SAN FRANCISCO — Google has seen the future, and it is littered with cardboard boxes.

At its Google I/O developer conference here on Thursday, the search giant announced several programs that aim to put its virtual reality viewer, called Cardboard, at the center of a growing online world in which people can use their smartphone and YouTube to watch videos rendered in 3-D.

Google introduced its virtual reality viewer — a cardboard box, with some lenses and a magnet, that looks a lot like a plastic View-Master toy — as a gift at last year’s I/O conference.

The idea was to create an inexpensive virtual reality device that allowed anyone with a smartphone to do things like fly through a Google Earth map of Chicago or view personal pictures in three dimensions.

It is a comically simple contraption: A smartphone slips into the front so it sits just inches from a user’s eyes. Peering through a pair of cheap, plastic lenses renders the images on the phone’s screen in 3-D. It costs around $4.