Houdini 21.0 Nodes Geometry nodes

Otis Muscle and Tissue Configure geometry node

Creates Muscle & Tissue constraints compatible the Otis Solver SOP.

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Since 21.0

This node merges Muscle, Tissue and bone geometries into a combined simulation geometry that the Otis Solver SOP uses as input to muscle and tissue simulation. Constraints are created based on the attributes on the incoming geometries, and are passed to the solver via the second output.

Parameters

Reference Frame

A reference frame that all inputs are shifted to while creating constraints. This allows the constraints to be created & computed only once during a simulation.

Rest Blend

Blends in any effects that would change the rest state of the simulation, like muscle flexing effects caused by the muscletension attribute.

This is typically used to fade in these effects during the first few frames of simulation, reducing any popping which may cause collision detection to fail or simply excessive jiggling which would take a while to settle. To do this set a keyframe on this parameter at the start of the simulation and set the value to 0. Set a keyframe with a value of 1 a few frames later.

Muscles

Simulate

When enabled, this sets up muscle geometry for simulation. If tissue is connected as well, muscles and tissue will both be simulated at once, reacting to one another.

Enable Muscle End Constraints

Enables muscle end constraints. These attach muscle ends to the nearest bone. This would typically be enabled, disabling is usually only advisable for debugging purposes.

Muscle End Mask Threshold

Only create end constraints for points with a muscleendmask values above this threshold.

Muscle Ends Mode

Determines the type of target the Muscle Ends constraint will constrain the Muscle Ends to.

Constrain to Input Animation

Constrains to input animation. This requires that muscle points (at least those with muscleendmask above the configured threshold) be moving with bone geometry.

Constrain to Nearest Bone

Constrains each muscle end point (points with muscleendmask values above the configured threshold) to the nearest point on any bone. With this option, muscle geometry can be left at rest (must not be animated) on the input.

Enable Muscle Glue Constraints

Enables muscle-to-muscle glue constraints.

Tissue

Fascia Collisions

Enables fascia to muscle & bone collisions. With this enabled, muscles & bones collide with the outer surface of fascia geometry. Disabling this might improve reliability in difficult scenarious with a lot of pressure on collisions. You should still see most of the wanted effects of fascia, like to coherent muscle motion, thanks to muscle to tissue constraints.

Enable Rigid Group

Enables rigid points that follow the input animation.

Rigid Points Group

Tissue points in this group will rigidly follow the input bone animation. To use a subset of bones to drive animation, use the Bone Group parameter.

Rigid Points Mode

Determines the type of target the points in the Rigid Group be constrained to.

Constrain to Input Animation

Constrains points in the Rigid Group to their input animation.

Constrain to Nearest Bone

Deforms points in the Rigid Group with the nearest bone geometry. With this option, tissue geometry can be left at rest (must not be animated) on the input.

Enable Tissue to Bone Constraints

Enables tissue to bone constraints, i.e. constraints that cause tissue to move with bone animation. This is usually required for reasonable simulation results. The toggle serves as a debugging tool.

Bone Group

Bones in this group will drive muscle & tissue animation when “Constrain to Nearest Bone” options are used for Rigid Points Mode or Muscle Ends Mode.

Enable Tissue to Muscle Constraints

Toggles the creation of tissue to muscle constraints. These are typically needed for good simulation results. The toggle exists as a debugging tool.

Tetrahedron Quality Tresholds

Use Quality Thresholds

Enables quality thresholds for incoming tetrahedra. Constraints created from tetrahedra that fail to match the thresholds have their stiffness values set to 0 in an attempt to stabilize simulations.

Min Quality

Uses the FEM Validate SOP to measure quality. Tetrahedra with quality below the threshold will not contribute to the simulation, potentially improving solver stability.

Min Volume Fraction

Computes volume of each tetrahedron as a fraction of mean tet volume. Tets with a fraction below the threshold will not contribute to the simulation, potentially improving solver stability.

T-Pose Attributes

Muscle T-Pose Attribute

The position attribute on muscle geometry to use while building constraints.

Tissue T-Pose Attribute

The position attribute on tissue geometry to use while building constraints.

Bone T-Pose Attribute

The position attribute on bone geomtery to use while building constraints.

Visualizations

Always Show Visualizations

Always show the visualizations configured below, even when not entering the state of the node.

Show Bone Geometry

Display any bone geometry.

Show Muscle Geometry

Display any muscle geometry.

Show Tissue Geometry

Display any tissue geometry.

Muscle End Constraints

Show muscle end constraints when enabled.

Muscle Ends

The color of muscle end constraints.

Muscle Glue Constraints

Show muscle glue constraints when enabled.

Muscle Glue

The color of muscle glue constraints.

Rigid Points

Visualize rigid points when enabled.

Rigid Points

The color of rigid points.

Tissue to Bone Constraints

Visualize tissue to bone constraints when enabled.

Tissue to Bone

The color of tissue to bone constraints.

Tissue to Muscle Constraints

Show Tissue to Muscle Constraints when enabled.

Tissue to Muscle

The color of tissue to muscle constraints.

Cleanup

Clean Up Attributes

Delete any attributes not directly related to Otis simulation. You can specify additional attributes to keep using the Keep Point Attributes, Keep Vertex Attributes, Keep Primitive Attributes and Keep Detail Attributes parameters.

Keep Point Attributes

Additional point attributes to keep on the output geometry.

Keep Vertex Attributes

Additional vertex attributes to keep on the output geometry.

Keep Primitive Attributes

Additional primitive attributes to keep on the output geometry.

Keep Detail Attributes

Additional detail attributes to keep on the output geometry.

Clean Up Groups

Removes all groups not needed by the Otis Solver SOP.

Outputs

Otis Geometry

The simulation-ready configured geometry, to be connected to the first input of the Otis Solver SOP.

Constraint Geometry

The simulation-ready constraint geometry, to be connected to the second input of the Otis Solver SOP.

See also

Geometry nodes