= Glue =

Houdini lets you "glue" disconnected RBD objects together. The objects
stay together until forces pulling them apart exceed the strength of the
glue.

There are two main workflows for using glue:

* Glue an ordinary RBD object to another.

* Create "chunked" geometry (where the geometry is actually made up of
  individual pieces in groups) and import it as pieces glued together.

This feature is especially useful for breaking an object into chunks,
gluing them together, then colliding the glued object with another
object to make the glued object "shatter".

TIP:
    A convenient way to create a shatter an object is to start with the
    whole model and cut it up into chunks using the [Cookie
    SOP|Node:sop/cookie] and a cutting surface such as a sphere (to
    create smooth cuts), or a jagged polygonal surface.

    Connect the results of each cookie to a [Group SOP|Node:sop/group]
    to create the "chunk" groups. Then use a [Merge SOP|Node:sop/merge]
    to merge the resulting chunks together.

TIP:
    A useful way to create groups out of large numbers of disconnected
    "chunks" of geometry is to use the [Connectivity SOP|Node:sop/connectivity]
    followed by the [Partition SOP|Node:sop/partition].
    
    Connectivity creates an attribute (`class` by default) and assigns
    it a unique value each set of connective primitives or points.
    You can then use Partition to make groups. In the __Rule__ parameter,
    enter a group name containing the `$CLASS` variable, for example
    `chunk$CLASS`.

tasks>>
    Glue one RBD object to another:
        # In the RBD object's parameters, click the __Glue__ tab. Set
          the __Glue to object__ field to the name of the RBD object you
          want to glue this object to.

          See  [how to create an RBD object|dyn_rbd_obj]  for more
          information on objects.

        # Set the __Glue strength__ and __Glue impulse half life__ to
          control how much force is required to break apart the glued
          objects. See the online help for the [RBD Object
          operator|Node:dop/rbdobject] for information on these
          options.

    Set up chunked geometry:
        # In a Geometry object or SOP network, create the pieces of the
          model.

        # Assign the geometry of each piece to a  [group|/model/groups]
          .

          Use meaningful names with a pattern (for example, `chunk1`,
          `chunk2`, `chunk3`, or `chunk_leftarm`, `chunk_head`,
          `chunk_rightleg`). This will let you pick out the groups using
          the pattern parameter in the glue object.

        # Merge them together to create the final geometry.

    Import chunked geometry as glued-together RBD objects:
        # Use the  [tab menu|/basics/tabmenu]  to create an [RBD Glue Object
          node|Node:dop/rbdobject].

        # In the glue object's parameters, click the + button next to
          the __SOP path__ parameter and choose the SOP node or SOP
          network containing the chunked geometry (see above).

        # Use the __Group mask__ pattern to choose which groups to
          import as pieces (for example `chunk*`), or leave it as `*` to
          use all groups.

        # Click the __Internal Glue__ tab, and set the __Glue strength__
          and __Glue impulse half life__ to control how much force is
          required to break apart the glued objects. See the online help
          for the [RBD Glue Object operator|Node:dop/rbdobject] for
          information on these options.