Attributes and Groups

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Houdini to Unreal
Unreal to Houdini
Groups
Standard Houdini Attributes
Parameter Tags
Generic UProperty Attributes
String Tokens

Certain special groups and attributes are used when marshalling data between Houdini and Unreal.

See the referenced topics for more details.

Note

Although attributes may indicates a preferred type, the plugin will try to automatically convert an attribute that has an unexpected type. For example, if you expected an int attribute but found a float attribute. The plugin logs a warning when an attribute’s value is converted to its expected type.

Note

When using packed primitives, either for instancing or creating multiple mesh outputs, the attribute’s location is important. Attributes created before packing will be applied to the generated mesh, whereas attributes created after packing will be applied to the generated component/actor.

Houdini to Unreal ¶

This table lists special attributes to set in an HDA and the plugin recognizes when you translate the Houdini data to Unreal outputs. You can setup these attributes on your assets to control and override some properties and behaviours of the generated Unreal outputs.

Bake Outputs ¶

Attribute Name	Owner	Type	Description
`unreal_uproperty_tag_*`	any	string	Prefix used to specify tags on the output object. This will apply the tags on the actor and all components related to this output object
`unreal_uproperty_actorTag_*`	any	string	Prefix used to specify Actor tags on the output object
`unreal_uproperty_componentTag_*`	any	string	Prefix used to specify Component tags for all components on the output object
`unreal_uproperty_mainComponentTag_*`	any	string	Prefix used to specify Component tags on only on the main component of the output object. If the output object is an actor, these tags will only be applied on the root component
`unreal_output_curve`	prim	int	Curves that have this attribute set to 1 will output as SplineComponents
`unreal_output_curve_linear`	prim	int	Indicates whether or not an output curve should be linear
`unreal_output_curve_closed`	prim	int	Indicates whether or not an output curve should be closed
`unreal_level_path`	any	string	Determines the level to which outputs are baked when baking to actors / foliage. Meshes, instancers, foliage and landscapes are baked to the specified level. This can be especially useful for world composition, baking landscape tiles and their associated instancers or foliage to a separate level per tile. This attribute is also available on inputs (where it is set to the path of the level where the input originated). The default value is `.`, which will generate geometry in the the current persistent world, paths starting with a `/` are considered absolute, otherwise paths are relative to the current persistent world’s Map. (supports String Tokens).
`unreal_bake_folder`	prim, detail	string	Unreal path of a Folder used to override the default Bake folder for this asset. Default value: `{bake}`. (Supports String Tokens)
`unreal_bake_name`	any	string	(deprecated) use `unreal_output_name` instead
`unreal_bake_actor`	any	string	Unreal path to an Actor that will be created/used when baking the given output
`unreal_bake_actor_class`	any	string	Unreal path, or classname, of the Actor class to use when spawning the bake actor. If missing/blank then Actor is used
`unreal_bake_outliner_folder`	any	string	Unreal path to a world outliner folder that will be created/used when baking the given output

Generic UProperty ¶

Attribute Name	Owner	Type	Description
`unreal_uproperty_*`	any	int, float, string	Attribute prefix used to modify UProperties of the generated output objects/actors/components

Geometry Collections ¶

Setting up these attributes on your asset allows you to control and override some properties and behaviours of the generated Unreal outputs.

Attribute Name	Owner	Type	Description
`unreal_gc_piece`	prim	int	Specifies the primitive as a GeometryCollection piece. The value represents the clustering level, or 0 to disable this behaviour
`unreal_gc_cluster`	prim	int	Specifies the primitive clustering index, to group multiple pieces of the same level to different groups
`unreal_gc_clustering_damage_threshold`	detail	float	Specifies the clustering damage threshold
`unreal_gc_collisions_collision_type`	detail	int	Specifies the collisions collision type. 0 = Implicit-Implicit, 1 = Particle-Implicit
`unreal_gc_collisions_implicit_type`	detail	int	Specifies the collisions implicit type. 0 = Box, 1 = Sphere, 2 = Capsule, 3 = Level Set, 4 = None, 5 = Convex
`unreal_gc_collisions_min_level_set_resolution`	detail	int	Specifies the collisions min level set resolution
`unreal_gc_collisions_max_level_set_resolution`	detail	int	Specifies the collisions max level set resolution
`unreal_gc_collisions_min_cluster_level_set_resolution`	detail	int	Specifies the collisions min cluster level set resolution
`unreal_gc_collisions_max_cluster_level_set_resolution`	detail	int	Specifies the collisions max cluster level set resolution
`unreal_gc_collisions_min_level_set_resolution`	detail	int	Specifies the collisions min level set resolution
`unreal_gc_collisions_collision_object_reduction_percentage`	detail	float	Specifies the collisions collision object reduction percentage
`unreal_gc_collisions_mass_as_density`	detail	int	Sets the collisions mass as density. 0 = unset, 1 = set
`unreal_gc_collisions_mass`	detail	float	Specifies the collisions mass
`unreal_gc_collisions_minimum_mass_clamp`	detail	float	Specifies the collisions minimum mass clamp
`unreal_gc_collisions_collision_particles_fraction`	detail	float	Specifies the collisions collision particles fraction
`unreal_gc_collisions_maximum_collision_particles`	detail	int	Specifies the collisions maximum collision particles
`unreal_gc_name`	prim, detail	string	Specifies the name of the GeometryCollection. Used to differentiate multiple GC outputs

Geometry Collections - Unreal Engine 5 ¶

These attributes are specific to Unreal Engine 5. UE5 Allows you to specify multiple “Size Specific Data”. In addition, each element of “Size Specific Data” allows you to specify an array of collision shapes.

Attribute Name	Owner	Type	Description
`unreal_gc_clustering_cluster_connection_type`	detail	int	Specifies the clustering connection type. 0 = Point implicit, 1 = MinimalSpanningSubsetDelaunayTriangulation, 3 = PointImplicitAugmentedMinimalDelaunay
`unreal_gc_collisions_max_size`	detail	float, float	The max size of the Size Specific Data. Required to specify multiple Size specific data
`unreal_gc_collisions_damage_threshold`	detail	int, int	The collision damage threshold for each Size Specific Data
`unreal_gc_collisions_collision_type_X`	detail	int, int	Specifies the clustering damage threshold. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_implicit_type_X`	detail	int, int	Specifies the collisions implicit type. 0 = None, 1 = Box, 2 = Sphere, 3 = Capsule, 4 = Level Set. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_min_level_set_resolution_X`	detail	int, int	Specifies the collisions min level set resolution. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_max_level_set_resolution_X`	detail	int, int	Specifies the collisions max level set resolution. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_min_cluster_level_set_resolution_X`	detail	int, int	Specifies the collisions min cluster level set resolution. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_max_cluster_level_set_resolution_X`	detail	int, int	Specifies the collisions max cluster level set resolution. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_collision_object_reduction_percentage_X`	detail	float, float	Specifies the collisions collision object reduction percentage. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_collision_particles_fraction_X`	detail	float, float	Specifies the collisions collision particles fraction. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_maximum_collision_particles_X`	detail	int, int	Specifies the collisions maximum collision particles. The `_X` specifies the index of the size specific data
`unreal_gc_collisions_collision_margin_fraction_X`	detail	float, float	Specifies the collisions margin fraction. The `_X` specifies the index of the size specific data

The X in the attributes that contain _X represents the index of the size specific data. Additionally, some of the collision attributes can either be a value or an array of values. An element at index i represents the value for the collision object at index i.

A value is identical to a value array of size one with only that value in it for backwards compatibility.

If you do not add the _X suffix, then it will be equivalent to index 0.

If you want to have more than one size specific data, then it must be specified using the unreal_gc_collisions_max_size attribute. For instance, the sequence of attributes unreal_gc_collisions_max_size = {1234, 12345} and unreal_gc_collisions_collision_type_1 = {0, 1} means that you have a GeometryCollection with two size specific datas, and the second size specific data has two collision shapes: One with a collision type of Implicit-Implicit, and the other with a collision type of Particle-Implicit.

Instancers ¶

Attribute Name	Owner	Type	Description
`unreal_instance`	point, detail	string	Unreal path to an Asset that shall be instanced at the given transform. In version2, this attribute can also be a Class Name (`PointLight` for example)
`unreal_foliage`	detail, prim, point	int, float	When used on instances (and set to 1), the plugin will add the instances to the current level’s foliage system instead of creating new actors/components
`unreal_foliage_attachment_type`	point	int	Determines whether foliage should to attach to other objects in the level - 1 for yes, 0 for no, a value of 2 attaches to landscapes only.
`unreal_foliage_attachment_distance`	point	float	Distance to search vertically when using `unreal_foliage_attachment_type`. Default is 1000.
`unreal_split_attr`	any	string	Indicates the name of another attribute to be used to split the instancers into multiple components depending on that second attributes values
`unreal_split_instances`	detail, prim	any	(deprecated) use unreal_split_attr instead - Indicates that the generated instances should be split into `StaticMeshComponents` instead of one `InstancedStaticMeshComponent`
`unreal_instance_color`	prim	float(4)	(deprecated) Used with unreal_split_instances to specify a per-instance color to override the generated StaticMeshComponents vertex colors
`unreal_hierarchical_instancer`	any	int	When set to 1, forces the creation of HierarchicalInstancedStaticMeshComponent instead of `InstancedStaticMeshComponents`. This will also force the creation of a `HierarchicalInstancedStaticMeshComponent` even in cases where the instance count is only 1
`unreal_force_instancer`	any	int	When set to 1, forces the creation of an instancer component (`InstancedStaticMeshComponent` or `HierarchicalInstancedStaticMeshComponent`, the latter based on having LODs or `unreal_hierarichal_instancer == 1`) even if there is only one instance of a static mesh
`unreal_num_custom_floats`	any	int	Indicates the number of custom floats to be used for an instancer’s Per Instance Custom Data
`unreal_per_instance_custom_dataX`	any	float	Per-Instance Custom float data, where X is the zero-based index of the custom data

Landscapes ¶

Attribute Name	Owner	Type	Description
`unreal_material_hole`	prim, detail	string	Unreal path of a Material asset used for Landscape holes
`unreal_landscape_shared_actor_name`	any	string	Name for the main/shared landscape actor when using landscape streaming proxies. The name for landscape tile actors will be read from `unreal_output_name`. Default Value: `{hda_actor_name}_SharedLandscape`. (Supports String Tokens)
`unreal_landscape_layer_min`	any	float	Specify the minimum values to be used for when converting heightfield layers/height values to landscapes. This is especially useful to ensure all tiles are converted in the same manner
`unreal_landscape_layer_max`	any	float	Specify the maximum values to be used for when converting heightfield layers/height values to landscapes. This is especially useful to ensure all tiles are converted in the same manner
`unreal_landscape_write_locked_layer`	any	int	Allows the layer’s data to be written to a locked Landscape Edit Layer
`unreal_landscape_lock_layer`	any	int	Locks the Edit Layer after writing
`unreal_landscape_section_size`	any	int	Specifies section size for landscapes. unreal_landscape_sections_per_component must also be set
`unreal_landscape_sections_per_component`	any	int	Specifies sections per component for landscapes. unreal_landscape_section_size must also be set
`unreal_unit_landscape_layer`	prim, detail	int	If set to 1, indicates that a heightfield mask’s value should be considered in `0, 1` when converting their values to landscape layers
`unreal_landscape_layer_nonweightblended`	prim, detail	string	Names of heightfields masks, separated by spaces, that should be created a non-weight blended landscape layers
`unreal_landscape_layer_info`	prim	string	Unreal path of an existing LandscapeLayerInfo object to be used when converting a given heightfield mask to a landscape layer
`unreal_landscape_layer_noweightblend`	prim, detail	int	Set the `NoWeightBlend` property on the corresponding paint layer’s LayerInfo object in Unreal to unchecked `0` or checked `1`. This attribute takes precedence over `unreal_landscape_layer_nonweightblended`
`unreal_landscape_output_mode`	any	int	Set landscape output mode to Generate Landscape `0` or Modify Edit Layer `1`
`unreal_landscape_editlayer_name`	any	string	Name of target edit layer
`unreal_landscape_editlayer_target`	any	string	(deprecated) use `unreal_output_name` instead
`unreal_landscape_editlayer_type`	any	string	Type of layer being output. `0` - Base layer, `1` - Additive layer. (Default: `0`).
`unreal_landscape_editlayer_clear`	any	int	Whether to clear the whole editor layer before drawing the output heightfield (Default: `0`).
`unreal_landscape_editlayer_after`	any	string	After which layer on the target landscape this output layer should be placed
`unreal_landscape_editlayer_subtractive`	prim, detail	int	This attribute can be set on heightfield masks to set the Subtractive Blend property to unchecked `0` or checked `1` on paint layers in Unreal
`unreal_landscape_partition_grid_size`	prim	int	This attribute controls the world partition grid size when creating landscapes. Only apply in levels that have world partition enabled
`unreal_landscape_landscape_size`	prim	int2	Used to indicate the total landscape size when importing a single tile

Landscape Splines general ¶

The table lists the general attributes that affect landscape splines output.

Attribute Name	Attribute Owner	Description
`unreal_landscape_spline`	point, vertex, prim, detail	Set to `1` for the plug-in to recognize the curve primitives as landscape splines
`unreal_landscape_spline_target_landscape`	prim	The landscape to create the landscape splines on. This can be set to `InputX` (0, 1, …) to target an input landscape of the HDA

Landscape Splines edit layer ¶

Attribute Name	Attribute Owner	Description
`unreal_landscape_editlayer_name`	point, vertex, prim	The name of the edit layer to create and apply the splines to
`unreal_landscape_editlayer_clear`	point, vertex, prim	Whether the edit layer should be cleared the first time it is altered during landscape spline translation
`unreal_landscape_editlayer_after`	vertex, prim	The edit layer specified in `unreal_landscape_editlayer_name` is moved to after this layer

Landscape Splines control point ¶

The table lists the attributes that are supported for the control points of the landscape splines. Many attributes can be applied to either the curve’s points or vertices, but not both at the same time.

Attribute Name	Attribute Owner	Description
`rot`	point, vertex	The rotation of the control point
`unreal_landscape_spline_control_point_id`	point, vertex	The id of the control point. Valid ids are greater than or equal to 0. Values that are less than `0` indicate the point is not a control point
`unreal_landscape_spline_control_point_lower_terrain`	point, vertex	The Raise Terrain property on the control point
`unreal_landscape_spline_control_point_mesh`	point, vertex	Control point static mesh
`unreal_landscape_spline_control_point_mesh_material_overrideX`	point, vertex	Control point mesh material overrides
`unreal_landscape_spline_control_point_mesh_scale`	point, vertex	Control point mesh scale
`unreal_landscape_spline_control_point_paint_layer_name`	point, vertex	The Paint Layer Name property on the control point
`unreal_landscape_spline_control_point_raise_terrain`	point, vertex	The Raise Terrain property on the control point
`unreal_landscape_spline_end_falloff`	point, vertex	The End Falloff property of the control point
`unreal_landscape_spline_half_width`	point, vertex	The Half-Width property of the control point
`unreal_landscape_spline_side_falloff`	point, vertex	The Side Falloff property of the control point

Landscape Splines segment ¶

The table lists the attributes that are supported for the segments and segment connections of the landscape splines. These attributes can be applied to each point or vertex and affect the segment starting at that point or vertex. If the attribute does not exist on the points or vertices of the curve then the primitive is checked, and any attribute found is applied to all segments in the spline.

Attribute Name	Attribute Owner	Description
`unreal_landscape_editlayer_name`	point, vertex, prim	The name of the edit layer to create and apply the splines to
`unreal_landscape_editlayer_clear`	point, vertex, prim	Whether the edit layer should be cleared the first time it is altered during landscape spline translation
`unreal_landscape_editlayer_after`	point, vertex, prim	The edit layer specified in `unreal_landscape_editlayer_name` is moved to after this layer
`unreal_landscape_spline_segment_connectionX_mesh_socket_name`	point, vertex, prim	Segment connection `0` and `1`: The socket name on the control point to use at the segment control point connection
`unreal_landscape_spline_segment_connectionX_tangent_length`	point, vertex, prim	Segment connection `0` and `1`: The tangent length of connection point at this end of the segment
`unreal_landscape_spline_segment_lower_terrain`	point, vertex, prim	The Raise Terrain property on the segment (whether or not the landscape can be raised when the spline is applied)
`unreal_landscape_spline_segment_meshX`	point, vertex, prim	Segment meshes. X is omitted for the first mesh, then 1, 2, 3…
`unreal_landscape_spline_segment_meshX_material_overrideY`	point, vertex, prim	Segment mesh material overrides
`unreal_landscape_spline_segment_meshX_scale`	point, vertex, prim	Segment mesh scales
`unreal_landscape_spline_segment_paint_layer_name`	point, vertex, prim	The Paint Layer Name property on the segment (the layer that is painted when the spline is applied to the landscape)
`unreal_landscape_spline_segment_raise_terrain`	point, vertex, prim	The Raise Terrain property on the segment (whether or not the landscape can be raised when the spline is applied)

Level of Details ¶

You can change the LOD settings on the Generic UProperty Attributes.

Attribute Name	Owner	Description
`unreal_uproperty_LODForCollision`	Detail	Sets the LOD used for collision
`unreal_uproperty_MinLOD`	Detail	Sets the minimum LOD
`unreal_uproperty_LODGroup`	String	Sets the LOD Group
`lodX_screensize`	Detail	Sets the screensize values where lodx is the name of the LOD Note Manual change of the screensize values turns off `AutoComputeLODScreenSize` on the static mesh
`lod_screensize`	Primitive	Sets the screensize values of the LOD Note Manual change of the screensize values turns off `AutoComputeLODScreenSize` on the static mesh

Meshes generated by Houdini Engine that have LOD groups will automatically create Hierarchical Instanced Static Mesh Components when instanced, either on Packed Primitives or Object Instancers.

Note

Make sure the geometry inside of each LOD group is not packed. The plugin will create a separate instancer instead of a LOD level for packed geometry.

Materials ¶

Attribute Name	Owner	Type	Description
`unreal_material`	any	string	Unreal path of a Material asset to apply to an output. You can specify the material slot by prefixing the path with the slot number in square brackets.
`unreal_physical_material`	prim, detail	string	Unreal path of a PhysicalMaterial asset to be used as a Physcial Material on the output
`unreal_simple_physical_material`	prim, detail	string	Unreal path of a PhysicalMaterial asset to be used for Simple Unreal Collisions
`unreal_face_smoothing_mask`	prim	int	Mesh smoothing mask data

Material Instances ¶

Attribute Name	Owner	Type	Description
`unreal_material_instance`	prim, detail	string	Unreal path of a Material asset to create an instance of
`unreal_material_hole_instance`	prim, detail	string	Unreal path of a Material asset to create an instance of, to be used for Landscape holes
`unreal_material_parameter_*`	detail	any	Attribute prefix used to modify generated material instances' parameters

Meshes ¶

Attribute Name	Owner	Type	Description
`unreal_lightmap_resolution`	any	int	Lightmap resolution for the mesh component
`unreal_output_name`	any	string	Name to be used for the output. Default value for single landscape actor: `Landscape`
`unreal_disable_gamma_correction`	any	int	Meshes	If not `0`, gamma correction is not performed when reading the 'Cd' attribute.
`unreal_generated_mesh_name`	any	string	(deprecated) use `unreal_output_name` instead
`unreal_nanite_enabled`	any	int	Enables Nanite on the generated meshes (UE5)
`unreal_nanite_position_precision`	any	int	The position precision attribute to be used for Nanite Meshes (UE5)
`unreal_nanite_percent_triangles`	any	int	The percent of triangles to keep for Nanite Meshes, zero by default (no triangles) (UE5)

Meshes Nanite ¶

(UE5 only) The plugin can control the Nanite settings on the meshes found in the outputs of your HDA by using the following attributes:

Attribute Name	Owner	Type	Description
`unreal_nanite_enabled`	any	int	Turns on Nanite on the generated meshes.
`unreal_nanite_position_precision`	any	int	The position precision attribute for Nanite Meshes.
`unreal_nanite_percent_triangles`	any	int	The percent of triangles to keep for Nanite Meshes, zero by default (no triangles).
`unreal_nanite_fallback_relative_error`	any	float	Fallback relative error - sets the maximum amount of relative error allowed when removing details from the source mesh. This relative error value doesn’t have a unit size and is relative to the size of the mesh.
`unreal_nanite_trim_relative_error`	any	float	Trim relative error - All detail in the source mesh with less visual impact than this relative error amount is removed. This relative error value doesn’t have a unit size and is relative to the size of the mesh.

Having any of those three attributes automatically enables Nanite on the generated Static Meshes. This only applies to refined meshes, as Houdini Proxy Meshes do not support Nanite.

Mesh Sockets ¶

Attribute Name	Owner	Type	Description
`mesh_socket_name`	point	string	Name of a mesh Socket generated by Point Groups
`mesh_socket_tag`	point	string	Tag of a mesh Socket generated by Point Groups
`mesh_socket_actor`	point	string	Name of an Actor to be automatically attached to a socket generated by Point Groups. In V2, this can also be a path to an asset that will be instantiateed as an Actor and attached to the socket
`mesh_socketX_pos`	detail	float3	Vector3 representing a Mesh Socket’s location
`mesh_socketX_rot`	detail	float4	Quaternion used for a Mesh Socket’s rotation
`mesh_socketX_scale`	detail	float3	Vector3 representing a Mesh Socket’s Scale
`mesh_socketX_name`	detail	string	Name of a generated Mesh Socket
`mesh_socketX_tag`	detail	string	Tag of a generated Mesh Socket
`mesh_socketX_actor`	detail	string	Name of an Actor to be automatically attached to

Unreal to Houdini ¶

These attributes are available in Houdini when using Input Types to marshall data from Unreal to Houdini.

These Standhard Houdini Attributes are generally available: position p, vertex colorsCd, Alpha, normals N* and UV setsuv, *uvX.

You can see these attributes and their values by Debugging the internal Houdini Scene (File ▸ Open Scene In Houdini) after initializing your asset’s Inputs.

This table lists special attributes which are created by the plug-in when importing data from Unreal to Houdini.

Geometry Collections ¶

All output attributes in the above table are imported into Houdini in addition to the attributes below:

Attribute Name	Owner	Type	Description
`unreal_input_gc_name`	detail	string	The path name of the geometry collection
`unreal_actor_path`	detail	string	Path to the actor that contained the input data/should be generated. Only available if Actor is specified as input
`unreal_level_path`	detail	string	Path to the level in which an actor should be generated or which contained the input data. Only available if Actor is specified as input

Inputs ¶

Attribute Name	Owner	Type	Description
`unreal_object_path`	prim	string	Path to the input object
`unreal_level_path`	prim	string	Path to the level that contained the input data
`unreal_actor_path`	prim	string	Path to the selected input actor
`unreal_input_mesh_name`	prim	string	Unreal path of the mesh uasset plugged in the input
`unreal_input_source_file`	prim	string	Source path of the uasset plugged into the input (file path to the source .fbx for example)
`unreal_material`	prim	string	Path to a material asset used on the input
`unreal_material_hole`	prim	string	Path to a material asset used as hole material on the input landscape
`unreal_material_parameter_*`	prim	string	Prefix used when importing all the Scalar/Vector/Texture parameters of a material as attributes. The parameter’s name then follow this prefix
`lodX_screensize`	detail	Float	Screensize value for LOD number X of the input mesh
`unreal_tag_*`	prim	string	Prefix used to import the input object/actors tags as attributes
`unreal_data_table_*`	point	string	Prefix used when importing table via a Geometry input, each attribute will be named: `unreal_data_table_COL::_NAME`
`unreal_datatable_rowstruct`	point	string	Attributes storing the type of data table (`FDataTableRowStruct`) for the input data table.
`unreal_level_instance_name`	point	string	Name of the level being instanced in a level instance actor.

Materials ¶

Attribute Name	Owner	Type	Description
`unreal_simple_physical_material`	prim	string	Unreal path of a PhysicalMaterial asset taken from simple collisions

Mesh Sockets ¶

Attribute Name	Owner	Type	Description
`mesh_socket_name`	point	string	Name of a mesh Socket imported from the input object
`mesh_socket_tag`	point	int	Tag of a mesh Socket imported from the input object
`mesh_socketX_pos`	float3	int	Vector3 representing the location of the socket imported from the input object
`mesh_socketX_rot`	float4	string	Quaternion representing the rotation of the socket imported from the input object
`mesh_socketX_scale`	float3	int	Vector3 representing the scale of the socket imported from the input object
`mesh_socketX_name`	detail	string	Name of the imported Mesh Socket
`mesh_socketX_tag`	detail	string	Tags of the imported Mesh Socket

Landscapes ¶

Attribute Name	Owner	Type	Description
`unreal_vertex_index`	point	int2	Component vertex indices (indices of vertices within the grid - x,y)
`unreal_landscape_streaming_proxy`	prim	int	Set if the input landscape actor is a streaming proxy

Groups ¶

Some special group names have naming schemes which specify generation behavior when marshalling data from Houdini to Unreal. See the referenced topics for details on how each works.

Collisions ¶

Complex collision ¶

Group name	Description
`collision_geo`	Creates a complex collision (invisible)
`rendered_collision_geo`	Creates a complex collision (visible)

Warning

DO NOT use the rendered_collision_geo attribute for your custom collision. This results in Unreal generating a collision based on your original asset and not your custom collision.

Convex collision ¶

Group name	Description
`collision_geo_ucx`	Creates a convex hull collision (invisble)
`rendered_collision_geo_ucx`	Creates a convex hull collision (visible)

Simple collision ¶

Group name	Description
`collision_geo_simple`	Creates a default simple collision (invisible)
`rendered_collision_geo_simple`	Creates a default simple collision (visible)
`collision_geo_simple_box`	Creates a simple box collision (invisible)
`rendered_collision_geo_simple_box`	Creates a simple box collision (visible)
`collision_geo_simple_sphere`	Creates a simple sphere collision (invisible)
`rendered_collision_geo_simple_sphere`	Creates a simple sphere collision (visible)
`collision_geo_simple_capsule`	Creates a simple capsule collision (invisible)
`rendered_collision_geo_simple_capsule`	Creates a simple capsule collision (visible)
`collision_geo_simple_kdop10x`	Creates a simple 10DOP-X collision (invisible)
`rendered_collision_geo_simple_kdop10x`	Creates a simple 10DOP-X collision (visible)
`collision_geo_simple_kdop10y`	Creates a simple 10DOP-Y collision (invisible)
`rendered_collision_geo_simple_kdop10y`	Creates a simple 10DOP-Y collision (visible)
`collision_geo_simple_kdop10z`	Creates a simple 10DOP-Z collision (invisible)
`rendered_collision_geo_simple_kdop10z`	Creates a simple 10DOP-Z collision (visible)
`collision_geo_simple_kdop18`	Creates a simple 18DOP collision (invisible)
`rendered_collision_geo_simple_kdop18`	Creates a simple 18DOP collision (visible)
`collision_geo_simple_kdop26`	Creates a simple 26DOP collision (invisible)
`rendered_collision_geo_simple_kdop26`	Creates a simple 26DOP collision (visible)

Level of details ¶

Group Name	Description
`lod_*`	Prefix used for defining a Mesh’s LOD level

Mesh Sockets ¶

Group Name	Description
`socket_*`	Prefix used for adding sockets

Standard Houdini Attributes ¶

Certain standard Houdini attributes are used when marshaling data between Houdini and Unreal.

Attribute Name	Description
`instance`	For object-level instancing, See Instancers
`p`	position
`rot`	rotation
`scale`	scale
`pscale`	uniform scale
`Cd`	color
`Alpha`	opacity
`N`	normal
`uv`	uv
`uvX`	additionnal uv channels X from (2..8)

Note

Since Houdini 16.5, uv SOP nodes allow you to change the attribute name used for storing the uvs. These attributes are supported by the plug-in, and will be converted to uvs as long as the total number of uv attributes doesn’t exceed the MAX_STATIC_TEXCOORDS value in Unreal (8 by default).

The transform of the Houdini Asset in Unreal is available on the asset’s parent object transform in Houdini. For example, you could obtain the X Position by using the following python expression in your HDA: hou.parent().worldTransform().extractTranslates('trs').x()

Parameter Tags ¶

Certain parameter tags can be used to control the behaviour fo the exposed parameter in Unreal:

Parameter Tag Name	Associated Parameter Type	Description
`unreal_ref`	string	When set to 1, the string parameter will be created as an AssetPicker in Unreal, that sets the string’s value to the selected asset’s path
`unreal_ref_class`	string	When used with the “unreal_ref” tag, can be used to specify a class used to filter the asset picker
`hengine_noswap`	Float (tuple3)	Indicates that the Vector3 Y and Z values should not be swapped in Unreal
`filechooser_mode`	File	When set to read, the file parameter will be Read-only
`default_dir`	File	Default directory used when opening the Browse dialog

Generic UProperty Attributes ¶

The aim of this system is to allow you to modify any available property in the objects and meshes generated by the plug-in by using generic attributes. Since you can’t set all the properties in the components generated by the plugin, this system allows you to preset these properties using attributes.

To set these properties:

Add an attribute to your HDA that starts with unreal_uproperty_
Append the name of the uproperty you want to modify.
Houdini Engine then tries to find the uproperty that corresponds to the attribute in the generated mesh components and set its property’s value to your settings.

For example, if you want the static mesh component generated by your asset to have the Simulate Physics property activated, add a detail attribute called unreal_uproperty_SimulatePhysics, and set its value to 1. The static mesh generated by your asset now has the Simulate Physics property enabled.

The uproperty attributes can be floats, integers, or strings. The plug-in will always try to convert the attribute’s value to the uproperty’s type.

For example, the boolean uproperty UseEmissiveForStaticLighting can be set to true by using an int attribute set to 1, a float attribute set to 1.0 or a string attribute set to true if the attribute is named unreal_uproperty_UseEmissiveForStaticLighting.

Vector Uproperties, like Center Of Mass Offset, can be set using an attribute of size 3.

Correspondance between Uproperties and the attributes are done using either the uproperty’s name (the name of the uproperty in the source code) or it’s display name without space (the name used in the details panel).

The Center of Mass Offset property can for example, be modified either by using an attribute called unreal_uproperty_centerofmassoffset (using the display name) or unreal_uproperty_comnudge (using the uproperty name).

Generic Property attributes can also be used to modify properties of the Houdini Asset Component itself. This allows you to preset some of the Houdini Asset Component’s default properties, like the Cook Triggers, Auto-Bake, Use Output Nodes etc… In order to be applied to Houdini Asset Component itself, these attributes must be set on the details.

ie: i@unreal_uproperty_bUseOutputNodes = 1;

If you want to get a list of property attributes for a given object type/class, you can use the Houdini.DumpGenericAttribute Log Command. This will list all of the generic property attribute that the plugin sees for the given type, listing its attribute name, unreal name and display name, as well as its Unreal and Houdini types.

To use it, simply open the “Output Log” panel, and in the “Cmd” box, type “Houdini.DumpGenericAttribute XXXX”, replacing XXX with the Class you want the list for.

ie: Houdini.DumpGenericAttribute StaticMesh

String Tokens ¶

Not all attribute values can be determined ahead of time and may need more contextual information (post-cook) to fully resolve the output values. For example, the default output name or path for a Static Mesh asset depends on whether the HDA is currently running in Temp mode or in Bake mode.

Token	Description
`world`	Path to the Map that contains the current persistent world
`hda_level`	Path to the Map that contains the level in which the current HDA has been placed
`hda_name`	The type name of the current HDA
`hda_actor_name`	The name of the current HDA actor
`object_name`	Name of the package we want to create. If null, we’ll generate one from: `ASSET_OBJ_GEO_PART_SPLIT` (without PDG), or `ASSET_TOPNET_TOPNODE_WORKITEMINDEX_PART_SPLIT` (with PDG)
`pdg_topnet_name`	For temporary PDG outputs: the TOP network name
`pdg_topnode_name`	For temporary PDG outputs: the TOP node name
`pdg_workitem_name`	For temporary PDG outputs: the TOP node name
`guid`	A GUID that identifies the owning Houdini Asset Component
`out`	Contextual output folder, depending on whether the HDA is operating in Temp mode or Bake mode. If the HDA is in Temp mode, this value will match the value of the temp token. If the HDA is operating in Bake mode, this value will match the value of the bake token
`temp`	Base folder that will be used when creating assets in Temp mode
`bake`	Base folder that will be used when creating assets in Bake mode

Examples ¶

Bake to the HDA level ¶

To bake actors to the same level that contains the HDA, as opposed to the persistent level, set unreal_level_path attribute to “{hda_level}”.

Bake to a target level ¶

To bake actors to a level (named MySubLevel) that is relative to the current persistent level, set unreal_level_path attribute to {world}/MySubLevel.
To bake actors to a specific level (using an absolute path), set unreal_level_path attribute to the package path /Game/Maps/MyTargetLevel.

Houdini to Unreal ¶

Bake Outputs ¶

Generic UProperty ¶

Geometry Collections ¶

Geometry Collections - Unreal Engine 5 ¶

Instancers ¶

Landscapes ¶

Landscape Splines general ¶

Landscape Splines edit layer ¶

Landscape Splines control point ¶

Landscape Splines segment ¶

Level of Details ¶

Materials ¶

Material Instances ¶

Meshes ¶

Meshes Nanite ¶

Mesh Sockets ¶

Unreal to Houdini ¶

Geometry Collections ¶

Inputs ¶

Materials ¶

Mesh Sockets ¶

Landscapes ¶

Groups ¶

Collisions ¶

Complex collision ¶

Convex collision ¶

Simple collision ¶

Level of details ¶

Mesh Sockets ¶

Standard Houdini Attributes ¶

Parameter Tags ¶

Generic UProperty Attributes ¶

String Tokens ¶

Examples ¶

Bake to the HDA level ¶

Bake to a target level ¶

Unreal

Getting started ¶

Basics ¶

Using Houdini Engine ¶

Scripting ¶

Reference ¶