5.10Soft Bodies and Muscles

To make a soft object, such as a jelly or a rubber toy:

1. Start from a closed mesh: every edge shared by two faces, the caps of a cylinder on.
2. Add Tnpix Soft Body and choose a Material. Add Tnpix Gravity and a Tnpix Solver above it, with Tnpix Collision for what it lands on.
3. Play. The status line says how many tetrahedra the flesh has; raise Resolution for finer flesh.

To set up a muscle with fibres between two bones:

1. Model the muscle as a closed mesh between the two bones, for example a Cylinder with its caps on.
2. In a Tnpix Channel paint each tendon end into a channel of its own, for example upper and lower.
3. Add Tnpix Soft Body and choose Material Muscle: Fibres turns on.
4. In the Soft Body Fibres rollout pick the two bones, or helpers linked to them, as Start and End.
5. Add a Tnpix Pin for each end: channel upper following the upper bone, channel lower following the lower bone.
6. Add Tnpix Gravity and a Tnpix Solver.
7. Animate the bones. With Auto tension on, the muscle tenses as the bones close in and bulges; or animate Activation yourself.
8. Set or animate the Tension point, or drag the yellow marker at the modifier's Tension Point level, to move the bulge along the muscle.

To slide a fat layer over the muscle:

1. Model the fat as a closed shell around the muscle, for example a Tube.
2. Paint the fat's inside surface into a channel in a Tnpix Channel.
3. Add Tnpix Soft Body with Material Fat, and a Tnpix Stitch: that channel, Stitch to the muscle, a Search distance that reaches the muscle's surface.
4. Turn on Slide along the surface and keep a little Friction (0.3).
5. Put the muscle and the fat on one Tnpix Solver.

To let only part of a skinned character jiggle:

1. Give the character's closed mesh its Skin below the Tnpix Solver.
2. In a Tnpix Channel, paint two channels: skin where the character must follow the animation exactly (head, arms, hands, legs and feet), and belly where the flesh should move.
3. Add Tnpix Preserve bound to skin and, above it, Tnpix Soft Body bound to belly. Above the Preserve the Soft Body's paint wins its area, so skin may cover the belly too.
4. Add the Solver on top and play from the first frame. The preserved parts ride the Skin; the belly jiggles on top of it, and a soft edge in the paint blends the two.