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This is just a small article I wrote on stealth in an RPG. Perhaps you'll find some of the ideas interesting.

 

You know what my main beef has always been with the Thief games? Difficulty- it's too low. Unless you impose some artificial constraints on your gameplay (which basically means you're not enjoying the game to the fullest), the game gets insanely easy- especially if you're experienced with Blackjacking. I've been thinking how- through employing a certain amount of realism- can the gameplay be made more balanced, presenting a challenge to both your dexterity and wits.

 

(As usually I categorize things and assign stupid acronyms, please excuse that).

 

The guards keeps track of the events going on basing on Supspicion Indices assigned. The first thing to remember when calculating the exact values of these indices, is that a guard has been working for months and nothing's ever happened. That's why they're not going to alert the whole mansion just because they see a candlestick missing. The effects of weird events are cumulative though.

 

The Suspiciousness Index (SI) of an event becomes greater with every instance, so the second time a guard finds an extinguished torch, he'll be more alarmed than the first time.

 

Alarm Status (AS) levels:

0: Another day of work, nothing going on

1: Certain unusual events going on, at least it's not as boring as always.

2: Weird things going on and on, perhaps one of the guards is gone somewhere, loot missing. A guard will pass this AS to 50% of the guards he meets (for realism?).

3: The situation is very fishy, more than two people missing, torches drenched, lights gone out. A guard will pass this AS to 100% of the guards he meets

4: One of the guards was found unconscious, a tresspaser is most certainly in the house. Sound the alarms! A guard that has a patrol mission will actively search for help and pass the AS.

 

To allow the situation to revert back to normal after you've made slight mistakes, the effect of the lower valued events dissipates over time, depending on the AS (alert status): for example

AS0: events up to 6 points dissipate at 1 point per 30s after a 1 minute caution period. Another event will stop the dissipation and bring the value back up if it hasn't dissipated completely.

AS1: 5 points, 1,5 minute caution period

AS2: 4 points, 2 minute caution period

AS3: 3 points, 3 minute caution period

 

 

Suspicion factors: (just examples, not balanced, has to be tested)

1-A slight noise (like stomp on a wooden surface)

3-A small lightsource gone out (like a candle)

4-A medium noise (like a book falling on a carpet)

5-An object missing

6-A drenched torch (light arrows)

7-A loud noise (like the sound of a falling metal object)

8-A valuable object missing

9-A person missing

25-A person discovered unconscious/dead.

 

The behaviour...

...of a person changes with his AS:

-People that aren't guards will generally ignore events with a low SI (up to 4?), provided that they ARE guarded (servants, noblemen and so on). Of course, the NPC might have his plot-based reason to be constantly alarmed.

-Unalarmed guards will notice quiet sounds, but will mostly ignore them and do their patrols, stand still looking straight. A patrolling guard will occasionally look around.

-Moderately alarmed guards will look around constantly and react more suspiciously

-An alarmed guard will actively search: he will sometimes stand still to listen for any more noises and look for good hiding places and possibly cry for help. Once the guards learn that there's an intruder in the house, they will keep searching until morning.

 

Other things

To make things even more difficult, a 3d game may introduce shadow based reactions: if an NPC can notice the PC's shadow, it's impossible to blackjack him if in order to do that, you have to come between him and a lightsource. (this is, once again, to decrease the immense power of the blackjack)

Some NPCs could carry tinderboxes to light the extinguished lightsources back (a special servant, some guards). They would probably be the first ones to notice that a torch was drenched with a water arrow (a bad thing!)

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-While implementing this kind of features one should be very careful to consider the possible exploitation of it.   Let's think of an AI guard walking through his normal route where he ignores all the

I really like that!

 

When I noticed I could keep making a noise on the tiled floor and simply stop and wait a few seconds for the guard to calm down, I realised I'd hit the "limit" of the realism, and now it became a game. Make a noise, wait, make a noise, wait...

 

It would be so much more exciting if you made a couple of noises and the guard finally gets pissed off and goes to see what that annoying noise is :)

 

I wonder what our AI programmers think of this. Then again maybe it already works like this and I've just been out of the loop for too long. I wouldn't be surprised.

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We've spent a lot of effort on tweaking how AIs respond to / calm down from alerts, and I'm not naive enough to think that we're nearly done yet. :) That's one of the things that we'll have to pay a lot of attention to next year.

 

Given that, we obviously we can't promise anything about how it's going to behave in specific situations, except to say that we won't release an unplayable game.

 

As for the specific implementation details mentioned above, that's not quite how the system works internally and it's too late to change it at such a fundamental level. Having said that, I think our current system is just as workable; we merely(!) need to tweak constants, which we'd have to do with that system anyway.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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Certainly it's a factor. I believe they will eventually subside though.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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Not Yet Implemented, I believe.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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I think this was publicly discussed before but its pertinent here. Would it be possible to assign that level of alertness to an object or situation where an object is not where it should be? I was thinking of say an important key or other object goes missing and the AI immediately go nuts at its loss. As if I were an AI guard and suddenly realized that all of the armory's keys were missing from the safe box, I would be screaming for help.

 

Edit: I see now that Mike addressed that in his stealth scheme, thats an interesting piece MM.

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We talked about it, but it would be hard to cover all the conceivable situations. In reality, there would be other suspicious factors rather than just whether they're in bed or not. For example, a person seeing someone in a bed might wonder:

 

Are they supposed to be awake and performing a job?

 

Whose bed are they in?

 

Who is in bed with them?

 

Why are they fully clothed?

 

Granted, if they were already asleep in that particular bed, it probably shouldn't cause an alert to put them back to sleep in that particular bed, but in general it wouldn't work to just toss someone in some random bed.

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I dunno, when I first played T2, I did exactly this. Just in case it worked. I kept chucking bodies in the nearest random bed.

 

I guess, as realistic as the game is, you have a certain level expectation from the realism. I expected "bed sleeping" as a cover-up might be in the game, but not "everyone sleeping in their right beds" seeing as beds for every AI were not present.

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I imagine there will be some mechanism to make AI ignore stimulus in a particular area--you could perhaps make a stim out of it and put it on the beds.

 

I admit I did the same thing with bodies, or I would drop a few bottles nearby so they looked drunk. :ph34r:

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I imagine there will be some mechanism to make AI ignore stimulus in a particular area--you could perhaps make a stim out of it and put it on the beds.

That's a neat trick, it could work - though only if it was able to be tied to the bed object in the def file or something, and not as something you have to place while mapping, on every instance of a bed. Otherwise maps will be annoyingly inconsistant there, depending on how thorough the mapper was. Would save time too.

 

And you could tie this "stim negator" to bottles too, for placing them around supposedly drunk bodies.

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I imagine there will be some mechanism to make AI ignore stimulus in a particular area

I don't believe that's in the current design. If people want to add it, it will need to be discussed.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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I imagine there will be some mechanism to make AI ignore stimulus in a particular area--you could perhaps make a stim out of it and put it on the beds.

 

I admit I did the same thing with bodies, or I would drop a few bottles nearby so they looked drunk. :ph34r:

 

-While implementing this kind of features one should be very careful to consider the possible exploitation of it.

 

Let's think of an AI guard walking through his normal route where he ignores all the five knocked out guards, only because there is some bottles lying around or the bodies are placed on the nearby beds.

 

As a player I'd still like to worry about finding the remote cleaning closet no one visits to dispose of the bodies. =)

Clipper

-The mapper's best friend.

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I'm speculating, but the current plan for AI alerts is that lots of little alerts will have an incremental effect, which only dissapates over time.

 

So the "stim negator" idea shouldn't really negate the stim, just lower the alert value of the nearest alert stims within its specified radius, eg. unconcious body is worth 50, bottle nearby takes 40 off it, lowering it to 20. (arbitrary numbers I chose). Of course it should only lower per object type - so more bottles won't make it less suspicous. But a bottle, AND a bed, would.

 

So then, a guard seeing a single "drunk" guard on the ground would be a "huh, that's wierd", but 5 drunk guards in one hallway, or even 5 drunk guards seen within the past minute, should be enough to go to search level alert.

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Mmmm. I'm gonna call that not-a-1.0-feature.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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Of course.

 

Actually rather than look for surrounding stims and lower them, it could just send out a negative alert amount, lowering the alert level of the AI that way, like a cop saying "nothing to see here, move along". I wonder how much of a stretch that is outside the current stim system?

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I imagine there will be some mechanism to make AI ignore stimulus in a particular area

 

I don't believe that's in the current design. If people want to add it, it will need to be discussed.

 

We already have the "low/high security area" concept, where guards ignore certain kinds of stimulus (or are less excited about them) in low security areas. Couldn't the bed be made a very small low-security area?

 

Not that I think the feature is a big deal or a 1.0 goal, just musing out loud.

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We already have the "low/high security area" concept, where guards ignore certain kinds of stimulus (or are less excited about them) in low security areas. Couldn't the bed be made a very small low-security area?

I suppose that could work. We'd have to try it out once low/high security areas are implemented to see how well it works.

My games | Public Service Announcement: TDM is not set in the Thief universe. The city in which it takes place is not the City from Thief. The player character is not called Garrett. Any person who contradicts these facts will be subjected to disapproving stares.
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I guess, as realistic as the game is, you have a certain level expectation from the realism. I expected "bed sleeping" as a cover-up might be in the game, but not "everyone sleeping in their right beds" seeing as beds for every AI were not present.

 

You know what would be great? If TDM AI could actually sleep *IN* their beds, not just flop on top of the covers in their street clothes. Apparently nobody in The City makes pajamas.

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You know what would be great? If TDM AI could actually sleep *IN* their beds, not just flop on top of the covers in their street clothes. Apparently nobody in The City makes pajamas.

Yes, it was OK for a grunt flopping out in the barracks but not the lady of the manor. I see one half-possible compromise...

 

A set of AI wearing nightdresses (or attachments)

A humped up blanket model (shaped as if a body beneath)

A flattened but dishevelled blanket

 

The AI is placed by the mapper horizontal below the humped blanket. If disturbed a 'roll to one side and stand animation' triggers and the humped blanket is switched for the flat one.

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That would be a bit of a shock for the unprepared thief sneaking through as some fat naked guy leaps out of bed shrieking.

 

I envision only Scrooge in his nightshirt and nightcap - it would be fun for victorianesque missions :)

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