Foot sliding can occur for many reasons but in all cases, it creates a disconnect between the character and the environment around them and reduces immersion. Game developers go through great lengths to reduce or even hide foot sliding in high fidelity games, sometimes employing several techniques to achieve the final result. Some causes are as follows:
Poor Source Animations
With poor source animations that contain foot sliding in the source, foot sliding is to be expected. This is usually not an issue as animations should be cleaned to contain no food sliding from the beginning. However, in lower budget projects where mocap data may be used with minimal cleanup this may still occur. This kind of foot sliding is relatively minor and can be resolved easily with foot locking.
While source animations may be clean and contain no foot sliding, blending of animations can create foot sliding where it doesn’t exist in the source. This can occur in both regular blending and inertial blending. This results in relatively minor foot sliding but it is noticeable especially in motion matching where several animations could be blended in quick succession.
Root Motion Disparity
The biggest cause of major foot sliding is the use of realistic animations while not using root motion. The more the in game motion does not match with the animation’s root motion, the more exaggerated the issue. Obviously the first solution is to design animations to move and turn at the same speed/rate as the character in game. However, this can be difficult to achieve due to realistic human motion being very complicated. Usually in this case several techniques are required to reduce foot sliding.
A Cursed Problem
Foot sliding can be considered a cursed problem in the extreme case of Root Motion Disparity. Often developers want both realism and snappy ‘twitch’ based movement. However, these two aspects directly oppose each other. Realistic humans do not stop, start or turn on a dime. They take time, they have momentum and the movement is complex. If one is to modify the animations to achieve ‘twitch’ movement then realism is lost. Tools such as the foot locking node and other techniques can only do so much to bridge the gap between realism and gameplay and it is up to the developers to find the middle ground that best suits their game. One way or another, compromises must be made.