Materials

This section describes which of Unity’s material parameters are used when exporting USD.

Supported Materials by Render Pipeline

Render Pipeline	Shader
Built-In	Standard
URP	Universal Render Pipeline/LitUniversal Render Pipeline/Complex Lit (When using Clear Coat)
HDRP	HDRP/Lit

For each, the value is retrieved using the parameter name provided in the Shader. We recommend you use parameter names commonly used in Unity (_MainTex, _MetallicGlossMap, etc.) because then you may be able to get material parameters with other Shaders than what is listed.

Type of material to be exported to USD

Select Settings in the Omniverse menu to open the Omniverse Settings panel.

Select the material type in “Material Type”.

Material Type	Description
None	No material assignment
MDL	Assign OmniPBR or OmniGlass
UsdPreviewSurface	Assign UsdPreviewSurface

Note

MaterialX is not supported yet.

Built-In: Standard

In the Built-In Standard Shader, the following parameters outlined in red are the USD export targets.

Rendering Mode supports: * Opaque * Cutout * Transparent

Main Maps supports: * Albedo Color / Albedo Map * Metallic * Smoothness * Metallic/Smoothness Map * Normal Map * Occlusion Map * Emission Color / Emission Map * Texture transform: Tiling, Offset

Render Mode: Opaque

Assign Opaque to an solid shape.

Render Mode: Cutout

For shapes that involve trimming, such as tree leaves, assign Cutout.

In this example, the cutout is made according to the alpha value of the Albedo Map.

Alpha Cutoff is the threshold value.

Render Mode: Transparent

Translucency is represented by Transparent for see-through shapes.

When passed to USD, Opacity is assigned.

Transparent uses the alpha channel of the Albedo Map and the alpha value of the Albedo color.

• If the Albedo Map does not exist, the alpha value of the Albedo Color is output as the Opacity value of the USD.

• If an Albedo Map exists and the alpha value of the Albedo Color is 1.0, the Alpha channel of the Albedo Map is used as the Opacity Map for USD (Opacity Mono Source=“mono_alpha” in OmniPBR).

• If an Albedo Map exists and the alpha value of the Albedo Color is not 1.0, the Alpha channel of the Albedo Map is multiplied by the alpha value of the Albedo Color and used as the Opacity Map for USD (Opacity Mono Source=“mono_average” in OmniPBR).

Albedo

If both Albedo color and Albedo Map are present, they will appear multiplied in the USD export. In USD, the Albedo map and Albedo Color each have their own parameters.

Metallic/Smoothness Map

In Unity, Metallic/Smoothness and Occlusion maps are packed into one texture.

Occlusion is often a separate texture.

Channel	Property
Red	Metallic
Green	Occlusion
Blue	None
Alpha	Smoothness

Smoothness = 1.0 - Roughness

The Metallic/Smoothness map is decomposed into a USD metallic map and a roughness map.

If the Metallic/Smoothness Map is not specified, specify the Metallic and Smoothness values as numbers from 0.0-1.0.

Normal Map

When specifying a Normal Map, the strength of the Normal can also be specified.

When exporting USD, if the material type is MDL, both Normal Map and NormalMap strength will be output.

If the material type is usdPreviewSurface, the strength value is ignored because it does not have a Normal Map strength parameter.

Occlusion Map

Occlusion Map is output when using UsdPreviewSurface as the material type for USD export.

Note

Occlusion Map output is not supported when OmniPBR is used.*

If an Occlusion value is specified (If not 1.0), the Occlusion Map and Occlusion value are baked into the texture and output.

Emission

When the Emission checkbox is checked, Emission Color and Emission Map can be specified.

If both are used, they are exported as a multiplied and baked texture.

It is also possible to specify a texture with HDRI (exr/hdr file) dynamic range as an Emission Map.

Texture transform: Tiling, Offset

If a texture is specified, the same values for “Tiling” and “Offset” are used for all textures.

Note

Secondary Maps in Unity are not used in the USD export.*

URP: Universal Render Pipeline/Lit

In the case of URP, the material is specified with parameters similar to those of the Built-In Standard.

Since there are a few differences, we will explain only the differences.

In the URP Lit Shader, the following red parameters are the USD export targets.

• Base Color / Base Map

• Metallic

• Smoothness

• Metallic/Smoothness Map

• Normal Map

• Occlusion Map

• Emission Color / Emission Map

• Texture transform : Tiling, Offset

Surface Type can be “Opaque” or “Transparent”.

Check Alpha Clipping to represent “Cutout”.

Double Sided

If Render Face is set to “Both”, the double sided will be displayed in Unity.

Note

when exporting USD, Render Face information is not yet output. Currently, as a USD, it is always displayed on single sided. In Omniverse, it is always displayed double sided.*

HDRP HDRP/Lit

In the case of HDRP, the material is specified with parameters similar to those of the Built-In Standard. Since there are a few differences, we will explain only the differences.

In the HDRP Lit Shader, the following red parameters are the USD export targets.

• Base Color / Base Map

• Metallic

• Smoothness

• Mask Map (Metallic, Smoothness, Occlusion Map)

• Normal Map

• Emissive Color / Emissive Map

• Texture transform: Tiling, Offset

In HDRP, specify Metallic, Smoothness, and Occlusion Map in Mask Map.

Surface Type can be “Opaque” or “Transparent”.

Check Alpha Clipping to represent “Cutout”.

HDRP : Exporting OmniGlass

HDRP allows for glass representation using IOR with HDRP/Lit Shader. When specifying some parameters, OmniGlass is used when the material is MDL in the USD export.

1. Use HDRP

2. SurfaceType = Transparent

3. BaseMap.alpha = 0.0

4. RefractionModel != None

In this case, OmniGlass is used in HDRP.

Parameters supported by HDRP’s Glass when exporting USD

The following parameters can be specified for Glass and are passed to OmniGlass in USD.

• Smoothness

• Index Of Refraction

• Thickness

• Transmittance Color (Color or Texture)

Below is the Transmittance Color and Texture specified in Unity.

Exported to USD, imported into Omniverse Composer, and displayed in RTX-Real-Time as follows.

In Omniverse, the correct refraction is by ray tracing.

Clearcoat

When using “Universal Render Pipeline/Complex Lit” in Shader for URP and “HDRP/Lit” in Shader for HDRP, a Clearcoat of the material can be used.

Clearcoat in USD

Clearcoat in USD can be handled using UsdPreviewSurface. OmniPBR does not have Clearcoat parameters.

Two Clearcoat parameters exist for USD’s UsdPreviewSurface.

Parameter name	Default	Description
clearcoat	0.0	Clearcoat value (0.0-1.0)
clearcoatRoughness	0.01	Clearcoat roughness (0.0-1.0)

Both clearcoat and clearcoatRoughness can use float values or textures.

Clearcoat (URP)

For materials using the Universal Render Pipeline/Complex Lit in URP, the Clearcoat parameter can be used.

Two parameters exist in the Clearcoat of the URP.

Check the ClearCoat checkbox to use Clearcoat.

Parameter name	Description
Mask	Clearcoat value (0.0-1.0)
Smoothness	Clearcoat smoothness (0.0-1.0)

These two parameters can be textures as well as numbers.

The Mask Map in Unity has the following channel configuration.

[R] Mask

[G] Smoothness

[B] None

[A] None

USD’s clearcoatRoughness is converted to Unity’s ClearCoat Smoothness.

This can be calculated using the following formula.

> ClearCoat Smoothness = 1.0 - clearcoatRoughness

Clearcoat (HDRP)

Clearcoat in HDRP has only Coat Mask value.

The ClearCoat Smoothness that was present in URP is not present in HDRP and this is always treated as 1.0.

Parameter name	Description
Coat Mask	Clearcoat value (0.0-1.0)

In the Clearcoat Mask texture, Clearcoat Mask was set on the R, G, and B channels.

[R] Mask

[G] Mask

[B] Mask

[A] None

In Unity’s HDRP, the ClearCoat Mask Map seemed to reference only the R channel.

Color Space

• Colors in Unity are often managed in sRGB.

• In USD, colors are linear.

• Color space is considered when specifying a single color or texture.

Color Space in Unity

There are multiple places to specify color space in Unity.

Project Settings

• Select [Edit]-Project Settings from the menu.

• In Player - Other Settings, under Rendering, you can select “Color Space.”

• The default is “Linear”.

• This unifies the rendering process with Linear.

• This can be changed to “Gamma” for Built-In, but should be handled as “Linear.”

Texture

• In the Inspector, when you select a texture in the Project window, if sRGB (Color Texture) is checked, the texture will be treated in sRGB.

• In Unity, textures representing “color,” such as Base Map (Diffuse Map) and Emissive Map, are generally handled in sRGB.

• HDRIs such as hdr/exr are passed directly to the renderer as linear.

• Normal maps, metallic and smoothness maps, etc., are not colors and are passed to the renderer as linear.

• In Unity, textures are automatically converted to linear when passed to rendering.

• Therefore, users and developers do not need to be aware of color space.

sRGB Color

For the color of the material, it is to be specified in sRGB.

The color (sRGB) specified in the Base Map can be confirmed to be the same color (sRGB) in the rendering result.

These complex differences in color space are unified linearly at rendering time (linear workflow), and the flow is converted to sRGB, which is appropriate for the display when it is displayed.

Color Space in USD

All colors in the USD format are linear and unified.

This conversion by color space is automatic in the Omniverse Unity Connector’s importer and exporter.

Linear Color

For color, it is converted and passed so that it is in a linear color space.

The exporter in the Omniverse Unity Connector converts sRGB colors on Unity to linear and passes them to USD. Importers in the Omniverse Unity Connector convert linear colors in USD to sRGB and pass them to Unity.

Texture

For each material texture, you can select auto/raw/sRGB as the color space.

The color space of this texture is specified as follows, as is the case on the Unity side.

Texture Type	Color Space
Albedo Map	sRGB (auto)
Emissive Color Map	sRGB (auto)
Normal Map	raw
Roughness Map	raw
Metallic Map	raw
Ambient Occlusion Map	raw
Opacity Map	sRGB (auto)

Note

The Opacity Map of a material exported from the Omniverse Unity Connector uses the A of the RGBA texture specified in the Albedo Map.