  Real-time character animation in dynamic environments requires the generation
of plausible upper-body movements regardless of the nature of the environment,
including non-rigid obstacles such as vegetation. We propose a flexible model
for upper-body interactions, based on the anticipation of the character's
surroundings, and on antagonistic controllers to adapt the amount of muscular
stiffness and response time to better deal with obstacles. Our solution relies
on a hybrid method for character animation that couples a keyframe sequence
with kinematic constraints and lightweight physics. The dynamic response of the
character's upper-limbs leverages antagonistic controllers, allowing us to tune
tension/relaxation in the upper-body without diverging from the reference
keyframe motion. A new sight model, controlled by procedural rules, enables
high-level authoring of the way the character generates interactions by
adapting its stiffness and reaction time. As results show, our real-time method
offers precise and explicit control over the character's behavior and style,
while seamlessly adapting to new situations. Our model is therefore well suited
for gaming applications.
