Behind the critical success of BioShock Infinite is the game's heart and soul, Elizabeth. Not only did Elizabeth carry the narrative weight of BioShock Infinite on her shoulders, she was also a robust AI that allowed for many systemic interactions. The creation of Elizabeth was an organic process that evolved over time and included members from every department at Irrational. Shawn Robertson, Animation Director of Irrational Games, broke down the complex nature of bringing Elizabeth to life, from an AI perspective as well as an animating perspective.
The Start of Elizabeth
The BioShock series had little player-to-human reactions throughout the first two games. All major character interactions in the first game occurred through radio sequences or heavily scripted events from a distance so the player could not directly interact with what was occurring. The relationship between the Big Daddy and the Little Sister was the most direct character connection. The idea for a companion character in BioShock Infinite began early, and the first question the team needed to ask was "Can she talk?".
Most of the team at Irrational felt they were only capable of a non-speaking companion. In a pre-alpha build of the game, Elizabeth was mute and would directly grab the player's attention, which was too obtrusive and not the character relationship the developers wanted.
Over time, the team warmed up to the idea of making Elizabeth a speaking character, and the task of bringing her to life was immensely complicated.
The team attempted a full motion capture of scenes with an actress in order to test the limits of what they could develop. Two versions were made: one with the actress's natural face during the scene, and where a team re-animated her facial expressions. The key-framed facial animation turned out to look much better than natural motion capture.
Realism was never the goal when it came to the look and movement of Elizabeth. The team purely focused on the emotional impact that the character would have. Having an exaggerated look to the character could help convey emotions from a greater distance. The limitations of the uncanny valley also led the team to stylize the character designs.
The dress of Elizabeth was very difficult to animate for the team. Having a closed geometric shape around a character led to clipping or wacky proportions.
Giving Elizabeth Humanity
The team had to create a variety of different effects to give the illusion of humanity to Elizabeth. The team developed a host of clever AI systems to create an array of custom movement. They had early success with fully scripted moments with custom animations, but they realized systematic movements would have much higher interactivity.
The illusion of life falls on the AI's ability to interact with the player and other AI. Bad animation and pathfinding can completely kill the illusion. An internal team was created, called the Liz Squad, that was entirely focused on creating a lifelike Elizabeth.
Elizabeth had little to no natural emotion at the beginning stages of the game. She was disconnected from the environment, and the team sought to create a complex emotion system. Basically a library of emotions that would be systematically triggered by what she sees. A scripted narrative event could clash with the default emotion of the character. So the team created a wide variety of little animations.
These animations included facial expressions, blinking frequency, movements for the head and arms, and some full body animations when she's standing still. They created an 'after combat' emotion that would begin after the last enemy AI was killed. This would run for a set amount of time before returning to the narrative emotions. This gave better flow to the character, instead of her being instantly OK after a gunfight.
Irrational created a gesture system that allowed Elizabeth to call gestures at certain points. If the player began combat, she'd have specific limitations on these gestures. A system was also put in place for head and eye tracking.
Smart Terrain System
One of the keys of Elizabeth coming to life was the creation of the Smart Terrain System: a single object in the environment could be directly interacted with by Elizabeth. The team would program a variety of these interest points throughout the world. They were not directly scripted, but merely 'suggested' to the AI's code. Elizabeth would act out these specialized actions with the environment and then never repeat them.
If the player was not viewing Elizabeth when she began this animation, she would halt the action and usually teleport to a different location. This was to make sure the player saw this action occur.
- Preproduction is a good place to have fun, but you need to make the tough decision.
- The player experiences everything, so observe from their perspective
- Failure is good, but do it quickly
- Small systems can be used to create powerful results when combined together.