If the "exit burrito" in Owlchemy Labs' Job Simulator is an excellent example of VR game design fundamentals, I'd contend that the crosshair in High Voltage's Damaged Core is an equally excellent illustration of how hard it is to adapt traditional game design practices to VR.

"That is one of our crowning achievements, right there," High Voltage producer Doug Seebach told me this week, with a laugh. "It was not easy to do."

Damaged Core is one of two Rift-exclusive VR games High Voltage brought to an Oculus demo event at GDC this week (the other being VR CCG Dragon Front) and its core concept is pretty straightforward: you play an AI who fights killer robots with guns, and you can "leap" your consciousness between the robots to move around the world.

The game's UI has everything you'd expect -- a damage indicator, a health meter, a crosshair et al. But according to Seebach, the process of getting those elements in place was nothing like what High Voltage expected.

"UI in this world is tough"

"It's surprising how much doesn't work in VR that works in standard traditional games. Even the reticle took us three months to figure out how to draw it right to make it feel good," said Seebach. "UI....UI in this world is tough."

The reticle looks like a bog-standard FPS reticle, and Seebach says that was precisely the goal -- to make it non-obtrusive, something players would find familiar and useful.

The problem is (and experienced VR devs know where this is going) that reticle has to be drawn at varying depths, depending on where the player is focusing their eyes. If you just had it float in front of the VR goggles as a static element, it would be out of focus for players most of the time.

"We tried putting it in the HUD. When you try putting it in the HUD, because your focal point is at a different place, most of the time you get double vision. Your reticle is here and your object is out there," said Seebach. "You don't know what to focus on; you're either focusing on the reticle or you're focusing on the object in the world."

So High Voltage decided to render the crosshair dynamically as a 3D object in the world, and thus they had to design a system that would render it binocular (i.e. draw it from two different angles, for the players' two eyes) on whatever the player is looking at in the moment, in real-time.

"The point where [players' eyes] meet in the world -- what they meet on -- such as the camera or geo or any of the other art in the world -- we have to take into account the math as to how far away that is from you and then do the angle of where it intersects at that point," said Seebach. " It was incredibly tough, I'll tell you right now; it was not a fun experience, but we came up with something that works and that's the key."

The crosshair is just one part of High Voltage's UI solution. The rest of the Damaged Core HUD is actually attached to the player camera ("I forget how far away it is from you") and lit up using in-game light sources because, according to Seebach, looking at a well-lit, translucent UI is much more comfortable for most VR game players than the "heavy" UI design common in non-VR games.

"It's a matter of translucency and color and -- well, I can't tell you how many iterations of UI that we've been through," said Seebach. "We [originally] went with a little more heavy, like Eve [Valkyrie]. It just doesn't work for us because it's so close to you. Something that's that heavy people want to focus on, and then it becomes a matter of discomfort."

High Voltage has been designing shooters (and shooter UIs) for some time, so Seebach's caution to fellow developers that the process has to be rethought from the ground up for VR seems notable.

What's also interesting is that -- based on playtests -- Seebach says VR shooters (if they're comfortable) are actually more approachable than their compatriots on PC and consoles.

"The delta between a really good player and a not-so-good player has narrowed, because it's so much easier to look at something and shoot," he said. "The barrier to entry in this type of thing is much less than your traditional twin joystick or mouse-and-keyboard, WASD control scheme."