Apply materials in Bifrost-USD

Bifrost-USD includes high-level compounds that make it easy to create a UsdPreviewSurface material, as well as to bind it to geometry in any of several ways.

Create a material prim

The UsdPreviewSurface material that is available in USD is a simple but modern, physically-based material that covers many cases. It is supported by many renderers.

To add a prim that defines a material:

1. Right-click on the prim_definitions port of an add_to_stage node or on the children port of a prim definition node, and choose Create Node > Usd::Shading::define_usd_preview_surface.
2. Set path to a path and name to identify the material, and set its parameters as desired.

Bind a material using the material port

The simplest and sometimes most convenient way to apply a material to a primitive is to connect the output of a define_usd_preview_surface to the material port of a prim definition node. When this "recipe" is processed by an add_to_stage node, the binding is created automatically.

The drawback of this method is that it creates a copy of the material under each prim with a material connection, so it is suitable only for simple situations.

Bind a material using tags

Tags let you bind materials automatically by name. They are convenient for selecting a material from a library previously defined in the stage.

1. Optionally, add a define_usd_material_tag node to the graph, connect its output to the attribute_definitions port of a define_usd_preview_surface node, and set its value to a unique string for identifying the material.

2. Add another define_usd_material_tag node to the graph, connect its output to the attribute_definitions port of a prim definition port, and set its value to the name of a material prim definition.

   Alternatively if you connected a tag to the material prim definition, you can set value to the same tag — in this case, you can reuse the output from the same define_usd_material_tag node.

3. In the add_to_stage node downstream, make sure that use_material_name_or_tag is enabled.

Bind a material using relationships

You can use a relationship to bind a material explicitly.

1. Right-click on the relationship_definitions port of a prim definition node, and choose Usd::Prim::define_usd_relationship.
2. By default, the define_usd_relationship is already set to create a material:binding relationship. You only need to set target to the path of the material to bind to.

Bind a material using assign_usd_material

1. Add an assign_usd_material node to the graph, and connect its stage input and output ports.
2. Set material_path to the full path of the material to use.
3. Set prim_path to the full path of the prim to bind.