Houdini Engine for Unreal uses a headless version of Houdini meaning an internal Houdini scene is running in the background hidden from the user.

Houdini Engine manages an internal Houdini scene when:

• a Houdini asset is instantiated in Unreal

• you connect input geometries from Unreal to the Houdini asset, the Unreal geometry is marshalled to Houdini in an Input node

• asset parameters set in Unreal are mirrored in the Houdini scene

• manipulators like curves and handles are replicated and linked to the Houdini scene

• geometries from the Houdini asset outputs are replicated into Unreal.

At times, you may want inspect the internal Houdini scene when an assset doesn’t behave as expected.

These three methods launches or saves the current internal Houdini scene and allows you to debug any issues on the Unreal asset. It’s also useful to see the data and metadata available in the Houdini scene.

There are three methods to debug your assets:

1. Open the scene in Houdini

2. Save out a .hip file

3. Use Session Sync

Open scene in Houdini ¶

This method opens the current internal Houdini scene in a new Houdini application.

• In the Houdini Engine menu in Unreal, select Open Scene in Houdini.

A new Houdini application lauches with the internal Houdini scene.

Save out HIP file ¶

This method saves out the current internal Houdini scene to a .hip file.

1. In the Houdini Engine menu in Unreal, select Save Houdini scene (HIP).

2. Save the file.

3. Open the .hip file in your Houdini application.

Use SessionSync ¶

This method creates a sync and allows you to send iterations between Houdini and Unreal.

You must be connected to a SessionSync session. See Start a SessionSync documentation.

1. In Unreal’s Content Drawer, select your HDA asset.

2. Right click your asset, and select Instantiate at the origin.

3. Your asset now appears at the origin of Houdini.