Dynamic implicit muscles for character skinning

Abstract

Most current methods for character skinning can be categorized into 1) geometric techniques, which are fast and easy to use but often lack physical realism, 2) data-driven approaches, which require a large set of examples that are tedious to edit, and 3) physics-based methods, which are highly realistic but slow and difficult to use. Recently introduced geometric Implicit Skinning methods can solve contact interactions and skin elasticity with results comparable to physics-based simulation in real-time. In this paper we introduce an animation method that adds anatomical plausibility while benefiting from the advantages of Implicit Skinning. We propose an efficient way to model muscle primitives with implicit surfaces. Volumetric extrusions of individual muscles are attached to muscle center lines simulated with a fast, low-dimensional physics-based approach (Position Based Dynamics of one-dimensional line segments). This combination of physics-based simulation with implicit modeling allows us to elegantly resolve muscle-muscle and muscle-bone collisions and add dynamic effects such as flesh jiggling while guaranteeing volume preservation (which is a property of real biological muscles) and producing visually plausible skin-skin contact behavior. Our method runs at interactive frame-rates and features intuitive modeling parameters which allow animators to quickly explore a variety of designs and physics-based effects.

Velocity Skinning for Real‐time Stylized Skeletal Animation

“…Simpler dynamic deformers have also been explored, from early work coupling particles and implicit surfaces to achieve cartoonphysics effects [OM94], through extra bones attached to the skeleton to model flesh oscillations [LCa05], or the use of sub‐bones connected by springs to achieve curvy, dynamic shapes [KL08]. Muscles approximations have also been developed both in explicit [RL13] and implicit [RRC*18] formulations. Similar to our approach, kinodynamic skinning [AS07] proposes an integrated velocity‐based formulation for skinning that can be tuned to exaggerate dynamic visual effects.…”

Efficient and realistic character animation through analytical physics-based skin deformation

“…Murai et al [30] presents an algorithm that generates skin deformation (movement and jiggle) from joint angle data sequences by two steps: identification of parameters for a quasi-static muscle deformation model, and simulation of skin deformation. Roussellet et al [33] proposes an efficient way to model muscle primitives with implicit surfaces. Inspired by [43] that uses a curve-defined model to animate skin deformation, Chaudhry et al [5] integrate geometric transformations, example-based, and physics-based approaches to simulate dynamic skin deformations.…”

Spring Rigs for Skinning

“…[Vaillant et al 2013[Vaillant et al , 2014. Implicit surfaces have also been used for surface authoring, such as sketch-based editing [Angles et al 2017] and making plausible volumetric deformations alongside skinning [Roussellet et al 2018].…”