Forums Solaris and Karma Creating Primvars with Python in LOPs

Creating Primvars with Python in LOPs

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Hypershader
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Hi,

I was wondering how I would go about creating a primvar using python inside of Solaris?

I hope someone can help!

Best,
Rich
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marcosimonrbl
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primitive.CreateAttribute(attributeName, Sdf.ValueTypeNames.<type>)

Types I found on the nVidia website: https://developer.nvidia.com/usd/tutorials [developer.nvidia.com]

also helpful: https://graphics.pixar.com/usd/release/api/class_usd_prim.html#a935381d7c7100b583fdcdb0e10dae9e6 [graphics.pixar.com]
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Hypershader
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Hey,

Thanks this seems to work great for creatiing an attribute but unfortunately it isn't a primvar so i cannot reference it in a shader

node = hou.pwd()
stage = node.editableStage()
from pxr import Sdf, Usd, UsdGeom

asset = stage.GetPrimAtPath('/Asset')
asset.CreateAttribute('test', Sdf.ValueTypeNames.String)

I do need to be able to create a Primvar so any more info in regard to this would be useful
Edited by Hypershader - Feb. 18, 2022 07:55:17
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Hypershader
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for anyone interested you just need to add 'primvars:'+ to the front and then set the custom to false with 0 at the end

example.

asset.CreateAttribute('primvars:test', Sdf.ValueTypeNames.String,0).Set('hi')
Edited by Hypershader - Feb. 18, 2022 14:01:32
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mtucker
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Actually, there is a whole dedicated API for authoring primvars with python:
https://graphics.pixar.com/usd/release/api/class_usd_geom_primvars_a_p_i.html [graphics.pixar.com]

So something like (I didn't actually test this):
primvarsapi = UsdGeom.PrimvarsAPI(asset)
primvar = primvarsapi.CreatePrimvar('test', Sdf.ValueTypeNames.String)
primvar.Set('hi')

The advantage is that you don't need to know all the precise details of how primvars are expressed. You also get a python API for setting the interpolation metadata, using indexed primvars, etc. All of which is equivalent to building the attributes and setting the metadata yourself, but less error prone.
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