Houdini 11 Modeling

Parent objects

Connecting the output of object A to the input of object B makes object A the parent of object B.

Note

In computer graphics parlance, we say that we “parented” B to A. This might seem backwards, but that’s the way it is.

An object which is parented to (that is, the child of) another object inherits the transformations of the parent object. Moving or rotating the parent moves/rotates the child as well.

You can also put objects inside an object subnetwork (use the tab menu to create a Subnet node at the object level). All objects inside the subnetwork inherit the transform of the subnet’s parent, if any.

Some other information is inherited from parent objects besides transformations. For example, motion blur can be inherited from a parent object. If the rendering parameters are not enabled for an object, they will be inherited from the parent object.

For example, to view the scene from the point of view of a particular object, you can parent the camera to the POV object so the camera transforms with the object.

Each object can have only one parent.

To...Do this
Parent an object in the network editor
Parent an object in the 3D viewport

  1. Click the Parent tool on the Modify shelf tab.

  2. Select the child object(s) and press Enter.

  3. Select the parent object and press Enter.

Unparent an object in the network editor
Unparent an object in the 3D viewport

  1. Click the Parent tool on the Modify shelf tab.

  2. Select the child object(s) and press Enter.

  3. Select nothing and press Enter.

Tip

When you parent an object, its current transforms will be added to the parent's, usually resulting in the child object changing position and/or rotation. To keep the object at its current position when parenting, turn on Keep position when parenting in the object’s parameters before you parent it.

Edit an object's origin/pivot

All transformations are relative to an object’s pivot point. An object scales toward/away from the pivot point and rotates around the pivot point.

To...Do this
Set an object’s pivot point in the viewport

  • Press Ins, use the handle to move the pivot point, then press Ins again.

  • You can temporarily move the handle, which scaling and rotating is relative to, by pressing ', using the handles, and the pressing ' again. This does not move the actual pivot point.

Set an object’s pivot point numerically

  1. In the parameter editor, click the Transform tab.

  2. Use the Pivot text fields to set the pivot point’s X, Y, and Z relative to the object’s origin.

Pre-transform

The pre-transform is like an invisible parent Null inside each object . The position, scale, and rotation values in the object’s parameters are relative to the (normally hidden) values in the pre-transform.

The pre-transform is useful, especially in character rigging , for setting a certain position, rotation, and/or scale as the “rest” or “zero” state for that object. After that, values you enter are relative to the pre-transform values.

Warning

The pre-transform uses a fixed, non-configurable transform order. If you try to copy a non-uniform scale into the pre-transform, you can get shearing.

To...Do this
See the values in an object’s pre-transform

Press MMB on the object’s tile in the network editor.

Make the object’s current transform the “zero” state

In the object’s parameter editor, click the Transform tab and choose Pre-transform > Clean transforms.

This moves the object’s current transformation into the pre-transform and resets the transformation parameters to the “identity” (position and rotation = 0, scale = 1).

The opposite action is Extract pretransform (see below).

Make only the object’s current position, rotation, or scale the “zero” state

In the object’s parameter editor, click the Transform tab. Open the Pre-transform pop-up menu and choose Clean translates, Clean rotates, or Clean scales.

Delete the pre-transform

In the object’s parameter editor, click the Transform tab and choose Pre-transform > Reset pretransform.

This will probably change the position, rotation, and or scale of the object because the current values in the parameters will no longer be relative to the pre-transform.

Move the pre-transform values into the parameters

In the object’s parameter editor, click the Transform tab and choose Pretransform > Extract pretransform.

This moves the object’s current pre-transform values into the parameters and resets the pre-transform.

The opposite action is Clean transforms (see above).