“Titanic” director James Cameron worked in tandem with game developer Ubisoft Montreal on a video game based on his upcoming sci-fi epic “Avatar.”

Opening Dec. 18, the film stars Sam Worthington as a paralyzed human soldier who takes on the form of an exotic blue-skinned alien species called Na’vi on their home world Pandora, a remote paradise.

“James Cameron did something really smart,” said Kevin Shortt, story designer of “Avatar: The Game.” “When he started preproduction on the movie 3 1/2 years ago, he said, ‘I want a game. I know I want a game. I want them working on it right now.’ Because, what often happens is they make the movie, and then somebody says, ‘Hey, let’s tack on a game.’ ”

In a plot that diverges from the film’s story line, players can portray a blade-wielding member of the Na’vi or a gun-toting human soldier for the Resources Development Administration, which mines Pandora’s rare natural resources.

The game’s parallel narratives explore the implications of aligning with either the Na’vi or RDA.

“Let’s face it,” Cameron said. “Games derived from movies, historically, some of them have kind of sucked. And I didn’t want ‘Avatar’ – I didn’t want anything associated with ‘Avatar’ – to suck. So I proposed to Ubisoft this theory that the game should not be a slave to the movie.”

The game will be out Tuesday.