Houdini 13.0 Nodes

interface version 1

Creates center points for geometry primitive groups ('PrimGroup family' SOP).

Useful for generating center points for fractured geometry pieces. (As with other Houdini tools, geometry pieces can either be represented by primitive groups (e.g. piece*) or by a per-primitive name attribute.)

It also supports:

  • Generation of convenience attributes, which allow easy mapping between group names and point indices (in both directions – index-to-name and name-to-index lookup).

  • Measuring the geometry area/volume of each primitive group and storing the results on the center points. This allows using more advanced techniques, for instance to...

    • ... apply different dynamic properties (friction, mass, etc.) for differently-sized pieces

    • ... use RBD dynamics on “large” pieces and particle simulation for “small” ones

    • etc.

Note

When using primitive groups, the order of the groups and their corresponding centroids should always match (if not, that’s a bug).

When using name attributes, however, this is not guaranteed. In this case an index attribute should be copied from the primitives to the centroid points. The centroids then should be sorted using this attribute as the Sort’s expression.

Most related Houdini nodes can provide such index attribute. Example parameters include:

Parameters

Mode

Mode for detecting each geometry fracture (by primitive groups or name attribute).

IMPORTANT: See the information above (note) about pieces and centroids' ordering.

Group Mask

Primitive groups matching this mask will be treated as individual pieces. A single center point for each piece will be generated.

Tip

The matched results are shown as guide geometry.

Attrib Name

Name of the attribute used to determine the geometry pieces.

Tolerance

A tolerance value name attribute values (in case it contains numerical values, e.g. fracture indices). Values that differ less than the tolerance are considered equal.

Add Attributes
Group Indexing
Group Name Attribute

A per-point string attribute that stores the group name for each centroid (or the value of the name attribute).

Group Index (from Group Name)

The index value of the corresponding primitive group (or name attribute) is extracted from the name and stored into this (integer) attribute.

Group Index Attribue

If enabled, it creates a detail attribute for each piece, where the attribute name is the same as the piece group name, and the value is the group index (same as the __origpt attribute from the Voronoi Fracture SOP).

Note

The name-to-index detail attributes (if created) can be used by the PrimGroup Add IDs qL SOP (providing much more reliable behaviour; see PrimGroup Add IDs SOP).

From Primitives
Copy Attributes From Primitives

Copy specified per-primitive attributes to the corresponding centroid.

Attribs from Prims

The attribute(s) to copy. (Note that an empty field means no attributes. Use * to copy all attributes.)

Promotion method

The mode of converting the attributes to per-point before copying it to the centroid.

Measure Pieces

Various geometric measurements of each primitive group can be performed, and the results stored in the given point attribute(s) on the centroid that belongs to the primgroup.

Surface Area

Measure the geometric surface area of each primitive group. The result is stored on the corresponding centroid points (as a float attribute with the specified name).

Volume

Measure the volume of each primitive group. The result is stored on the corresponding centroid points (as a float attribute with the specified name).

Transformation Related
Rest Position

Store centroid positions as their rest positions as well (rest attribute).

Orientation Vectors

Generate aim and up vectors for the centroids (with default values.)

None

No vectors are generated.

N, up

Use the N (normal) and up attributes.

v, up

Use the v (velocity) and up attributes.

Aim, Up

Values for the aim and up vectors.

Preview

These options are for providing visual feedback of the current settings – they do not affect actual geometry output.

Preview Individual Pieces

If enabled, only a single piece is displayed as guide geometry.

Piece to Display

Index number of the preview piece to display in individual piece preview mode.

Center Pt Size

When previewing a single piece, its centroid is also displayed. This value specifies the centroid’s size on display.

Pieces Info

These fields show additional information (non-editable), such as the total number of pieces and the group name of the currently displayed piece.

Note

You need to press MMB on the Current Piece field if you see an expression instead of a group name.

Release Notes

interface version 1 —

2013-05-05

  • Faster centroid generation (depending on geometry, could be as much as ~2x)

  • Added inheriting of per-primitive attributes on centroids (to allow inheriting of name attribute, piece indices, etc.)

  • Help card update

older versions —

Version 0.0.3

Support for measuring individual primitive group geometry area/volume and store them as attributes on the generated center points.

Version 0.0.2

Support for fracture grouping with a name attribute (H12+).

Version 0.0.1

Initial release.