Fantastic Contraption, a virtual reality game in which you use motion controls to build all sorts of interesting things in virtual reality, is coming to the Oculus Rift. It's also a game that requires, if not room scale, than at least a little bit of space to play in an optimal setting.

So how do you make a game that many assumed would be an "exclusive" for the the HTC Vive, a system that comes with motion controllers packed in and room-scale sensors, work on a platform that sells itself as a seated, non-moving experience? It turns out that, once the Touch controllers are released, the systems become nearly identical.

"The whole differences between the systems thing? They are slightly different," Andy Moore, one of the developers working on Fantastic Contraption, told Polygon. (He's also written about the different ways to play the game for this publication in the past.) "But if you were to blindfold me and change the controller model or whatever and ask me to guess which system I'm using, I probably wouldn't be able to tell all that easily."

Despite what endless online comparisons may suggest, the two platforms have more in common than they have differences. "The hardware is almost identical. The software and APIs [application program interface] are almost identical. The specs are almost identical," Moore continued. "The Vive can do seated and standing and the Vive you can mount both your lighthouses on one wall. And on the Oculus you can move one of the cameras to the back corner and get room scale."

It's more about how the technology is presented than the differences in how the two platforms work, Moore claims. "The only difference is marketing," he said. "Oculus is putting all their chips behind the fact that no one has a living room or wants to sacrifice the space, and and Valve is saying it's better this way. It's all a marketing thing."

The APIs reflect this, with Oculus' software being geared towards seated experiences. "But it's not limited to that," Moore said. "So we're really excited about room-scale Oculus support. But we understand that most people will have both cameras set up on their desk with the Oculus."

That introduces a problem with room-scale VR in that your body could potentially block the line of sight from the camera to one of the controllers in that situation, which would introduce tracking problems. This is called "occlusion," and blocking the camera and losing tracking on a controller yanks you right out of the game. This called for a change in how the levels of Fantastic Contraption are set up.

"In our game we don't have a sense of forward normally — we drop you in a sandbox and let you do whatever you want," Moore said. They had to change this for the Rift version. "So we spawn the player in the back of the space ... and then you can take a step forward, and turn left and right and build a car and you can see everything laid out in front of you. And that works. And that's what we demoed at the Oculus even just before GDC."

That relatively small design change allowed the player to face forward while playing most of the time, limiting the risk of occlusion while keeping the room-scale aspect of the game. This is possible due to the two cameras the Rift provides however, since the Touch controllers will come with a second camera.

"The hardware is almost identical"

"The single camera on the PlayStation is concerning," Moore said. It should be fine for most games where your hands can be far apart, but in Fantastic Contraption you sometimes need to bring your hands close together to manipulate your contraptions, and the team worries the PlayStation VR may have trouble keeping both hands tracked separately.

But that's down the road. For now, Moore stresses that porting between the Rift and Vive isn't as taxing as one might think.

"I mean, we're using Unity so most of it is drag and drop kind of easiness, but I think the APIs are pretty much identical and identically easy to get into," he said. "We started development on Contraption before we had the Vive dev kit, and converting that to work in Steam VR took three to four hours, and doing the same going to the Oculus API, that was another three to four hours. It's almost nothing. You could have taken a half day off and gotten it all done."

In fact, if you're a developer with the Touch development kit you can try it now, since Steam VR supports the Rift. "If you have a Rift and hands and cameras you can boot up Steam and play Contraption," he said. "It works. It's already in the game."