# Flattening scene index

**URL:** <https://forum.aousd.org/t/flattening-scene-index/1483>\
**Category:** Hydra\
**Created:** [April 27, 2024, 9:44am UTC](https://forum.aousd.org/t/flattening-scene-index/1483 "2024-04-27T09:44:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![BaptistePerrin](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.aousd.org/baptisteperrin/32/390_2.png) [@BaptistePerrin](https://forum.aousd.org/u/BaptistePerrin)\
**Post date:** [April 27, 2024, 9:44am UTC](https://forum.aousd.org/t/flattening-scene-index/1483/1 "2024-04-27T09:44:02Z")

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Hi,  
I am investigating the Hydra 2.0 scene index chain and have a question regarding the flattening scene index. I did some test changing the transform of an xform prim and I thought that with a chain scene index containing the flattening scene index that modifying a transform will call PrimDirtied on all child. But I still get only one \_PrimDirtied on the prim I changed. After investigation it seems that the root cause is `_PrimLevelWrappingDataSource` in the function  
`bool _PrimLevelWrappingDataSource::PrimDirtied( const _DataSourceLocatorSetVector& relativeDirtyLocators)`  
when doing the

`HdDataSourceBaseAtomicHandle& dsAtomicHandle = computedDataSources[i]; HdDataSourceBaseHandle const ds = HdDataSourceBase::AtomicLoad(dsAtomicHandle); if (!ds) { continue; }`  
the datasourcehandle is empty and we break the loop.  
Is this normal behaviour or am I missing something ? Maybe I am doing something wrong…  
Any thought ?

Thanks,  
Baptiste

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**Author:** ![BaptistePerrin](https://sea2.discourse-cdn.com/flex016/user_avatar/forum.aousd.org/baptisteperrin/32/390_2.png) [@BaptistePerrin](https://forum.aousd.org/u/BaptistePerrin)\
**Post date:** [April 29, 2024, 3:38pm UTC](https://forum.aousd.org/t/flattening-scene-index/1483/2 "2024-04-29T15:38:28Z")

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I finally found out my mistake. As I’m trying to trick hydra, I was never calling the XFormSchema. Doing so fixes my issue (which is finally a mistake). Hope it can helps other if anyone is struggling with this in the future.