Import USD deformable bodies (cable, cloth, volume) in add_usd()

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ### Added
 
+- Import USD deformable bodies in `ModelBuilder.add_usd()` (experimental; based on the proposed [AOUSD Deformable Body Physics schema](https://github.com/aousd/OpenUSD-proposals/blob/5d89c0ed46a26de92f4d3fefef3bfad6500c07ce/proposals/physics_deformables/wp_deformable_physics.md)). Curves become cables (capsule bodies joined by cable joints, each cable wrapped in its own articulation), meshes become cloth (FEM triangles with bending edges), and tet meshes become soft bodies. Bound deformable materials supply thickness, stiffness, and density, and the proposal's mass precedence (per-point `physics:masses`, then body `mass`/`density`, then material density) is honored. Each imported deformable's element ranges and authored material attributes are returned by prim path when the experimental `add_usd(..., return_deformable_results=True)` option is passed; the returned maps are build-time snapshots (not live selections), and the default return shape carries no deformable entries. Collision participation follows `PhysicsCollisionAPI` / `physics:collisionEnabled`: cables without an enabled collider import without collision, while cloth and volume deformables warn that particle collision cannot be disabled yet. Standard `physics:filteredPairs` pairs involving a cable expand to its segment shapes; pairs naming a cloth or volume deformable warn and are not lowered. Disabled or kinematic deformables and malformed topology warn and are skipped. Cable and cloth material attributes are returned as authored in `path_cable_attrs` / `path_cloth_attrs`, so solvers with richer cable or cloth models can rebuild from the import. See the USD parsing documentation for the supported subset and limitations.
+- Import AOUSD proposal `PhysicsAttachment` prims for cables in `ModelBuilder.add_usd()`. Cable `point` / `segment` sites with an `xform` target become hard ball joints, returned in `path_attachment_map` (with `return_deformable_results=True`); cloth/volume attachment sites warn and are kept in `path_attachment_attrs`. A hard, coincident `point`->`point` attachment between two cables welds them into one rod graph; a springy or non-coincident junction warns and is kept as data instead of welded.
+- Import AOUSD proposal `PhysicsElementCollisionFilter` prims in `ModelBuilder.add_usd()`: collisions between the paired element groups of `src0` and `src1` are filtered (group counts pair element-wise; a count of `0` or an empty counts array selects all elements). Sources resolve to imported cables, rigid bodies, or collider prims; cloth/volume element sources warn and are skipped.
 - Add scalar value-based OpenCV, F-theta, and Kannala-Brandt fisheye camera ray helpers to `SensorTiledCamera.utils`, plus pinhole aperture/focal-length parameters, `compute_camera_transforms_usd()`, `compute_camera_rays_usd_pinhole()`, and optional preallocated ray output writes.
 - Add `cloth_stiff_material_hanging` and `cloth_stiff_material_stretch` examples regression-guarding the new Neo-Hookean triangle material (stability under gravity at extreme stiffness, and bulk area-preservation across a Poisson-ratio sweep)
 - Add `newton[onnx]` for ONNX policy inference through Warp-NN; `ControllerNeuralMLP`, `ControllerNeuralLSTM`, and RL policy examples can run exported `.onnx` policies without requiring PyTorch for ONNX execution.
@@ -61,6 +64,10 @@
 - Deprecate passing option-heavy helper API parameters positionally, including `ModelBuilder.ShapeConfig`, `ModelBuilder.JointDofConfig`, `Contacts`, `ArticulationView`, and selected `ModelBuilder` body, joint, shape, rod, cloth, soft-body, and FEM helpers. Keep stable identifiers such as `body`, `parent`/`child`, capacity counts, and topology indices positional; migrate calls such as `add_shape_box(body, xform, hx=...)` to `add_shape_box(body, xform=xform, hx=...)`.
 - Deprecate loading TorchScript (`torch.jit.save`) and dict (`torch.save`) neural-network checkpoints in `ControllerNeuralMLP` and `ControllerNeuralLSTM` in favor of pt2 archives saved via `torch.export.save`.
 - Deprecate omitting `body_frame_origin` in `ModelBuilder.add_rod()` and `ModelBuilder.add_rod_graph()`; the implicit behavior still uses the existing start-node body-frame convention during the deprecation window, but the implicit default will change to `body_frame_origin="com"` in a future release. Pass `body_frame_origin="start"` to preserve the legacy frame or `body_frame_origin="com"` to opt into the future COM-centered frame.
+- Change VBD Neo-Hookean membrane/tet damping to an objective metric based on the rate of `C = FᵀF`, so rigid-body rotations no longer generate damping force.
+- Change VBD spring damping to act only along the spring axis (damping edge-length rate), so transverse and rigid-rotational motion is no longer damped by springs.
+- Deprecate reading legacy vendor-namespaced deformable material attributes (`omniphysics:`, `physxDeformableBody:`) off any bound material in `newton.usd.get_tetmesh()`, `newton.TetMesh.create_from_usd()`, and `ModelBuilder.add_usd()`. They are still read during the deprecation window, with a `DeprecationWarning`; a future release will read only canonical `physics:` attributes from a material applying `PhysicsVolumeDeformableMaterialAPI`. Migrate by authoring the canonical attributes, or keep the old behavior without the warning via `compat_namespaces=newton.usd.DEFORMABLE_LEGACY_NAMESPACES` (`get_tetmesh` / `create_from_usd`) or `schema_resolvers=[..., SchemaResolverPhysx()]` (`add_usd`). `compat_namespaces` is now keyword-only; pass `()` to opt into the canonical-only behavior today.
+- Align MJCF and USD margin/gap import with MuJoCo 3.9+. Drop the `mj_margin - mj_gap` subtraction; `Model.shape_margin` now matches authored `margin`, and `Model.shape_gap` matches authored `gap`. Pass `legacy_margin_gap=True` to `ModelBuilder.add_mjcf` or `ModelBuilder.add_usd` to restore the pre-3.9 translation for files authored against MuJoCo <= 3.8.
 - Deprecate the `indices` argument of `MeshAdjacency` in favor of `tri_indices`
 - Deprecate `MeshAdjacency.add_edge`; construct a `MeshAdjacency` with `edge_indices` (`[o0, o1, v0, v1]` rows) instead
 

docs/api/newton_usd.rst

@@ -46,3 +46,13 @@ resolver types used by :meth:`newton.ModelBuilder.add_usd`.
    has_attribute
    type_to_warp
    value_to_warp
+
+.. rubric:: Constants
+
+.. list-table::
+   :header-rows: 1
+
+   * - Name
+     - Value
+   * - ``DEFORMABLE_LEGACY_NAMESPACES``
+     - ``('omniphysics', 'physxDeformableBody')``