Houdini 19.5 Geometry

Create, edit, and use Null objects

Null objects are basically object nodes with transforms, but no rendered geometry.

Null objects are very useful in keyframe animation and character rigging . By parenting objects to the Null, you can transform them using the Null instead of directly.

The default representation of a Null in the viewer is a small green jack, however you can change it to use arbitrary geometry. This is very useful with character rigging as you can make the “user interface” Nulls into shapes corresponding to what they do.

To...Do this

Create a Null object

Change the geometry representation of a Null

  • Select the Null object. In the parameter editor, click the Misc tab and set the Control type parameter.


  • Double-click the Null object’s node in the network editor to go inside. The Null object contains surface nodes just like a regular Geometry container object. The surface nodes inside define the look of the Null object in the viewer.


    Use the Font surface node to display text in the Null’s geometry. You can use this, for example, to display a character’s name in the character’s root Null’s geometry.

Change the color of a Null in the viewer

  • In the Null object’s parameter editor, click the Misc tab. Turn on Set wireframe color, then edit the Wireframe color parameter.

Make Null geometry always appear in wireframe

Often when you change the geometry of Nulls you want them to stay as wireframe even if you are in a shaded view. By making Null’s the curves/surfaces open instead of closed, you can prevent them from being shaded.

To open any curve (except a primitive circle), add an Ends surface node and set the Close U parameter to “Unroll”.

(You can also make a circle open from the beginning by setting its Arc type parameter to “Open arc”.)

To open a surface, add a Carve surface node. In the Carve node’s parameter editor:

  • Turn on First U and set it to 0.

  • Turn on Second U and set it to 1.

  • Turn on First V and set it to 0.

  • Turn on Second V and set it to 1.

  • Click Breakpoints.

  • Click Extract.

This extracts the breakpoint curves from the input surface. Then, you can use an Ends operator with the “Unroll” setting as above to open the resulting curves.






Next steps

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