Keep base properties when applying references in composition

[rdeioris]

While attempting to load the KitchenSet with the Unreal Engine plugin i am working on, i noticed that the references resolving system swallows the base properties.

Example:

def "Refridgerator_1"
                (
                    prepend references = @./assets/Refridgerator/Refridgerator.usd@
                )
                {
                    string HelloWorld = "Hello World"
                    double3 xformOp:translate = (259.9341506958008, 95.84612274169922, -0.5277154445648193)
                    uniform token[] xformOpOrder = ["xformOp:translate"]
                }

By flattening/applying the reference you get:

def Xform "Refridgerator_1"
                (
                    kind = "component"
                    assetInfo = {
                        asset identifier = @assets/Refridgerator/Refridgerator.usd@
                        string name = "Refridgerator"
                    }
                    payload = @./Refridgerator_payload.usd@</Refridgerator>
                    variants = {
                        string modelingVariant = "Decorated"
                    }
                    prepend variantSets = ["modelingVariant"]
                )
                {
              
                }

without the original properties (i have added the HelloWorld one to keep track).

This patch addresses it by re-adding the properties that are not found in the applied reference.

Once applied i was able to correctly get the KitchenSet transforms:

[syoyo]

Thanks!

Let me give some time to verify/double-check the behavior of 'references' using openUSD.

[syoyo]

Confirmed the issue.

input.usda

#usda 1.0

( defaultPrim = "a"

"""
repro scene for https://github.com/lighttransport/tinyusdz/pull/195
Issue 195: base properties(e.g. 'HelloWorld') disappear after `--flatten`.
"""
)

def "a" 
(
    prepend references = @./issue-195-ref.usda@
)
{
    string HelloWorld = "Hello World"
    double3 xformOp:translate = (259.9341506958008, 95.84612274169922, -0.5277154445648193)
    uniform token[] xformOpOrder = ["xformOp:translate"]
}

issue-195-ref.usda

#usda 1.0

( defaultPrim = "a" )

def Xform "a"
(
    kind = "component"
    assetInfo = {
	asset identifier = @assets/Refridgerator/Refridgerator.usd@
	string name = "Refridgerator"
    }
    #payload = @./Refridgerator_payload.usd@</Refridgerator>
    variants = {
	string modelingVariant = "Decorated"
    }
    prepend variantSets = ["modelingVariant"]
)
{

}

Result from openUSD

usdcat --flatten input.usda

#usda 1.0
(
    """
repro scene for https://github.com/lighttransport/tinyusdz/pull/195
Issue 195: base properties(e.g. 'HelloWorld') disappear after `--flatten`.
"""
    defaultPrim = "a"
    doc = """Generated from Composed Stage of root layer /mnt/nvme02/work/tinyusdz/tests/usda/composition/references-prepend-195.usda
"""
)

def Xform "a" (
    assetInfo = {
        asset identifier = @assets/Refridgerator/Refridgerator.usd@
        string name = "Refridgerator"
    }
    kind = "component"
)
{
    string HelloWorld = "Hello World"
    double3 xformOp:translate = (259.9341506958008, 95.84612274169922, -0.5277154445648193)
    uniform token[] xformOpOrder = ["xformOp:translate"]
}

Result from tusdcat

tusdcat --flatten input.usda

#usda 1.0
(
    defaultPrim = "a"
    """
repro scene for https://github.com/lighttransport/tinyusdz/pull/195
Issue 195: base properties(e.g. 'HelloWorld') disappear after `--flatten`.
"""
)

def Xform "a"
(
    kind = "component"
    assetInfo = {
        asset identifier = @assets/Refridgerator/Refridgerator.usd@
        string name = "Refridgerator"
    }
)
{
}

[syoyo]

And also confirmed the PR fixes the issue:

With this PR, tusdcat --flatten input.usda gives

#usda 1.0
(
    defaultPrim = "a"
    """
repro scene for https://github.com/lighttransport/tinyusdz/pull/195
Issue 195: base properties(e.g. 'HelloWorld') disappear after `--flatten`.
"""
)

def Xform "a"
(
    kind = "component"
    assetInfo = {
        asset identifier = @assets/Refridgerator/Refridgerator.usd@
        string name = "Refridgerator"
    }
)
{
    double3 xformOp:translate = (259.9341506958008, 95.84612274169922, -0.5277154445648193)
    uniform token[] xformOpOrder = ["xformOp:translate"]
    string HelloWorld = "Hello World"
}

[syoyo]

Merged! Thanks!