Instead of converting to a string immediately, only convert to a string
when necessary, like for trace logging. This reduces the size of the
`USDPrimReader` base class by 24 bytes, makes several Vectors and Maps
smaller at runtime, and reduces some unnecessary string allocations and
conversions in various other places.
The recently added python Hook `get_prim_path` dictionary will now
contain `SdfPath` objects rather than strings; removing the string
conversion cost when calling other USD APIs like `GetPrimAtPath` which
take in `SdfPath` objects to begin with.
This also makes the code a bit more self explanatory since the type
makes it clear what kind of path you are dealing with.
Pull Request: https://projects.blender.org/blender/blender/pulls/133954
Since the `usd_path_to_mat_name` map seems to always be used in tandem
with `mat_name_to_mat` to get the material, change it from a map of
[string, string] to [string, Material] and store the Material directly.
This removes the need to do a secondary lookup through `mat_name_to_mat`
and less memory will be used at runtime due to the smaller Value size.
Pull Request: https://projects.blender.org/blender/blender/pulls/132647
Supporting a new on_material_import() USDHook callback.
Also added support for import_texture() and export_texture()
utility functions which can be called from on_material_import() and
on_material_export() Python implementations, respectively.
Pull Request: https://projects.blender.org/blender/blender/pulls/131559
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:
- Variations of Midlevel and Scale values
- A constant Height setup
- Negative scenarios checking that only Object space is supported
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
Pull Request: https://projects.blender.org/blender/blender/pulls/128909
EEVEE-next has removed the MA_BM_CLIP / alpha_threshold material
properties in favor of using nodes for equivalent functionality. This
changes USD to build and traverse node graphs during import and export
accordingly. Indirectly this allows Cycles to correctly render such
materials now too.
A complicating factor is that the UsdPreviewSurface defines its opacity
threshold using greater-than-equals[1], which Blender does not support
(and for which was technically already incorrect as EEVEE-legacy only
used greater-than for its shaders). Due to this we actually need to use
2 nodes: A less-than, followed by a one-minus invert, to arrive at the
proper value. We'll translate UsdPreviewSurface to this form on Import.
For Export we will look for either this 2-node pattern or a Round
node plugged into Alpha. Looking for Round is a result of the glTF
documentation which recommended the use of this node for thresholds of
0.5[2]. It's a tiny addition that seems reasonable to accommodate.
[1] https://openusd.org/release/spec_usdpreviewsurface.html (search for "opacityThreshold")
[2] https://docs.blender.org/manual/en/4.2/addons/import_export/scene_gltf2.html#alpha-modes
See PR for example images
Pull Request: https://projects.blender.org/blender/blender/pulls/122025
