Page 5: Wild Experimentation
"As she lifts her arms up her breasts rise and flatten," says Valve's Ken Birdwell. He's showing off one of the character models for Alyx Vance, the female lead in Half-Life 2. Birdwell, who once wrote software to create custom shoe insoles, was the man tasked with making more-believable characters for Half-Life 2--characters who could express emotions through their faces and have full musculatures, as evidenced by the breast demonstration.
Why did Valve place such an importance on creating more-believable in-game characters? Birdwell says the decision was a result of the player reaction to the primitive but engaging characters in the first Half-Life. "We didn't spend a lot of time on them in the first game," he says. "But people anthropomorphized them a great deal. People genuinely felt bad when Barney was killed in the original." For the sequel Newell wanted the team to take those characters to the next level by adding believable facial animation and body movement. "I told Ken I wanted players to see the characters as real people and stop thinking of them as automatons or robots," Newell says.
That was an ambitious goal, considering that Hollywood animation houses had yet to crack the problem of creating realistic CG humans. Nevertheless, Birdwell began researching how he might create lifelike in-game characters. He spent some time working with Dr. Ken Perlin, a professor at NYU who is one of the leaders in the computer-graphics field. Perlin's Web site at NYU includes a demonstration of his computerized characters. Birdwell also came across the work of Dr. Paul Ekman, a psychologist who had trained police officers how to detect liars by studying facial expressions. Back in the '70s, Ekman wrote an influential book that laid out a set of rules about how facial muscles work together to create expressions like sadness, glee, anger, and puzzlement. (Eckman's rules were also used to help diagnose mental illness). Birdwell thought that by setting those rules inside the computer he could create in-game characters who would never make unnatural expressions.
Jay Stelly, meanwhile, focused on integrating physics into Valve's new Source engine. For years game companies had attempted to use physics to make more-believable worlds, often to disastrous results. (Remember Trespasser?) Valve was determined to do physics the right way. "We wanted integrated physics that mattered in gameplay," Newell says. As Stelly puts it, "We wanted to do physics so they would reinforce your presence in the world. If we did it right, players would be able to impact their surroundings and take the game beyond the constraints of scripted action." The idea was to take a regular game level and turn it into a playground of sorts where players could manipulate objects and solve puzzles in multiple ways.
While the core technologists worked on the engine, the rest of the team began thinking about the gameplay and story. Still, they kept an eager eye on the new technology. "We wanted to be like Hitchcock and use our new technology in deliberate ways that could have a huge impact on gameplay," says Marc Laidlaw, Valve's resident writer. "I always think of how Hitchcock used the zoom lens for the first time in Vertigo. It was a very specific effect and afterward everyone did the zoom in and out just like him."
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