David OReilly spent months working on his video game, Mountain, in secret. He tweeted the announcement — “Theres [sic] gonna be a real actual David OReilly game available in a couple weeks” — on June 10, as E3, the massive game-industry conference, took over the L.A. Convention Center. The following day, he asked his Twitter followers how to get his game reviewed. The day after that, he brought Mountain to Horizon, an artier alternative to E3, held at MOCA.

There is no quest. You save nothing. You solve no problems. You compete with no one.

The hype came fast and the buzz grew loud. Big tech sites such as Kotaku, Engadget and Polygon jumped on the story: The guy who made the fictional video game for Spike Jonze's movie Her now is making one in real life.

It was a little out of the ordinary for the Irish animation artist, who lives and works in downtown Los Angeles.

Normally, OReilly makes short films that appear in international film festivals. Even when his work wins prizes, and it often does, he doesn't get that much press out of it.

Video games, though, are a completely different world, a big-money industry supported by an army of blogs and YouTube channels, which discuss little more than the new releases. OReilly is intrigued by this. “I think it's great that a big technology or game blog will talk about a simple art project as well as a Call of Duty type of game, and that the same audience will read both,” he says.

Mountain, which became available July 1 for Mac, PC and Apple mobile devices, is the kind of project that has gamers arguing whether it's actually a game. There is no quest. You save nothing. You solve no problems. You compete with no one.

Instead, you're a mountain and your situation is determined by answers you give to questions at the start of the game. From there, you observe as the days cycle by.

Fog might roll over the summit. Rain might shimmer over grass. Snow might cap the tiny rows of trees. If you fiddle around with your computer's keyboard and touch pad, you'll stumble on some Easter eggs.

OReilly stresses that every experience is going to be different. “Some people will be frustrated by it,” he says. He doesn't want to give away too much.

Brandon Boyer of Venus Patrol, a website focused on artistic, independent games, booked OReilly for Horizon before seeing Mountain. He says Mountain's simplicity makes it beautiful and significant.

“It's pretty effective as thinly veiled allegory for a life spent enduring and accumulating hurt and mass,” Boyer adds via email.

OReilly, 29, grew up in Kilkenny, Ireland, about an hour from Dublin. At 14, he stumbled into an animation studio that had opened nearby, and was quickly taken in by the animators. Within two weeks, he knew that animation was what he wanted to do with his life.

He learned traditional 2-D animation. He started making his own, simple video games. Once OReilly hit 18, he bounced around Europe — Ireland to the United Kingdom to Italy, then back to the U.K. before settling in Germany — as he learned the trade.

He liked how animation felt like a magic trick that doesn't lose its luster after all has been revealed. He can make static images move over and over again. It doesn't get old.

“Even though you know how the trick works, it still functions,” he says. “That's kind of an amazing thing.”

In London, armed with a beginner's portfolio, OReilly got a job at Shynola, working on the feature film The Hitchhiker's Guide to the Galaxy and a Beck video. On his own time, he made a fan video for a track from electronic music artist Venetian Snares. It was dark and glitchy, with 3-D animation cut at a pace as frantic as the music. It was OReilly's first stab at directing, and he was smitten with it.

As a filmmaker, though, OReilly had little success in London. He pitched ideas for 40 music videos. None was accepted. He left for Berlin and started working on his own.

His first two festival entries were attention getters. RGB XYZ, about a boy who gets kicked out of his home and moves to the city, earned a Special Mention at the Berlin International Film Festival in 2008. Please Say Something, a tale of cat and mouse, won a Golden Bear award for best short film, the top prize, at the same event the following year.

The stories are simple, the art deceptively so. RGB XYZ uses big blocks of color and bare-bones character designs, but shots will spin and flip upside down while pieces of the scene break up to resemble glitches. It's computer-generated psychedelia.

Please Say Something has a smoother look but still is linked together by a quick flash of a malfunction.

Three years ago, OReilly headed to Los Angeles. He thought it would simply be a respite from another brutal Berlin winter, but he decided to stay. He now works out of a small office with two assistants.

The people he met didn't fit the Hollywood stereotype. “There were a lot of creative, independent artists, people who dip in and out of the industry but who do a lot of their own work,” he says. Plus, the cost of living was more affordable than in other major cities. OReilly could pursue both commercial work and his independent projects.

Now he's working at the nexus of art, film, television and video games, something that's unusual even in L.A.

He wrote, directed and produced “A Glitch Is a Glitch,” an episode of the popular Cartoon Network series Adventure Time.

But his big break was getting the gig to direct the animation for the “Alien Child” video game in Her. Multiple people referred him for the job, and Jonze had seen one of OReilly's films.

OReilly initially was brought in as an animation consultant, providing drawings of the Alien Child based on Jonze's concepts plus 3-D sketches to show how the animation would work with the live action.

Inevitably, he ended up supervising the animation sequences, working closely with Jonze for nine months and doing everything from storyboards to team building.

It was a technical challenge involving forced perspective and a virtual camera. He had to contact the scientists who make 3-D software to find the best way to achieve the effect. “In the end, the fastest way was still dizzyingly technical,” he says.

OReilly's animation has long been influenced by the aesthetics of video games, particularly older games, which didn't rely as heavily on realism. He appreciates the way the artistic limitations pushed the player to use his imagination to flesh out the image.

But actually making a game using current technology was a new experience.

He spent the earlier part of this year learning Unity, a game engine, while working on another project for the Oculus Rift virtual reality device.

Through that project, he met programmer Damien Di Fede, who became his only collaborator on Mountain.

The game itself can be passively played. It's possible to run it as you're performing other tasks on the computer. Or you can take an active part in the world, striking keys until you figure out which ones trigger a response.

It's interesting on both levels. Watching the mountain can be soothing. Trying to make it do something might elicit an emotional response.

Exploration, OReilly says, is part of the game. Whether that's exploring the terrain or exploring yourself is up to the player.

OReilly says, “It's a truly spiritual project and something that I feel I put a lot of myself into in a new way.”

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