Creates a number of RBD Objects from SOP Geometry. These individual RBD Objects are created from the geometry primitive groups, and are glued to each other.
The RBD Glue Object DOP creates multiple RBD Objects inside the DOP simulation. Like the RBD Fractured Object DOP, it takes the geometry from the given SOP Path and breaks it into pieces according to the Group Mask. Each piece is an independent RBD Object. An additional RBD Object (with name Object Name) is also created, and each piece is glued to that object.
The RBD Fractured Object and RBD Glue Object will make one object for each group. If you have meta groups such as inside and outside, try using
piece* instead of
Using RBD Glue Objects
Select the geometry to convert to an RBD glue object.
Click the RBD Glue Object tool on the Rigid Bodies tab.
Once you convert geometry to an RBD glue object you can only transform, rotate, and scale it when it is on the first frame.
The RBD Glue Object has an additional tab called Internal Glue in the parameter editor at the dynamics level. This tab lets you set the Glue Strength, which determines how strong the glue will hold. If the glue strength is set high the object will need more force to break part.
Additionally, if you increase the Glue Impulse HalfLife parameter, the accumulated force decays over a longer period of time.
You can create attributes on the RBD object’s geometry to influence its behavior. Most of these attributes allow fine-tuning of the RBD by overriding default values set in this node.
Defines a per-point velocity.
This can either be used to define the initial velocity of an RBD object if Inherit Velocity is selected, or the local deformation of the object is Use Per Point Velocities is turned on.
Defines a per-point friction. This will override the friction set in the physical parms page.
Defines a per-point dynamic friction. This will override the dynamic friction set in the physical parms page.
Defines a per-point bounce value. This will override the bounce value set in the physical parms page.
Points with this attribute set to true will not be included in the collision information when point sampling is chosen.
Edges with this attribute set to true will not be included in the collision information when edge sampling is chosen.
|Creation Frame Specifies Simulation Frame|
Determines if the creation frame refers to global Houdini
The frame number on which the object will be created. The object is created only when the current frame number is equal to this parameter value. This means the DOP Network must evaluate a timestep at the specified frame, or the object will not be created.
For example, if this value is set to 3.5, the
Timestep parameter of the DOP Network must be changed to
The name for the created object. This is the name that shows up in the details view and is used to reference this particular object externally.
While it is possible to have many objects with the same name, this complicates writing references, so it is recommended to use something like
The path to a SOP (or an Object, in which case the display SOP is used) which will be the geometry for this object.
|Fracture By Name|
The SOP’s geometry is divided into one or more sub-objects. For every unique value of the name attribute, a sub-object will be created with only the primitives that have that attribute value.
The SOP’s geometry is divided into one or more sub-objects. For every group that matches this mask, a sub-object will be created with only the primitives that belong to that group.
|Use Deforming Geometry|
Causes the geometry for the object to be pulled from the chosen SOP at each timestep. If the SOP contains animated geometry, the RBD object’s geometry will also animate.
If this option is used, the Use Point Velocity parameter of the RBD Solver should also be turned on to take into account the deformations when calculating collision responses.
|Use Object Transform|
The transform of the object containing the chosen SOP is applied to the geometry. This is useful if the initial location of the geometry is defined by an object transform.
If you want to transfer an object whose movement is defined at the object level, you should use the Object Position DOP instead.
|Create Active Objects|
Sets the initial active state of the objects. An inactive object doesn’t react to other objects in the simulation.
Controls if the geometry is displayed in the viewport. Does not reset the simulation when it is changed.
Initial position in world space of the object.
Initial orientation of the object. This is in RX/RY/RZ format.
Initial velocity of the object.
Initial angular velocity of the object. This is the axis of rotation times the rate of rotation. Speed of rotation is measured in degrees per second, so a value of 360 will cause the object to rotate once per second.
When one brings in a moving piece of geometry from an external source one does not always know the precise velocity and angular velocity.
If this toggle is set, the point velocity attribute of the geometry will be used to calculate the estimated velocity and angular velocity of the object. If the geometry does not have velocity point attributes, you can add them with a Trail surface node.
This allows one to effect a smooth hand off even if the source geometry came from a sequence of geometries rather than a simulation.
|Glue to Object|
The name of an object to glue to. If this is blank, the object is glued to no other object and acts normally. If it is the name of another RBD Object which it mutually affects, this object becomes glued to the other object. Its relative position to the other object is maintained by the solver.
The amount of accumulated force required to break a glue bond. A value of -1 will prevent the bond from ever breaking. A value of 0 will cause the bond to break with the first external force. When the bond breaks, the glue impulse is reset and the frame is resimmed.
To find the maximum glue impulse, run it at -1 and see what it peaks at.
The impact value is determined by the Mass of each sub piece by its velocity. Both can be found in the Position sub-data for each object. You can create a SOP solver that adds a detail attribute to each RBD object and set that to Mass x Velocity. If mass*vel is greater than impact force, then you have a release.
|Glue Impulse HalfLife|
The number of seconds for the glue impulse to decay by one half. Whenever a glued object gets hit, it accumulates a glue impulse force. This controls how fast that force decays.
The amount of accumulated force required to break an internal glue bond.
A value of -1 will prevent the bond from ever breaking. A value of 0 will cause the bond to break with the first external force.
|Glue Impulse HalfLife|
The number of seconds for the glue impulse to decay by one half. Whenever a glued sub-object gets hit, it accumulates a glue impulse force. This controls how fast that force decays.
|Use Volume Based Collision Detection|
Turning on this option causes the RBD solver to use a volume representation of this object for collision detection.
The volume representation results in very fast collision detection and very robust results that are tolerant of temporary interpenetrations. The disadvantage is that a volume representation cannot be used to represent a flat object such as a grid, or a hollow sphere.
When this toggle is turned off, the collision detection is geometry-based rather than volume-based. In this case, the collision code will track the trajectories of moving objects over time to find out whether collisions occurred. This allows more accurate results than volume-based collision detection. For this to work, Cache Simulation must be enabled on the dop network.
If Non Square is chosen, the specified size is divided into the given number of divisions of voxels. However, the sides of these voxels may not be equal, possibly leading to distorted simulations.
When an axis is specified, that axis is considered authoritative for determining the number of divisions. The chosen axis' size will be divided by the uniform divisions to yield the voxel size. The divisions for the other axes will then be adjusted to the closest integer multiple that fits in the required size.
Finally, the size along non-chosen axes will be changed to represent uniform voxel sizes. If the Max Axis option is chosen, the maximum sized axis is used.
When By Size is chosen, the Division Size will be used to compute the number of voxels that fit in the given sized box.
Controls the creation of the volumetric representation of this object. This should be set fine enough to capture the desired features of the geometry.
The resolution of the key axis on the voxel grid. This allows you to control the overall resolution with one parameter and still preserve uniform voxels. The Uniform Voxels option specifies which axis should be used as the reference. It is usually safest to use the maximum axis.
The explicit size of the voxels. The number of voxels will be computed by fitting an integer number of voxels of this size into the given bounds.
In laser scan mode the volumetric representation is built by sending rays along the primary axes. Only the closest and farthest intersections are used. The space between these two points is classified as inside, and the rest outside.
The laser scan mode will work even with geometry which has poorly defined normals, self intersects, or is not fully watertight. The disadvantage is that interior features can’t be represented as they are not detected.
When laser scanning is turned off, the volumetric representation is still built by sending rays along the primary axes. All intersections are found, however. Each pair of intersections is tested to see if the segment is inside or outside. This relies on the normal of the geometry being well defined (i.e., manifold, no self intersections), and the geometry being watertight. Complicated shapes with holes can be accurately represented, however.
Even with the best made geometry, numerical imprecision can result in incorrect sign choices. This option will cause the volumetric representation to be post-processed to look for inconsistent signs. These are then made consistent, usually plugging leaks and filling holes.
This takes time, and can be turned off in cases where the volumetric representation is known to generate without problems.
The Fix Signs method alone will smooth out, and usually eliminate, sign inversions. However, it is possible for regions of wrong-sign to become stabilized at the boundary of the volumetric representation. This option will force all voxels on the boundary to be marked as exterior. The Fix Signs method will be much less likely to stabilize incorrectly then.
If you want a hollow box, one method is to build one box inside the other and not use Laser Scanning. A more robust method is to just specify the inner box and use sign inversion. This treats everything outside of the box as inside, allowing the more robust Laser Scanning method to be used.
|Sign Sweep Threshold|
After the fix signs process is complete there can still be inconsistent areas in the SDF. Large blocks can become stabilized and stick out of the SDF. A second sign sweep pass can be performed to try to eliminate these blocks.
The sign sweep threshold governs how big of a jump has to occur for a sign transition to be considered inconsistent. If the values of the sdf change by more than this threshold times the width of the cell, it is considered an invalid sign transition. The original geometry is then ray intersected to determine inside/outside and the result used to determine which sign is correct. The correct sign is then propagated forward through the model.
|Max Sign Sweep Count|
The sign sweeps are repeated until no signs are flipped (ie, all transitions are within the threshold) or this maximum is reached. Too low of a sign sweep threshold may prevent the process from converging. Otherwise, it tends to converge very quickly.
A constant amount to offset the signed distance field by. This can be used grow the object slightly or shrink it. Note that it can’t be grown much beyond its original size or it will hit the bounding box of the signed distance field.
This specifies the tolerance used for ray intersections when computing the SDF. This value is multiplied by the size of the geometry and is scale invariant.
|Show Collision Guide Geometry|
The internal representation used for collision detection is converted to visible geometry. This is useful for debugging problems with collision detection.
|Collision Guide Color|
This parameter controls the color of the guide geometry.
The geometry which will be used rather than the base geometry for computing the SDF. This can be a volume in the case of Volume Sample mode to allow one better control over the cached data.
Controls the operation for this object’s volume data.
The name of the file to access according to the choice of File Modes above. This is always .simdata file format. Saving to a .bgeo extension will not save a .bgeo file.
Chooses between colliding points against volume or colliding edges against volume.
Optionally, the point attributes “nopointvolume” and “noedgevolume” may be added to the geometry to disable individual points/edges from participating in collision detection against a volume object. An edge is disabled if either of its endpoints is disabled.
|Convert To Poly|
This enables conversion of primitives (such as spheres) in the geometry into polygons. Only polygons are used for collision detection.
When this flag is turned on, polygons in the geometry are triangulated.
This controls the Level Of Detail of the triangulation. It is used to specify the point density in the U and V directions.
The barycenters of each polygon can be included in the collision detection as points or edges (connected to the vertices of the primitive).
The shape used by the Bullet engine to represent the object.
|Polygons As Convex Hulls|
When Geometry Representation is “as-is”, creates a convex shape from the geometry points. When this option is off, Houdini creates a concave shape.
|AutoFit Primitive Boxes, Capsules, or Spheres to Geometry|
When enabled, the object’s Geometry subdata will be analyzed instead of using the Position, Rotation, Box Size, Radius, and Capsule Length values.
When Geometry Representation is “Box”, “Sphere”, or “Capsule”, use the geometry bounds to create the shape.
Position of the object shape in the Bullet world. Available when Geometry Representation is “Box”, “Sphere” or “Capsule”.
Orientation of the object shape in the Bullet world. TAvailable when Geometry Representation is “Box” or “Capsule”.
The size of the object shape. TAvailable when Geometry Representation is “Box” or “Capsule”.
The radius of the sphere shape. Available when Geometry Representation is “Sphere” or “Capsule”.
The length of the capsule in the Y direction. Available when Geometry Representation is “Capsule”.
Shrink the object representation to accomodate the Collision Padding required by Bullet.
Shifts each polygon in the representation geometry inward by Collision Padding times Adjustment Factor.
With this option on, if you leave the Adjustment Factor at 1, when an object comes to rest (say, on a ground plane), no space will remain between the object and the ground.
Adjusts the resizing done by Adjust geometry. You should generally leave this value at
A padding distance between shapes during collisions. You may need to scale this value depending on the scale of your scene. For objects that need to stay packed together, you can set this value to
Disables simulation of a non-moving object until the object moves again.
Determines if the mass will be calculated automatically from the object’s volumetric representation and glued sub-objects.
The mass of an object is its volume times its density.
The absolute mass of the object.
When an object receives a glancing blow, it will often acquire a spin. The amount of spin acquired depends on the shape and mass distribution of the object, known as the inertial tensor.
The Rotational Stiffness is a scale factor applied to this. A higher stiffness will make the object less liable to spinning, a lower value will make it more ready to spin.
The elasticity of the object. If two objects of bounce 1.0 collide, they will rebound without losing energy. If two objects of bounce 0.0 collide, they will come to a standstill.
The coefficient of friction of the object. A value of 0 means the object is frictionless.
This governs how much the tangential velocity is affected by collisions and resting contacts.
|Dynamic Friction Scale|
An object sliding may have a lower friction coefficient than an object at rest. This is the scale factor that relates the two. It is not a friction coefficient, but a scale between zero and one.
A value of one means that dynamic friction is equal to static friction. A scale of zero means that as soon as static friction is overcome the object acts without friction.
Temperature marks how warm or cool an object is. This is used in gas simulations for ignition points of fuel or for buoyancy computations.
Since this does not relate directly to any real world temperature scale, ambient temperature is usually considered 0.
The RBD objects created by this node are sent through the single output.
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
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
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”,
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.
|BlendSolverWithRBDGlue||Load | Launch|
This example shows how to grab animated key frame data from an RBD Glue object and blend it into a simulation of a cube fragmenting into multiple pieces on impact.
|BreakingRock||Load | Launch|
This is an example of how to use the RBD Glue Object node to create an RBD object that automatically breaks apart on collision. It also demonstrates one technique for breaking a model into pieces appropriate for this sort of simulation.
|ChoreographedBreakup||Load | Launch|
This example shows how one can control the break up of any glued object through the use of the RBD State node.
A torus, composed of spheres, is glued together. An additional sweep plane is defined. Any sphere which ends up on the wrong side of the sweep plane is broken off the torus and left to bounce on its own. This lets the break up of the torus to be controlled over many frames.
|ChoreographedTubeBreakup||Load | Launch|
This example shows how one can control the break up of any glued object through the use of the RBD State node.
In this version of the choreographed breakup example, a moving plane is used to choreograph the breakup of a fractured tube. As the plane passes each piece, it is allowed to break off from the rest of the tube.
|ShatterGlass||Load | Launch|
This example uses an RBD projectile to shatter a piece of glass. The glass is made up of simple trangular shards glued together.
This example also demonstrates a situation where using volume based collision detection would not work, and so the objects are treated as infinitely thin surfaces when performing collision detection.
Examples that use this node
|Example for||Example name|
|Voronoi Fracture Solver||FractureExamples||Load | Launch|