If your background is from a C or C-like background, this next tip may come as a bit of a surprise.
#usda 1.0
def Xform "root" (
prepend variantSets = "something"
)
{
variantSet "something" = {
# ...
}
}
The "something" variantSet is not inside of </root>. It wraps
</root>. This means that you can change metadata depending on the
selected variant.
#usda 1.0
def Xform "root" (
prepend variantSets = "something"
)
{
variantSet "something" = {
"option_a" (
some_metadata = "foo"
) {
}
"option_b" {
}
}
}
- Open metadata_swap.usda in usdview to see the above example, live.
- Open arcs.usda to see an example of how to use variants to control composition arcs.
When there's no variant selection, </root> has no "some_metadata"
authored. Metadata is missing for "option_b", too. But if it's '"option_a",
"some_metadata" is authored with a value of "foo".
As mentioned in the relationship_forwarding article, you can use VariantSet as multiplexer and de-multiplexer.
Since we can modify opinions inside a Prim's ()s, that also means that we can modify its composition arcs, using variant selections.
#usda 1.0
(
startTimeCode = 0
endTimeCode = 10
)
def Xform "transform" (
add references = [
@model.usda@,
@surfacing.usda@,
]
prepend variantSets = "state"
)
{
variantSet "state" = {
"blue" (
add references = @surfacing_blue.usda@
) {
}
"motion" (
add references = @animation.usda@
) {
}
"sphere" (
add references = @sphere.usda@
) {
}
}
}
In conclusion, variantSets aren't strictly "inside" of a Prim. They are that Prim.
From basic experimentation, it looks like you cannot
- Delete a reference within a variantSet of the same Prim
- Cannot dynamically change the type of a Prim using a variant
- Cannot change the name of the Prim
Everything else though, metadata, attributes, whatever, is all up for grabs.