USD: enable material displacement support #128909
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Michael Kowalski
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Reference: blender/blender#128909
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Delete Branch "deadpin/blender:hydra-displacement"
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This enables material displacement for UsdPreviewSurface import and
export. Scenarios are limited by what's supported by the preview surface
itself. Namely only Object Space displacement can be used (no vector
displacement)[1] and the Midlevel and Scale parameters are maintained by
adjusting the scale-bias on the image texture controlling the Height
(this means that Midlevel and Scale must be constants).
Hydra/MaterialX support is more complicated. First, there is a bug which
prevents scalar displacment from working correctly and that needs USD
2408+ for the fix[2]. Second, is that there's an open question about
which coordinate system to use for MaterialX's vector displacement maps.
Lastly, Hydra GL does not render displacement, making verification using
only Blender impossible[3]. As a result, this PR only makes MaterialX
"ready" for support, but stops short of actually connecting the final
piece of the node graph until more of the above can be sorted out.
Tests are added which cover:
and that midlevel and scale need to be constants
[1] https://openusd.org/release/spec_usdpreviewsurface.html
[2] https://github.com/PixarAnimationStudios/OpenUSD/issues/3325
[3] https://forum.aousd.org/t/materialx-displacement-hydra-storm/1098/2
New test data has been checked in:
tests/data/usd/usd_materials_displace.blend@blender-bot build
This is great! USD displacement export is something we've been waiting for on Poly Haven so we can publish all our materials as USD. (Re #106375)
@GregZaal Yes, this is meant to address your issue :) Do you require MaterialX export at all or are you considering only using the preview surface? It just determines if I'll close out your issue after I checkin or if I leave it open until material x support lands.
@deadpin I'm not sure yet! We'll be working on compatibility with other 3D software via USD soon, so for now I'd say close the issue. MaterialX support is a bigger task than just "displacement support" right?
These changes look good on a high level and work well in the tests. I'll take a closer look at the details and hope to finish my review in the next day or two.
The changes look good!