Houdini 11 Dynamics

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 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 to create the “chunk” groups. Then use a Merge SOP 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 followed by the Partition SOP.

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.

To...Do this
Glue one RBD object to another

  1. 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 for more information on objects.

  2. 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 for information on these options.

Set up chunked geometry

  1. In a Geometry object or SOP network, create the pieces of the model.

  2. Assign the geometry of each piece to a group .

    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.

  3. Merge them together to create the final geometry.

Import chunked geometry as glued-together RBD objects

  1. Use the tab menu to create an RBD Glue Object node.

  2. 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).

  3. Use the Group mask pattern to choose which groups to import as pieces (for example chunk*), or leave it as * to use all groups.

  4. 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 for information on these options.