How to add textures to a mesh with pxr (usd-core) library

Omniverse Synthetic Data Generation (SDG)
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n order to create a new material I have followed the documentation here: Create an MDL Material — Omniverse Developer Guide latest documentation

I used one of the materials that can be found in vMaterials. When I use one of the mdl via the isaac-sim UI it automatically adds a new Look that can be later applied to a mesh.

When trying via python API it does not seem to work, the final mesh has a red colour on the surface and not the mdl one.

Test if one green mdl can be applied to the mesh:

def test_material_visibility(stage, mesh_path):
    """
    Prueba de visibilidad con un material simple para verificar que el mesh
    puede recibir materiales correctamente
    """
    # Crear un material de prueba
    material_path = Sdf.Path("/World/Looks/TestMaterial")
    material = UsdShade.Material.Define(stage, material_path)
    
    # Crear un shader de prueba (USD Preview Surface)
    shader = UsdShade.Shader.Define(stage, material_path.AppendChild("Shader"))
    shader.CreateIdAttr("UsdPreviewSurface")
    
    # Establecer un color base visible (verde brillante para test)
    shader.CreateInput("diffuseColor", Sdf.ValueTypeNames.Color3f).Set(Gf.Vec3f(0, 1, 0))
    shader.CreateInput("metallic", Sdf.ValueTypeNames.Float).Set(0.0)
    shader.CreateInput("roughness", Sdf.ValueTypeNames.Float).Set(0.4)
    
    # Conectar shader al material
    material.CreateSurfaceOutput().ConnectToSource(
        shader.CreateOutput("surface", Sdf.ValueTypeNames.Token))
    
    # Aplicar al mesh
    mesh_prim = stage.GetPrimAtPath(mesh_path)
    if mesh_prim:
        UsdShade.MaterialBindingAPI(mesh_prim).Bind(material)
        print(f"Material de prueba aplicado a {mesh_path}")
        return True
    else:
        print(f"Error: No se encontró el mesh en {mesh_path}")
        return False
    
test_material_visibility(stage, "/World/marco_grande/marco_grande")

It does work! The mesh now looks green.

But if I want to apply the mdl on the mesh it does not work properly:

mtl_path = Sdf.Path(“/World/Looks/OSB_Wood”)
mtl = UsdShade.Material.Define(stage, mtl_path)
shader = UsdShade.Shader.Define(stage, mtl_path.AppendPath(“Shader”))
shader.CreateImplementationSourceAttr(UsdShade.Tokens.sourceAsset)

# MDL shaders should use “mdl” sourceType

shader.SetSourceAsset(material_url, “mdl”)
shader.SetSourceAssetSubIdentifier(“OSB Wood - Rough”, “mdl”)

# MDL materials should use “mdl” renderContext

mtl.CreateSurfaceOutput(“mdl”).ConnectToSource(shader.ConnectableAPI(), “out”)
mtl.CreateDisplacementOutput(“mdl”).ConnectToSource(shader.ConnectableAPI(), “out”)
mtl.CreateVolumeOutput(“mdl”).ConnectToSource(shader.ConnectableAPI(), “out”)

material = UsdShade.Material(stage.GetPrimAtPath(material_path))

mesh_prim = stage.GetPrimAtPath(door_mesh_path)
binding_api = UsdShade.MaterialBindingAPI(mesh_prim)
binding_api.Bind(material)

I have also tried with this attributes:


mesh = UsdGeom.Mesh.Define(stage, Sdf.Path(door_mesh_path))

# Paso 2: Definir el material MDL y cargarlo en la escena

material_path = “/World/Looks/OSB_Wood”
mdl_material = UsdShade.Material.Define(stage, Sdf.Path(material_path))

# Usa UsdShade para crear un shader MDL en Omniverse

mdl_shader = UsdShade.Shader.Define(stage, Sdf.Path(f"{material_path}/Shader"))
mdl_shader.CreateIdAttr(“mdlMaterial”) # Especifica que este shader usa MDL

# Define la ruta al archivo MDL y el nombre del material en el archivo

mdl_shader.CreateInput(“mdl:sourceAsset”, Sdf.ValueTypeNames.Asset).Set(mdl_file_path)
mdl_shader.CreateInput(“mdl:sourceAsset:subIdentifier”, Sdf.ValueTypeNames.String).Set(“OSB Wood - Rough”) # Cambia al nombre del material

# Conecta el shader MDL al material

surface_output = mdl_material.CreateSurfaceOutput(“mdl”)
surface_output.ConnectToSource(mdl_shader.ConnectableAPI(), “out”)

# Paso 3: Asignar el material a la malla

UsdShade.MaterialBindingAPI(mesh).Bind(mdl_material)

But nothing seams to work. When i load the generated stage I can see some problems in the loggers.

2024-11-06 12:18:21 [24,902ms] [Error] [omni.usd] USD_MDL: in LoadModule at line 247 of ../../source/plugins/usdMdl/neuray.cpp -- 'rtx::neuraylib::MdlModuleId' for '/isaac-sim/src/mdl/vMaterials_2/Wood/OSB_Wood.mdl' is Invalid

2024-11-06 12:18:21 [24,902ms] [Error] [omni.usd] USD_MDL: in GetSdrFromDiscoveryResult at line 178 of ../../source/plugins/usdMdl/moduleRegistry.cpp -- Module: '/isaac-sim/src/mdl/vMaterials_2/Wood/OSB_Wood.mdl' with version '1' not found in 'MdlModuleRegistry::ModuleDataMap'.

2024-11-06 12:18:21 [24,902ms] [Error] [omni.hydra] Failed to create MDL shade node for prim '/World/Looks/OSB_Wood/Shader'. Empty identifier: '' 	and/or subIdentifier: ''

How can mdl be invalid if its downloaded from vMaterials? Identifier and subidentifier are setted, what am I missing?

Thank you in advance.

3

Hi! I met the same error, have you solved it yet?