Breasts swing. They sag. They flop. They can move. Over the years, many games have tried to emulate the way breasts behave. There's even a term for it: "Breast physics."

If you've played games that have breast physics, you've probably seen how uncommon it is for games to show breasts that move like what they actually are: bags of fat affected by gravity. Instead, it's more likely for a game to depict breasts as helium balloons that have minds of their own. Certain games have failed at rendering realistic breasts so widely that some people seem convinced that bad breast physics are the result of sexism, or of an industry that likes to objectify women. I've seen unfair conjecture about whether or not developers have ever interacted with real-life breasts. I've seen people imply that developers simply don't know how to properly characterize women in games, and that gaming's ocean of unrealistic breasts is what happens when we have so few women developing games.

Are any of these sorts of claims true, I wondered? Plenty of people theorize about why games often feature bad breast physics, but there is little hard information about the actual breast-creation process. After looking into it a bit, I found that many amateur developers seemed to genuinely have a problem figuring out how to tackle breast physics in their games. There are a startling number of forum posts and tutorials where people discuss the best ways to achieve good breast physics online. One person even created a four-part Powerpoint presentation titled "The Quest for Boob Jiggle In Unity." People have developed specialized tools for other developers to use, to help demystify the enigma that is "how do breasts work."

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Meanwhile, veteran game developers have been messing around with the way breasts move for almost two decades now.

And in case it needed to be said...NSFW warning!

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1992: It Begins

In 1992, a fighting game called Fatal Fury 2 was released. Described by some as a "blatant clone" of Street Fighter II, Fatal Fury 2 did actually have a few noteworthy quirks of its own: it was a gorgeous-looking game that allowed players to perform "desperation moves" when their health bar was low, and it gave players a chance to get out of danger quickly through a hopping mechanic.

But let's be real. One of Fatal Fury 2's biggest contributions to the medium was that it was the first game to introduce a character with breasts that moved on their own.

(Source: TheInnocentSinful1)

Known as Mai Shiranui, that character is famed for having very, uh, lively breasts. Though Fatal Fury may not be a huge franchise nowadays, its legacy is very much alive: many top fighting games include a similar jiggle effect:

Street Fighter 4

(Source: CeruleanNight)

Soul Calibur

(Source: Thegamerwalkthroughs)

Skullgirls

Of course, fighting games aren't the only games that have wrangled with breast physics over the years.

Tomb Raider

(Source: sys2074)

Resident Evil

Metal Gear Solid

Ryse

When developers don't include breast physics, it's not uncommon for savvy players to take matters into their own hands via modding. A popular type of Skyrim mod adds most robust breast physics to the fantasy game:

(Source: Marek Iwanowicz)

In 2009, there was also a Second Life mod that allowed players to add breast physics to characters. It became so popular, the actual game ended up incorporating the same feature—and now players try to advise each other on how to fiddle with their characters to achieve the best effect.

(Source: BlakOpalDesigns)

Even Minecraft players have figured out ways to add breast physics to their game. Then again, Minecraft players have tried their hand at adding pretty much everything to their games, haven't they?

The Most Famous Breast Physics of Them All

When it comes to breast physics, the most notorious game of them all has to be Dead or Alive. While breast physics might just be a minor 'feature' in the games I mentioned above, for Dead or Alive, breast physics are woven into the identity of the game. That emphasis might give the games a bad rap, as Mike Fahey argues in his piece about Dead or Alive, since fans find plenty to love in the way the game plays, some of which have nothing to do with breasts. Still, you can't really divorce Dead or Alive from its breast physics.

(Source: Thegamerwalkthroughs)

"I wanted to do something that would attract people's attention as I worked on the DOA game," Itagaki said in a Game Informer interview from 2004. "Of course, DOA is known for its bouncing breasts...when I applied [breast physics] to a 3D game, it was almost too much for people."

One of the big selling points for the latest game, according to the marketing at least, is the new engine—which will allow players to adjust the breast physics on their characters.

"We call the technology we used to advance skin and breast physics and make that a reality, the 'Yawaraka Engine,'" Yosuke Hayashi, producer on Last Round, told Famitsu. "Once you see it on the new consoles, you won't be able to go back."

What they're saying: thanks to the power of technology, the development team has realized more complex breast physics. The marriage of technological prowess and sexuality is a curious one...of course, anyone that watches footage of Dead or Alive knows that the series doesn't care about realistic physics, not really. Instead, the game has always featured outlandish physics, both for the breasts and for the gravity-defying fighting moves. Whatever misgivings people have about the realism of the breasts, the intense physics seem like a deliberate choice meant to realize a particular aesthetic.

Can the same be said of other games? I've spent the past few months trying to talk to developers about breast physics. It's been surprisingly difficult getting people to talk—I've had an easier time trying to poke people for details about high profile unreleased games than I have asking them about why games depict breasts the way they do. Despite speaking to a number of developers on the subject, only a few would speak to me on the record. Fortunately, I've managed to get a basic handle on how breast physics work.

How Video Game Breast Physics Work

Basically, in a modern game with 3D graphics, each character has a model. Underneath the textures that cover them like a "skin," these models are made up of "bones," which can be manipulated so that the character can move. The number of bones a character can have depends on the game's graphics engine; certain engines allow for more bones than others. The number of bones a character has also depends on the overall number of characters rendered at any given moment—the more characters there are, the more taxing it is on whatever hardware is processing the game, so the fewer number of bones each of these characters is likely to have. (Thankfully, real life doesn't work this way!)

All of these bones are prepped to be animated via a process called "rigging." Rigging allows developers to determine the extent to which a model can move, and how. Breasts don't generally move of their own volition, they move in reaction to something else, much like hair and clothes do. If a developer wants breasts to move, then they'll likely "rig" a character's chest area. How the breasts move depends on how many bones are in the bosom area: when breasts both move in unison, it's likely that the model's chest has a single joint. If both of the breasts move independent of one another, the chest likely has at least a couple of bones rigged.

(Source: Maya Learning Channel)

"Mechanically, breasts anchor off the pectoral but loop up and connect at the shoulder, so they get pulled back when the clavicles move," Tim Dawson, an indie developer that has previously worked on games like LA Noire, told me.

Once breasts are rigged, developers can add breast physics in a couple of ways. Breast movement might be dictated by a simulation system that lets developers add "springs" to breasts. These springs take motion and use it to determine how much something should move after, say, a character jumps up and down. Springs help make it so that breasts can continue to move even after a character becomes still. If a character has two springs, one might be used to determine how far a breast bone is distanced from the sternum, and a second spring might control how much the breast deviates from its starting point. Then, on top of all of that, developers can add a dampening effect that determines how long it takes for the breasts to settle down.

"Imagine the character standing up," Dawson said. "The sudden movement would pitch the breast bones downwards. Then when the character reaches their standing height, the bones catch up, pitching upwards slightly, then back down and come to a rest. This would be a procedural breast bounce and settle. The rest just comes from thinking it through: how much heft are [the breasts] likely to have, how well-supported are they?"

Why Developers Get It Wrong

I'm told that a good number of games use this system. Thing is, a spring system isn't necessarily effective in creating realistic physics, but it is considered a cheap, easy solution to add breast physics. Some engines even come with it built-in. Spring systems are meant to help with something called "rigid body physics," and, well, breasts aren't rigid. To create realistic breasts, you'll need something called "soft body physics simulation," and it's a lot more taxing for a computer to calculate.

Another way to add breast physics involves animating the breasts by hand—that is, the breasts would be treated no differently than other major body parts, like arms or legs. In this case, the breast physics aren't left up to a simulation system but instead determined on a case-by-case basis by an animator. I'm told hand-animated breasts are rarer than a sim system, due to how time-consuming it is. Animating breasts is a real handful, so to speak. (Sorry.)

While those aren't the only ways to animate breasts, they help explain a few things. Why distinct breast physics are so prevalent in fighting games, for example: when you only have to worry about two characters on the screen on any given moment, of course developers can add details like breast physics. Fighting game characters characters can likely have more bones than characters in an average game. The difficulty of crafting breast physics may also explain why so many games have strange-looking breasts: developers who are interested in adding this detail can't financially justify doing so, so they have to cut corners any way they can.

(Source: Huy Tran)

Still, it'd be a stretch to suggest that unrealistic breast physics are purely the result of technological shortcomings. Breast physics are a choice, after all, and not every game implements them.

One developer who I'll call "Alex," because they didn't want to be identified by their own name, told me about a situation where breasts had gone wrong—and it wasn't the result of tech limitations. Alex told me that their studio was very concerned with its depiction of breasts. Even so, there were stumbles along the way.

"The very first thing I noticed when [the studio was] animating breasts is, I would look at them, and they were just not moving in a way that was even remotely natural," Alex said.

"I remember saying to the artist, 'the breasts are moving wrong.' And I remember directly asking him, 'Have you watched breasts move? Have you actually watched breasts move?"

Chances are good that the animator in question had in fact seen breasts before. The thing to remember is, it's actually damned hard to remember how breasts actually move. As a card-carrying Breast Haver™, even I'd have to check how my breasts act before being able to properly gauge them in a game. Of course, it's an animator's job to figure this stuff out.

"I think [people] remember the fantasy of breasts, like how we remember lips being redder, how we see waists as [smaller than they actually are,]" Alex explained.

"If you're around animators working, you often will see them stand up, or they'll ask someone they're working with—they're trying to watch the motion, they will film themselves doing that motion. Interestingly enough, I've never worked with any female animators.

"Anyway, while doing these things, [animators would] swing their arms, and try to get an idea, they're looking at what the animation is like, and I think...breast physics are often accentuated in a game, without the movement that would create that accentuation."


"People remember the fantasy of breasts."


Absurd breast physics aren't always unintentional, though. A couple of developers described situations to me where people took breast physics too far on purpose, because if they put the work into making sure breasts can move, they're probably going to want people to actually notice it. This phenomenon is not exclusive to breasts. If a developer puts time into any detail in a game, they probably want players to notice it. That's why we get development videos about how a game handles things like wind, or how a character's cape sways: these aren't the sort of things that truly determine the quality of the game, but they are things actual humans likely spent a lot of time implementing.

"When a developer goes to the trouble of setting up the breasts to move, there's probably someone keen to see it working,"Dawson told me. "So, if you're not careful, that translates into breasts that swing and bounce at the smallest hint of motion. Picture the boss of the studio coming in and wanting to know why he can't see any breast-bounce when the character is talking. The effect is increased until her breasts are reacting to the chest movement of her dialogue animation, but now it's going to look ludicrous when the character runs around performing actions. But the person implementing it is told to leave it like that because somebody thinks it's cool that way.

"Ultimately though, I sort of suspect that when a developer doesn't get breast physics looking right, it's because, for whatever reason, somebody wanted them to look that way," Dawson said.

Obviously, Dawson can't speak for the decisions made at studios he doesn't work for, but what he's saying makes sense. Soul Calibur developers, for example, have been pretty open about the fact they have an entire system revolving around the depiction of breasts in their games:

There's no doubt there that they very much want the breasts to look and function the way that they do. But just because it's intentional doesn't mean it'll be received well.

"Every other woman in the universe has sort of a cringe reaction, you know? 'Boobs just wouldn't move that way. That's not natural'" Alex said. Alex would know; at Alex's studio, the models were all focus tested. The developers actually received feedback from women who saw the game. While it may not be typical for most studios to do this, in this case, research was conducted because there weren't many women game developers on the team that could weigh in on the subject.

"Across the board, [the response from women] wasn't a neutral response, it was a negative response," Alex said. Curiously, the negative response occurred both when the physics were unrealistic, and when the physics were turned off. It seems as if there's a very fine line to walk when it comes to breast physics: they can't be too exaggerated or too toned down without having people feel as if something is wrong. You might think of it as "the uncanny valley of breasts."

We Like It Like That

It was through focus testing, the usage of good reference materials, and honest conversations about anatomy that Alex's studio was able to improve their breast physics. But, when I say "improved," I don't necessarily mean "made more realistic."

"Many games are full of exaggerated [male] forms," Alex said. "We don't point at those and go, huh, that doesn't look realistic at all. Of course it doesn't! It looks superpowered, and we like that. The same thing would apply to breasts."

Tim Dawson seems to agree. To him, developers tend to include unrealistic breasts, because exaggerated bodies have become a staple of the medium.

"The developers might be playing fast and loose with their anatomy, like breasts that are too large or too unsupported for what the character does, or that are just in an unnatural shape," Dawson said. "I once received a female enemy model that appeared to have balloons protruding out of her torso and couldn't convince the art director that it needed fixing.

"But even when well-modelled, if a character with breasts the size of watermelons is wearing a metal string bikini and attacks enemies with cartwheels, it's going to be hard to make the breast physics look realistic because the scenario is not realistic," he said.

"People like the movement of breasts, that's a hard-wired thing in our heads," Alex said. "So, for some people, exaggerating that is a net positive. I think [breast physics] are in games for that reason."

Ideas For Game Developers

Regardless of whether a studio is going for realism or digital beauty, there are still video-game breasts that look good, and breasts that look ridiculous. Game developers can do some things to help swing more toward the former.

"Just run it by a few people, run the animations by people," Alex said. Alex emphasized to me that this was particularly important if the studio doesn't have many women.

It's also worth considering what kinds of breasts the game has on display. Alex pointed out that there's a difference between natural breasts and augmented breasts. A person's specific body-type can influence how breasts move, as well. Some people are bigger than others, and this affects the way their breasts move. Some people have breasts situated at different heights on their chests. Some people have perkier breasts than others. The list goes on. "Even the absolute best natural breasts have some sag," Alex said. It's important for developers to think about these things, if they're interested in better breast physics.

Another thing that Alex suggested was for development studios to make use of porn, particularly older pin-up nude magazines. Really. It's apparently great for reference material.

"[They give you] a really good opportunity to see, 'where is the nipple placed? Where do the line on the chest? What is the curve underneath?'

"I don't [think] breasts need to be realistic in games, unless that's what [developers] are going for…but [developers] should be aware that if the breasts are moving in a weird way, then it just becomes the uncanny valley for women."

With these things in mind, maybe games can get better at depicting breasts. And when that happens, maybe the game industry can move on to figuring out the mystery that is…dick physics.

"If I were animating a naked man walking, I really honestly have no idea how balls move," Alex joked. "I don't!"

Illustration by Jim Cooke.

To contact the author of this post, write to patricia@kotaku.com or find her on Twitter @xpatriciah.