Fanciful Titles and Greater Understanding
After more source hunting I eventually honed the question down to the following, with a fancy title on top: “Stealth Games: Shadows and Sounds, or ‘How do stealth games make use of audio and visual cues/feedback to improve the player’s immersion'”.
The sources I found discussed at length the composition of stealth games, their general attributes as well as common systems that are found in most games. For example, many games give guards simulated ‘eyes’ and ‘ears’.
The former will make use of vision cones to spot the player within line of sight. However a single vision cone makes the AI easily exploitable, which renders them useless. As such, when dealing with vision cones many games make use of multiple cones in addition to the direct vision. For example in Tom Clancy’s Splinter Cell, guards have a primary sightlight, then a much wider cone to simulate peripheral vision, and finally vision cones at the back to simulate the ‘sixth-sense’ of having someone over your shoulder.
For cover scenarios, games might use raycasts instead to determine whether or not the guard can see the player. Once again, depending on the complexity of the game, guards might raycast to various body parts instead. Depending on the amount of bodyparts properly connected by the raycast, the player will be spotted.
A final common factor to stealth games is an awareness meter, that makes it so players aren’t immediately spotted when they are seen by guards. Depending on the conditions in which the player finds themselves, such as being in the distance, in dim light, immobile or crouched, the enemy’s awareness meter will fill up to eventually detect the player. When this happens, guards will become alert and start searching for them, or attacking them if within direct line of sight.
Guards can also be made aware of interesting objects that tell of the player’s passing: open doors, mines, dropped objects, etc. In return, this might place the guards and enemies in a searching state until they inevitably track the player down should the latter not change position or move.
In Thief, guards can exchange information depending on what they’ve discovered. In one of my playthroughs, I had left a door openleft a door open and ignored a guard, only to find out that the NPC had communicated my actions to other patrols which led them all to remain in a curious state, swords drawn and making my playthrough a tad more difficult.
Simulating hearing becomes more difficult, however put simply: all sound in stealth games have a distance depending on the volume of said sound. Tossing a stone is going to create sound that travels less than firing a gun. Guards have a predetermined range of hearing, and should the sound waves reach that range, then they are made aware of it. Thief thrives off of its soundscape, allowing both player and guards to closely monitor each other’s movements through listening to the sounds they produce. Mark of the Ninja makes all of these typical systems clear to the player due to the 2D limitations of the medium, in an effort to reduce ambiguity and increase the clarity of how systems work.
For Thief its clearly delineated shadows and the light gem at the bottom of the screen, as well as the audio cues that are emitted by enemy NPCs and guards. Thief does keep a certain amount of ambiguity, however, which creates an air of tension and an immersive sense for the player to judge whether or not their actions will be safe. Tom Leonard, Lead Programmer, puts this as: “Its about getting the player’s heart pounding by holding them on the cusp [of being found].”
For Mark of the Ninja its the player’s sprite turning into its darker form when hidden in shadows, and the way systems are displayed make for a more binary perception system. If you’re in the enemy’s vision cone, you’re visible. If you’re in light, you’re visible. If you make noise, guards will be attracted to said noise. This grants the player more control over their environment, which emphasises the mastery your character is supposed to have over lowly thugs and basic guards.
Even then, handicapping awareness and detection systems is essential in order to give the player an enjoyable playthrough. Players will feel cheated if they’re noticed by a guard from the other side of the game map, even if their character is in an open field. In a sense, many stealth games push for a semi-realism that borderlines on immersive simulators more than video games.
Sources Used:
Mark of the Ninja (Klei Entertainment, 2012)
Thief: The Dark Project (Looking Glass Studios, 1998)
School of Stealth, Game Maker’s Toolkit: https://youtu.be/Ay-5g36oFfc
Essential Building Blocks of Stealth Play