The Unreal Engine (DATASMITH) exporter provides efficient data transfer from CityEngine to the Unreal Engine Editor. The main purpose of this exporter is for architectural and design visualization workflows, but will obviously also work for games and other tasks.
- The Unreal exporter is only available on Windows.
- To use the Unreal exporter in CityEngine, at least the Unreal Engine Launcher needs to be installed as a prerequisite.
- The CityEngine Model Loader Project is not needed anymore and will eventually be removed from the Unreal Engine Launcher.
In addition to the general export options, the Unreal Engine DATASMITH has the following options:
Global offset for generated geometry for x, y and z axes (Cartesian coordinate values).
Different options on how the resulting meshes are merged:
Different options on how instancing is handled:
Metadata can be exported when the Mesh Merging mode is set to either Per Initial Shape or Per Initial Shape by Material. Metadata export options:
The exported metadata is attached to the root object of each initial shape in Unreal.
Terrain layers can be exported to Unreal Engine Landscapes . The following options are supported:
Use Texture Atlases
Enables texture atlases that combine exported textures and reduce the number of materials. Texture atlases typically have the biggest impact when used on slower hardware, for example, on mobile VR devices such as the Oculus Quest.
Enables the export of Level of Detail (LOD). Exporting LODs is only enabled when exporting Per Initial Shape.
The name of the CGA attribute which specifies the LOD. The attribute needs to have an Enum annotation. For each element of the Enum annotation a derivation will be triggered where the LOD attribute will be set to this element value.
The following example
generates three LODs per Initial Shape.
Note:If the attribute is defined in multiple CGA files it needs to have the same elements (LODs).
The semantic order of the LOD Attribute.
For example, if the LOD Attribute is defined as follows:
the order is ascending, as the lowest level of detail is defined first.
Defines how default objects are exported.
Mapping between CityEngine and Unreal entities
Materials are translated to Unreal by passing CGA material attributes to an Unreal Material Instance which is based on a certain primary (or parent) material.
By default the exporter generates appropriate primary materials which handle the translation from CGA material attributes to Unreal material attributes (see also Default primary materials).
Custom primary materials
A custom primary material can be assigned by setting the material.shader CGA attribute to the corresponding Unreal material path, e.g. /Game/Materials/CityEngineMaterials/M_CE_MyMaterial.
Each CGA material attribute is exported and can be accessed in Unreal by using a material parameter with a specific name and data type. The following table lists the CGA material attributes and their respective Unreal parameter name and type:
|CGA attribute||Unreal parameter name||Unreal type||Note|
For OpacitySource value:
Default primary materials
By default, an appropriate primary material (opaque, transparent or masked) is generated during export, based on the following rules:
- If material.opacity is smaller than 1 or material.opacitymap is set
- and the opacitymap.mode is blend, a Transparent primary material is used.
- and the opacitymap.mode is masked, a Masked primary material is used.
- Otherwise the Opaque primary material is used.
The Unreal Engine sorts transparency per actor. Exporting overlapping transparent actors will lead to rendering artifacts. Masked binary opacity is not affected by this limitation.
Default material attribute translation
The default primary materials translate the CGA material attributes roughly to a physically based Unreal Material. If the material.shader is set to CityEnginePBRShader (this happens automatically if for example an inserted glTF model is exported), the default primary materials in Unreal will use the PBR material attributes (roughness, metallic, and emissive).
The specular color is not used in Unreal. The specular color in Unreal depends on the base color and how metallic the material is.