Adam Saltsman's day job is running Semi Secret Software, the self-publishing company he founded with Eric Johnson in 2008. However, he's probably better known for the games he's managed to create in his spare time, many of which have been published on mobile devices through Semi Secret. These include Wurdle, Canabalt, and Gravity Hook.

When Saltsman released the flash version of Canabalt on an unsuspecting world in 2009, he had no idea that it would blow up as it did. At the time, he wasn't even sure why it did. Has he figured anything out since? You'll have to read on.

I meet the game designer in a tent at the GameCity festival in Nottingam, England. It's wet and cold, but rather than complain about the flip-flops on his feet, or the effects of late nights and jetlag on his back, Saltsman is eager to talk about the festival's site-specific version of Capsule (which was originally made for backers of the Venus Patrol Kickstarter, and now available for its subscribers), dubbed Capsule Capsule.

The game begins when the player is led through the city's streets by a "scientist", listening to instructions on the control of a spacecraft. Then, they're enclosed in a tiny, pitch-black room with just the radar monitor of Capsule's game screen and a control panel in front of them, and the sounds of space swirling in their headphones.

Let's start with Capsule Capsule: why the repetition?

Adam Saltsman: That was really more [GameCity] than me. Iain [Simons, festival director] likes to call it "the slowest theme park ride ever". It's a game about an enclosed space, so they actually engineered an enclosed space to play the game in to make it extra uncomfortable, which is exactly what that game is about.

Capsule Capsule

Was that the original idea?

AS: It came from a couple of different places. One of the big inspirations was Lunar Lander, which is a game that I just adore. It has a great physics model and a really great sense of scale. It has a really nice intrinsic sense of challenge, difficulty and accomplishment. It's kind of self-directed: you can choose where you want to land and what risks you want to take. And it also has a thing which I decided I wanted to exaggerate, which is that [after a lot of work] you can just run out of fuel. There are consequences; your lunar lander plummets to the surface of the moon and you ostensibly die a fairly horrible death. That's the game; it's classic arcade fun!

To me, it feels really different to Space Invaders. They're all dire scenarios, but Lunar Lander doesn't have catchy music or the [imitates Space Invader's SFX]. Space Invaders doesn't feel lonely to me. Lunar Lander doesn't even have enemies; the only enemy is the horrible terrain and the crappy landing pads. They have a cabinet at the Exploratorium in San Francisco and playing that for the first time in years [I thought], "How do I not own this machine?"

The controls for it -- nobody would design an arcade machine like this now -- the thrust controls are tiny little push buttons, they look like the kind of thing you would have in a spaceship, like a crappy switch that you're supposed to thumb a little while you look at some meter. Then the thrust meter is this big, clunky thing and the contrast adds to this cool, lonely authentic kind of [feeling]. I wanted to take that and really exacerbate it. What if when you ran out of fuel you didn't crash and die? You just landed and sat there, and now you can't go anywhere. You're stuck.

Lots of the games I make are just the makeable versions of more ambitious ideas. Canabalt, for example, was inspired by Super Mario 1 and Sonic the Hedgehog but the game I really wanted to make was a game where you're a guy running through a city being chased by water. It's like Escape from New York. There's a horrible flood, and some particle physics, [you're] surfing on flotsam and jumping up and parkouring off buildings and rooftops. But it would have been so hard, and especially back then, I had absolutely no patience for projects of that scope. So the slimmed down version of that is Canabalt. I had to take out the water, take out climbing up ledges, and focus on something else.

I always wanted to make a game -- that was not even a game. The game would just be: you're an astronaut on a space walk and your tether breaks. You're doing an EVA [extravehicular activity] and now you're floating through space, and that's it. There's nothing to do. You would be in first-person view, you would see gloves, and the astronaut control box on your chest, and you can look around. It would just be that until you ran out of oxygen. For like four hours. It would be the worst game, but a little bit of that ended up expressing itself in Capsule. You're out of fuel, and the consequences of that are not that you die, but that you have to listen to yourself die, which is horrifying and uncomfortable.

At one point I found my breathing syncing up with the breathing in my headphones.

AS: We talked about that a lot. When Robin Arnott was doing the sounds for the original version and for this festival version, we had a lot of discussion about whether or not we should put them in, whether it would be too corny. Some people think it sounds like a dude who's getting it on, rather than being legitimately terrified. To me, it makes it sound like an enclosed space; you never hear somebody breathing when it's not reverberating off a helmet.

It's realistic, and it's also kind of a gimmick, but it's actually communicating something about the game's environment that we can't communicate, because the game is the monitor. You're supposed to pretend you're in this capsule, and the sound is something that helps you do that. The breathing tells you something about the size of the space you're in.