How Stealth Game Guards See and Hear | School of Stealth

How Stealth Game Guards See and Hear | School of Stealth


There aren’t many genres with such a strong
core fantasy, as the stealth game. These are games about staying unseen, and
then striking from the shadows. About outsmarting an entire army of enemies,
without them even knowing you exist. These are games about spies, assassins,
and, uh, Batmen. But making this fantasy work means balancing
a number of complicated game systems: from enemy awareness, to information gathering,
to robust detection systems. Get any of them wrong, and the whole thing
can crumple in on itself. So, welcome to the School of Stealth. This is a short, GMTK mini-series about how
stealth games work. In each episode, I’m going to take one system
from the stealth game formula and break down how it works – looking, where necessary, at the
technical side of things, the design considerations, and the end user experience. For episode one, we need to start where most
stealth games begin: with the player being hidden. And then ask ourselves: how do guards actually
see and hear the player? Ultimately, guards in games are given virtual
eyes and ears that are designed to simulate the two main human senses: sight and sound. To simulate vision, video game guards typically
have a viewcone – which is an invisible, cheese-like entity that is stuck to the enemy’s face. If the player character enters the cone, they
get detected. It’s a touch more complicated than that,
of course. A simple cone would allow characters to stay
unseen even if they were right next to the enemy – so more complex shapes are often used. In Splinter Cell Blacklist, there’s a basic
vision cone for the guard’s primary sightline, but a second, much wider box to simulate peripheral
vision. And even a small area behind the guard to
mimic that sixth sense of knowing when someone’s just over your shoulder. Developers will also need to consider the
height of the cone, depending on whether the character should be able to hide when they’re
above enemies. To know if the player is in cover, a game
will typically use a raycast – which is basically when an invisible line is drawn between two
elements to see – in this case – if anything is in the way. You can make this more complex to catch moments
of partial cover: so, in Splinter Cell, the enemy raycasts to eight different bones in
Sam Fisher’s player model – and will only spot him if a certain number are visible. Now, if the player enters the cone and isn’t
in cover, they probably don’t get immediately spotted. Instead, the guard’s awareness of the player
starts to grow. The speed at which this meter fills might
be slower if the character is further away, or only in the guard’s peripheral vision,
or in low light, or crouching down, or staying perfectly still. When the meter tops out, though, the guard
will know exactly where you are. It’s also important to note that guards
can be aware of more than just the player character – such as open doors, interesting
objects, or dead bodies. This can be used to make interesting plans
like traps and distractions – but it can also help give the impression of intelligence and
awareness. Now, simulating hearing is a different problem. When you make a sound, like firing a gun,
walking on a loud floor board, or throwing a stone – the sound will be given a distance
– related to the volume of that noise. Any guard who is within that distance can
then be told to go check out the source of the sound. However, a straight line between the sound
and the guard won’t work, because we expect noises to be muffled by walls. So the typical solution is to use the game’s
pathfinding system – the same tech that allows an enemy to find their way around a world
without bumping into objects. Make the sound travel across that, and you’ll
more realistically capture the way sound propagates through an environment in real life. That’s the gist of things, then, but more
complex stuff might be included in certain games – for example, in Thief, guards can
have second-hand information about the player based on what other enemies are up to. And in Hitman 2, enforcer characters are way
less perceptive of Agent 47 if he’s facing away from them, which gives disguises more
power. Links to more detailed technical information
can be found in the description beneath this video. When done well, this system should create
a pretty realistic representation of a human’s visual and auditory perception. You can then make educated decisions about
where you will be safe, using your real-world knowledge of how sight works in different
light conditions, or how sound might be muffled by a wall. But there’s always going to be a certain
level of ambiguity for the player to deal with – which can lead to friction and frustration. I’m sure you’ve played a stealth game
where you thought you were totally invisible, but the guard saw you anyway. So to help players make sense of this stuff,
there’s a few smart ways that devs can make these perception systems more obvious. The first is helpful interface elements. Even way back in Thief, the developers knew
that it was tough for players to understand how lit their character was from a first-person
perspective, so there’s a light gem at the bottom of the screen to show your current
visibility. And in Splinter Cell, the awkward challenge
of knowing how much sound you’re making, is helped by a visualiser on Sam’s head’s
up display. Also, most games have some kind of detection
indicator on their interface, which mimics the guard’s awareness meter from earlier. This helps the player know that they’re
about to be made – and sometimes even shows you the location of the guard who’s seen
you. Next up is using animation and audio to help
communicate a guard’s status to the player. A guard who is idly lazing about might suggest
that they have pretty weak perception, but a suspicious enemy with their weapon raised
will be way more alert to potential threats. Audio barks also let you know that the guard
is starting to become aware of you. Then there are refuge spaces. These are places in the game world where,
in normal circumstances, you are unambiguously hidden. That might be the high-up gargoyles in Batman,
or areas of long grass in Assassin’s Creed, or crates and cupboards in Hitman. These give you at least one place where you
can scout and plan from a position of total safety. Another big solution is player favouring – which
is the art of handicapping systems to bias the player. As Splinter Cell Blacklist programmer Martin
Walsh says, “it doesn’t matter what the NPC can see or hear from a simulation perspective. It’s what the player thinks the NPC should
be able to see or hear”. So in his game, a guard’s hearing is reduced
by half when they’re offscreen, because it feels unfair to be heard by someone you
can’t even see. And in The Last of Us, enemies typically raycast
to Joel’s head to determine line of sight – but that changes to his chest when he’s
crouching, to let him peep over cover without being spotted. And then the biggest help of all, as discussed
earlier, is a fuzzy detection system. If you were immediately spotted when you touched
the guard’s vision cone, that wouldn’t feel very fair. So it makes sense that guards take a few moments
to become aware of your presence before being totally alerted. Now there’s one final, and rather bold solution
to this problem: and that’s to simply reveal these systems to the player. In the excellent side-scrolling sneak ‘em
up Mark of the Ninja, the guard’s perception is about as unambiguous as you can get: Their vision cones are displayed on screen. The ninja is either in shadow or in light
– and that’s shown on the character’s sprite. And when you make noises, you can see them
emanating from the source as big round pulses. This is also shown to you before you even
make the noise, which is helpful for knowing whether your noisy distraction or sneaky getaway
will be successful. With the info on screen, there’s no arguing
about what’s happening in the system. You’re either in the cone, or you’re not. And that sound either reached the guard’s
ears, or it didn’t. And so Ninja’s binary perception system
can be paired up with a totally binary detection system of instant awareness – though, there
is a slight analogue fuzziness on the very edges of the enemy’s view cones. GUARD: “Is someone up there?” For a slightly more nuanced take on this,
check out Shadow Tactics: Blades of the Shogun. Here, the vision cone is split into three
zones: the bright green part near the enemy’s face is the danger zone and leads to a pretty
instantaneous detection. In the dark green part, you can stay hidden
if you’re crouched down, but will be spotted if you stand up. And the dotted part is for refuge zones like
bushes and high grass, where you will always be invisible. If you do trip the viewcone, the whole cone
will fill up with yellow – and if the yellow part touches your character, you’re spotted. It’s a very elegant way of displaying all
the necessary information, right there on screen. Of course, it’s a lot harder to show this
sort of stuff in a fully 3D game. The original Metal Gear Solid’s solution
was to simply photocopy the game world into a top-down, 2D representation on your radar,
and then draw the vision cones on that. It’s a sorta hand-wavey solution that’s
still being used in games like Deus Ex: Mankind Divided. But it’s not impossible. The Sly Cooper series has guards with torches
that cast obvious pools of yellow light. If you find yourself inside the light, you
get spotted – but otherwise you’re safe. Cartoony, yes. But also, immediately readable. The most important thing, though, is the experience
that these different perception systems lead to. When the system is made analogue and ambiguous,
the player must evaluate the environment with an immersive and realistic understanding of
light, shadow, distance, and sound. And it also gives the game a certain level
of tension – where you can never been 100% sure that you’re safe. And I think this fits quite nicely with the
core stealth fantasy: these are games where your power doesn’t come through sheer brute
force, but only through your ability to hide from the enemy. So having your sneaky status be fragile and
fuzzy reminds you that you’re always at risk of losing your tenuous advantage over
the enemy. As Thief programmer Tom Leonard says, “it’s
about getting the player’s heart pounding by holding them on the cusp” of being found. And it’s especially important to hide this
stuff in survival horror games that borrow stealth elements. In a game like Alien Isolation, it would be
rubbish if you could see exactly where the Xenomorph was looking. A huge amount of fear and anxiety is derived
from your shaky knowledge of the alien’s senses. But making the system completely obvious has
its own advantages. It puts way more power in your hands, and
allows you to play with a huge amount of confidence. You can feel more like an apex predator, luring
enemies into traps or sneaking in for a silent kill. As Ninja producer Jamie Cheng put it, “as
we were iterating, I found that I wasn’t nearly as interested in guessing whether a guard
would hear me or not, and way more interested in creating an elaborate death trap”. Of course, the predator feel can be achieved
through other methods, like those aforementioned refuge zones and by giving the player a bucketload
of gadgets and super powers – but the more accurately they can predict the enemy’s
perception, the quicker the player will get to that experience. So, that’s it for lesson one. Stealth game guards see and hear through a
system of simulated eyes and ears – and developers can create very different experiences, depending
on how much of that system they surface to the player. Come back next time for more deep dives into
sneak ‘em up design. And if you subscribe to my channel, you’ll
get access to the new episode as soon as it goes live. Hey. Thanks for watching. I hope you’re all doing okay in the midst
of this awful coronavirus pandemic. It’s such a scary situation, so please stay
safe, wash your hands, and follow the necessary guidelines. I’ll do my best to keep making interesting
stuff to keep you busy and entertained.

100 thoughts on “How Stealth Game Guards See and Hear | School of Stealth

  1. Hey! Google has set the default video quality on YouTube to be standard definition (480p) for the duration of the coronavirus pandemic, to help reduce internet traffic. If you'd prefer to watch the video in high definition (1080p), please click / tap the cog and change the video quality from there.

  2. I don’t know if it’s been done or not but someone should make a vr stealth game.
    I don’t know how a vr game would improve the stealth genre besides increasing immersion but I think that’s still plenty reason for a vr stealth game to be made

  3. great video as always, happy to see what's next 🙂
    no mention of Batman making the guards unable to turn 180° when he's behind them?

    PS: I think it's funny how some games can feel turn into stealth games although they are not entirely meant for that…like the new Wolfensteins where run and gun often doesn't work at all but sneaking does…or Metro Exodus on higher difficulty, where the enemies have infinite accuracy and every shot hits while every second hit kills you..therefore you take out what you can, without being detected…

  4. Stealth game is my favorite genra. So every time you make a video about it, I'm like <3 <3
    And this time, it's an entire serieeees !

  5. You should looking into the Styx series, Styx: Master of Shadows and Styx: Shards of Darkenss. Two criminally underrated and seldom talked about titles that are stealth masterpieces.

  6. Thanks for the vide!
    This episode has reminded me of a game jam where I was trying to get those principles based on my own knowledge of the genre. It wasn't easy and some parts of it went through trial and error. The hardest part was not making an instant failure after being seen, this took some research into the state machines.

  7. Good video, my favourite enemy detection system is from the Tenchu series, they use a ki meter instead of a radar, how it work is this the meter shows a symbol to tell you the status of an enemy a green ?, Means the enemy has not seen you and is on normal patrols, a yellow caution symbol means the enemy is about to spot you, a red !! means the enemy has seen you and is on full alert, a purple !? means you have evaded the enemy's attacking you but are still on alert trying to find you. Next to the symbol is a number that tells you how close you are to an enemy, 1 being you're right next to them to 100 being far away from them

  8. So being in quarantine has given me an opportunity to touch on some games I haven't finished. I picked up Dishonored and wow, what an awesome game. What a coincidence that you make a video about stealth after I played that! But it's funny how you never mentioned Dishonored in this video despite playing clips from it. Lol

  9. I hope you talk about games like Payday or Monaco in one of your future episodes. Cooperative stealth/heist stuff is a super cool underexplored idea imo

  10. They all have a super elaborate and complex perception and awareness systems, but then:
    Guard: *gets hit by an arrow*
    Player: *hides*
    Guard: "Must have been the wind…"

  11. Wow, I was literally just looking through your channel for videos on stealth game mechanics earlier today. I'm working on my own, thinking of not using combat in it. A bit of a twist on the genre, like a cross between Mr. Robot (the tv series), The Stanely Parable, and Hitman.

  12. 10:25 Except if you put a lot of hours in that stealth game. If that the case, you are just a badass stealth vision abuser.

  13. Marvelous Miss Take needs more love. It's a delightful game!

    And Invisible Inc is one of my favorite games ever!

  14. I really miss all these games! when is splinter cell coming back? Will there ever be another good MGS? I still have to play mark of the ninja, maybe that will satisfy for now.

  15. "What game guards see and hear" A rock, another rock, a few more rocks. All from the same place. Then a suppressed shot and hurried footsteps, a noisy roll. The thump of a body, more shots, some kind of flashbang grenade

    Game guards are stupid

  16. Great work Mark! I'm not a fan of stealth games (I dragged through Plague Tale Innocence), but I appreciate this take on the genre considering different aspects of different games. Will there be different "School of" miniseries for other genres?

  17. Favorite genre MGSV, Hitman 2 and Dishonored are among the best games released the last decade all make my top 20. I need to play the splinter cell games and finish Mark of the Ninja. It's like the 3rd or 4th time you are praising it.

  18. I never thought I'd see Sly Cooper in a video about stealth games. Usually it is only brought up as a platformer.

  19. I feel stealth games are never fully realistic. I love Splinter Cell Chaos Theory, but I could never get over the fact that you are completely invisible in the shadows. Human vision adjusts to the level of light. I'm no expert, but I would say it is VERY hard to not be seen by someone who is directly looking at you from a few meters away.

  20. Major I need to complete the objective but the clapping of my ass cheeks keeps alerting the enemies to my location.

  21. I can enjoy the empowering type of stealth game. I do not enjoy the stress of the vulnerable type of stealth games.

    I'm here to enjoy a game, not to stress out.

  22. Another example of biasing the system in the player's favour is the leaning system in Dishonored – as long as your body is hidden, when you lean around walls you can't be seen by enemies.

  23. Stealth games are by far my favourite. So excited for this series!
    I hope you talk in a future video about NPCs having the hive mind-like ability to know your exact position when only one of them has spotted you. It's one of the things that break games the most for me.

  24. Almost every stealth game will not have you be detected if you're simply a very long distance away from a guard, even if they're looking in your direction. This is so massively unrealistic, since obviously if you can see them, they should be able to see you exactly as much.

  25. I would love to see a stealth game where guards get higher awareness whenever they almost spot the player. Like when that guard saw something suspicious, it would take a better look at the surrounding and would react faster if something occured again. However, in most games, guards merely take a quick look at the place where they spoted something and return to idling around like nothing happened.
    So some kind of rising alert level for guards would be cool. From reducing the time they need to spot the player to actually leaving their idle status permanently and actively searching for something until they find some explanation (like a cat or something, which could actually be used as an distraction to lower the alert level).

  26. awesome new series! One thing always bother me about stealth game is when you have practically invisible AI companion. Yes, it will be super annoying to have your companion get caught by the enemies but making 'em walk or bump around the enemies like they are invisible always break the immersion for me, especially on serious, grounded games like The Last of Us or Ghost Recon

  27. Funny thing: There are several studies proving that such a sixth sense (sensing someone behind your shoulder) doesn’t exist.

  28. Why ? Why ? Why does Styx : Shards of Darkness only appears during the outro ? It is not even mentionned… so sad for such a great game…

    Uh ? Biased ? Me ? Nah…

  29. Very excited about this deep dive mini-series. Leveraging the pathfinding system for sound propagation is pretty clever.

  30. Awesome, I loved the Splinter Cell music and also how much praise Mark of the Ninja got, loved those two games. I used to love stealth games, especially Splinter Cell: Chaos Theory and Metal Gear Solid 3. After that it took kinda long for me to find any good ones, the newer SC games just didn't cut it for me and while I loved MGS: The Phantom Pain I often just didn't like to play super stealthy if I have an attack chopper that I can call in – even with the point loss, I just loved to blaze through everything in the game when stealth failed.
    I kinda miss the times when you could get every detail of a mission and just clear it flawlessly. In SC: Chaos Theory there's a bank heist that I completed 100% on expert mode, it made me feel like a super spy or some bandit out of an Oceans 11 movie. Dishonored is kinda similar in the way that you can play missions multiple times and get fun out of just reading the guards routines etc., but you are still pretty powerful in open combat. Creating stealth mechanics is something that is very difficult to do in my opinion and some games just don't strike the nerve, so I really admire every game that gets it right.

  31. Omg hell yeah boi. I'm as giddy as a school girl for this series on stealth 😁👌. Just made my day. Gracias por todo 🙌👏🙌👏🙌👏🙌👏

  32. Probably worth mentioning the variable factors for sound like you did for vision such as surface texture and environments like famously in the Thief games.

  33. I wonder if after the School of Stealth you do a School of Shooter. While mechanics of shooter seem to be simple, there is a ton of difference between a good shooter and bad one.

  34. Razorfist: we need more respect and love for the stealth genre
    GMTK: *bursts through a wall like the Koolaid Man

  35. I hated shadow tactics : blades of the shogun cause I am colorblind and couldn't see the cones very well or just not see them at all. People should really take colorblind modes more seriously when making games.

  36. "Xenomorph" …. "Looking"

    Xenomorphs don't have eyes bro. They hunt through sound bro. That's why it can walk right by you and miss you bro.

  37. Are we going to get some mention of the Zelda series? Fair bit of guard sneaking throughout the series and stealthing around enemies in BotW

  38. In addition to stealth principles, I hope this series includes instances of them done poorly. For example, Rogue Warrior has hilariously terrible enemy patrol behavior: instead of moving around and watching the maneuverable space, they mostly just stand around looking at the wall. It's meant to incentivize the player into using the game's touted melee takedowns, but it just comes across as them looking out for the Kool-Aid Man.

  39. Can you please try to not include a game footage of a recently released game? Such as Doom Eternal here. If it isnt in topic or obvious to us that its here, it would be great to at least have a spoiler warning at the beginning. I know there wasnt anything big in that footage, but I would like if you did do a spoiler warning.

  40. So glad Blades of the Shogun was mentioned. It's free on Xbox Game Pass to anyone interested and that's where I picked it up first. I was completely enraptured by the game and how intuitive it's stealth mechanics work. I'd love to see more of it in this series.

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