Ken Levine: scripting Elizabeth "is the most complicated thing" in Bioshock Infinite

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NPC companion, Elizabeth, is set to a vital part of Bioshock Infinite's storyline. She follows playable tough-guy, Booker DeWitt around the floating metropolis of Columbia, trying to evade the nightmarish Songbird that has kept her captive for years.

In spite of her torrid past, Elizabeth is a playful, funny sidekick. Some of the best moments from the superb fifteen minute E3 demo (above) were Elizabeth's brief, incidental skits in which she banters with Booker and at one point puts on a giant Abe Lincoln head for a quick impression. According to creative director, Ken Levine, these small acts are the "most complicated" development task for Irrational.

We spoke to Ken Levine about Bioshock Infinite in the latest issue of PC Gamer UK , and he told us that while those small story moments were scripted for the E3 demo, they will happen dynamically in the final game. The Abe Lincoln head sketch can only activate if the player turns away and Elizabeth is near the head at the time.

“If we want Elizabeth to do a bit of business, like the part where she picks up the Abraham Lincoln head - what if the player doesn't go there? What if the player's busy? What if he's in combat?” says Levine. “Liz says to the game, 'Hey, I'd like to pick up the Lincoln head now and show it to the player, can I do that?' And the game says, 'Yes, this is a good time,' or, 'No.' And if the game says no, we'll place this other opportunity somewhere in the level for her to do that bit of business and again, it'll check 'Hey, is this a good time?'”

"Say she picks up the Lincoln Head and all of a sudden the player gets attacked - she has to get rid of it,” says Levine. “So we need to account for that, or she's carrying this stupid Lincoln head throughout the level.”

The AI will also determine where the player is in a given level. If you're near the start or end, these sketches won't trigger, which should stop Elizabeth from plopping on a giant Abe Lincoln head in the middle of a climactic confrontation with the Songbird.

“Those bits, you could say that they're scripted in a sense, but they could happen at numerous places throughout the level, because we don't know what the player's going to do,” says Levine. “So we have to account for it, and Elizabeth has to seem fluid and consistent. That is probably the most complicated thing – in fact, I wouldn't say probably, I'd say it is the most complicated thing in the game, because she's so content-heavy.”

The system has evolved from Irrational's work designing the movements of Big Daddies and their Little Sisters in Bioshock. “Their paths weren't entirely pre-determined, and their actions on that path weren't entirely pre-determined,” he says. “So she's just like an incredibly, incredibly more complicated version of that. I don't think anybody's done anything exactly quite like this, because she's performing these continually scripted things in areas where we can't control the action.”

“It's always been our approach back from System Shock 2 to Bioshock,” says Levine. “We try to tell a story that is deep in narrative, but without asking the player to be restricted for it - and that's very tough to do. But we think it's worth it.”

You can read more about Bioshock Infinite in our interview with Ken Levine, in the latest issue of PC Gamer UK.