As gamers, we’re often too caught up fighting for our lives in heated gun or melee battles to appreciate the countless hours of work that go into character animation. Motion capture has been standard fare for many action/adventure projects these days but there are still a lot of hurdles to overcome in terms of properly applying this animation to a specific game setting. This was evident in the high turnout for the GDC panel titled, “Animation Driven Locomotion for Smoother Navigation”.
Just as it takes countless man-hours for Pixar animators to design a garbage bag in Toy Story 3, it might surprise many how much work goes into making sure a non-player character’s feet animation looks realistic, let alone believable. The speakers at this panel know a thing or two about animation, namely:
Shawn Harris - Senior Programmer, Big Huge Games/38 Studios
Gabriel Leblance - AI Programmer, Eidos Montreal
Bobby Anguelov - AI Programmer, IO Interactive
In a room presumably filled with attendees with AI and animation responsibilities, it took little time for me to have renewed appreciation for the work that goes into something as subtle as a foot pivot. Shawn talked about his experience with Kingdoms of Amalur: Reckoning and how a motion graph does a great deal in helping a character transition in speed from walking to jogging to full-on running. It’s not an easy task when you can’t get away with simply speeding up walking animation and call that ‘running’.
Even in 2012, animators still struggle with the unsightly issue of “footsliding” where the foot moves without being anatomically convincing. Shawn used this subject to further emphasize the important of motion planning, namely the need for a solid blending solution such as the unique animation used to depict a character climbing uphill or pulling a bow & arrow.
Gabriel and Bobby’s portion of the panel was even more enlightening, partly because they shed light on their animation experience with a game that hasn’t hit store shelves yet, Hitman: Absolution. As we’re previously reported, Absolution will be filled with enough enemies befitting a Hitman game. Can you imagine the work it takes to make sure those thugs don’t run into each other? Along with Collision Avoidance, here were some of the key notes of the panel:
-Collision Avoidance in ADL: You can’t talk about locomotion without discussing collision avoidance. Collision avoidance is tied to the locomotion system used in the game. CA is a pretty common problem andc an be taken for granted.
-Collision Avoidance Footstep Re-planning: Once a collision is detected, we can react to it by either changing speed or by navigating around it. With footstep planning, all avoidance actions will require re-planning of all footsteps along the remaining path. The re-planning may also require a new path post-process step.
-Why make a footstep planner? A character can stay on the path at all times with a footstep planner. This is beneficial because an NPC can only correct so much when external forces try to push it away from the path. Pair this planner with a library of animation and all you’d need to do is remove or add footsteps accordingly,
-If executed well, characters subjected to a path can convey an emotional state through their navigation (eg. A scared character hiding in a corner).
-Simple path containing segments: Starting at an Origin, then determining the Pivot point, and finally the Destination. So how many steps are in between?
-Funnel Algorithm: Questioning why AI characters take the shortest path & hug corners when humans don’t habitually walk like that. They proceeded to show a wireframe demo of the benefits of a “push-away” path.
-Path Post Processing / Corner Push Away. Create a path push-away vector at each path vertex. The push-away vector can be any vector directed away from the corner. One approach is to average the orthogonal vectors of the previous and subsequent path segments at a vertex. The path can be pushed away from the corner and thereby its length can now be dynamically modified.
Even from a gamer’s perspective, this was an insightful panel on best practices in character animation. And it was a great to see it presented from different perspectives with Reckoning’s animation being very action driven, while Hitman’s emphasis was about crowd control. This was also an opportune moment for Gabriel and Bobby to remind the attendees that while Assassin’s Creed might be getting a lot of news this week, the true original assassin, Agent 47 will be ready to reclaim his title this year.