Houdini Engine for Unreal Documentation

Houdini Engine For Unreal

Houdini Engine for Unreal Engine is a plug-in that allows integration of Houdini technology into Unreal.

This plug-in brings Houdini's powerful and flexible procedural workflow into Unreal Engine through Houdini Digital Assets. Artists can interactively adjust asset parameters inside the editor and use Unreal assets as inputs. Houdini's procedural engine will then "cook" the asset and the results will be available in the editor without the need for baking.

Version 2 is a significant rewrite of the core architecture of the existing Houdini Engine plugin, and comes with many new features, and improvements.

For more information:

• Houdini Engine for Unreal
• FAQ

For support and reporting bugs:

• Houdini Engine for UE4 Forum
• Bug Submission

Note

This documentation is for Version 2 of the plug-in. For the Version 1 documentation, please read the Houdini Engine for Unreal 18.0 documentation.

Since Houdini 18.5 ships with both Version 1 and Version 2 of the plug-in, the plug-in is NOT copied automatically to Unreal after running the Houdini installer. You need to manually copy the Houdini Engine folder for the desired version of the plugin to Unreal's "Engine/Plugin/Runtime" folder.

Documentation Overview

• Getting Started
• Session
• Assets
• Parameters
• Special Attributes and Groups

Inputs and Outputs

• Inputs
• Curves
• Handles
• Outputs
• Meshes
• Instances
• Landscapes
• Materials
• Collisions
• Mesh Sockets
• PDG Asset Link
• Blueprints
• Session Sync

Other Topics

• Debugging
• Using FBX Files
• Asset Cooking and Packaging
• Coordinate Systems
• Settings
• Custom Commands
• Houdini Engine Tools
• Public API
• Houdini-Niagara Plugin
• Houdini Live Link Plugin

What's New?

You can see the latest updates and bug fixes made to the plugin in the Daily Changelog.

Here are some of the new features and improvements currently available in Version2's Beta2:

Core:

• New and redesigned core architecture, more modular and lightweight. All the Houdini Engine/HAPI logic is now Editor-only and contained in the “HoudiniEngine” module. All the custom runtime components and actors used by the plugin now simply acts as data-holders, and are processed by the HoudiniEngine modules, removing the need to bake HDA before packaging a game.
• The plugin now relies exclusively on native, UProperties based serialization, so operations like cut and paste, move between level, duplicate etc.. do not exhibit any of the issues that version 1 had with those operations.

Outputs:

• Static Mesh creation time has been optimized and now uses Mesh Descriptions. Alternatively, you can also decide to use an even faster Proxy Mesh generation while editing the HDA. Those can then be automatically refined to Static Meshes, either on a timer, or when saving/playing the level.
• World composition support: Tiled heightfields can now be baked to multiple landscape actors/steaming proxies, and will create/update the levels needed for world composition. You can specify the level's path by using the new “unreal_level_path” attribute, that is also used by meshes and instancers so they can also be baked out to separate levels.
• Material overrides and generic uproperty attributes can either be applied on the instancer, or per instance (when using mesh split instancers or instanced Actors).
• It is possible to create foliage instances directly, without baking, when using the “unreal_foliage” attribute on an instancer.
• Classes can now be directly instantiated by the "unreal_instance" attribute (ie “PointLight”, “AudioVolume”… ).
• Curves can be outputed to SplineComponents by using the "unreal_output_curve" primitive attribute.

Inputs:

• Colliders on a Static Mesh can now be imported as group geometry.
• World inputs can now read data from BSP brushes.
• Instancers and Foliage are now imported as packed primitives.
• World inputs have an improved bound selector mode, that lets them send all the actors and objects contained in the bounds of the selected object.
• World inputs can now import data from all supported input objects (landscape, houdini asset actors..)
• World inputs can now import data from actors placed in a different level than the Houdini Asset Actors's.
• A single curve input can now create and import any number of curves.
• You can alt-click on curve inputs or editable curves to create new points.

Parameters:

• A parameters and inputs editing now support multi-selection.
• Parameter UI/UX has been improved:
• Folder UI (tabs, radio, collapsible) has been improved
• Ramps UI has been improved, and it is easy to turn off auto-update while editing them.
• When an asset is dropped on a string parameter, it automatically sets its value to the asset ref.
• String parameters can now be turned into an asset picker via the “unreal_ref” tag.
• Support for File parameters has been improved (custom extension, directory, new file...)
• Multi-line strings, Column Labels, Button Strip, Log Int and Floats are now supported.

General:

• The plugin's UI has been completely revamped, a new Houdini Engine menu has been added to the editor.
• bgeo/bgeo.sc files can be imported natively in the content browser (Mesh and instancers).
• The PDG Asset Link has been added, allowing control of TOP networks nested in HDAs, and works similarly to the one in the Unity plugin.
• Session Sync is supported, allowing the plugin to connect to a session of Houdini Engine running inside Houdini. The state of Houdini Engine can be viewed in Houdini while working with the plugin in Unreal, and changes on either end, whether in Unreal via the plugin or in Houdini via its various interfaces, will be synchronized across so that both applications will be able to make changes and see the same results.
• Blueprint support: It is now possible to use Houdini Asset Components in the Blueprint Editor. This lets you preset and use HDAs on Blueprint Actors, and changing parameters/inputs on the Houdini Asset will automatically update all placed instances of that Blueprint.