
itself but it doesn't matter what number
it equals it's just a nicer way of
writing it so that we remember what
state is what and I can write state
equals e underscore state and dot chase
as well it's just an easier way easier
way to keep track of what state were in
rather than just using num
okay so now we've got those we've got
that enumerator so can go ahead and
close creation code for this room now
the reason we do that integration codes
because when you create an enumerator
it's it's global scope so it's still the
same was like when you create a global
variable and it lasts between rooms and
it's like full ecosystem enums are
constants okay they are fixed values
that are set to something at the
beginning in your game and they are that
way from that point on which you can't
change an enumerator if you set you can
actually set
Unum values to equal specific values so
I could have set so if I open that back
up I could even set like Idol to equal
50 for example and then whenever I type
e state dot Idol and essentially
referencing the number 50 forever
okay now useful things for constants
might be the night number PI for example
is a classic one in programming is very
classic constant this is just a way of
essentially creating your own in a easy
to refer to way especially when it's
like ooh they're grouped together in
something you create an enum I'm
creating a group of states and linked
it's a different number of states do you
see just an organizational tool more
than anything okay now we've created
that I'm going to go ahead and make our
enemy object so I'm going to make obj
underscore enemy classic naming
convention as always set the sprite to
be s PR and score enemy and we're going
to add the create event the first thing
yeah well the only thing I'm going to do
in here really is just initialize three
variables first of all the state
variable we need to declare that one and
then set that to e underscore state dot
a needle just to start our enemy off in
its idle state and then V SP 2 equals
zero and H SB T equals zero if you're
familiar with my platforming stuff
that's vertical speed and horizontal
speed because we're just going to use
exactly the same collision code that our
player uses we're literally just going
to cut and paste it later so we're going
to be using the same vertical speed and
horizontal speed variables that we
always use okay so that's all we need
for the create event and then go ahead
and add the step event now before when
we when I was demonstrating state
machines I demonstrated it using like
everything split into different scripts
we're not actually going to split
everything into different scripts this
time we're just going to actually keep
the code contained within the switch
statement for switching third for
checking what state were in just because
there's not really a lot of code in this
specific tutorial and it'll just keep it
easier and more it just be clearer to
see it on the screen rather than
splitting it off into different scripts
really just the sake of the video you
can split it off into different scripts
if you like and we'll probably do that
later on as this gets more complicated
but for this video we're just going to
keep everything in one place in which
and we're still using a state machine as
you will see so I'm going to make switch
state okay so I'm creating a switch for
our current state ok our variable state
at the moment as we know is set to e
underscore state idle or the set in the
create event and my creating switch time
we're going to check what state equals
and we're going to do something based on
if it equals a number of different
things number of different cases you
might say so the first case will be if
state equals e underscore state dot idle
which it does is what it equals at the
beginning of the game open another Kara
yeah another cat another pair of braces
and in here I'm going to say horizontal
speed is going to be zero because we're
moving into X bar idle a VSP our
vertical speed is going to equal and
I'll just do a quick mean thing to do
gravity I guess so min so the smallest
number out of either seven I guess it
the highest we want to move downwards
and VSP plus not 0.05 okay so it'll add
no point no five to a vertical speed
every frame just like refer you might
want to do that as a graph variable or
something I'm just keeping this as
simple as possible for now rather than
just hard coding numbers in but um yeah
that's just really simple way of doing
gravity with a maximum speed now and
then all we need to do that all really
we ever want to do in our idle state
other than obviously calculating
movement which will do late calculating
collisions and stuff which we can do
later separate from a state checking
really because collisions can generally
always be on for our me object I don't
think there's really many conditions and
we might move them into the state
machine later but right now we're going
to have it exists outside of X just we
don't need it to exist inside at the
moment so the only other thing
our state our Iowa state needs as a way
to move from the idle state to the chase
state so I'm going to say if distance to
object obj I'm Scott player less than 96
state equals e underscore state dot
chase let me go on okay simple as out
and I forgot to add bracket up there
close that always make sure you close
your back it's interesting I don't know
if I point those out before but if you
highlight brackets like that or if you
click near brackets you see it comes up
in blue and highlights the dealer
closing one so you can see which should
be a brackets are close properly in song
which can help you fix done the stakes
every now and again okay so to finish
off that case we write break there so if
it is if that case does run it'll run
all this code and then it'll break which
ends the switch statement okay um so but
if that's not the case if we no longer
in the idle state because we're it quite
well within 96 pixels of the player that
means we're going to be in state dot
chase okay
oh it also to proper colon at the end of
these case statements okay not a
semicolon which is an important note I
don't know what resolution you're
necessarily watching the video in but in
case you can't it's very important that
you put a proper code on there not a
semicolon semicolon will end the line
whereas the colon is telling us what we
want to do afterwards okay right
semicolons when you want to end the line
another common mistake I see people make
this is kind of off topic but it's like
when they do an if statement breaking
off and floss things buying semicolon
there which you never want to do you
never want to put a semicolon at the end
of the if statement before the commands
from that statement cuz you're telling
gate maker but the line is ended anyway
sorry about that I was minor saying um
just something I've noticed a lot of
people doing lately in the comments and
so on anyway so if we are in our chase
state then what we're going to do is
we're going to decide on a direction as
long as and dir equals a sign obj
underscore player dot x-
okay so I'm going to take the
x-coordinate of our player and subtract
a the x-coordinate of this enemy and
that'll be negative if the player is on
the left of us and it'll be a positive
number if the player is on the right of
us meaning if we get the sign from that
we'll get +1 if we want to move to the
right and negative 1 if we want to move
to the left okay so having note now that
we know that I'm just going to say HS be
our horizontal speed equals dir times 2
or whatever you want your movement speed
to be in pixels I'm just doing something
that's slower than the player just so we
can kind of outrun in then and stray the
whole state thing working the SP we're
going to do the exact same kind of
gravity thing again plug that in there
and then all we need here again is a way
to change between states and go back to
the idle state so I'm gonna say if
distance to object obj Scot player
greater than 1 to 8 state equals on e on
the score state dot needle semicolon and
then a break there as well to break that
specific a switch case okay and I could
go on adding like more cases and things
the different states that our enemy
might be in or I might break these off
into scripts that can call so if they
start to get larger and like our total
read on one page I might split them up
into different scripts and so on but for
now just these two things are all we
want just to kind of get the basics of
this on the go okay so that's already
worked out what are HSB and VSP are
going to be based on what state we're in
so now we just need the collide move
code which we can just Nick from our
player objects I'm just going to go into
the step event of our player just down
here the horizontal and vertical
collision no it's exactly the same code
that's how HSB and VSP work just this
little chunk now it's a very useful just
chunk of code that you can just kind of
fling around and it'll it'll just work
because it's a HSB MVS beer that's just
like checking to see whether or not
our position plus HSB or plus VSP is
going to be a wall and if there is a
wall we move to it and we stop and then
we commit to moving however much we
wanted to move in those directions it's
really simple okay
that's really all it is that's that's
all ye for this now so I'm go ahead and
close that close this and open up rooms
they're on just actually plunk when
these objects in the room plonk him like
settled and set up there I only raised
the platform a little just so you can
kind of see the gravity working and you
see them falling just like a player does
anyway and if I get close enough to him
he'll start chasing me and if I move far
enough away he'll stop okay so simple as
that really
and I demonstrated it with the radius
thing at the beginning but I'm going to
repeat that code now that's the basics
of like how you can start to begin start
to begin how you can start to create
like a basic enemy AI um this specific
thing might be more useful in the
context of like top-down things I
suppose but we'll get into more stuff
that's like kind of platforming specific
getting our enemy to maybe jump when he
needs to and do different things like
that later on but this is just I just
want to kind of get the foundation
across of like what you kind of need
what direction you need to go in with
your code to kind of get this stuff to
work okay I hope that was useful here
you guys any suggestions leave them in
the comments below um thank you all for
watching liking subscribing sharing all
those awesome things you do all the time
continue to do and I'll catch you guys
next time thanks guys
you