GameMaker: State Machine Tutorial Video Lecture | Game Maker Tutorial: Build Games from Scratch - Game Development

hello game developers and welcome back I
hope you're sitting comfortably because
today we're going to be covering
something very important we're going to
be looking at the concept of finite
state machines and how you can use them
in game maker to do lots of awesome
exciting things now finite state machine
is a very complex sounding term it's
actually not really that complicated of
a thing although it is quite difficult
to kind of explain and it's actually
really not all that complex of a concept
really all it is is just using the idea
of an object being in a given state and
Qi being able to change its state in
order to control how your game works
it's really in terms of how we're going
to be using it in game maker all you
really have to think of it as it's a way
of organizing your code in a way that
makes making much more complex games
much more manageable and possible to do
so let's take a look at an example of
say a platformer game that doesn't use
state machines here I've set up a
platformer game just using the same sort
of code that we've used in like my
previous tutorials if you follow it
along with any of my platforming stuff
how it works we have a player object
who's established just a couple of
little variables and then has this step
event okay so who has it gets a the
player gets all the inputs at the start
of a frame we perform some calculations
based on those inputs on where we want
to move and then we check to see if
there's going to be a collision in the
place that we want to move and we move
towards that place if there isn't we
move as close as possible to the wall
and stop if the if we're about to
collide with something okay simple like
30 lines of code and it's manageable
while our game is that simple but now
say that we want to add ladders into the
game okay so I'll set up these ladders
around here now normally what we would
do in that situation is change this code
to something more like this code okay so
what I've done in this code is I've
created a new variable called ladder
that checks whether or not we're on
ladder and if we're not on a ladder then
we do our regular movement and if we are
on a ladder then we do a specific type
of movement like going just going up and
down and checking to see whether or not
we press a key to detach from the ladder
and so on so forth and if we're not on
the ladder we check to see if we're
touching a ladder and if we are touching
ladder and pressing up then we attach to
the ladder now this is an OK way of
doing things while you've got a very
small number of kind of mechanics going
on in your game you play if I just
wanted a platform with just ladders and
then this would be fine and there's not
really any problem in doing this however
if I wanted to start doing more and more
complex things say I had ropes that I
wanted to swing off of or like NPCs to
talk to or different kind of states you
might see where I'm going with this that
my player needs to be in at any given
time it gets more and more complex and
more and more unmanageable to write code
just using like the odd variable to
check whether or not you're doing
something because then you have to wrap
everything you do in different if
statements already here I have to wrap
all of my movement code my normal
movement code into this if statement to
check to see whether on what we're on a
ladder and if we're not on a ladder then
do this and all of the rest of the code
of still gets run regardless and so if
anything and letting my collision needed
to change based on whether or not I was
on a ladder I would have to wrap that an
if statement as well and so on so forth
and it gets really really complex and
manageable as you start to wrap more and
more things if not on a ladder if not
talking to NPC if this if that if the
other you know what I mean
the problem is we're only looking at our
players logic as being a single step
event ok this single event the single
big chunk of code that's executed every
single frame of the game so whenever we
want to do anything we're always
checking against every other possibility
impossible kind of state the player
might be in or we want to do instead of
having just this one step event that
contains all of the possibilities for
this character and has to juggle between
all these different if statements just
based on what our character is doing at
any given time what we want to do is
divide that into a different state
that our player can be in at any given
time and then when each frame comes
around instead of running one huge chain
of logic we run one specific chain of
logic depending on what state our
character is currently in you can have
states for everything so you can have
states for talking to an NPC for being
in the air as opposed to being on the
ground for swimming for climbing for
anything you can really imagine and what
this does is it means that we own we get
to choose specifically what code is run
we're without having to divide
everything into lots of different if
statements and then when all we need to
do is define the conditions for changing
between those states inside the states
themselves if that explanation made no
sense whatsoever let's take a look at
what this exact game our little dude
running around climbing on ladders would
look like if it used a state machine so
why I have here is a copy of the exact
same game just has a little dude can run
around can climb on time on ladders only
this time we're using a state machine
and instead of having a single step
event I've divided this all the code
that would go into this step event into
a number of different scripts but how do
I decide which script a call well when I
initialize the game in the first place
in room 0 just stuck it in the creation
code I create an enumerator for States
now if you've never used an enumerator
before what an enumerator is is
essentially just another way of creating
a constant variable a variable that will
never change
but giving it a more English readable
name that's really all that they're
there for so I've created one called
States and what that means is I can
refer to States dot normal that will
always equal I think 0 or I think 1 it
doesn't really matter just a number
that's different from States dot ladder
as I've defined here which would be I
think 2 in this circumstance doesn't
really matter the number is not relevant
the fact is it's just a different number
that's given a different name by doing
that that just allows me to refer to
instead of just having to set state
equal 1 or state equal 2 I can say state
equal States normal or state equal
states ladder
just so it's more readable to me and I
don't have to remember what number is
what state so after creating that
enumerator I've gone into the player
object and in the create event I set my
state to be state equals states normal
now in the step event for player where
we would normally run all of our our
huge chain of logic that would just be
like Oh first of all getting our inputs
then checking all of our movement and
checking on whether or not we're on a
ladder and so on to both then doing
collision while you body bar what I do
is I run a single state that a single
switch statement based on our current
state now our state is set to states
normal so by default it'll run this
first case which is case States not
normal it'll run this script script
player underscore normal break and if
our state is ladder it'll run this
script instead
s.coups s ER and the score player
underscore ladder so what actually
exists in those states into the scripts
even sir if I go into SCR underscore
Player underscore normal this is what
happens
I've even divided the inputs into
separate scripts as well and the
collision section which means that we
can decide in these states whether or
not we actually want to call collision
or whether or not we even need to get
the players input in the first place
without having to just copy and paste
huge chunks of code around we can just
call the script or not so we're going to
SCR underscore get inputs you can see
it's just that thing that was at the top
of our step then before get input key
left equal keyboard check left and so on
so forth all just called at the start of
SCR underscore player underscore normal
so this is like a standard step event
this is basically everything that would
happen normally in our step event
without any of the ladder stuff okay
does all of our normal movement stuff
but then importantly oh and also what
does all of our collision stuff at the
end just like how it normally would but
importantly in the middle here it does
this thing where it says or if I'm
colliding with a ladder and I'm pressing
up or down then set my HSB and vs b to 0
set my speeds to be 0 and then set state
the equal states dot ladder okay and
then it will do all its collision and
everything like that but then the next
time around the the step event happens
it's going to come back into here run
this run this switch again and then this
time it's going to run SCR on the score
player on to score ladder meaning it's
going to skip all of the stuff from the
previous step event it's going to ignore
all of it and it's just going to go
straight to s you're on just go play on
the score ladder now this is just a
different version of our step event so
basically I'm just sending the player to
a different step event instead of just
having one we've just divided it into
multiples that can happen depending on
what state were in and in this one I'm
going to gang our inputs again but this
time I'm ignoring all the movement
calculations stuff from before and I
don't have to wrap it in an if statement
or anything like that because we already
know that we're on a ladder because
we're in the ladder state so I do the
movement that's only moving us up and
down ignore any ability to move left and
right you can't move left or right on a
ladder right and then just said or if
key jump or if I'm not touching the line
anymore because I climbed off the top
cell speeds to be 0 again and set state
back to state dot normal so I have a way
to transition between both states very
easily and then when I'm back in states
normal it runs our normal step event
again and of course at the bottom I run
our collision code which I've just
bundled into a script rather than just
have in copied and paste it into each
one since I know it's going to be the
same in most states
okay now this results in exactly the
same kind of game that we would have if
we coded it how we used to how I've
coded it and want my platform our
tutorials but by using a state machine
suddenly we have a ton more power and a
ton more freedom in terms of how we're
organizing our code to be able to do all
different kinds of complex states and
much more easily and much more
manageable without running into loads of
problems like having a triple check
everything like oh if this and if that
if the other because all of that stuff
is handled by the fact that when we're
in the latter event we only have to
worry about everything the player needs
to know when they're on a ladder which
is that they can move up and down right
they don't need to do it they don't need
to need to register the left and right
arrow keys because that they don't don't
mean anything you know I don't have to
like wrap the section the controls
horizontal movement
oh don't do this if you're on a ladder
because we don't need to were already in
that stepper gun okay
now this isn't just relevant to
platformer games this is relevant to
basically any kind of game you can
create okay you can have States view
different enemies okay this is why I'm
covering this tutorial so I'm going to
platform or AI and doing enemy AI stuff
okay is that you can create enemies that
are like have an alert state or an aggro
state or like our Idol or a walking
around and stuff like that basically
anything you can imagine that any object
you can imagine that has complex
behavior based on link Oh being in a
different state or being in a different
conditions you can apply this technique
and it's a really really solid way of
organizing your code and basically will
empower you to be able to make much more
complex games without your code just
becoming a totally unmanageable mess
they have it I hope that made any kind
of sense that's how you state machines
in game maker and I hope I really really
hope you were able to understand it make
sense fix it's really really useful
thing to know I hope you enjoyed that
leave any comments or suggestions below
and I'll catch you guys next time thanks
for watching see you guys
you