Hong Hua, an optical sciences professor at the University of Arizona and coauthor of a recently published paper on the work, says the display—made initially for just one eye—is kind of like a telescope system. Lenses image a real-world view on a spatial light modulator (these are used to control beams of light in things like projectors), which is used to make a mask that, pixel by pixel, blocks out the portion of the real world that the virtual object will sit in front of. The modulated light and the virtual image then travel through the eyepiece and reach your eye.

Hua, it should be noted, is also a consultant for the mysterious augmented-reality startup Magic Leap and is listed as an inventor on some of the company’s patent applications and patents, including two patents granted in 2017 for a headset with a see-through display featuring mutual occlusion and opaqueness control that looks very similar to this work. She won’t say precisely what she does for Magic Leap, but she does say this academic research is unrelated. Still, given its importance for making AR seem realistic, it would make sense if the company were also pursuing the work (when asked about it, Magic Leap had no comment).

Hua says a big challenge to making this kind of dual occlusion work in AR is dealing with light—specifically, you have to be able to precisely control light from the real world in order to superimpose, say, a digital teapot onto a shelf so it appears to be in front of things like a can of compressed air as well as behind a can of spray paint (as Hua and graduate student Austin Wilson did with their prototype). Head-mounted displays available today can’t do that.

In order to make it eventually work in real time in an AR headset, Hua says, you’d need a depth sensor, which is becoming increasingly common on headsets such as HoloLens.

The hardware needed to make this kind of occlusion possible would also have to get a lot smaller. Right now it’s pretty bulky, she says, because she and Wilson were concentrating on making the system inexpensive rather than compact. They’re working on a new prototype now to make it wearable, Hua says, but it will still be helmet-size.

“To make it into the popular glasses form factor is probably going to take a while,” she says.