The unseen art of invisibility in games

In 1985, brothers James and Jim Thomas penned a film script, The Hunter, about an otherworldly creature armed with near-magical powers of camouflage. The script has a counter-intuitive take on the concept of invisibility. Rather than a mere blank spot, the Hunter exists as traces of motion without coherent form, designed to produce "a dizzying, subliminal experience" and "an intensely visual, highly emotional confrontation for the viewer." During production, special effects teams used ‘inline mattes' to superimpose concentric images of background foliage onto an actor. This fake translucency turns the landscape itself into an aggressor: when the Hunter or, as we know him today, the Predator finally attacks, it's "as if the entire wall of the jungle were rushing in". 

Paid homage to in every halfway-stealthy game from Crysis to Deathloop, the Predator is the nearest we have to a patron saint of invisibility in games. The weirdness of invisibility in the film – not just a Clancy-esque gizmo, but an assault on the viewer's consciousness – reflects the startlingly varied forms invisibility takes in different species of game. Invisibility can be the ultimate power fantasy, as anybody who's ever been brain-jacked by Sombra in Overwatch can attest. By extension, it can be a nightmare to balance, whether you're designing a PvP shooter or simulating the reactions of AI guards to a cloaked invader. 

But it can also be an atmospheric device, a source of dread and uncanniness even in the mind of the camouflaged player. At its most arcane, it speaks to a long association between computer technology and magic, between feats of stage illusion and the ocular tricks all videogames necessarily consist of. 

Behind the curtain

Among the Predator's least expected descendants is Maid Marian or rather, Marianne, one of the playable characters in Sumo Newcastle's bloodthirsty medieval heist game Hood: Outlaws & Legends. A grisly retelling of English folklore, Hood is all about completing objectives undetected: two teams of four must escape with a treasure chest while quietly murdering each other and fending off AI guards who double as a map-wide surveillance system, fl agging anybody they spot on the enemy team's HUD. Marianne is the team's assassin (Robin Hood, of course, is the sniper), and while she doesn't have infrared vision, she's every bit as fearsome in the right hands as the interplanetary terror she's inspired by.

Hood's AI is slower to notice Marianne than other characters, and her passive Shadow ability lets her perform assassinations from the front. She can also toss smoke bombs to set up multiple targets for a takedown. But her most devastating trick is Shroud, which untags her and turns her character model semi-transparent. "We wanted it to almost feel like God mode," says Andrew Willans, game director. "This ability that allows her to literally to walk in front of AI to assassinate them and chain those assassinations together using perks, so that hopefully when you get into the fl ow, it's like shiv shiv shiv, one after another, and the AI just has this delayed response, ‘Ooh, Steve's just been killed', but they can never quite pinpoint you."

Designing Shroud to work against AI was straightforward enough, Willans says. Designing it to feel fair in PvP was a different story. "I think that was probably one of the hardest things throughout development to get right." Sumo experimented with total invisibility, but this proved "impossible" for opponents, "so it was kind of working back from there." Some early prototypes for Shroud were downright horrifying. "We had a bug for about three months where her eyes stayed visible while cloaked. It looked so sinister – now that was truly the Predator."

View to a Kill

A pivotal moment for Sumo was remembering that the Predator is much more apparent in motion. The creature's camouflage acts like a camera lens running over the backdrop, distorting the scenery. The challenge then became to decide exactly how transparent Marianne's Shroud should be – and how much control players should have over the effect.

"She's roughly 50% [transparent] with her base ability," says Willans. "If you use a perk, you can actually increase that to more like 75-80." The Hood team also drew on the lessons of Eve: Valkyrie, its VR space dogfighting game for CCP Games, which features a stealth ship influenced by the cloaking Klingon warships in Star Trek. In Valkyrie as in Hood, the faster you travel the more conspicuous the shimmer of the background through your craft.

Marianne's invisibility formed part of a larger conversation during development about immersiveness and mood. Sumo considered adding a visibility gauge, akin to Thief's light gem, but removed this for a couple of reasons, one being an inevitable gap between HUD feedback and what other players could actually see. "People would look at the user interface, and they'd go, ‘all right, I'm safe. I'm in darkness', and then somebody comes up behind them and cracks them on the head, and [they're] like, where did that come from?"

But Sumo also wanted to cultivate an atmosphere of dread, even in the mind of a hidden player. "I like to leave a little bit of ambiguity there," Willans says. "[So] that there's a bit of tension for you, even as the assassin – am I hidden enough? You almost want to get one of your mates to check – can you see me? Can you see the whites of my eyes? Can see the glint on my weapon?" Grounding the stealth in what players perceive makes Hood's strangely ahistorical setting more convincing, of course. "If you're hiding behind a tree which is breaking line of sight, that feels more natural than [saying that] you're crouched in a bush and are now fully invisible to other players."

You might expect Battlefield, the definitive photo photorealistic military shooter, to have similarly elaborate ideas about camouflage, but in a game of large-scale PvP with a fanbase of millions, questions of balance take priority. The recent Battlefield 2042's reconnaissance ‘specialists' may seem dressed to blend in quicker than other types of soldier. Take Casper, described in-game as a "master of camouflage": he sports a ghillie suit, an iconic variety of stealth gear which uses long strips of cloth, twine and foliage to break up the wearer's profile against matching scenery. But as I learned during a discussion with the multiplayer design team, DICE wanted every character in the game to have the same "baseline for visibility", ghillie suit or no.

Uniform appeal

The game's generous spread of camo patterns are more about visual variety – and, reading between the lines, microtransactions – than letting players seek tactical advantage. In practice, stealthy characters in Battlefield 2042 are distinguished less by their ability to hide than by their ability to spot and tag using UAVs and sensors.

DICE has, however, flirted with invisibility modes at times in Battlefield's tumultuous history. Battlefield 2042 is the gritty, near-future ‘sequel' to Battlefield 2142, a work of outright science fiction featuring an active camouflage gadget that renders the wielder up to 90% transparent. Where Hood riffs on Predator, DICE's primary inspiration was anime film Ghost in the Shell, whose cyborg protagonist has thermo-optic mesh for skin. This idea of invisibility is far-fetched, but not impossible: real-world active camo technologies exist that continuously adapt an object's appearance to resemble its environment, such as Ray Alden's 2001 US patent for a "cloaking process" made up of segmented pixels.

Active camo in Battlefield 2142 comes with hefty constraints. The device has a short-lived battery, gives off a telltale whine when activated, stands out more in well-lit chambers, and can't be wielded alongside a gun. But even given these drawbacks, it is an eerie and compelling tool of war – warping the environment behind it and so encouraging both user and victim to think harder about the game's light levels and play of indoor and outdoor spaces. Hood's Shroud ability takes this further: to survive Marianne's attentions, you must ceaselessly monitor light sources, corners or high-contrast foliage for that telltale ripple of interference.

Playing as Marianne, you grow acutely conscious of how the Shroud interacts with certain textures or colours, and how conspicuous you are based on relative position and motion. Well, providing you can see yourself at all. "This is something that I struggle with even now in the game," Willans says. "When I use her perk to make her even more invisible, like 75% transparency, I lose connection with the character – suddenly I'm kind of just looking for an input that says ‘assassinate'. I'm less connected with the game world. So you know, it's all psychological."

Grid versus Ego

That eerie sense of disconnection is integral to Invisigun, Sombr Studio's same-screen top-down blaster in which every player is invisible by default. Characters pop into view when firing or using their special abilities, but are otherwise only perceptible when they interact with the terrain – brushing through foliage, splashing in puddles and leaving footprints in snow.

Invisigun's lead programmer, designer and audio engineer Shadi Muklashy came up with the concept while working on mech shooter Hawken, which features an invisibility device. Earlier versions of the game used analog movement, but this was confusing. "It was almost impossible to sneak around without bumping into anything, and while it was fun, it lacked precision and strategy. One of my game design friends suggested movement on a grid, with the rationale being that since invisibility is a challenging concept for the player, simplifying everything else would help."

The addition of the grid proved transformative. It allows you to deduce your movements by counting the steps from your last known position, turning an exercise in shooting first into a game of careful measurement and misdirection with a generous pinch of gut instinct – a wholly different way of using the environment in an arcade shooter. Muklashy invokes the concept of ‘yomi' in competitive fighting games like Street Fighter. "[It] roughly translates to mind-reading, or knowing what your opponent is thinking and playing strategically in response. There's a back-and-forth dance throughout fighting game matches where the concept of yomi can snowball and shift dramatically as players learn each other's tendencies. I like to think that Invisigun has unlimited yomi due to the invisibility. Some players can make their opponents panic by simply doing nothing at all!"

Where Sumo's challenge with Marianne in Hood was to balance her Shroud ability for PvP, Muklashy's big hurdle with Invisigun was preserving this element of mind-reading when designing bot behaviour. "Everything the player does broadcasts ‘disturbance' events, such as bumping into walls or stepping through puddles. The bots will notice the location of these events and work their way towards that location and possibly attempt to shoot towards that spot. Depending on the type of disturbance, they will seek out either an exact location, or a rough estimate within a certain radius when they reach line of sight to that spot."

Locking movement to a grid made things easier here too "since disturbance locations are often exact, and path-finding algorithms on a grid are straightforward." Invisigun bots have moments of believable disorientation or uncertainty, depending on their skill level. "There are tolerances and random ranges for almost everything they do. This could be their reaction time when responding to a disturbance, to every once in a while making a misstep or two […] to even not ‘remembering' the precise spot they are seeking."

Decoy Polloi

Thinking about how a player or enemy should feel about an invisible foe opens the way to thinking about invisibility not as a weapon, but an unacknowledged cousin of stage illusion – reliant on manipulating your states of mind as much as the limits of human perception. Digital artist and researcher Mariano Tomatis links the disappearing and reappearing tricks performed by magicians such as John Henry Pepper to modern heads-up displays on car windshields and augmented reality headsets. Both, he points out, are essentially the result of cunning combinations of light and glass. Tomatis also makes connections between military tech and stagecraft: take dazzle camouflage in naval warfare, designed to confuse observers about the type of ship under scrutiny. This too is "based on the same principles used to decorate props involved in stage magic tricks".

Videogames featuring invisibility and camouflage inherit this strange, ancient relationship between gadgetry and sorcery, summed up by the famous Arthur C Clarke quote that "any sufficiently advanced technology is indistinguishable from magic". In a more immediate sense, videogames are all feats of illusion magic themselves. "All stage magic is based on an invisible ingredient – the trick," Tomatis notes.

This is no less true of virtual worlds: all are generated from the unseen workings of computer code, and not even the most expensive and painstaking simulations are literally and exactly what they appear to be.

One game that embraces the strangeness of this is Nix Umbra, a first-person horror ritual set in an enchanted forest. Visible only by the short-ranged glare of your flaming sword, the game's world is randomly generated: its horror comes from not knowing how much of the unseen landscape really exists to be interacted with, and how much has yet to be conjured.

"It's that uncertainty of what secrets the world is hiding from you that make me want to play a game," says ilzard, the game's sole developer. "Also there is a sense of wonder of discovering things by yourself without being told how it works." The developer describes Nix Umbra as a work of the "occult", a term that stems from the Latin for concealment. "I tried to build everything on top of this concept and to let the players try to bring to light its mechanics with each new death."

Groving threat

It would be a shame to spoil too much of Nix Umbra, but suffice it to say that certain… entities are invisible even in the light of your sword, their presence telegraphed by screen distortion and trees bursting into flame. "I was interested in making something abstract," ilzard explains. "So it is not so much a creature in the traditional sense [but] the concept of death itself that I wanted to project.

When ‘death' is close, flashing lights, subliminal skulls and kaleidoscopic shapes start to assault your vision." These ‘psychedelic visual stimuli' – which riff as much on surrealist or folk horror cinema as the likes of Amnesia or Slender – are designed to turn your imagination against you. As with the Predator, it's like the forest itself is closing in.

Invisibility in games, is about more than avoiding detection. It's a complex ambient device that cuts to the heart of videogames as a technological art form. Visualizing equipment like active camo, ensuring foes are just perceptible enough, and imagining how bots should respond – all these challenges invite haunting questions about our interactions with virtual worlds that are fundamentally works of the unseen.