UV/ST difference between UsdPreview and MaterialX?

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I have exported a Megascans asset out of Unreal as .usda and imported it into Solaris. The default generated material (USD Preview Material) has the texture looking correct. However when rebuilding the material network in a USD MaterialX Builder, the textures seem to occupy a different space, or be distorted somehow. Has anybody come across this before?

In the first 2 images you can see the USD Preview Material network and the correct intended render.
In the second set of images you can see the MtlX Material and the associated incorrect render. Both are using the st primvar.

USD Preview Material

Correct Render:


MaterialX

Incorrect Render:
Edited by Hamilton Meathouse - 2026年11月3日 19:54:23

Attachments:
usdpreview_network.jpg (54.1 KB)
usdpreviewmtl.jpg (321.5 KB)
mtlx_network.jpg (63.2 KB)
MtlX_mtl.jpg (339.1 KB)

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For somewhat of a ground truth test, I plugged the same grid texture ($HFS/houdini/materialx_resources/Images/grid.png) into both materials and they gave an identical result, so i think that rules out interpretation of UVs?

USD Preview Material


MtlX Material

Attachments:
usdpreviewmtl_grid.jpg (194.0 KB)
MtlX_mtl_grid.jpg (232.7 KB)

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Don't know, can you send an example hip file with a part of mesh to try to understand ?
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I started cleaning up the scene and and changing full texture paths to relative paths and it started working. Hmm, will keep investigating and see if I can repro and upload here.
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Okay, this is weird. Getting rid of the $HOME variable in the texture paths seems to have fixed the issue. I'm not sure why $HOME was being used...
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