What’s new Muscles & Tissue

Otis solver improvements ¶

The Otis Solver SOP has major improvements:

Added Sliding constraints support that allows for sliding between tissue layers.
- You can set this in Tissue Solidify Otis SOP using the Method parameter option called Separated Shell and Core (Sliding). This generates separate tetrahedral meshes for the shell and core tissue layers.
- Tissue Properties Otis SOP has a new tab called Shell to Core to create sliding constraints between the separate tissue layers.
- The two muscle simulation recipes Test Geometry: Otto Muscle Transfer and Test Geometry: Otto Muscle and Tissue Simulation have a new, optional sliding_tissue_setup subnet.
- The solver has a new Update Sliding Topology option which allows you to choose between a faster, GPU based topology update, or a more accurate, CPU based one.
Added Velocity blending support which helps to prevent muscles and tissues from being left behind when bones move quickly.
- This can be turned on and adjusted in the Otis Configure Muscle and Tissue SOP.

A new Damping Method option allows you to use the improved Constraints Only damping model, which provides more realistic damping when you want highly damped materials but don’t want to affect the overall linear velocities of the simulation.

Note

This option requires much larger (Vellum-like) damping ratio values than those required for the existing damping model, Constraints and Inertia.
Added a DOP Dive target which allows for dynamic POP forces such as wind or drag to be included. This also allows custom VEX or OpenCL scripts to dynamically modify properties based on certain sim attributes.
- New option Output Stress Attributes is available in the solver to use in custom scripts.
The solver’s Adaptive Stiffness now also affects spring-like constraints. This improves simulation stability.

Test Geometry: Otto SOP is now in V2 with improved muscle geometry in the upper torso area. A Version parameter exists that allows you to switch between versions for backwards compatibility.
For Tissue layers, the outer Tissue Solid layer has been renamed to the more descriptive Tissue Shell.
- Various parameters in Tissue Solidify Otis SOP and Tissue Properties Otis SOP have label changes to reflect this.
Skin Deform SOP has a new option to Slide on Full Resolution Skin, which preserves high resolution detail that was previously lost by the low resolution relaxation. This allows you to reduce the Resolution Percentage for more sliding without loss of detail.

The following updates are also backported into H21.

Target shape support for Otis:
- Multiple target shapes can be specified on Otis Configure Muscle and Tissue SOP.
- Muscle Mirror SOP improvements:
  - New Shape Attribute parameter to allow custom target shapes to be mirrored.
  - Now does bidirectional mirroring for muscle dictionary values. e.g. L_pec:R_pec now mirrors to R_pec:L_pec.
  - Outputs a warning message if the muscles to mirror are on both sides of the mirror plane. This is to help prevent muscles from unwittingly being duplicated.
- FEM Deform improvements for better Otis compatibility.
Otis Configure Muscle and Tissue SOP improvements:
- Can now deform the muscles and tissue/fascia to the bone position at the initial frame.
Muscle Paint SOP has a new parameter Otis Attributes Only to remove the Vellum only muscle attributes from the paintable attributes. This prevents unnecessary attributes from being created.

Tissue Solidify Otis SOP improvements:
- Improved shrinkwrap on mesh borders and blurred regions.
- New toggle to display blurring on the External Remesh.
- Added option to blur boundaries of the input group to reduce jagged edges. Useful for transferred characters where the transferred group doesn’t have neat edge loop boundaries.
- Outputs a warning message and a group called tiny_tets if very small tetrahedra that cause issues during simulation are detected. Also added a Tiny Tetrahedra Visualization option which displays these tets if they exist.
- Outputs a warning message if some of the muscle geometry is located outside the skin surface.
Muscle Solidify SOP now has the Iterations parameter from the internal Remesh SOP exposed.
Muscle Tension Lines Activate SOP, Muscle Constraint Properties Otis SOP and Muscle Tension Lines SOP have viewer state improvements.

Test Geometry: Otto Muscle Transfer has new Biped Retargeting for animation transfer in the rig transfer setup.
Test Geometry: Otto Muscle and Tissue Simulation has overall improvements as a starter recipe.