Purpose

Soft Body simulates deforming volumes with a finite element solve. Co-rotational and Neo-Hookean material models control the elastic response. Multiple bodies can share the solver, with optional world, self and inter-body collisions.

Use

Place Soft Body in the Geometry view, under Solvers. For a first test without authored input, reduce Demo Bodies to 1, keep Demo Resolution at 3 and choose World Only in Collision Mode. Collision Mode starts off, so the enabled floor alone does not make the body collide.

For your own object, connect vertices carrying tetrahedral data to the geometry input. A surface mesh alone does not define the volume. The Tet attribute stores groups of four vertex indices; bodyid separates bodies and pin values above 0.5 fix vertices. Prepare this data upstream.

Inputs and outputs

Connections accepts sdf obstacles, xforms, velocity and contacts. The solver publishes vertex P, v, id and Cd, plus a contact set when enabled.

Use Attribute Material reads youngs, poissons and density attributes, taking each body’s values from its representative vertex. Without those attributes, the parameter values apply. Live Wire Surface can publish boundary-triangle topology with the deformed vertices; it is off by default and adds work.

Controls

• Dt Override at 0 follows host timing. Start with two Substeps and six Iterations. Simulate pauses advancement; Reset rebuilds the starting state.
• Young’s Modulus controls stiffness. Begin at 250000 and lower it for a softer response. Poisson Ratio starts at 0.35 and controls the material’s lateral response to compression.
• Linear Damping, Elasticity Damping and Velocity Scale affect settling. Keep the starting values while checking the volume and pins.
• Collision Mode selects Off, World Only, or World + Self + Inter. Contact Radius, Collision Iterations, Friction and Contact Damping tune the active collision mode.
• Velocity Field Coupling starts at 0. Publish Contact Set and Couple Weight control contact exchange once resources are connected.
• Max Vertices, Max Tets and Max Bodies are capacity limits. With Auto-Rebuild off, structural edits wait for Rebuild; check Status before expecting them to appear.

Notes

Check for DEMO FALLBACK in Status when authored input does not produce your intended body. Valid tetrahedra are required; the solver does not tetrahedralize a polygon shell.

Self and inter-body collisions, large tetrahedral counts and Live Wire Surface increase the work per step. Establish one body with world collisions before adding a pile.

Ports

Inputs

• geometry points
• sdf sdf collider
• xforms transforms
• velocity velocity field
• contacts contacts

Outputs

• P points
• v points
• id points
• Cd points
• contact contacts

Parameters

Soft Body

Auto-Rebuild on Build Params (Autorebuild) Toggle op('soft').par.Autorebuild

Default:

On

Options:

Off, On

Rebuild (Rebuildnow) Pulse op('soft').par.Rebuildnow

Default:

None

Simulate (Simulate) Toggle op('soft').par.Simulate

Default:

On

Options:

Off, On

Reset (Resetsolver) Pulse op('soft').par.Resetsolver

Default:

None

Solver

Solve (Hdrsolve) Str op('soft').par.Hdrsolve

Read only.

Default:

"" (Empty String)

Dt Override (0=host) (Dt) Float op('soft').par.Dt

Default:

0

Range:

0 to 0.5

Substeps (Substeps) Int op('soft').par.Substeps

Default:

2

Range:

1 to 16

Iterations (Iterations) Int op('soft').par.Iterations

Default:

6

Range:

1 to 64

Gravity (Gravityx) Float op('soft').par.Gravityx

Default:

0

Gravity Y (Gravityy) Float op('soft').par.Gravityy

Default:

-9.81

Gravity Z (Gravityz) Float op('soft').par.Gravityz

Default:

0

Linear Damping (Lineardamping) Float op('soft').par.Lineardamping

Default:

0.02

Range:

0 to 1

Velocity Scale (Velocityscale) Float op('soft').par.Velocityscale

Default:

0.85

Range:

0 to 1

Max Linear Velocity (Maxlinearvelocity) Float op('soft').par.Maxlinearvelocity

Default:

200

Range:

0.1 to 1000

Max Vertices (cap) (Maxvertices) Int op('soft').par.Maxvertices

Default:

200000

Range:

4096 to 4000000

Max Tets (cap) (Maxtets) Int op('soft').par.Maxtets

Default:

800000

Range:

8192 to 8000000

Max Bodies (cap) (Maxbodies) Int op('soft').par.Maxbodies

Default:

2048

Range:

1 to 100000

Material

Material (Hdrmat) Str op('soft').par.Hdrmat

Read only.

Default:

"" (Empty String)

Material Model (Materialmodel) Menu op('soft').par.Materialmodel

Default:

0

Options:

Co-rotational, Neo-Hookean

Use Attribute Material (Useattribmaterial) Toggle op('soft').par.Useattribmaterial

Default:

On

Options:

Off, On

Young's Modulus (Youngs) Float op('soft').par.Youngs

Default:

250000

Range:

1 to 100000000

Poisson Ratio (Poissons) Float op('soft').par.Poissons

Default:

0.35

Range:

0.01 to 0.49

Density (Density) Float op('soft').par.Density

Default:

1

Range:

0.000001 to 10000

Elasticity Damping (Materialdamping) Float op('soft').par.Materialdamping

Default:

0

Range:

0 to 1000

Collision

Collision (Hdrcoll) Str op('soft').par.Hdrcoll

Read only.

Default:

"" (Empty String)

Collision Mode (Collisionmode) Menu op('soft').par.Collisionmode

Default:

0

Options:

Off, World Only, World + Self + Inter

Collision Iterations (Collisioniters) Int op('soft').par.Collisioniters

Default:

3

Range:

1 to 16

Contact Radius (Contactradius) Float op('soft').par.Contactradius

Default:

0.05

Range:

0 to 1

Contact Stiffness (Contactstiffness) Float op('soft').par.Contactstiffness

Default:

1

Range:

0 to 1

Contact Damping (Contactdamping) Float op('soft').par.Contactdamping

Default:

0.6

Range:

0 to 1

Friction (Friction) Float op('soft').par.Friction

Default:

0.3

Range:

0 to 1

Self Collision (Selfcollision) Toggle op('soft').par.Selfcollision

Default:

On

Options:

Off, On

Floor Enabled (Floorenabled) Toggle op('soft').par.Floorenabled

Default:

On

Options:

Off, On

Floor Y (Floory) Float op('soft').par.Floory

Default:

0

Range:

-100 to 100

Coupling

Coupling (Hdrcouple) Str op('soft').par.Hdrcouple

Read only.

Default:

"" (Empty String)

Publish Contact Set (Publishcontacts) Toggle op('soft').par.Publishcontacts

Default:

On

Options:

Off, On

Couple Weight (Coupleweight) Float op('soft').par.Coupleweight

Default:

1

Range:

0 to 2

Max Foreign Contacts (cap) (Maxforeign) Int op('soft').par.Maxforeign

Default:

262144

Range:

1024 to 4000000

Velocity Field Coupling (vel:) (Windcoupling) Float op('soft').par.Windcoupling

Default:

0

Range:

0 to 1000

Authoring

Authoring (unwired demo) (Hdrauthor) Str op('soft').par.Hdrauthor

Read only.

Default:

"" (Empty String)

Demo Bodies (Demobodies) Int op('soft').par.Demobodies

Default:

64

Range:

1 to 100000

Demo Resolution (Demores) Int op('soft').par.Demores

Default:

3

Range:

1 to 6

Demo Spacing (Demospacing) Float op('soft').par.Demospacing

Default:

0.75

Range:

0.05 to 10

Color

Color (Hdrcolor) Str op('soft').par.Hdrcolor

Read only.

Default:

"" (Empty String)

Color Mode (Colormode) Menu op('soft').par.Colormode

Default:

0

Options:

By Speed, By Body

Base Color (Colorr) Float op('soft').par.Colorr

Default:

0.25

Range:

0 to 1

Base Color G (Colorg) Float op('soft').par.Colorg

Default:

0.48

Range:

0 to 1

Base Color B (Colorb) Float op('soft').par.Colorb

Default:

1

Range:

0 to 1

Color Speed Lift (Colorspeed) Float op('soft').par.Colorspeed

Default:

0.15

Range:

0 to 4

Color Speed Normalize (Colorspeedmax) Float op('soft').par.Colorspeedmax

Default:

5

Range:

0.01 to 100

Outputs

Live Wire Surface (heavy) (Wiresurface) Toggle op('soft').par.Wiresurface

Default:

Off

Options:

Off, On