When developing Assassin’s Creed 3 Ubisoft rebuilt what made the Assassin’s Creed games novel: how the player moved.
As explained during a talk at this year’s GDC, Assassin’s Creed 3’s AI Tech Lead at Ubisoft Richard Dumas explained how the game’s on-foot action was rebuilt from the sole, upward: and the implications of making an open world game with hills.
As Richard explained, the team knew they’d be launching in the current console cycle but approached the level of simulation that the next generation would provide them. They “aimed for next-gen before next-gen”.
In the previous Assassin’s games the designers were working within strict restrictions about how they built the world that Altair and Ezio explored. They largely used flat surfaces. Slopes steeper than 30 degrees were a taboo asset round the Ubisoft offices, kept locked away in the draw of forbidden tools. Why? The engine simply couldn’t handle them. Animation looked strange, while character models would often sink through the terrain.
When it came to Assassin’s Creed 3, though, Ubisoft wanted to “refresh the look and the feel of the game.” They focussed on four areas to improve the core free running and navigation elements of the game: ground navigation, free running, climbing, tree running.
The big challenge was uneven terrain and broken ground. According to Richard, Ubisoft Montreal wanted to explore the heady world of plus 30 degrees. For this, they needed character’s feet to connect to the ground convincingly. The game needed to both accurately detect player footfall and generate character animations that made its placement look natural. Ubisoft had to avoid rigid poses that might leave Connor’s feet hovering David Blaine style above the terrain.
The answer: a technology called “predictive foot placement.” It did the trick but it’s at the outer reaches of what the current generation of consoles can process. Optimising for predictive foot placement proved tricky.
The game analyses each character’s step, detects what the highest point a character will need to step over is and then creates a string of animations around that piece of information, creating a path of travel for the foot and pelvis. Once that’s established the rest of the body animation are generated to fit with the lower body movement.
Assassin’s Creed 4 is making the shift from landlocked America to the pirate-filled seas of the Caribbean. Hopefully, they’ll improve their predictive feet further; particularly given that Assassin’s Creed 4 will still be releasing on the current and next-gen consoles. It does look quite good though.
With additional reporting by Rob Zacny and Tim Edwards.