0:00:01.750,0:00:04.910
This is Game Maker's Toolkit, I'm Mark Brown.

0:00:04.910,0:00:10.250
If there's one game I've played more than[br]any other, it's Spelunky - a viciously hard

0:00:10.250,0:00:16.020
platformer that takes the side-scrolling thrills[br]of games like Mario and Castlevania, but snatches

0:00:16.020,0:00:21.670
away your ability to learn the level layouts[br]and enemy spawns by mixing up the map, every

0:00:21.670,0:00:22.630
time you die.

0:00:22.630,0:00:27.670
But what makes Spelunky so special is that[br]even though the levels are randomly cobbled

0:00:27.670,0:00:33.440
together, they're always fair and enjoyable.[br]Even after 1000 runs, I've never stumbled

0:00:33.440,0:00:35.460
upon a crappy level.

0:00:35.460,0:00:40.230
They just don't feel like the product of an[br]algorithm - which, in some games, spits out

0:00:40.230,0:00:46.070
levels that are messy and unfocused and full[br]of dead ends. In Spelunky, these procedurally

0:00:46.070,0:00:52.360
made stages are as sharp and satisfying[br]as the levels in some hand-crafted games.

0:00:52.360,0:00:58.129
And that's because creator Derek Yu struck[br]the perfect balance between random and authored

0:00:58.129,0:00:59.879
content.

0:00:59.879,0:01:04.989
He explains how he pulled it off in his new[br]book, titled Spelunky, which I highly recommend

0:01:04.989,0:01:10.299
to anyone interested in design. But, while you're[br]waiting for it to come in the post, I'm going to use

0:01:10.299,0:01:16.659
some info in the book to explain how a Spelunky[br]level is half generated, and half designed.

0:01:16.659,0:01:21.189
And then we'll look at why it was so important[br]for the game to have an infinite supply of

0:01:21.189,0:01:22.110
unique levels.

0:01:22.110,0:01:26.520
Though, first, we need to go back to where[br]it all began - because while you might think

0:01:26.520,0:01:31.820
of Spelunky as looking like this, it actually[br]started life as a free, pixel art game, now

0:01:31.820,0:01:34.160
named Spelunky Classic.

0:01:36.840,0:01:42.060
So, every level in Spelunky is generated by[br]a script that starts with the same basic shape

0:01:42.060,0:01:46.290
and size: 16 rooms in a boxy 4 by 4 grid.

0:01:46.290,0:01:51.159
The first thing the script does is pick a[br]random room from the top row, and makes this

0:01:51.159,0:01:51.799
the entrance.

0:01:51.799,0:01:57.720
It will then randomly place a room to the[br]left, right, or beneath this room. This process

0:01:57.720,0:02:01.990
is repeated from room to room - and if the[br]path hits the edge of the level, it also goes

0:02:01.990,0:02:06.590
down - until we get to the lowest level; when[br]it tries to go down once more, an exit is

0:02:06.590,0:02:07.619
made.

0:02:07.619,0:02:11.150
Every room on this main path has openings[br]to the left and right, but rooms where the

0:02:11.150,0:02:15.879
path drops also have exits on the bottom,[br]while the rooms you drop into are given exits

0:02:15.879,0:02:17.000
at the top.

0:02:17.000,0:02:21.030
What you end up with is a guaranteed path[br]through the level that you'll always be able

0:02:21.030,0:02:26.340
to get through without using ropes or bombs.[br]The other rooms are not on the critical path,

0:02:26.340,0:02:30.160
so they may be open, or they may be walled[br]off depending on their design.

0:02:30.160,0:02:36.870
Next, each room is randomly given a template.[br]Derek Yu hand crafted a number of room designs,

0:02:36.870,0:02:41.459
with different layouts for rooms where you[br]drop down, rooms you land in, corridors you

0:02:41.459,0:02:44.650
run through, and rooms not on the critical[br]path.

0:02:44.650,0:02:49.230
But these templates are not set in stone,[br]and parts of them are randomly generated.

0:02:49.230,0:02:54.650
Sometimes entire chunks of tiles are plastered[br]on at random. This means that while you might

0:02:54.650,0:02:59.099
start to see familiar set-ups, they will always[br]have their own unique quirks.

0:02:59.099,0:03:03.909
Next, a script checks every tile on the map[br]and rolls a dice to see if it should place

0:03:03.909,0:03:09.190
down a monster, some treasure, or another[br]object. Again, it's not entirely random - gems

0:03:09.190,0:03:14.349
and crates are more likely to appear in spaces[br]surrounded by walls, and enemies generally don't spawn

0:03:14.349,0:03:19.409
in cramped spaces. And everything is weighted,[br]so a level isn't filled with fire frogs or

0:03:19.409,0:03:22.580
crates containing jetpacks.

0:03:22.580,0:03:27.700
Describing his level-making algorithm, Derek[br]Yu says "This system doesn’t create the

0:03:27.700,0:03:32.659
most natural-looking caves ever, and players[br]will quickly begin to recognize certain repeating

0:03:32.659,0:03:37.180
landmarks and perhaps even sense that the[br]levels are generated on a grid. But with enough

0:03:37.180,0:03:42.409
templates and random mutations, there’s[br]still plenty of variability. More importantly,

0:03:42.409,0:03:47.040
it creates fun and engaging levels that the[br]player can’t easily get stuck in, something

0:03:47.040,0:03:51.879
much more valuable than realism when it comes[br]to making an immersive experience.”

0:03:51.879,0:03:57.010
There's still more to a Spelunky level, of[br]course. Those rooms not on the critical path

0:03:57.010,0:04:01.830
can contain golden idols that set off a boulder[br]trap, or a sacrificial altar where you can

0:04:01.830,0:04:03.830
trade bodies for helpful items.

0:04:03.830,0:04:09.330
A room can also be a shop where you can buy,[br]or steal items. “The difficulty of buying

0:04:09.330,0:04:13.640
all the items you want and the consequence[br]to your score" - your final score is based

0:04:13.640,0:04:18.410
on how much loot you found - "creates a strong[br]temptation to steal from the shop", says Yu.

0:04:18.410,0:04:22.660
If you do pilfer an item, the shopkeeper will[br]not only try and kill you with his shotgun,

0:04:22.660,0:04:26.720
but his buddies will appear at the end of[br]every level for that run, and attack you in

0:04:26.720,0:04:29.430
a mad, unpredictable fury.

0:04:29.430,0:04:35.160
Every level also has a damsel in distress,[br]which gives you one extra health point.

0:04:35.160,0:04:39.800
While the health pick-ups in other games - be[br]it a mushroom or a turkey leg or a pizza - are

0:04:39.800,0:04:44.860
activated immediately, Spelunky makes you[br]carry the damsel to the exit, leading to tricky

0:04:44.860,0:04:48.750
moments where you have to lug multiple items[br]through an unpredictable maze.

0:04:48.750,0:04:52.880
And finally, there's the ghost. Stick around[br]in one level for too long and a spectre will

0:04:52.880,0:04:55.590
appear and instantly kill you if it touches[br]you.

0:04:55.590,0:05:01.110
All of these additions, which are highly authored,[br]but scattered about the procedurally generated

0:05:01.110,0:05:06.580
worlds, are about making choices and weighing[br]up your options. Derek Yu says "I wanted to

0:05:06.580,0:05:10.990
force [the player] to make difficult decisions[br]and experience both the satisfaction of choosing

0:05:10.990,0:05:13.979
correctly and the regret of choosing poorly".

0:05:13.979,0:05:18.289
So do you sacrifice your score by spending[br]money on the shop? Or do you just rob it and

0:05:18.289,0:05:22.660
deal with the consequences? Do you risk throwing[br]a damsel down here, or leave your shotgun

0:05:22.660,0:05:27.389
behind? Do you grab the golden idol, and risk[br]getting smushed by a boulder? And can you

0:05:27.389,0:05:29.669
collect these gems before the ghost appears?

0:05:29.669,0:05:33.630
Those decisions would be far less interesting[br]to make if you had already played the level

0:05:33.630,0:05:37.820
before and knew the right path to take or[br]could predict the exact outcome of snatching

0:05:37.820,0:05:42.169
a golden idol. But because you never know[br]how the stage will be laid out, the game forces

0:05:42.169,0:05:47.550
you to read the situation and make a plan,[br]before watching it all go hideously wrong.

0:05:47.550,0:05:50.710
And that's all the more painful when you know[br]you'll be sent back to the very start of the

0:05:50.710,0:05:55.820
game, now with all new levels to tackle. The stakes in this game are super high.

0:05:55.820,0:05:59.840
Plus, not allowing you to master the stages[br]means you'll need to master the mechanics

0:05:59.840,0:06:04.600
instead. You'll need to understand the quirky[br]physics of your jump and the tiny reach of

0:06:04.600,0:06:08.419
your whip. You need to learn the unique properties[br]of each enemy, so you can to predict what

0:06:08.419,0:06:12.160
will happen when you enter their domain. And[br]you have to learn about the items, and the

0:06:12.160,0:06:15.080
secrets, and the tricks that will keep you[br]alive for longer.

0:06:15.080,0:06:20.240
So Spelunky proves that an algorithm doesn't[br]necessarily lead to soulless levels - balancing

0:06:20.240,0:06:25.069
authored and random content can lead to levels[br]that are satisfying to play. And by removing

0:06:25.069,0:06:31.020
the ability to learn levels - either after[br]you die or on your second or 1000th playthrough - this

0:06:31.020,0:06:35.590
game encourages you to learn the underlying[br]mechanics, and makes you read the situation

0:06:35.590,0:06:38.970
carefully before making those very difficult decisions.

0:06:40.380,0:06:42.080
Thank you so much for watching!

0:06:42.080,0:06:45.780
Spelunky is one of my favourite games of all[br]time so it's great to be able to dig into

0:06:45.780,0:06:48.440
just one aspect of what makes it so special.

0:06:48.440,0:06:52.539
I will no doubt come back to the other bits[br]- like the emergent gameplay and the crazy

0:06:52.539,0:06:54.539
secrets - in future videos

0:06:54.539,0:06:57.819
if you would like to help this show please[br]consider subscribing on YouTube to get new

0:06:57.819,0:07:02.970
episodes delivered directly to your inbox, or even[br]pitch in a few dollars per episode over on Patreon.

0:07:02.970,0:07:04.910
just like these top tier subscribers have[br]done