Add builder.add_joint_free in parse_body in import_usd by apradhana · Pull Request #426 · newton-physics/newton

apradhana · 2025-07-16T17:14:34Z

Purpose: In import_usd, free_floating_bodies should have free_joint. This should only be applied to bodies that are added by import_usd.

We want the result of parsing a USD as a model to also work with MJWarp. As MJWarp requires at least one joint, we add a free joint in the body that has none when we add a body to the builder. Here's an example of a simulation that we get after running the result of import_usd through MJWarp:

Here's the result of simulating cube_cylinder.usda that is in tests/assets through MJWarp and XPBD:

Summary by CodeRabbit

New Features
- Automatically adds free joints to bodies not connected by existing joints, enhancing simulation accuracy and flexibility.
- Introduced a detailed 3D scene asset featuring physics-enabled objects with realistic materials and lighting.
Tests
- Added a test verifying joint count correctness and material properties when importing the new 3D scene file.

Signed-off-by: apradhana <andre.pradhana@gmail.com>

coderabbitai · 2025-07-16T17:14:43Z

📝 Walkthrough

Walkthrough

The update adds a new method add_free_joints_to_floating_bodies to the ModelBuilder class in newton/sim/builder.py, which adds free joints to bodies that are not children in any joint and have positive mass. The import_usd.py script is modified to call this new method after setting inverse inertia matrices for bodies with the PhysicsMassAPI schema, before collapsing fixed joints. A new USD test asset cube_cylinder.usda is added, along with a unit test verifying the joint count and material properties after import. No other logic or function signatures are changed.

Changes

Cohort / File(s)	Change Summary
ModelBuilder core logic `newton/sim/builder.py`	Added `ModelBuilder.add_free_joints_to_floating_bodies()` method to add free joints to floating bodies.
USD import integration `newton/utils/import_usd.py`	Inserted call to `builder.add_free_joints_to_floating_bodies()` after setting inverse inertia matrices.
Test assets `newton/tests/assets/cube_cylinder.usda`	Added new USD scene file defining physics-enabled objects with materials, joints, and environment.
Unit tests `newton/tests/test_import_usd.py`	Added test `test_import_cube_cylinder_joint_count` to verify joint count and material properties after importing `cube_cylinder.usda`.

Sequence Diagram(s)

sequenceDiagram
    participant import_usd
    participant builder

    import_usd->>builder: set_inverse_inertia_matrices()
    import_usd->>builder: add_free_joints_to_floating_bodies()
    import_usd->>builder: collapse_fixed_joints()

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🎯 2 (Simple) | ⏱️ ~10 minutes

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Milad-Rakhsha-NV

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newton/sim/builder.py (1 hunks)
newton/tests/test_import_usd.py (1 hunks)

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newton/tests/test_import_usd.py
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coderabbitai

Actionable comments posted: 1

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Reviewing files that changed from the base of the PR and between e649ced and 0bc3284.

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newton/utils/import_usd.py (1 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (1)

newton/utils/import_usd.py (1)

newton/sim/builder.py (1)

add_joint_free (1106-1157)

Signed-off-by: apradhana <andre.pradhana@gmail.com>

coderabbitai

Actionable comments posted: 0

🧹 Nitpick comments (1)

newton/tests/test_import_usd.py (1)
158-167: LGTM! Test correctly validates the new free joint functionality.

The test properly validates that the new add_free_joints_to_floating_bodies functionality works as expected, ensuring MJWarp compatibility by adding at least one joint to USD imports.

Consider enhancing the test with additional assertions to make it more comprehensive:
 @unittest.skipUnless(USD_AVAILABLE, "Requires usd-core")
 def test_import_cube_cylinder_joint_count(self):
+    """Test that floating bodies get free joints added for MJWarp compatibility."""
     builder = newton.ModelBuilder()
     parse_usd(
         os.path.join(os.path.dirname(__file__), "assets", "cube_cylinder.usda"),
         builder,
         collapse_fixed_joints=True,
         invert_rotations=True,
     )
     self.assertEqual(builder.joint_count, 1)
+    # Verify the added joint is a free joint
+    self.assertEqual(builder.joint_type[0], newton.JOINT_FREE)
This would provide better validation that the correct type of joint is being added and include documentation explaining the test's purpose.

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newton/tests/assets/cube_cylinder.usda (1 hunks)
newton/tests/test_import_usd.py (1 hunks)

🧠 Learnings (1)

newton/tests/test_import_usd.py (1)

Learnt from: dylanturpin
PR: #394
File: newton/tests/test_ik.py:119-119
Timestamp: 2025-07-15T21:00:03.709Z
Learning: In the Newton physics engine codebase, it's acceptable to test private API functions (those prefixed with underscore) in unit and component tests, as the maintainers consider this appropriate for testing internal functionality.

✅ Files skipped from review due to trivial changes (1)

newton/tests/assets/cube_cylinder.usda

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🧠 Learnings (1)

newton/tests/test_import_usd.py (1)

Learnt from: dylanturpin
PR: #394
File: newton/tests/test_ik.py:119-119
Timestamp: 2025-07-15T21:00:03.709Z
Learning: In the Newton physics engine codebase, it's acceptable to test private API functions (those prefixed with underscore) in unit and component tests, as the maintainers consider this appropriate for testing internal functionality.

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Signed-off-by: apradhana <andre.pradhana@gmail.com>

codecov · 2025-07-30T02:48:35Z

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

Signed-off-by: Eric Heiden <eheiden@nvidia.com>

apradhana · 2025-07-31T17:23:19Z

pre-commit.ci autofix

…s#426) Signed-off-by: apradhana <andre.pradhana@gmail.com> Signed-off-by: Eric Heiden <eheiden@nvidia.com> Co-authored-by: Eric Heiden <eheiden@nvidia.com>

Add builder.add_joint_free in parse_body for result to work with MJWarp.

0bc3284

Signed-off-by: apradhana <andre.pradhana@gmail.com>

apradhana temporarily deployed to external-pr-approval July 16, 2025 17:14 — with GitHub Actions Inactive

eric-heiden reviewed Jul 16, 2025

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Comment thread newton/utils/import_usd.py Outdated

coderabbitai Bot reviewed Jul 16, 2025

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apradhana added 4 commits July 16, 2025 20:24

Use add_free_joints_to_floating_bodies in builder.

117d09f

Signed-off-by: apradhana <andre.pradhana@gmail.com>

Add unit test to test cube_cylinder.usda.

81def7c

Signed-off-by: apradhana <andre.pradhana@gmail.com>

Add cube_cylinder.usda.

1143ab8

Signed-off-by: apradhana <andre.pradhana@gmail.com>

Update cube_cylinder.usda.

7af8c10

Signed-off-by: apradhana <andre.pradhana@gmail.com>

coderabbitai Bot reviewed Jul 23, 2025

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eric-heiden reviewed Jul 25, 2025

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eric-heiden reviewed Jul 25, 2025

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Comment thread newton/utils/import_usd.py Outdated

apradhana added 3 commits July 29, 2025 18:52

Simplify cube_cylinder.usda.

bf3402c

Signed-off-by: apradhana <andre.pradhana@gmail.com>

Add more test for import_usd.

92a0bc1

Signed-off-by: apradhana <andre.pradhana@gmail.com>

Add Iterable argument to add_free_joints_to_floating_bodies.

89e3b09

Signed-off-by: apradhana <andre.pradhana@gmail.com>

eric-heiden approved these changes Jul 31, 2025

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Merge branch 'main' into apradhana/fix_import_usd_add_free_body

e200ac4

Signed-off-by: Eric Heiden <eheiden@nvidia.com>

eric-heiden enabled auto-merge (squash) July 31, 2025 04:31

pre-commit-ci Bot and others added 2 commits July 31, 2025 17:25

[pre-commit.ci] auto code formatting

bde49e4

Merge branch 'main' into apradhana/fix_import_usd_add_free_body

9a3d056

eric-heiden merged commit a406a95 into newton-physics:main Aug 1, 2025
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This was referenced Aug 18, 2025

Simple articulation USD import fails #517 #527

Merged

Usd examples parsing tests #572

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coderabbitai Bot mentioned this pull request Aug 30, 2025

Add UR10 example #691

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4 tasks

coderabbitai Bot mentioned this pull request Sep 10, 2025

Improve USD parsing, MJC conversion for Allegro hand #730

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coderabbitai Bot mentioned this pull request Nov 14, 2025

Update ModelBuilder API for creating articulations #1073

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coderabbitai Bot mentioned this pull request Jan 22, 2026

Add support for parsing external joints from USD #1442

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This was referenced Jan 30, 2026

Support floating, base_joint and parent_body arguments for importers #1498

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Fix import of non-articulated joints #1535

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coderabbitai Bot mentioned this pull request Feb 11, 2026

Collapse fixed joints with non articulated bodies #1608

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coderabbitai Bot mentioned this pull request Feb 26, 2026

Add joints_to_keep attribute for selective fixed joint collapsing. #1795

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coderabbitai Bot mentioned this pull request Mar 9, 2026

Fix for USD import for assets with fixed bodies acting as an articulation #2018

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adenzler-nvidia mentioned this pull request Apr 23, 2026

Unify treatment of free joint with other joints #2558

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