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The FEM Slide Constraint DOP node sets up sliding between two FEM objects, an FEM object and an animated static object, or the connected components of a single FEM object. For example, you can use this constraint to create skin-sliding effects over bones, muscles, or fascia, or set up sticky sliding between muscles.
This constraint forces a source object and a target object to remain in contact while allowing for relative tangential movement between the objects. Essentially, the source object behaves like it is magnetic and the target object behaves like it is a slippery surface.
In addition to the sliding behavior, you can also use the constraint’s Damping parameter to create a friction-like effect.
This controls how quickly the constraint point will adapt its position to the relative position that it is sliding against.
This controls how quickly the constraint point will adapt its velocity to the goal.
FEM Object to constrain.
This position attribute is used as a basis for computing all link lengths and directions.
FEM Object or Solid Object. Choose the same object as A to allow sliding between connected components of this object.
This position attribute is used as a basis for computing all constraint distances and directions.
No points outside this group will be constrained.
Use Distance Threshold
Enable the use of a distance threshold when determining which points to constrain.
Only points that have a goal surface within this distance threshold will be constrained.
Enable Distance Threshold Attribute
Name of a multiplier point attribute for the Distance Threshold.
Distance Threshold Attribute
Specifies the name of a multiplier point attribute for the Distance Threshold
Filter by Source Border Side
Constrain source points only when the link to the closest target point touches that source point on Source Border Side
Source Border Side
The side of the source mesh border at which links are allowed: Interior or Exterior.
Filter by Source Self Occlusion
Constrain source points only when the link to the closest target point does not intersect the source border
Filter by Target Border Side
Constrain source points only when the link to the closest target point touches that target point on Target Border Side
Target Border Side
The side of the target mesh border at which links are allowed: Interior or Exterior.
Two-Sided: Attract And Repel
FEM Objects will repel each other on contact, but also attract each other. This is useful when you need to introduce some stickiness between objects. For example, like a magnet sliding over a smooth surface.
One-Sided: Only Repel
FEM Objects will repel each other on contact, but not attract each other. This is useful when you are setting up collisions between smooth objects.
This Behavior can be a more efficient, higher quality alternative to regular collisions in FEM. For example, you can use this option to make tissue slide on underlying bones and muscles without sticking to those bones and muscles.
One-Sided: Only Attract
FEM Objects will stick to each other and be prevented from separating. Allows interpenetrations.
Enable Strength Multiplier Attribute
When enabled, Strength is locally scaled by a point attribute
Strength Multiplier Attribute
Name of a multiplier point attribute for the Strength.
Enable Damping Multiplier Attribute
When enabled, Damping is locally scaled by a point attribute
Damping Multiplier Attribute
Name of a multiplier point attribute for the Damping.
Enable Target Position Attribute
When on, allows the target position of each constraint link to be written to a point attribute on the source.
Target Position Attribute
Specifies the name of the attribute to which the target position is written at each frame.
Target Primitive Attribute
Specifies the name of the attribute that keeps track of current target primitive. This attribute should not be modified.
Target Subindex Attribute
Specifies the name of the attribute that encodes on which part of a current target primitive the current target location lies. This attribute should not be modified.
Target Face Id Attribute
Specifies the name of the attribute that encodes a face (point, line segment or triangle face) that the current target location lies on. This attribute should not be modified.
Target Bary Attribute
Specifies the name of the attribute that encodes barycentric coordinates of the current target location. This attribute should not be modified.
Show Guide Geometry
Turning on this option causes guide geometry to be displayed in the viewport representing this constraint.
Controls the radius of the spheres drawn in the viewport as guide geometry for this constraint.
Controls the color of the guide geometry.
Determines if this node should do anything on a given timestep and for a particular object. If this parameter is an expression, it is evaluated for each object (even if data sharing is turned on).
If it evaluates to a non-zero value, then the data is attached to that object. If it evaluates to zero, no data is attached, and data previously attached by this node is removed.
This optional input can be used to control which simulation objects are modified by this node. Any objects connected through this input and which match the Group parameter field will be modified.
If this input is not connected, this node can be used in conjunction with an Apply Data node, or can be used as an input to another data node.
All Other Inputs
If this node has more input connectors, other data nodes can be attached to act as modifiers for the data created by this node.
The specific types of subdata that are meaningful vary from node to node. Click MMB an input connector to see a list of available data nodes that can be meaningfully attached.
The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).
If no object stream is connected to this node, the output is a data output. This data output can be connected to an Apply Data DOP, or connected directly to a data input of another data node, to attach the data from this node to an object or another piece of data.
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.
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).
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.
This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.
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
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).
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).
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).
This string contains a space separated list of the unique object identifiers for every object being processed by the current node.
This string contains a space separated list of the names of every object being processed by the current node.
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 == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).
This value is the simulation frame (see variable SF) at which the current object was created.
This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).
This is a string value containing the name of the object being processed.
Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.
The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named “myobject”,
strcmp($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).
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.
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.