Universal Material Mapper

Universal Material Mapper (UMM) 1.0, which shipped with prior versions of Blender, allowed for round-tripping of shaders between Blender and Omniverse Kit applications. Unfortunately, it was limited and most users were forced to bake complex shading networks to textures before export.

UMM 2.0 doesn’t require materials to be structured in a specific way to be exportable/importable; instead, UMM2 attempts to convert the entire material network to the best possible equivalents in the target shading system. For example, UMM2 will map the parameters of a Blender Principled BSDF node to the parameters of an MDL OmniSurfaceBase node or the parameters of a Blender Image Texture to the parameters of an MDL Bitmap Texture. Currently, a subset of material nodes are supported for conversion and with some limitations on specific nodes, such as exporting Blender Bump and Normal Map shader nodes. The list of currently supported nodes can be found here: List of Supported Nodes. More nodes will be supported over time, and eventually, the ability for users to define their own conversion mappings will be exposed.

Unlike UMM 1.0, there is no longer a need to use material templates, as Blender’s Principled BSDF and Glass BSDF nodes are now automatically converted into OmniPBR and OmniGlass.

Using UMM2

UMM2 in Blender can be used for exporting Blender materials to UsdShade MDL or for importing UsdShade MDL materials into Blender.

To use UMM2 in Blender, all you need is Blender 4.0.0-usd.201.0 or greater installed from the Omniverse launcher.

Exporting Materials

Materials will automatically be converted by UMM2 when exporting via the File → Export → Universal Scene Description (.usd) menu item, or when using the Import USD button in the Omniverse Panel.

Example of Exporting a Scene

The Einar hair grooming scene (available here: https://studio.blender.org/films/charge/gallery/?asset=6072) is an excellent example of a scene with complex shading that UMM2 can convert.

We can export the scene to USD using File → Export → Universal Scene Description (.usd) and then open the exported usd file in Omniverse Usd Composer (RTX - Interactive or RTX - Accurate rendering modes will need to be used to get a comparative result):

One of the most apparent differences in the converted result is the lack of normals. This is because the normals in the Blender Shader Editor are procedurally generated in a way that can’t be replicated in MDL (note the network of material nodes connected to the Bump shader node).

If we have an Image Texture Node directly connected to a Bump Node, this can be converted to an MDL equivalent - so we export the Einar scene by baking the normals and replacing the Bump section of the network with a simple Image Texture and NormalMap node combination:

Now after using File → Export → Universal Scene Description (.usd) and opening the exported usd file in Omniverse Usd Composer, we see a result with normals on the skin:

Importing Materials

Materials will automatically be converted by UMM2 on import when using the File → Import → Universal Scene Description (.usd) menu item or the Omniverse Panel → Nucleus → Import USD button.

List of Supported Nodes

Export to Usd

Node Type	Notes
Add Shader	Supported only if an Emission node is directly connected to one of the inputs
Anisotropic BSDF
Bump	Only if an Image Texture is directly connected to the input
Color Ramp
Combine Color
Combine XYZ
Diffuse BSDF
Emission
Float Curve	Currently does not work when exporting to Nucleus servers. This will be fixed soon.
Glass BSDF
Glossy BSDF
Hair BSDF
Hue/Saturation/Value
Image Texture
Invert
Map Range
Math
Mix
Mix Shader
Musgrave Texture	Noise models differ, so outputs will not match visually
Noise Texture	Noise models differ, so outputs will not match visually
Normal Map	Only if an Image Texture is directly connected to the input
Material Output
Principled BSDF	Default maps to OmniSurfaceBase now rather than OmniPBR
Principled Hair
RGB Curves	Acts as a pass-through. Will be supported soon.
Reroute (dot node)	Bypassed
Seperate Color
Seperate XYZ
Translucent BSDF
Transparent BSDF
Value
Vector Math
Voronoi Texture	Noise models differ, so outputs will not match visually

Import From Usd

Node Type	Notes
Bitmap texture
Bitmap texture, bump
Normal map texture
Perlin noise texture	Noise models differ, so outputs will not match visually
Flow noise texture	Noise models differ, so outputs will not match visually
Cellular noise texture	Noise models differ, so outputs will not match visually
OmniPBRBase
OmniSurfaceBase
OmniPBR
OmniSurface
Simple Diffuse
OmniGlass
Thin Glass
Thick Glass
Surface Blender
Add Emission
Color Ramp	MDL color ramps are custom shaders created by UMM on export from Blender to UsdShade MDL
Add float
Subtract float
Multiply float
Divide float
Pow float
Log float
Sqrt float
Rsqrt float
Abs float
Exp float
Minimum float
Maximum float
Compare
Sign float
Round float
Floor float
Ceil float
Frac float
Sin float
Cos float
Tan float
Asin float
Acos float
Atan float
Atan2 float
Radians float
Degrees float