tut_helloworld_redux.rst

Hello World Redux - Using Generic Prims

In this tutorial, we revisit the :doc:`Hello World! <tut_helloworld>` example, but this example passes in hard-coded typenames :usda:`Xform` and :usda:`Sphere`, which correspond to the typenames appearing after the :usda:`def` specifiers in the :usda:`usda` scene description representation.

The UsdGeom API used in the :doc:`previous tutorial <tut_helloworld>`, is part of USD's built-in geometry schema. These prim types and associated C++ and Python API have first-class support in USD and provide domain-specific interfaces to create, manipulate, introspect and author properties upon them.

Note that :usdcpp:`UsdGeomXform::Define` returns a schema object on which the full schema-specific API is available, as opposed to :usdcpp:`UsdStage::DefinePrim` which returns a generic :usdcpp:`UsdPrim`. In USD, all schema classes have a GetPrim() member function that returns its underlying :usdcpp:`UsdPrim`. Think of a :usdcpp:`UsdPrim` as the object's generic, persistent presence in the scenegraph, and the schema object as the first-class way to access its domain-specific data and functionality.

from pxr import Usd
stage = Usd.Stage.CreateNew('HelloWorldRedux.usda')
xform = stage.DefinePrim('/hello', 'Xform')
sphere = stage.DefinePrim('/hello/world', 'Sphere')
stage.GetRootLayer().Save()

The code above produces identical scene description to the previous tutorial, which you can see using :ref:`toolset:usdcat`:

#usda 1.0

def Xform "hello"
{
    def Sphere "world"
    {
    }
}

In the :doc:`next tutorial <tut_inspect_and_author_props>`, we'll look at UsdGeom API in action on prim properties.