Houdini 16.5 Nodes Dynamics nodes

Cloth Configure Object dynamics node

Attaches the appropriate data for Cloth Objects to an object.

On this page

The Cloth Configure Object DOP takes a simulation object and attaches the data which is needed for it to be used as a Cloth Object.

This DOP is very similar to the Cloth Object DOP, except it allows you to explicitly control the creation of the object using another DOP, such as the Empty Object DOP. This can be used for more advanced instancing or creating objects every 10 frames.

See cloth forces and cloth collisions for more information.

Parameters

Material

Overall Stiffness

This determines how strongly the cloth object resists deformation. The Overall Stiffness is independent of the resolution of the mesh. If the materialuv attribute is used to specify cloth UV coordinates are specified on the mesh, then the effect of stiffness is also independent of the orientations of the triangles and quads in the mesh. The default setting for the Overall Stiffness works the best if you model the simulation geometry to real size. If you don’t model your geometry in meters, then make sure that you set the correct units of length in the Hip File Options. This should be done before you create your DOP network. When using real-size models, you should make sure that you have your length units set correctly before you create your DOP network: You should set the correct Unit Length in Edit > Preferences > Hip File Options before you create your DOP network.

Overall Damping Ratio

This value should lie between 0 and 1. The Overall Damping Ratio controls the rate of energy loss as a result of the rate of deformation. A value of 0 means that there is no loss of energy due to internal damping forces. A value of 1 means that the object is critically damped, in which case the object comes to rest in the quickest possible way without oscillating. The higher the damping ratio, the less the cloth oscillates and the quicker the object’s motion will come to rest. The effect of damping is independent of your geometry’s resolution.

Surface Mass Density

This is the mass per square meter. The mass density can be made lower or higher in parts of the object using the primitive attribute surfacemassdensity, which works as a multiplier for the parameter.

Relative Stiffness

These values should lie between 0 and 1 and act as modifiers to the Overall Stiffness for specific types of deformation. The Relative Stiffness parameters determine the relative strengths of the internal forces that counteract planar shape changes and bending. Together, the Relative Stiffness contributions for stretch and shear determine the resistance against changes within the local cloth surface plane. The contribution for Weak Bend and Strong Bend determine how strongly the object resists bending. The Weak Bend model can be used to create thin silky kinds of cloth sheets. The Strong Bend model can be used to create a strong resistance against bending, for example, for leather or thick rubber. The effect of Relative Stiffness is independent of the amount of detail and the shapes of the triangles and quadrangles your simulation geometry.

The stretch and shear contributions of Relative Stiffness work in the directions of the cloth material UV’s. These UV coordinates can be specified by the materialuv vertex or point attribute. When no UV coordinates are specified, the material directions are determined by the polygon edges. The Visualization tab of the Cloth Object has an option that allows you to see which UV directions are being currently used by the cloth object.

Relative Damping Ratio

These values should lie between 0 and 1 and act as modifiers to the Overall Damping Ratio. The Relative Damping Ratio parameters allow you to determine separately how much energy loss is introduced by the rate of changes in planar shape (stretch + shear) and the rate of bending.

Anisotropic Strength

These values allow you to very the strength of the internal stress within the cloth surface separately for the U and V directions. The U and V directions can be provided using the vertex and point attributes materialuv. For example, to make the cloth more stretchy in the U direction than in the V direction, you could set a lower value (say 0.5) for the U component of the Anisotropic Strength while keeping the V component unchanged.

Seam Angle

This is the rest angle along edges between two primitives that belong to separate panels. Panels are connected by pinning together two cloth objects using a stitch constraint or by specifying separate per-vertex rest positions within a single cloth object. The seam angle does not affect the rest angle for polygons that lie within a single panel. If you want to make parts of the object have different rest angles, then you can locally multiply the rest angle using the primitive attribute seamangle.

Geometry

Initial Geometry

This geometry determines the initial simulated state of the object. It determines the initial position and velocity for each of the points.

This is the geometry that is used for the computation of internal forces and for collision detection. Your cloth geometry should satisfy guidelines that ensure a fast-running and good looking simulation.

In many cases, you can use the Remesh SOP to help you create a suitable simulation mesh. When using triangulated geometry, it is recommended that you provide a materialuv point or vertex attribute to specify the directions of the cloth fabric.

Enable Embedding

Turns on/off the use of embedded geometry.

Embedded Geometry

This geometry is embedded into and deformed along with the simulated tetrahedral mesh.

Import Rest Geometry

This option allows you to specify and animate the rest positions that are used by the simulation inside the SOP network (without having to use a SOP solver). The option defines whether the rest positions should be imported from a SOP geometry node at each frame. When enabled, the solver will copy rest positions from the point attribute restP of the SOP geometry node onto the attribute restP on the simulation geometry at each frame. If no restP exists, then the 'P' attribute from the SOP geometry node is copied instead.

Rest Geometry Path

The path to the SOP node that will serve as the source of the rest positions.

Import Target Geometry

This option allows you to specify and animate the target positions that are used by the simulation inside the SOP network (without having to use a SOP solver). The option defines whether the target positions should be imported from a SOP geometry node at each frame. When enabled, the solver will copy target positions from the point attribute targetP of the SOP geometry node onto the attribute targetP on the simulation geometry at each frame. If no targetP exists, then the P attribute from the SOP geometry node is copied instead.

Target Geometry Path

The path to the SOP node that will serve as the source of the target positions. The positions should be stored in an attribute with the name targetP. If this attribute is not found, the P attribute is used as a fallback.

Stiffness

This coefficient determines how strongly the finite element solver tries to make the point positions match the target point positions. The solver creates an imaginary potential force for this purpose.

Damping

This coefficient determines how strongly the finite element solver tries to make the point velocities match the target point velocities. The solver creates an imaginary dissipation force for this purpose.

Collisions

Collide with objects

If enabled, the geometry in this object will collide with all other objects. These other objects may belong to the same solver or they may be be Static Objects, RBD Objects, or the Ground Plane. When the Collision Detection parameter on the Static Object is set to Use Volume Collisions, then the polygon vertices will be tested for collision against the signed distance field (SDF) of the Static Object. When Collision Detection is set to Use Surface Collisions, then geometry-based continuous collision detection is used. The geometry-based collisions collide points against polygons, and edges against edges.

When geometry-based collisions are used, only polygons and tetrahedrons in the Static Object are considered. Other types of primitives, for example spheres, are be ignored. The geometry of the external objects (e.g. Static Object) is treated as being one-sided; only the outsides of the polygons, determined by the winding order, oppose collisions.

When volume-based collisions are enabled, only points will be colliding against the volumes, not the interiors of polygons and tetrahedrons. When colliding against small volumes, this may mean that you need to increase the number of points on your mesh to get accurate collision results.

Collide with objects in this solver

When enabled, this object will collide with other objects that have the same solver. These collisions are handled using continuous collision detection, based on the geometry (polygons and/or tetrahedrons). For collisions between objects on the same solver, the polygons are treated as two-sided. Both sides of the polygons collide. The surface of a tetrahedral mesh only collides on one side: the outside.

Collide within this object

If disabled, then no two polygons within this object can collide with each other.

Collide within each component

If disabled, then no two polygons that belong on the same connected component may collide with each other.

Collide within each fracture part

This option only has an effect when fracturing is enabled on the solver. If disabled, then no two polygons that belong on the same fracture part may collide with each other. Fracture parts are controlled by the integer-valued fracturepart primitive attribute.

Collision Radius

This is the radius of an imaginary padding layer around the polygons. This layer consists of the region of space that has a distance of at most Collision Radius to some polygon. For two-sided collision surfaces, such as cloth geometry, the layer applies to both sides of each polygon (back and front). For one-sided collision surfaces, such as polygons in a Static Object, the collision radius is applied only on the front side of the polygons. The Finite Element Solver tries to ensure that the layers for the objects don’t penetrate each other or pass through each other.

For example, when a pair of two-sided polygons collide, one with a thickness of 0.01 and one with a thickness of 0.02, the solver will try to separate polygons of these objects by a distance of 0.03.

The Thickness parameter is one of the very few parameters that is scale dependent. It is very important that you adjust this parameter when you change the scale or amount of detail of your geometry.

Use a Thickness that is significantly smaller than the length of the shortest edge in your simulation geometry. Typically, the Thickness should not exceed 1% percent of the average edge length. To avoid problems with self collisions, you should keep the polygons (and/or tetrahedrons) in your geometry fairly even-sized. Avoid polygons that have very small edges, compared to the average size of the polygons in your cloth geometry.

Friction

The coefficient of friction of the object. A value of 0 means the object is frictionless. This governs how much the velocity that is tangential to the contact plane is affected by collisions. When two objects are in contact, then the solver multiplies the friction coefficients of the involved object to get the effective friction coefficient for that contact.

Drag

Visualization

Collision Radius

Visualize the cloth’s collisionradius.

Collision Radius Color

Color of the cloth collisionradius guide geometry.

Attributes

Create Quality Attributes

This creates a primitive attribute 'quality' on the simulated geometry. The worst quality is 0, the best quality is 1. The better the quality of the primitives, the better the performance and stability of the solve will be.

Create Energy Attributes

This toggle allow the object to generate attributes that indicate the density of kinetic energy and potential energy. In addition, an attribute that indicates the density of the rate of energy loss is generated.

Create Force Attributes

This toggle allows force attributes to be generated.

Create Collision Attributes

Create Fracture Attributes

Inputs

First

The simulation objects to turn into cloth objects by attaching the appropriate data.

Outputs

First

The simulation objects which were passed into this node are output with the data required for them to be considered cloth Objects attached.

Locals

ST

This value is the simulation time for which the node is being evaluated.

This value may not be equal to the current Houdini time represented by the variable T, depending on the settings of the DOP Network Offset Time and Time Scale parameters.

This value is guaranteed to have a value of zero at the start of a simulation, so when testing for the first timestep of a simulation, it is best to use a test like $ST == 0 rather than $T == 0 or $FF == 1.

SF

This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.

This value may not be equal to the current Houdini frame number represented by the variable F, depending on the settings of the DOP Network parameters. Instead, this value is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).

TIMESTEP

This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.

SFPS

This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.

SNOBJ

This is the number of objects in the simulation. For nodes that create objects such as the Empty Object node, this value will increase for each object that is evaluated.

A good way to guarantee unique object names is to use an expression like object_$SNOBJ.

NOBJ

This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.

This value may return 0 if the node does not process each object sequentially (such as the Group DOP).

OBJ

This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just the object’s position in the current order of processing.

This value is useful for generating a random number for each object, or simply splitting the objects into two or more groups to be processed in different ways. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

OBJID

This is the unique object identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused.

The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.

This value is also the best way to look up information on an object using the dopfield expression function. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).

ALLOBJIDS

This string contains a space separated list of the unique object identifiers for every object being processed by the current node.

ALLOBJNAMES

This string contains a space separated list of the names of every object being processed by the current node.

OBJCT

This value is the simulation time (see variable ST) at which the current object was created.

Therefore, to check if an object was created on the current timestep, the expression $ST == $OBJCT should always be used. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJCF

This value is the simulation frame (see variable SF) at which the current object was created.

This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).

OBJNAME

This is a string value containing the name of the object being processed.

Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.

The object name can also be used to treat a number of similar objects (with the same name) as a virtual group. If there are 20 objects named "myobject", specifying strcmp($OBJNAME, "myobject") == 0 in the activation field of a DOP will cause that DOP to operate only on those 20 objects. This value will be the empty string if the node does not process objects sequentially (such as the Group DOP).

DOPNET

This is a string value containing the full path of the current DOP Network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP Network that contains the node.

Note

Most dynamics nodes have local variables with the same names as the node’s parameters. For example, in a Position node, you could write the expression:

$tx + 0.1

…to make the object move 0.1 units along the X axis at each timestep.

See also

Dynamics nodes