I suppose I should explicitly explain the low key, faux "calibration" we do to initiate the game since it's super not-obvious, on purpose.
tl;dr- it's a magic trick
I'll preface the full story with: I've had my ups and downs with Tobii, the manufacturer of the eye tracking hardware I use. That hardware consists of near-infrared lights and near-infrared cameras pointed at the player, measuring the orientation of their eyes in relation to the screen and the direction of their gaze. I believe it shines non-visible light on your face and sees the refraction off the lenses of your eyes. Maybe you remember when cameras had a big problem with red-eye. I think they're kind of doing it on purpose, exploiting that effect but they're not very transparent about how it works.
I dunno, I'm a Designer who is kind of just making stuff up, not an Optical Engineer but it feels magical. I know that sounds like hyperbole but it truly, truly feels like something wonderful and impossible is happening. The only other hardware that I have felt cast a spell on me like this was a high end AR Head Mounted Display made by a certain magical company that cost 10x the retail price of a Tobii.
I could say other good things about Tobii but that is the main thing that my reader is probably concerned with. The hardware itself is magic, all I had to do is let people see it, which I did by using more magic.
After singing all their blessings, I'll say one problem I've had with Tobii has been how they handle calibration. If I had followed their guidelines, I would've needed to make a custom calibration profile, busting out a mouse, a keyboard and a table on which to use those, for every single one of the thousands of players who have stopped by to play our 1 min game, in every different chair, in every different lighting, in every location. Their focus has been on making their calibration process, which takes at least as long as the game itself, more buttery and it's pretty good these days, I'll give them that, but it's not good enough and I don't think it ever can be.
From a user centered design perspective, the only good calibration is no calibration (well, no conscious calibration) and user centered design is best practices. If I let this one slip, I would be bad at my job.
I was willing to calibrate it a single time once I've brought the device to a new context, with a guinea pig first player, during setup. I gave Tobii that but it was my only concession. The system should be designed well enough that no other player should have to calibrate and I made sure it was.
The list of problems with their calibration goes on.
It also ruins the flow. You'd have to be constantly entering and exiting the game, playing with Tobii's lil' interface. At that point we're bringing the operating system into the experience, muddling up my thoughtfully crafted, begining-to-end design with ugly Windows boxes. gtfo of here.
Tobii's calibration design is not mine. It's not my game. It's not part of the multi-modal system I designed. It didn't match the style guide, it didn't match the mood board (at the top of this page), it didn't match the color palette, it didn't match the interaction conventions I established. That means, philosophically, it broke the main principle of all design- Gestalt which means "the whole precedes the parts." They were sticking parts on what was my whole and it started sending a mixed message which makes it look like the Designer doesn't know what they're doing.
This project is the highlight of my portfolio. I didn't want to risk people seeing Tobii's calibration and thinking it was part of my design... and then having to explain it. That was not the type of conversation I was looking for.
Also it would require tons of busy work, additional explanation and an active booth attendant 100% of the time. My goal was no explanation which we did achieve. There were booth chaperones to make sure no unattended children would break my shit (there was not always a chaperone and yes, some lil' shits did manage to kind of break my thrift shop bar chair.) If people were a bit timid the chaperones would sometimes convince someone to sit down in the chair which could be done with as little as a gesture or two.
Multiple times I've asked Tobii directly to make some kind of general calibration that works for most players or at least makes some kind of best attempt at an average. The last time I told them that that's what I needed they told me to leave the demo booth lol. It's silly because they need the same thing for their own demos!
Tobii's device was already good enough to catch any eye in front of it, but it couldn't guarantee accuracy without calibration. So we didn't get precision and I had to accommodate that in the design. I did this in several ways.
The player never sees where the Tobii thinks they're looking, there is no cursor in the computer perceived center of vision like most eye tracking experiences because that could be obviously broken without custom calibration for every player. The controls are x-axis only which means it doesn't matter where you look up or down, or what height it thinks you're looking at, all that matters is left and right, taking the up/down variable out of the equation entirely, less room for error. Hit boxes are extra large and there is only one long area along the bottom that enemies go left and right on, almost all the movement on the screen is the enemies moving horizontally in a wavy line and they were a very attention-drawing color so there's no reason for the player to be looking anywhere else.
But the gameplay design could only take us so far so I added my own form of "calibration" which actually did nothing on the back end but managed to get people to naturally sit in the chair and look at the screen with no signage or labeling. By reflecting what the hardware saw, simply drawing a circle for an eye, I showed players the position and orientation of their eyes in relation to the screen. They could see what the computer saw, when their body was waving around, and when the eye tracker was losing them and they'd sit like a normal human being which is really all I ask. When the player successfully gets the eye tracker to detect both eyes for couple moments, they would see the circles representing their eyes open wide and lock together, initiating the screen to scroll up smoothly, revealing and starting the level.
Instead of using Tobii's calibration, my design subtly convinced players to calibrate their bodies into a more ergonomic position and my programmer didn't have to get their hands too dirty to achieve it.