Tunable tension for gesture animation

Variation in muscular tension has important expressive impacts on agent motion; however, it is difficult to tune simulations to achieve particular effects. With a focus on gesture animation, we introduce mass trackers, a lightweight approach that employs proportional derivative control to track point masses that define the position of each wrist. The restriction to point masses allows the derivation of response functions that support straightforward tuning of system behavior. Using the point mass as an end-effector for an inverse kinematics rig allows easy control of both loose and high tension arm motion. Examples illustrate the expressive variation that can be achieved with this tension modulation. Two perceptual studies confirm that these changes impact the overall level of tension perceived in the motion of a gesturing character and further explore the parameter space. Practical guidelines on tuning are discussed.