A diegetic interface is when a game's interface elements exist In-Universe; the Player Character sees them, rather than just the player ("Diegetic" meaning "within the narrative", eg diegetic music). This is generally handled in one of two ways. Sometimes the normal player HUD is explained as being part of the character's equipment — common if he's robotic, a cyborg, or wearing Powered Armor, and justified if the game is in first-person perspective. Other times, the game simply uses in-game indications of things that a HUD would normally tell you; a wounded character will limp instead of having a Life Meter, for example.
Vehicle simulators call this a virtual cockpit, and it tends to be the most detailed and realistic interface mode short of a hardware sim with actual panels. In these cases, a 2-D control panel laid out for easier reading without scrolling is usually included as an easier-to-program option.
Generally, this is done in order to increase immersion and enhance Willing Suspension of Disbelief; it's much easier to believe that your character is a real person in a real situation when the screen isn't cluttered with inexplicable icons representing health and ammo. In some cases, this also leads to an aversion of Menu Time Lockout: browsing your inventory may leave the player open to attack, instead of pausing the action mid-battle while you apply a handy medkit.
It also helps that drawing the interface all the time can reduce the screen area that needs to be drawn using the more expensive world rendering.
Robo Cam is when one is applied to a character's view outside of video games. Justified Save Point is related. May justifyInterface Screw as well. See also Painting the Medium, where this is temporarily invoked for the sake of Post Modernism, and usually Played for Laughs.
Crysis, which overlaps with Interface Screw when certain enemies and weapons (like EMPs) cause your HUD to go fuzzy or fail entirely.
Crysis 2 also adds a gorgeous new bobbing effect for the HUD when you move, and makes it look more realistic (like a fighter plane HUD). All of this is a wee bit strange when you consider that the Crysis: Legion book calls it a "Brain-Up Display," like a neural interface, but there is some acknowledged discontinuity between the two.
Far Cry 2 has a mix of diegetic and traditional interfaces. Common things like your health bar and ammo counter are on screen for good. Other things, take form in the game world, like the weapon shop which is an old computer in a shack, or the map which is an actual map held by the Player Character in front of the camera.
For example, when Samus gets past certain enemies, they actually cause "interference". Rezbits in Echoes can actually make Samus' Power Suit crash, and the player has to reboot it by pressing a key sequence, much like pressing Ctrl+Alt+Del.
Several environmental effects also serve to remind the player that they have the suit's visor in front of them (e.g. steam fogs it up, water splashes droplets on it, bright flashes cause Samus's face to be briefly reflected on the inside, etc).
The four lights at the top of Samus' field of view, which did nothing in the first two games, represent the power level of the batteries in the Wiimote in the third and the Wiiversions of the first two.
The side-scrolling Metroid games naturally avoid this by virtue of being third-person, but they still manages this in a form: the pause menu from Super Metroid on is designed to look like the inside of Samus' helmet. Additionally, Metroid: Other M allows the player to go into first-person view to shoot at enemies, complete with a Prime-esque helmet view.
System Shock, as part of the cyber-interface implanted in the beginning of the game. The player can even improve the interface by finding hardware, such as targeting aids, health monitors, infrared, a widened field of vision, and a multimedia data reader (a CD drive?).
Likewise, the contents of the upper screen of the DS is identical to the display of the characters' Demon Summoning Program in Devil Survivor 2: this is where they find out the names of the monsters they're being attacked by and they directly refer to the skills shown there later in the game.
In Deus Ex: Human Revolution your HUD doesn't even exist until Adam Jensen gets cybernetic implants (including his eyes) after a brutal beatdown (despite the fact that he didn't actually need his eyes replaced; he signed a really terrible contract, so his boss decided to go with some upgrades in addition to repairs). A hit from an EMP weapon will cause it to short out and reboot, unless you buy an enhancement that renders you immune to electrical attacks.
It was also implied that this was also the case with JC Denton in the first game.
In Bulletstorm, the player character has no HUD until he puts on the Leash, which then injects him with nanomachines.
Battlefield 2142 has the HUD projected onto everyone's NetBat Helmet visor from within. Like the above example, the HUD disappears and the entire screen appears washed-out with flickering static if an EMP weapon goes off nearby. Interestingly, this disruption also disables the networked battlefield system that displays the positions of hostiles spotted by one soldier to everyone on the team.
FEAR 2's HUD is projected on the character's glasses and goes missing when they are briefly removed.
The Project Eden interface appears to be projected on some kind of contact lens as it is seen booting up when the character does something with their eye.
In Borderlands, the cute Claptrap robot gives you the device displaying your HUD before you can even move.
Tribes outfits everyone with Powered Armor as a rule, but the HUD doesn't look particularly diegetic until Tribes: Ascend.
In Uplink, you're a hacker running a computer program and connected to a BBS, and the game interface is said program.
I Miss the Sunrise is a Turn-Based Strategy example. Yes, really. The main character is a commander of a fleet who has a unique protein in their body that, when combined with a chemical, greatly augments their mental capabilities, allowing them to take as long as they want to formulate an order without taking any time from an outside perspective. The images displayed on the screen are what the character literally sees from their cockpit (probably not the menus, though).
In Perfect Dark, Joanna is equipped with a headset that deploys a small screen over her field of vision which acts as the game's menu, similar to James Bond's wristwatch computer from GoldenEye.
MechWarrior Living Legends has the visor HUD for battle armor. When the user's armor takes damage, the visor will start to crack. When the armor is breached and the player begins to take damage directly, it'll get splattered with blood and harjel sealant; at the brink of death, the visor will helpfully plaster USER DEATH IMMINENT on the side of the visor. When the Auto Doc kicks in, it displays that it is dispensing morphine. All of the HUD is built into it; weapons, missile status, radar, and health are all integrated into the visor's design.
In Ghostbusters: The Video Game, the HUD (health, ghost HP, and pack temperature) is displayed right on the Proton Pack itself. Things that pop out of the pack tell you which gadget is in use.
The computer game of Monty Python and the Holy Grail had a "King Arthur vs. the Black Knight" minigame. Playing as the Black Knight gives you a Robo Cam HUD with a (useless) sonar display, a very tiny screen (comparable to an actual knight's field of vision) and a miniature Black Knight icon showing which limbs are getting hacked off! When all arms and legs are gone, the "ATTACK" light changes to "BLEED," as King Arthur taunts, "What are you going to do, bleed on me?"
République has the player remotely controlling cameras using a phone/tablet-based interface that you are connected to via a third party.
Serious Sam gets his HUD, including a crosshair which tells him how much health a currently-targeted enemy still has and detailed info on his weapons and enemies, through having an AI implanted in his brain. Serious Sam II implies that the "Secret <whatever> found!" messages are also the result of said AI, due to her being Suddenly Voiced and announcing these found secrets to the player if they have her set to do so.
Ghost Recon: Advanced Warfighter has a helmet visor HUD, which displays the locations of visible enemies, allies, vehicles, and objectives. ECM devices or other disturbances will cause it to get jumpy and fill with static, and it even gets damaged in one of GRAW 2's missions. Future Soldier continues the trend, including having a mission (Ember Hunt) where the system has to be rebooted, denying you its use.
Similarly, Call of Duty: Black Ops 2 has a HUD accessed through the player character's Cool Shades. Unlike Ghost Recon, the game doesn't go out of its way to create a plot point existing solely to jam it for long periods of time - there are still a few Interface Screws, but they are temporary and usually self-afflicted at best. Modern Warfare 2 and 3 also treat the HUD like this in multiplayer, where getting hit with an EMP knocks it out entirely for a minute or two.
Quake IV has a HUD that gives your standard health, armor, and ammo readouts, at least part of which is given from the medchip implanted into every Marine, and displayed to Kane through his cybernetic eye. Additionally, most weapons in the game have some form of ammo counter on them to inform the user of how much ammo is left in the magazine (the SMC's Machine Gun and Shotgun have numeric readouts, while the Strogg's Nailgun and Lightning Gun have a series of pips and side-tube-things that depress, respectively).
Breakdown at first appears to provide you with a HUD as regular part of the gameplay. Then, about halfway through the game it reveals that you have been inside a machine reliving your memories, and the HUD was an artificial addition there. For the rest of the game you have to go without.
Interestingly, TheSplinter is an example of this in a Tabletop Rpg: You play a Player in a virtual reality simulation. Your Player must make a control test against their Avatar in order to bring up their HUD (which is the Avatar's IRL character sheet).
Many older Racing Games replace the HUD with the car's dashboard when using a first-person viewpoint.
Gran Turismo V has realistic simulated interiors for all its cars, a first for the series. "Premium" cars have painstakingly detailed interiors, while "Standard" cars have generic black interiors, though the standard HUD gauges are laid out in such a way that it looks like the car has working a working tachometer and speedometer.
Forza Motorsport has fully modeled interiors◊ for all its cars, with appropriate gauges depending on what the car is equipped with - tachometers, speedometers, boost gauges, fuel gauges, accelerometers, clocks, et cetera. In the high end purpose-built cars, you can actually disable the entire HUD and still remain fairly aware of your status - the car's electronic dashboard or wheel-mounted display will list lap times, your position, remaining fuel, RPMs, gear, speed, and so on. In cars like the Lamborghini Reventon, with its fully digital fighter-jet esque dashboard, it goes all the way to Technology Porn.
Descent and its sequels provide an optional cockpit view to increase the sense the player was Material Defender in the Pyro-GX and successor ships.
The MechWarrior series. The HUD is presumably a function of the neurohelmet every MechWarrior wears to help control the mech. MechWarrior Living Legends has several unique HUD designs to to make each asset feel it has a virtual cockpit - the mech HUD evokes a jet fighter heads-up-display◊. The tank HUD◊ is designed to look like a view through the tank's mirrored periscope/window. Most of the HUD laid out on individual monitors, such as a separate display showing the status of the various armor panels.
Steel Battalion, in spades. Every VT generation has its own cockpit, and Line of Contact adds even more cockpits with support/indirect-fire and Jaralaccs VTs now having their own. The VT Operations Manual goes into extensive detail on what all of the cockpit lights and gauges mean, and not a single one is there for mere decoration.
Orbiter has one for the most popular built-in spacecraft, and the space shuttle. Unfortunately (or maybe not) most of the switches on the shuttle panel are dummies, and most of the special functions aren't usable from the mouse interface. A lot of the better realized add-ons have them, but most skip the extra work and only include a 2D panel.
Too many combat flight simulators to count. Fully realistic settings in most of them will even enforce cockpit view, with no non-diegetic gauges to rely on. The HUD, radar, gauges, etc. may be disabled by damage. In extreme cases such as Falcon 4.0, DCS: Ka-50 Black Shark and DCS: A-10C Warthog, the cockpits are fully clickable to the point where the player can even go through a cold start procedure using the virtual cockpit!
The original Starsiege games: Metaltech: Earthsiege and Earthsiege 2 have virtual cockpits which were unfortunately not present in Starsiege. The entire HUD is displayed on the HERCULAN's cockpit displays, such as the ammo count being displayed from a small counter on the pillars of the cockpit. When the player switches to the command mode, they look down at a map display in-front of the cockpit's joystick. Each HERC had a different cockpit layout.
Ships in the X-Universe games from X: Beyond the Frontier to X2: The Threat had virtual 3-D cockpits, where parts of the HUD were also projected onto panels in the cockpit. On a fighter, for example, the hull, shield, weapon status, and speed may be incorporated into small screens built into the cockpit's pillars. Or on a capital ship, different aspects of the HUD may be incorporated into different "stations" in the virtual bridge, such as having a large Star Wars-esque radar screen to the left of the captain's seat. X3: Reunion removed the cockpits entirely, but they are easily re-added via mods, and some mods add new cockpit designs. The full cockpit returns in the seventh game, X Rebirth.
Aircraft and ground transports in PlanetSide 2 have a 3d cockpit, which displays the vehicle's height, speed, utility status (such as flares or turbo), weapon status, and lock-on warnings on various cockpit displays. Going into third person only shows the vehicle health and weapon ammo on the HUD. Tanks lack a 3d cockpit, though each empire has a faction-unique heads-up-display for the driver.
You can optionally choose to play any of the vehicle levels from the cockpit (including a first person perspective of the speeder bike) in the Rogue Squadron titles which were released for the Nintendo GameCube.
In Anachronox your game cursor physically exists in the world as a "LifeCursor", basically a flying, sentient PDA. Other characters will acknowledge it, and at certain points you'll even see other characters' LifeCursors. All interface screens are also presented as a function of the LifeCursor.
Jurassic Park: Trespasser was probably the first first-person game to have absolutely no HUD. Instead, the player character would verbally call out the amount of ammo left in a gun ("five shots left," "feels half full," etc.) and a tattoo on her chest (which could be viewed by looking down) indicated the amount of health the character had.
In Dead Space, everything is diegetic. Health levels and power-up charge are given via displays on Isaac's suit, menus are Holographic Terminals projected by either his suit or the machinery he's interacting with, and even the "Now, Where Was I Going Again?" hints are glowing lines on the floor generated by a projector in Isaac's glove, presumably in conjunction with the ship's computer (which would, naturally, know how to get you where you want to go).
It does blur the line a bit by providing instructions for Quick Time Events using the same holographic projections. The health bar is explicitly for the benefit of Isaac's coworkers, who can help monitor his wellbeing, but how does a big ol' display saying "MOUSE2!!" help them?
Metro 2033 handles almost everything diegetically. Damage causes your vision to narrow and red out, while low air causes blurry vision and labored breathing. One button lets you look at your watch (which shows time until air runs out and ambient light level, for sneaking) while another brings up his notes (listing your next objective, with a compass pointing the way). The only non-diegetic part of the interface is your weapon selection and ammo count — though for some weapons, even the ammo count is visible on the weapon. Even better, the hardest difficulties turn off the non-diegetic parts. Better count those bullets!
The Director in Crackdown refers to columns of light and other things visible in the game as being part of a graphical interface attached to the player character's eyes.
Fallout 3 and Fallout: New Vegas have diegetic menus in the form of a wrist-mounted computer called the Pip-boy 3000. It somehow lets you do things like use items, manage your equipment and other inventory, and physically examine yourself for wounds. It also runs on an equivalent of MS-DOS. Note, however, that the HUD itself is mostly non-diegetic, as the ammo counter, HP and AP meters, and compass pips aren't justified in-game.
An interesting case in that before you get the Pip-Boy, pressing Tab does nothing. In one quest scenario where you temporarily lose the Pip-Boy due to being in a VR simulation, however, pressing Tab will bring up your wrist... and it only has a Vault-Tec watch on it. This was a small issue for some modders, who sought to remove the visible Pip-Boy wrist model from their character, only to find out that the inventory screen would end up as a close-up of their wrist instead.
The StarCraft II research and armory screens are set up something like this. The entire ship may also count as well.
In the Sly Cooper game series, the sparkles that mark areas that can Sly and the others can use (Climbing, Crawling Under, etc.) are noted as being visible in-universe, to Sly at least, and represent "thieving opportunities". In the second and third games, the starting locations of missions and the locations of objectives are made visible with holographic markers that are also explicitly said to be visible to the characters.
Pretty much everything in the Assassin's Creed series. The HUD, highlighted targets, and even things like the pause menu are explained as being part of the Game Within A Game that is the Animus. Indeed, during the segments outside the Animus, the game goes out of its way to avoid having any sort of HUD at all, except when essential.
This is taken a step further in the modern-day segments of the third game, which include a quadrotor hovering about to serve as a diegetic third-person camera.
Any visual change to any aspect of the HUD are Hand Waved as either a problem with/updates to the Animus.
The Getaway doesn't have any kind of HUD to try and make the game more cinematic and immersible. Rather than a health bar, your character develops bloodstains and a limp the more they get hurt. Rather than floating health kits, leaning against a wall recovers you health (and removes bloodstains). And rather than a minimap or GPS arrow pointing you to your destination, your cars indicators will blink when you should turn, and both will flash when you reach your destination. The game did come with an actual map of London to help you find your way around though.
James Bond in Golden Eye 1997 could switch weapons using the readout on his laser watch. The bad guys would kindly stop shooting and wait for him to finish what he was up to before resuming the firefight.
Splinter Cell mixes it with Product Placement in the form of a Palm OPSAT or a Sony Ericsson phone in pause menus, or in the case of Double Agent, a Nokia 3250 in certain minigames.
In Hammerfight, the tutorial mentions that flying machines are controlled with a mouse.
Truth in Television: at least one bomb-disposal robot was deliberately designed to be driven using an Xbox 360 controller. Putting something familiar in the driver's hands helps him concentrate on piloting the machine, as opposed to fumbling with the interface. If a mouse is what helps...
In NieR, Grimoire Weiss functions as your menu/journal/inventory. When he's not in your party (such as before you meet him), your menu/journal/inventory is extremely limited.
Likewise Analogue: A Hate Story consists entirely of what the investigator sees on the monitor of their ship's comm system, down to the connection glitching when the Mugunghwa's reactor overheats. The ending screen pulls back slightly to show the rest of the cockpit 'you' have been working with.
Quite a few DS games use this with whatever's on the bottom screen, such as:
Similarly, Mega Man Battle Network 5: Double Team DS shows the PET on the bottom screen at all times. It even includes a 3D model of the Blue Bomber himself as a bonus.
In Minecraft, you have to craft your maps, and they only update if you're holding them.
The interface menus in Silent Hill: Shattered Memories are in the form of a shoehorned mobile phone. While it does result in funny things like a messaging menu that can only receive messages, it does add to the immersion—particularly when you are chased by monsters and you need to look at the map.
The video-game adaptation of Peter Jackson's King Kong remake deserves some mention because its Diegetic Interface is a total lack of HUD. Despite taking the exact opposite tactic, it still increases immersion by forcing you to pay attention to how many shots you've fired, your character's movespeed and labored breathing, the ambient noise of the game environment, and so on.
Silent Hill: Downpour is a minor example; there's no HUD, but there are context commands and an inventory screen. The easiest way to tell how much more damage Murphy's taken is Murphy's appearance — whether he can still run or just barely drag himself around and the extent of bruising visible on his body are the tell tale signs of damage. The light given off by his flashlight will also grime up as he takes damage.
Mad TV, set in an office building. You quit the game by going to your boss's office and literally quitting, save the game by opening the safe in your office, and change the game settings by tampering with the control panel on your office computer.
Command & Conquer: Tiberian Dawn didn't explicitly state it in the game itself (though there are hints), but supplementary materials and Renegade establishes that a commander's EVA interface looks and works like that of the game (the idea being that EVA allows for 'tele-generals' that command via computers, like the player is doing). This presumably applies to the sequels, as well.
In the visual novel, Nine Hours, Nine Persons, Nine Doors, the player as the character Junpei finds himself with eight other people engaged in a life-or-death test involving puzzle solving. Certain choices will lead to one of several alternate endings (most resulting in death). However, on subsequent playthroughs (via New Game+) Junpei will somehow remember choices from these previous endings, allowing the player to take a new, alternate path. Only once the player has taken all the available endings will they get the game's true ending, where it is revealed that Junpei has been in psychic communication (both across distance and time) to his friend June as a child, trapped in the same life-or-death game; effectively, the player has been playing through the possible futures that June had envisioned Junpei would lead to, and used her knowledge to provide him with hints to guide him to the only future that would allow her to escape in the past and Junpei to escape in his future. A truly great Mind Screw in narrative.
Mirror's Edge originally had no permanent user interface elements, just like a runner wouldn't have any in Real Life. However playtesting revealed that a lot of players suffered motion sickness, so a (very small) permanent crosshair was added to provide a fixed point of reference.
In Grand Theft Auto IV and expansions, the player character's cell phone. It pops up in the corner of the game screen, but if you look over the character's shoulder you can see it being used in their hand.
An interesting and very specific example in Odin Sphere. The in-between chapter menu has the player taking control of a little girl reading the events of the story, helping to serve as framing for the game's storybook style.
A relatively minor one: Portal has level numbers, as well as a few hints on what to expect, built into the white signs at or near the entrance of every test chamber. Of course, this stops being useful once you go Off the Rails.
Doom 3 features a minor example. It features a very classical HUD, but when the player is wielding a machinegun, the ammo counter disappears from the HUD and is replaced by a counter integrated inside the actual weapon (on a screen on its top).
Naissancee doesn't really have a HUD, unless you count the circle that shows you when to press the LMB to breathe.