# How to control the effects of voronoi fracture

## Control the shape of fractured pieces

There are two ways to control the fracture shape. You could use point distribution or cluster pieces together.

Point distribution

Each point becomes the center of a convex piece. So if you place points equally along a line, you get a series of slices. If you concentrate them in one area, you get small pieces in that area with larger pieces outside.

Clustering pieces together

There are three main ways of clustering pieces together.

Cluster attribute

Pieces with the same cluster attribute that are connected will be fused into one piece. The cluster attribute is on the points.

Cluster noise

This is simply some noise on a cluster attribute causing pieces to spontaneously fuse.

Random detachment

After clustering, pieces will break off according to the detach ratio.

## Control scattering of pieces

There are no built in tools for scattering, but you can always paint a density attribute, which is read by the Scatter SOP to control generation of the piece centers. You could also paint the cluster attribute.

## Control the shape and texturing of inside pieces

By default the interiors are always flat planes; however, you can enable the Add Interior Detail checkbox on the Interior Detail tab of the Voronoi Fracture SOP node. This gives you access to parameters to bricker the flat planes and add some noise.

## Create a volumetric fracture map

You can use the cluster attribute to control your cutting.

For example, if you have a boundary you want to cut along, you can seed points along the boundary and then make two copies offset in opposite directions. Set one copy to cluster 1 and the other to cluster 2. If these are used for the piece centers you will create a bunch of splintery pieces laying next to your desired cut boundary, which will be fused together.

# Dynamics

## Colliding objects

• How to break different types of materials.

## Simulation types

• How to simulate smoke, fire, and explosions.

• How to set up fluid and ocean simulations.

• How to simulate grainy materials (such as sand).

• How to create and simulate crowds of characters in Houdini.

• How to create and simulate deformable objects

• Vellum uses a Position Based Dynamics approach to cloth, hair, grains, fluids, and softbody objects.

• How to create, style, and add dynamics to hair and fur.

• How to create particle simulations.

## Next steps

• HQueue is Houdini’s free distributed render and simulation manager.

• Distribute shelf tools set up an object’s sim network so it can be solved in parallel on a farm of multiple machines using HQueue.