Interface FreeMoverOptions

an animation to play while standing still, given the current facing in radians

world units crossed per second

An animation to play while moving, given the current facing in radians (0 along +x, increasing clockwise in screen space). Bucketing that into however many directions a sprite sheet actually has (4, 8, whatever) is the game's own job - this stays unopinionated about how many facings exist, the same way GridMover's callbacks are unopinionated about animation names.