simulation overview

F lesh and fur were included in the same setup and usually run in sequence by the same artist. Animators exported skin, bone and muscle geometry to the FX team, where they used Houdini 16’s tissue solver framework for volume-preserving

01 tissue preparation

First, the animated bone and muscle geometry was made watertight (using VDBS), and was then simulated using the standard Houdini Tissue Solver setup.

02 tissue simulation

Usually we would merge both muscle and bone geometry and have the solver treat it all as one big rigid collider skin and flesh simulations. This tissue simulation would in turn drive a hair simulation, which would simulate the guides from their rest pose into place to follow the shot animation, then export those curves back into Maya for rendering. (using the input ports called ‘bones’ in the tissue solver). For more detailed simulations we would use the muscle ports on the tissue solver, which would treat ‘muscles’ as squishy colliders bound to rigid bones.

The render mesh would then be wrapdeformed to the resulting simulation and in turn deform the skin render mesh. Artists could paint weights to mix back the original animation skin, if desired.

03 hair simulation

Hair simulation was driven by the (flesh-simulated) render mesh. Our toolset was built on top of the standard Houdini guidesimulate and guidedeform nodes, with some customisations to enable us to reduce the number of guide hairs, raise or lower the strand resolution, inject skin-based forces into the simulation, and paint attributes to drive simulation parameters.