In order to better interop with the broader Alembic/USD ecosystem, align
the crease values we export with what we believe is expected by native
OpenSubdiv, a 0-10 range.
On import we will translate the native OpenSubdiv range back into
Blender's 0-1 range.
To account for SubD assets produced by Blender before this change, a
compat check is put in place for both Alembic and USD to use the old
methodology when encountering such files. The compat check makes use
of the Blender version we place inside the format's metadata fields. Old
assets loaded into a new Blender will look ok. New assets loaded into an
old Blender would need to be reworked.
Pull Request: https://projects.blender.org/blender/blender/pulls/132582
- There's only a few unit conversion options, just test all of them
- Use reference instead of pointer when passing export settings struct
- Organize scaling struct fields to keep similar options together
Pull Request: https://projects.blender.org/blender/blender/pulls/133774
Refactored USD instancing export to support instanceable references.
With this change, it's now possible to instance object hierarchies and
geometry types other than meshes (e.g., curves, point clouds, etc.).
No longer marking mesh prims as instances in
USDGenericMeshWriter::write_mesh().
USDTransformWriter::do_write() now marks the Xform as instanceable
with a reference to the prototype's Xform when the Blender object is
an instance.
In USDAbstractWriter::mark_as_instance() the target prim is now marked
as instanceable.
Added AbstractHierarchyIterator virtual functions include_data_writers()
and include_child_writers() to allow pruning children of instanceable Xforms
in AbstractHierarchyIterator::make_writers(). These functions return true
in the base class implementation, so that the iterator behavior for Alembic
exports is unaffected. In the USDHierarchyIterator subclass, these functions
are overridden to return false if instancing is enabled and the objects are
instances.
Added virtual function AbstractHierarchyIterator::should_determine_duplication_references()
which returns true if duplication references should be resolved for children
of a given context. This function is overridden in USDHierarchyIterator to
skip processing children of instances, which is more efficient for USD export,
since children of instances are pruned during traversal for writing. For nested
instances where the original prototype is not included in the export, this also
avoids designating a duplicated object parented to an instance as "the original",
which would cause USD errors since defining a prim under an instance
proxy is not allowed.
Extended logic in `AbstractHierarchyIterator::determine_duplication_references()`
to identify prototypes.
Added new function `HierarchyContext::is_prototype()`.
Disallowing merging with parent for instances and prototypes, since
the Xforms cannot be discarded in those cases.
Extended `USDWriterAbstract::ensure_usd_material()` with special logic
to ensure materials for prototype prims are defined in the subtree of the
prototype. This helps ensure the hierarchical encapsulation requirement
for prototypes and is required by certain renderers (e.g., Houdini's Karma)
for instance materials to render.
Added a new `process_scene_graph_instances()` function to ensure
prototypes are exported as abstract prims.
Added python tests test_export_native_instancing_true and
test_export_native_instancing_false.
Pull Request: https://projects.blender.org/blender/blender/pulls/131707
Makes use of recently added test data to ensure proper handling of child
objects, with animated transform constraints, parented to other objects
who also have animated transform constraints.
Also uses the `colored_print` module to better segment the test output.
Pull Request: https://projects.blender.org/blender/blender/pulls/133600
Cleanup and enhance our export of the USD `extent` attribute.
This does the following:
- The existing `author_extents` function now uses recently added common
code to write out the extents attribute
- A new `author_extents` overload allows the use of Blender's native
bounds for the types that support it. We now use this rather than
asking USD to recompute it for us.
- Meshes will now have their extents correctly written during animations
- Curves will now have their extents written as they were not doing so
prior to this PR
- Hair, Lights, Points, and Volumes make use of the `author_extents`
functions now
Since Curves need their extents tested, this PR also moves the test from
C++ to Python. Python tests allow for faster iteration, are more
straightforward to write, and allow usage of the USD validator.
Pull Request: https://projects.blender.org/blender/blender/pulls/132531
Export
Like we do for Mesh and PointCloud, export any "velocity" attribute on
the Point domain as native USD "velocities". While testing, a few
additional blender-internal attributes were discovered being exported
which are now excluded during export.
Import
Add the cache modifier as appropriate when we detect that UsdBasisCurve
data is animated. This includes time-varying positions, widths,
velocities, and general attribute values. Before this PR, only the
positions were considered. And like Export, the native USD "velocities"
attribute is now processed.
Adds test coverage as well.
Pull Request: https://projects.blender.org/blender/blender/pulls/133027
This rescales the whole scene by its root transform to match the same
visual size while not forcing the user to wait for scale to be applied to
each object.
This is requested by studios whose main applications / USD scenes are
in CM, because referencing and payloading scenes from disparate scales
can cause issues at resolution time.
If "Apply Unit Scale Conversion" is unchecked on import, the user now
has the ability to bring the objects in with a scale factor of 1.0, so that the
objects may be edited as if Blender's scene units matches the imported
stage's.
At export time, a "Stage Meters Per Unit" value can be chosen from a list
of common measurements, as well as setting a custom value.
Co-authored-by: kiki <charles@skeletalstudios.com>
Co-authored-by: Michael Kowalski <makowalski@nvidia.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/122804
Until the newer Hair Curves system can fully replace particle hair, add
a small test to ensure this continues to work.
Since the hair is exported as cubic bspline curves, we can also use this
same file to test bspline import now too.
Pull Request: https://projects.blender.org/blender/blender/pulls/131997
While adding tests I found that metaball export has been broken since
Blender 3.4. It would export each metaball geometry twice.
This looks to have been a side effect of a change to `object_dupli.cc`
which no longer sets the `no_draw` flag for metaballs[1]. With the flag
unset we would end up visiting this particular object twice.
Use a direct check for Metaballs now and add test coverage for the
scenario in general.
[1] eaa87101cd
Pull Request: https://projects.blender.org/blender/blender/pulls/131984
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
Make use of our sparse value writer in more places. Namely, when using
animated Camera or Light properties, this will prevent a needless stream
of unchanging values being written into the USD file [1]. Skeletons and
armatures benefit too but less so as typically the primary benefit only
applies to the comparatively small `scale` transform attribute, which
typically remains unchanged from frame to frame.
The newly added `set_attribute` common code can, and eventually will, be
used to reduce boilerplate elsewhere where we do the same sparse writing
dance.
Ref #130759
Pull Request: https://projects.blender.org/blender/blender/pulls/131333
Rather than using a default "Anim" name when exporting armature
animations, use the animation's Action name instead. Likewise use the
UsdSkelAnimation name for the Action's name during import.
Blendshapes/shapekeys still use the default "Anim" name as there's no
action for these situations.
Pull Request: https://projects.blender.org/blender/blender/pulls/131021
When EEVEE next removed the Alpha Threshold option a node graph setup
was used instead. Based on a USD test asset[1] the original code was
designed around only using the Image A channel during import to wire
up the nodes. However, the other channels (R, G, or B) are just as
valid.
We now handle this by wiring up the Separate RGB node, that is already
inserted for the scenario in general, to the shader nodes handling the
threshold calculation. Also adds additional test coverage for both
export and import as well.
The Round and LessThan+OneMinus networks remain the only shapes that
will be recognized for the processing.
[1] https://github.com/usd-wg/assets/tree/main/test_assets/AlphaBlendModeTest
Pull Request: https://projects.blender.org/blender/blender/pulls/130346
Adds the option `merge_parent_xform` to the USD export operator and
panels so the transform and shapes are merged into a single USD Prim.
Without the option (existing default), a top-level mesh would be
exported as a top-level `Xform` that has a `Mesh` child:
```
def Xform "MyBlenderMeshObject"
{
matrix4d xformOp:transform = ...
def Mesh "MyBlenderMeshData"
{
}
}
```
This matches the Blender data model, where a transformable object
contains a geometric shape (like a mesh). This structure is also very
valid in USD, where we don't want to directly instantiate geometric
primitives[1]
However, "since number of prims on a stage is one of the primary factors
that governs how USD scale"[2], to reduce the number of prims in a
stage, geometric primitives *are transformable* themselves (see the
inheritence diagram[3]).
As such, the new export option allows to export geometric primitives
without the parent transform:
```
def Mesh "MyBlenderMeshObject"
{
matrix4d xformOp:transform = ...
}
```
This MR adds a the `is_object_data_context` flag to the
`HierarchyContext` context structure. The point of this change is to
make unambiguous in `USDHierarchyIterator::create_usd_export_context`
the fact that an `object` or a `data` is currently being exported: the
new `merge_parent_xform` option is meaningless for `object`. Only `data`
can be exported with a parent `Xform` or as a child of said `Xform`.
Ideally this flag would not be needed at all: the final USD prim path
*could* be computed in an override of the virtual
`AbstractHierarchyIterator::get_object_data_path` method. However, this
would mean that an `object` and a `data` would have the same export path.
This does not currently play well with
`AbstractHierarchyIterator::ensure_writer`, where `writers` are cached
*by their export path*: it would cache a transform writer, but will skip
the subsequent data writer.
Additionally, another new `is_parent` flag is added to handle the case
where merging the Xform is invalid: objects that are parents to other
objects should remain unmerged as otherwise that would yield invalid USD
files.
[1] https://openusd.org/release/glossary.html#usdglossary-gprim
[2] https://openusd.org/release/glossary.html#usdglossary-instancing
[3] https://openusd.org/release/api/class_usd_geom_xformable.html
Co-authored-by: Odréanne Breton <odreanne.breton@ubisoft.com>
Co-authored-by: Sttevan Carnali Joga <sttevan.carnali-joga@ubisoft.com>
Co-authored-by: Charles Flèche <charles.fleche@ubisoft.com>
While adding test coverage for in-memory and packed texture scenarios, I
found that UDIMs were not being handled correctly in both cases. For
in-memory scenarios the per-tile generated/dirty status was not taken
into account. For packed scenarios the wrong filename substitutions were
being used.
This fixes both of these cases and adds test coverage for these
scenarios now. Both relative and absolute path options are validated.
Note: Both in-memory and packed images behave incorrectly when using the
'KEEP' and 'PRESERVE' texture export modes, so those remain untested
currently. A design on exactly what should happen in these modes is TBD.
Pull Request: https://projects.blender.org/blender/blender/pulls/130391
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
The existing Volume export, which already supports VDB file sequences
and static volumes created inside Blender, is now extended to handle
dynamically created and modified volumes. This allows scenarios where a
Volume Displace modifier is placed over-top an existing VDB sequence or
when Geometry Nodes is used to create animated volumes procedurally.
Detection of what counts as animation is simplistic and mimics what has
been used for Meshes. Essentially if there are any modifiers on the
volume we assume that the volume is "varying" in some way. This can lead
to situations where new volume files are written unnecessarily.
Volume import was also adjusted to correctly set the sequence "offset"
value. This is required to properly handle the case when a VDB sequence
begins animating at a different frame than what's implied by the file
name. For example, a VDB file sequence with file names containing 14-19
but the user wants to animate on frames 8-13 instead.
Tests are added which cover:
- Animated VDB file sequences
- Animated Mesh To Volume where the mesh has been animated
- Animated Volume Displacement where displacement settings are animated
- Animated Volumes created with a Geometry Nodes simulation
----
New test data has been checked in: `tests/data/usd/usd_volumes.blend` and files inside `tests/data/usd/volume-data/`
Pull Request: https://projects.blender.org/blender/blender/pulls/128907
Instead of running the ComplianceChecker during just one test, run it
for every export test. A common `export_and_validate` local function is
used in all relevant locations now.
Pull Request: https://projects.blender.org/blender/blender/pulls/128513
This includes tests for a "static" mesh where the materials have been
assigned and are expected to remain the same over time.
The test scenario also includes a "dynamic" mesh where both new faces
and new materials are assigned to the same mesh over time (inspired by
#118754). However, that cannot be tested right now due to missing
features of both the MeshSequenceCache and our USD IO code. No testing
will occur for that case until the features are implemented.
Pull Request: https://projects.blender.org/blender/blender/pulls/128341
Color primvars/attributes were historically treated as a special case
for both import and export. This was mostly done to align with how
painting and viewport display works in Blender. Export would generally
ignore color attributes except when they were found on a Mesh's Point or
FaceCorner domains. And import went out of its way to map incoming color
primvars to the FaceCorner domain in more situations than necessary.
To facilitate better roundtripping in Blender<=>USD workflows, and to
reduce code duplication, this PR teaches the common attribute utilities
how to handle color types. The color attributes will now work on all
relevant Mesh and Curve domains.
There were tests in place for this already but they were set to verify
the inverse state, i.e. the technically broken state, until this could
be fixed.
There remains one special case: "displayColor" primvars and attributes.
The "displayColor" is a special primvar in USD and is the de-facto way
to set a simple viewport color in that ecosystem. It must also be a
color3f type. In order to not regress import, if a "displayColor"
primvar is found on the Face domain we will map it to FaceCorner instead
so it can be displayed in the viewport; which has been the case for the
past several releases. We can drop this special-case if/when Blender can
display Face colors through the Viewport Shading "Attribute" color type.
Additionally, Blender will export this, and only this, color attribute
as a color3f.
Note: As was the case prior to this PR, the following 2 discrepancies
still prevent "perfect" round-trips:
- USD does not have an equivalent to Blender's byte colors; they are
treated as float during IO
- Blender does not have an equivalent to USD's color3 types; they are
treated as color4 during IO
Pull Request: https://projects.blender.org/blender/blender/pulls/127784
Export Blender Point Clouds as `UsdGeomPoints` primitives.
Summary
- Adds the `USDPointsWriter` class
- Adds tests to ensure that animated positions, velocities, radii, and
regular attributes are all written correctly (in a sparse format)
- Adds a new `export_points` operator property, mirroring the existing
`import_points` option
Pull Request: https://projects.blender.org/blender/blender/pulls/126389
Adds test coverage for the USD python hook machinery:
- Ensure processing occurs correctly when returning False or throwing
exceptions from all the hooks
- Validates that the hook arguments are valid (UsdStage, depsgraph, and
material parameters)
- Tests unregister to ensure hooks are fully removed from processing
Pull Request: https://projects.blender.org/blender/blender/pulls/126809
Newly validates the following:
- Image mapping transforms on import and export
- Typical normal map setups on import and export
- Alpha-clip node setups on import (was already tested for export)
Pull Request: https://projects.blender.org/blender/blender/pulls/126776
Additional coverage for the following scenarios:
- Ensures custom properties are exported and imported correctly
- Ensures that xform op modes and scene orientation options are properly
respected during export
Pull Request: https://projects.blender.org/blender/blender/pulls/126723
While adding test coverage for mesh subdivision surface scenarios, a few
problems were noticed with vertex crease support.
This PR fixes:
- Used incorrect `crease_sharpnesses` instead of `corner_sharpnesses`
- Used incorrect value for an "infinitely sharp" vertex crease
- Unnecessarily wrote out Blender's `crease_vert` attribute as a primvar
Tests are added which validate everything we support.
Pull Request: https://projects.blender.org/blender/blender/pulls/126209
The mesh velocity data was not using the UsdUtilsSparseValueWriter and
was writing out data for all frames even if the velocity didn't change.
Adds test coverage for this scenario as well as other situations where a
MeshSequenceCache (MSC) would be required:
- Ensures that when positions vary a MSC is added
- Ensures that when velocities vary a MSC is added (see blender/blender@c862d40e09)
- Ensures that when attributes vary a MSC is added (see blender/blender@3c394d39f2)
Pull Request: https://projects.blender.org/blender/blender/pulls/126208
Support the USD `color4f` (and related) types during import and use this
type when writing out Blender's color attributes.
This roundtrips Blender data correctly and will properly load data from
many more USD files as well.
Pull Request: https://projects.blender.org/blender/blender/pulls/125839
Add an export test to cover some simple animation scenarios that would
have protected against recent bugs:
- A simple object animation (would have prevented `122625`)
- An armature animation (would have prevented `724a674baed`)
- A shape key animation (would have indirectly found `6c5ce883e73`)
Pull Request: https://projects.blender.org/blender/blender/pulls/123458
This change adds the ability to export MaterialX networks into the resulting
USD layer.
Details:
A new export option has been added to the USD export to enable MaterialX
export. It is off by default currently due to reasons in the caveats
section.
When enabled, it exports the MaterialX shading network alongside the
UsdPreviewSurface network, on the same USD Material. This allows the same
material to be used by renderers that don't support MaterialX, using the
USDPreviewSurface as a fallback. This is similar to setups in other DCC
packages, and matches the format we've used in our Reality Composer Pro
asset library.
It uses the existing MaterialX framework used to generate MaterialX
documents for rendering, to act as the basis for the USD graph. In this
process it also re-uses the existing texture export code as well if provided
and necessary.
Once the MaterialX document is created, use usdMtlx to generate a USD
shading network. Unfortunately, usdMtlx generates a graph that is unlike
what other DCCs that support MaterialX-embedded-in-USD generates. It
generates several extra prim hierarchies, and externalizes all shader
inputs, making them difficult to edit in other MaterialX graph editors.
To workaround this, generate the MaterialX shading network onto a
temporary stage, where we then run various pre-processing steps to prevent
prim collisions and to reflow the paths once they're converted.
The PrimSpecs are then copied over to their new path. The resulting prim
hierarchy matches what many artists we've worked with prefer to work with.
Caveats:
The Export MaterialX check is off by default. When using the Principled
BSDF, the resulting graph is very usable. However, when using some of the
other BSDFs, the shading networks generated by the existing MaterialX
framework in Blender generate some shading graphs that are difficult for
usdview and other DCC's to understand. The graph is still correct, but
because we're trying to prioritize compatibility, the default is off.
In future PRs we can aim to make the graphs for those other BSDFs play
better with other DCCs.
Other Implementation Details:
As part of this commit we've also done the following:
* Place some of the materialx graphs inside a passthrough nodegraph to
avoid node conflicts.
* Better handle some shader output types , and better handle some
conflict cases.
* Moved the ExportTextureFunction to materials.h due to some difficult
to resolve header ordering issues. This has no effect on any runtime code.
* There is a test for the MaterialX export that does some basic checking to
make sure we get an export out the other end that matches our expectations
Authored by Apple: Dhruv Govil
This PR is based on an earlier implementation by Brecht van Lommel , as well
as Brian Savery and his teams' work at AMD to implement the general
MaterialX framework within Blender.
Pull Request: https://projects.blender.org/blender/blender/pulls/122575
This commit adds logic to convert between USD dome lights and Blender
world materials.
The USD dome light rotation is represented in a mapping node input to the
environment texture. If the dome light has a color specified in addition to
the texture map, the color will be converted to a vector multiply on the
the environment texture output.
I the imported USD has multiple dome lights, only the first dome light will
be converted to a world material.
Co-authored-by: kiki <charles@skeletalstudios.com>
Co-authored-by: Michael Kowalski <makowalski@nvidia.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/121800
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
Add support for reading and writing custom `Curves` attributes.
This allows us to roundtrip Blender's Hair grooms containing UVs and
other attribute data. Note that animated attribute values are not
supported with this change.
This will also address #120042
Pull Request: https://projects.blender.org/blender/blender/pulls/121928
Adds a test to validate the import of Mesh attributes for USD.
It reuses the recently added export attribute test file to generate the
USD file to load.
The test validates the current behavior in `main`. Missing data and bugs
are noted in comments and can be addressed afterwards.
Pull Request: https://projects.blender.org/blender/blender/pulls/121327
This PR adds the following changes:
A single root is always set as default. After talking to Wave and
Spiff, we settled on root being the best default. Users who don't
want a single root prim inserted, can choose to clear the field
The root prim no longer requires the user to prefix the field with /.
It will implicitly insert that for them.
On export, the root_prim hierarchy is now defined all as Xform
instead of just the final prim in the path. Each prim also has
custom metadata added to show that it was generated by Blender.
This follows convention in other DCCs as well.
On import, the code now finds the hierarchy of generated prims
using that metadata. It then skips importing them. This means that
you can roundtrip hierarchies even with an inserted root.
Co-authored-by: Dhruv Govil <dgovil2@apple.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/113187
Listing the "Blender Foundation" as copyright holder implied the Blender
Foundation holds copyright to files which may include work from many
developers.
While keeping copyright on headers makes sense for isolated libraries,
Blender's own code may be refactored or moved between files in a way
that makes the per file copyright holders less meaningful.
Copyright references to the "Blender Foundation" have been replaced with
"Blender Authors", with the exception of `./extern/` since these this
contains libraries which are more isolated, any changed to license
headers there can be handled on a case-by-case basis.
Some directories in `./intern/` have also been excluded:
- `./intern/cycles/` it's own `AUTHORS` file is planned.
- `./intern/opensubdiv/`.
An "AUTHORS" file has been added, using the chromium projects authors
file as a template.
Design task: #110784
Ref !110783.
This PR addresses issue “USD export does not respect opacity threshold for clip alpha blend mode #107062”
This commit extends the USD Preview Surface material support to author the opacityThreshold attribute of materials on export, when the Alpha Clip blend mode is selected.
When authoring alpha cutouts in Blender, one sets the Blend Mode to "Alpha Clip", and the Clip Threshold to some value greater than zero.
When this case is detected on export, we now author the opacityThreshold attribute to match the specified clip threshold.
Note that opacityThreshold is already handled correctly on import, so this change allows the feature to be fully round-tripped.
Co-authored-by: Matt McLin <mmclin@apple.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/107149
A properly authored USD file will have the extent attribute authored on all prims conforming to UsdGeomBoundable.
This cached extent information is useful because it allows the 3D range of prims to be quickly understood without reading potentially large arrays of data. Note that because the shape of prims may change over time, extent attributes are always evaluated for a given timecode.
This patch introduces support for authoring extents on meshes and volumes during export to USD.
Because extents are common to multiple kinds of geometries, the main support for authoring extents has been placed in USDAbstractWriter, whose new author_extent method can operate on any prim conforming to pxr::UsdGeomBoundable. The USD library already provides us the code necessary to compute the bounds for a given prim, in pxr::UsdGeomBBoxCache::ComputeLocalBound.
Note that not all prims that are imageable are boundable, such as transforms and cameras.
For more details on extents, see https://graphics.pixar.com/usd/release/api/class_usd_geom_boundable.html#details.
Note that when new types of geometries are introduced, such as curves in https://developer.blender.org/D16545, we will need to update the USD writer for that geometry such that it calls this->author_extent.
Update on Feb 2: This patch has been updated to include a unit test to ensure authored extents are valid. This test requires new test assets that will need to be submitted via svn. The test assets are attached in the d16837_usd_test_assets.zip file. To use, unzip and merge the contents of this zip into the lib/tests/usd folder.
This unit test also addresses #104269 by validating compliance of exported USD via UsdUtils.ComplianceChecker.
Pull Request #104676
