HdMoonRay Features

HdMoonRay provides a Hydra interface to MoonRay by translating Hydra data into MoonRay’s native RDL2 format. The following sections provide more information on what is supported.


HdMoonray supports all three types of Hydra geometry: meshes, curves and points. In USD these are represented by the Mesh, BasisCurve and Point prim types.

Primvars defined on the geometry are generally translated to their MoonRay equivalent : UserData objects. The data is then available for use by shaders.


Catmull-Clark and Bilinear subdivision surfaces are supported by MoonRay. Loop subdivision is not, and Catmull-Clark will be used if it is set. “holes” are not supported : holeIndices is ignored. triangleSubdivisionRule is ignored, since the alternate rule “smooth” is not supported by MoonRay.

GeomSubsets in Mesh prims are translated to MoonRay parts, which have essentially the same function. Hydra only allows GeomSubsets on meshes, so you cannot use them with curves and points.


MoonRay supports linear, bspline and bezier curve types. Catmull-Rom is not supported. “Pinned” and “periodic” USD curves are also not supported.


All of the Lux lights are supported by translating to a MoonRay equivalent.

HdMoonRay supports Light, Shadow and Light Filter linking using collections, as specified in the UsdLux Linking API.

The Lux “shapingAPI” changes the light class to the MoonRay SpotLight, if the shaping:coneAngle is less than 90. This will happen for any light type, but it does not match well unless a Lux DiskLight is used.

MoonRay-specific attributes can be set on lights by setting moonray:<attrname>. These override values set by translation from Lux. You can also select the MoonRay light class to use explicitly, by setting the attribute moonray:class.


Hydra cameras are translated to one of the MoonRay camera types PerspectiveCamera or OrthogonalCamera

As with lights, you can set any MoonRay-specific camera attribute using the moonray: prefix. You can also use any of the other MoonRay camera classes by setting moonray:class on the Camera prim.


Materials are defined using the UsdShade model : i.e. as networks of connected Shader prims nested inside the Material prim.

You can use any of the MoonRay material and map shaders inside a material network. The USD scene delegate requires shaders to be registered with SDR : see HdMoonRay Setup for information on how to set this up.

HdMoonRay creates a default material that is assigned to any geometry without an explicit assignment. This default material renders the geometry using the values of the displayColor and displayOpacity primvars. Also created is a solid magenta error material, used in place of materials that either cannot be found or fail to generate a valid MoonRay material object.


HdMoonRay supports Usd native instancing and PointInstancer

Nested (hierarchical) instance is supported, as is the inactiveIds metadata value used for non-animated masking.

Primvars defined on the PointInstancer are transferred to instances. Primvars that don’t have enough entries are repeated to give every instance a value.

MoonRay does not support different light links on different instances in the same instancer. Currently, the light links of the first instance encountered are used for all instances.

Hydra itself does not currently support light linking to prims inside an instance prototype graph. The links must point to the instancing prim (the prim creating the instanced composition arc) or to one of its ancestors. Links to prims below this are ignored.

Motion Blur

Moonray’s Motion blur features are fully supported by the delegate. The DCC should provide the appropriate primitive attributes (i.e. velocity) for geometric motion blur.