How the box works

The glass is the screen

The box is drawn as if the screen were the front of a real box, with the thing standing behind it. For each point inside, the page draws a straight line from your eye to the point and marks where that line crosses the glass. That crossing is where the point is drawn.

Your eye isn’t measured. It’s taken to be about 32 centimeters from a phone, straight in front of it when you first hold it (56 centimeters for a computer’s screen). When the phone turns, the motion sensors say by how much, and since your head stays where it was, the eye moves the other way, as seen from the phone. Tilt the top of the phone away from you, and the eye drops: you see more of the ceiling, and more of the underside of the thing.

The test

A parallax trick slides layers past each other. This doesn’t. The test is the front edge of the room: a point on the glass is its own crossing, so the four front corners stay exactly on the edges of the screen, from any eye. Everything behind them moves, and the farther back it is, the more.

Where it stops

The view follows the phone exactly up to 13 degrees. Past that it eases off toward 22 degrees and stops there, so the thing stays in the frame. The room is deeper than any phone is thick.

What falls, and where

Shake the box, and the Splash sheds grains, eight neighboring splats to a grain. They fall toward the real floor: the sensors give the phone’s turn, and gravity is turned into the phone’s own axes. Lay the phone flat and they settle on the back wall. Hold still, and they rise into the next thing.

On a computer, or with no sensor

A pointer, a thumb, or the arrow keys stand in for the sensors, through the same sum. A slow sway stands in until you touch anything. With reduced motion turned on, the box holds still until you move it.