Thursday, 13 March 2014

Thief and Stealth Systems

Yes, I know I'd said that this would be about plausible level design, but that's taking me rather longer to research than I expected, so instead let's talk about stealth systems. What I want to do here is define the characteristics of stealth in the original Thief games (particularly T1 and T2), compare these to stealth in Thief, and examine how the stealth systems have affected the rest of the game.1

In the beginning we lived as thieves

The easiest way to describe the stealth systems in Thief is to list the ways in which the player could be discovered by the AI. You could be seen, heard, or noticed. By 'noticed', I mean that a guard could become aware of your presence not because they saw you, but because they saw something you had done to the world, such as the dead or unconscious body of a guard. 'Noticing' is probably the area which changed the most over the course of the series: guards in T1 only responded to bloodstains or bodies, but by T:DS they could notice open doors, doused torches and missing loot. Covering most of one's tracks was easy, but hiding bodies was a slower process that frequently caused the player to become more exposed. In the first two games, bloodstains could only be removed by water arrows, forcing the player to balance the risk of a guard discovering them against the cost of the arrow.

This balance of risks was also present in the most prominent aspect of sound-in-stealth: footsteps. The sound of the player's footsteps was affected both by their speed (running and jumping were extremely loud; creeping was almost silent), and by the various surfaces, which ranged from grass and carpet (extremely quiet) to marble and metal (extremely loud). It would quite often be contrived so that areas with the 'loudest' flooring were also fairly well lit, forcing the player to make a choice between a quick dash from shadow to shadow (reducing the chances of being seen but increasing those of being heard), or creeping across in an agonising crawl, silent but completely exposed and expecting the shout of a guard at any second. Alternatively, one could fire a moss arrow at the offending surface, covering it in beautiful bryophyta and dampening your footfalls.

However, player sound was not just limited to footsteps. The click of a lockpick or the creak of a door could attract attention, as could the thud of a sword or an arrow. This last could also be used to create distractions (indeed, there was an arrow called the 'noisemaker' specifically designed for this purpose, though it was so expensive that I hardly ever used it), though these could also be created by throwing nearby objects.

Finally, a guard could see you. Visual stealth was based on a player's 'visibility' value, which determined the distance from which the player could be seen. Running or jumping increased visibility; crouching reduced it. Drawing the bow increased visibility slightly, drawing the sword increased it more, and notching a fire arrow increased it massively, lighting you up for the whole map to see. Light and shadow played by far the largest part of visibility, and the player quickly came to recognise light sources as their biggest enemy (after burricks). Fortunately, there were ways of dealing with these: water arrows could douse open flames, and some electric lights had switches.

According to thy visible systems shall they judge ye

Of course, you can have the most involved and detailed stealth system in the world, but it's all for nought if you can't communicate it to the player. The audio aspects tend to sort themselves out, and 'noticing' tends to be explained through tutorials, loading screen tips and guard reactions, but for visual stealth to work the player has to know how visible they are. The foul-mouthed sage of the industry once cited this as one of Thief's greatest strengths, and the way in which this was done was through the light gem, shown below.2
216 shades of grey
Of course, simply having a bright gem didn't necessarily mean that you were visible - you could be out of line of sight, or just have murdered all the people in the level - but it gave you a way of judging your visibility the same way that hearing your footsteps gave you an idea of how much noise you were making. The reason I bring this up is for self defence - I've almost certainly made some mistakes about the details of the systems somewhere in this article, but I'm reporting the systems as they were shown to me. If Dishonoured did in fact have a shadow-based stealth system I couldn't tell. Basically I'm working with reader-response (player-response?) here.

Back to the future

So, we have now, in fairly exhaustive detail, covered the stealth mechanics of the first three Thief games. So how does Thief measure up?

In terms of 'noticing' (still a terrible name, I know), the systems have mostly improved. Guards are now more responsive to doors mysteriously opening and closing themselves, and will become extremely suspicious if a light source near them is extinguished - they'll also relight it, which caught me by surprise an embarrassing number of times. There have also been environmental developments: it is now possible (and frustratingly easy) to knock over brooms and vases by moving too close to them, which will alert a guard. Dogs and birds (both in cages) have also been added, each of which can detect you in different ways. Dogs will bark if you get too close, no matter how stealthy you are, but birds will only react if you make any sudden movements or noises. At one point I was carefully picking a lock on a desk under a bird cage, and when I slipped and hit the pin incorrectly the click was sufficient to scare the animal and call a guard over. Another nice addition is the ability to store a couple of bottles or glasses in your inventory and throw them as distractions later (a distinct improvement on the original system).

However, the other systems have been ruthlessly simplified. The wide range of surfaces has been reduced to 'broken glass and water: extremely loud', and 'all other surfaces: silent except when running'. Similarly, the number of variables impacting visibility have been drastically reduced. Compare the shades of the .gif above to the three states shown below:
I know it seems unfair to contrast three still images with a looping gif, but those really are the only three states. I spent about ten minutes carefully sidling and jumping and moving in and out of light and that's all I could get. In practice, the middle state hardly ever occurs, and so for a good two-thirds of the game stealth is effectively a binary system: you're either fully illuminated and visible, or in shadows and invisible. Moreover, lighting is the only factor affecting your visibility; moving or crouching make no difference either way, and neither does drawing a weapon (even a fire arrow).

What's happened is that the focus of stealth has moved from shadows to cover. While line-of-sight was of course a part of stealth in Thief, it wasn't awarded anywhere near the degree of prominence it is in Thief. Levels like 'Dirty Secrets' (the brothel) are designed almost entirely around cover, as much of them are permanently fully lit. I find myself crouching much more while playing Thief than I did the earlier games, and it seems to be because there are so many chest-high walls to hide behind (disguised as crates, tables, chests of drawers, etc.).

Now, there's nothing intrinsically wrong with using cover instead of shadows, but it is an interesting choice, especially considering the effort that has clearly gone into creating the excellent lighting effects. Obviously we can only speculate as to why certain decisions are made, but it is certainly possible to feel the influence of previous games, particularly Dishonoured (2012) and Deus Ex: Human Revolution (2011) which, like Thief, was made by Eidos Montreal.

Stop copying me while I'm copying you

In both these games, the stealth is based primarily around cover and line-of-sight, and so both games necessarily have mechanics that allow the player to move quickly through the available cover. In DX:HR this comes in the form of the neatly-animated flips and rolls between crates, and in Dishonoured this mechanic is Blink, a short-range targeted teleport. Even more so than in DX:HR, stealth in Dishonoured was dependent on movement and keeping out of line of sight - lighting played absolutely no part. Verticality played a large part in this as well - Blink allowed you to teleport upwards as well as along - and any time I had my feet on the ground as opposed to a rooftop or drainpipe I felt as though I was playing the game wrong.

Thief, having begun to transfer its eggs into the cover basket, realised that it needed a cover-transfer mechanic too, and so 'swoop' was born. Swoop, activated by hitting the space bar and hoping that you're not standing near a context-sensitive jump-point (hah, just kidding, there are only about ten places you can jump in the entire game) moves the player forward very rapidly for a short distance. Thematically it's bizarre, but mechanically it works surprisingly well, helping you to quickly escape a tricky situation, silently approach a guard to blackjack or pickpocket them, or, and this is its main use, to pass gaps in cover. Crouched behind cover, by the end of the game I found that I was almost completely disregarding whether an area was well-lit or not in favour of simply remaining out of line of sight and swooping to my next hiding point.

But, really, why does that matter? Both Dishonoured and DX:HR were excellent games which relied on cover-based stealth, so it's clearly not an intrinsically bad mechanic. So is this preference for shadows over cover simply nostalgic conservatism?

Well, not completely. The thing about cover-based systems is that they require cover, and this necessarily limits the options open to the player and the designer. Unless there's some way of manipulating or moving the cover (and there isn't, really, in any of the three games being discussed here, occasional crate-dropping aside), the player is limited to the paths laid out by the designer, and the designer is forced to create those paths to make the level playable. Put simply, cover systems are waypoint graphs; shadows are navigation meshes.3 The shadows of the early Thief games allowed for much more emergent gameplay, as the player is freer to move around a particular area, as opposed to being spotted as soon as they move from cover or their conveniently placed overhead ledge. In DX:HR the relative linearity of the cover didn't matter, because the levels were only a small part of a much larger game which placed more emphasis on its mass of narratives, character interactions, and upgrade systems, and in Dishonoured Blink was such a powerful tool that it drastically reduced the amount of cover needed, in turn freeing the developers from having to build obvious paths for the player. However, Thief has no such saving graces, and it suffers for it.

An example. Below are two screenshots. The left-hand one is from Thief (2014), the right-hand one is from Thief II (2000). Both are from the second missions of their respective games, in both of which Garrett is required to break into a large warehouse. You should be able to click the images to embiggen them.

Imagine that in both these cases the player wants to cross the courtyard. In Thief, the cover-based stealth means that the route through the courtyard is an obvious choice from a very small number of possibilities. All the beautiful corpse ash floating around makes it a little hard to see, so I've highlighted the route in red. If you like, you can use water arrows on the flames circled in blue, but it's not really necessary as you can swoop through all the lights. You can of course move through the courtyard however you like, but there's a dog on the other side, which limits the area in which you can move undetected. The 'alternative route' here is located under the bridge, where there's a hatch which allows you to press 'E' to skip the courtyard (if you bought the wrench).

Now look at the right-hand image. I've turned the gamma up massively because otherwise it's basically a black screen, but observe how this courtyard (apart from being bigger than most of the level in Thief) doesn't use crates as primary cover. There are gaps between them into which you can dash if you hear a guard coming, but their cover is temporary, meant as a stopping point rather than the main means of approach. Instead, the player must stick to the shadows (which, sadly, aren't really shown here as a result of the aforementioned gamma tinkering) in the middle, and distract or dodge the guards as they approach. For alternative routes, the player can backtrack and climb up to the ledge on the building on the left, or go through the warehouse itself (or even all the way around it), or hug the right-hand wall and climb the crates wherever possible - a slow-fall potion in the crate I'm standing on means that should you wish you could float onto the next pile and work from there. The player has much, much more freedom, despite the level containing much less cover and clutter.

I don't want to talk too much about level design here - that's something I'm saving for next week - but I think I've made it clear how a level designed with cover in mind can overly restrict the player and produce unpleasantly linear levels. That's not to say that it's the only factor affecting a level, or that cover-based systems always produce bad results (see the discussion of Dishonoured and DX:HR above), or even that the above example is fully representative of Thief (though, sadly, it is more representative than it should be), but simply that in this case it's been more of a hindrance than a help.

Next time (hopefully), plausible level design.


1. In case it wasn't clear, I'm using 'Thief' (sans italics) to refer to the original series, and 'Thief' to refer to the 2014 release. If people in marketing weren't bitter, empty simulacra of actual human beings this would of course be unnecessary.
2. In many ways, Yahtzee is the Foul Ole Ron of the video game world, dropping occasional insights among amusing profanities.
3. For those who have absolutely no idea what I'm talking about, a nice basic guide can be found here. 

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