Watch Dogs 2’s crowd was born for YouTube stardom. The above video, which piled up 100,000 views shortly after the game’s November launch, is a perfect specimen. A marriage proposal is interrupted by a selfie-taker, which provokes a WTF fistfight between the two lovebirds. It all ends with one offering, “Maybe I'm not the unbalanced one, you are."
What made that less-than-magical moment for the unhappy couple? A spreadsheet more than 200 columns wide, spread across three monitors at Ubisoft Montreal.
At Game Developers Conference 2017, Roxanne Blouin-Payer, the designer responsible for the AI systems in Watch Dogs 2's open world, recreated the incident and detailed what it took to develop interactions like this, which were a high point in the mostly positive reviews the game received.
"In Watch Dogs, relationships between Aidan [that game's protagonist] and the citizens was mostly based in fear and collateral damage," Blouin-Payer said. "'Look out, don't shoot, stop him.' We wanted to give the player the impression the world was living by itself, and not through the player's interaction only."
It doesn’t take a designer or programmer with a speciality in AI to understand that is a grand ambition, fraught with all kinds of variables either to plan for or debug later.
Ubisoft Montreal called its approach the "anecdote factory," where NPC interactions more complicated than yelling at a passer-by or running away could be generated. These interactions had to play out naturally and not seem glitched or disruptive even if they ended bizarrely, as in the marriage proposal.
To give another example of the anecdote factory’s product, Ubisoft Montreal created an NPC who would sit on a street corner playing a guitar. Perhaps an NPC walking by decides to mock his playing. That sends a stimulus to other characters in the vicinity, and they all react, maybe with amusement or by confronting the heckler. That choice came from a set of situational attributes assigned to the characters, not necessarily because they had roles in this particular mini-drama.
The point is what happened in Watch Dogs 2’s San Francisco is retold a lot like it would be to a friend: I saw this woman beating up a really nice car with her baseball bat. Some guys walking by stopped and watched and, well, then I guess her girlfriend came out and tried to grab the bat out of her hands. They had a screaming match, and then this one guy sort of ineffectually stepped in after it was over like he was trying to break it up.
The above example was shown in Blouin-Payer’s GDC panel, by the way, verbatim.
The crowd AI in Watch Dogs 2 is not perfect, of course. It can’t realistically account for random encounters involving dialogue that aren’t confrontational or violent, because of the difficulty in synchronizing the dialogue. (People who are fighting, reasoned Blouin-Payer, don’t listen to each other, so talking over each other is fine.) Blouin-Payer said the capability did exist to at least try to synchronize dialogue arising from random encounters, but it was too costly within the resources of the AI to really pull it off.
But the results seem to suggest that Ubisoft Montreal’s goal of creating a world living on its own — or at least the illusion of it — was successful. Telemetry said Watch Dogs 2 players spent 30 percent more time exploring and interacting in the open world than they did in the first Watch Dogs.