OVPhysX DeformableObject — Design Spec

Issue: Needs creation — [OVPHYSX] DeformableObject asset
Date: 2026-04-20
Status: Draft

Summary

Implement DeformableObject and DeformableObjectData for the OVPhysX backend, enabling soft body simulation.

Critical finding: Unlike RigidObject and Articulation, DeformableObject has no base abstract class in core isaaclab/. It exists only in isaaclab_physx/ and inherits directly from AssetBase. This means the standard factory pattern cannot be used. A BaseDeformableObject must be extracted first.

Prerequisite: Extract BaseDeformableObject

Before OVPhysX can implement DeformableObject, the existing PhysX implementation must be refactored:

1. Create BaseDeformableObject in source/isaaclab/isaaclab/assets/deformable_object/:

   • Extract the abstract interface from PhysX's DeformableObject
   • Define abstract properties: data, num_instances, num_bodies, root_view, max_sim_vertices_per_body, max_sim_elements_per_body, max_collision_vertices_per_body, max_collision_elements_per_body
   • Define abstract methods: write_nodal_state_to_sim_index, write_nodal_pos_to_sim_index, write_nodal_velocity_to_sim_index, write_nodal_kinematic_target_to_sim_index, transform_nodal_pos
   • Inherit from AssetBase

2. Create BaseDeformableObjectData in the same location:

   • Abstract properties: nodal_pos_w, nodal_vel_w, nodal_state_w, root_pos_w, root_vel_w
   • Attributes: default_nodal_state_w, nodal_kinematic_target

3. Refactor PhysX's DeformableObject to inherit from BaseDeformableObject instead of AssetBase

4. Wire up factory pattern in backend_utils.py for deformable objects

This is a breaking change in architecture (not API) and should be reviewed independently before the OVPhysX implementation begins.

DeformableObject Interface

Key Properties

Key Methods

Data Properties

Where N=num_instances, V=max_sim_vertices_per_body.

Architecture

File Layout

source/isaaclab_ovphysx/isaaclab_ovphysx/assets/
└── deformable_object/
    ├── __init__.py
    ├── __init__.pyi
    ├── deformable_object.py       (~500 lines)
    ├── deformable_object_data.py  (~300 lines)
    └── kernels.py                 (~100 lines)

OVPhysX API Requirements

Blocker for @marcodiiga: Deformable body support in ovphysx is likely completely new work. This includes:

• FEM/soft body simulation in the ovphysx backend
• TensorBindings for nodal state (positions, velocities)
• Kinematic target support for volume deformables
• Mesh topology queries

This is the largest single piece of ovphysx-side work across all subtasks.

Phasing

Given the prerequisites, this should be implemented in two phases:

Phase 1: Extract BaseDeformableObject from PhysX (prerequisite PR)
Phase 2: Implement OVPhysX DeformableObject (depends on ovphysx soft body support)

Tests

Source: source/isaaclab_physx/test/assets/test_deformable_object.py
Target: source/isaaclab_ovphysx/test/assets/test_deformable_object.py

Dependencies

• Requires base class extraction (new PR, must merge before implementation)
• Requires ovphysx soft body support (significant ovphysx-side work)
• Requires PR ovphysx backend integration #4852 merged
• Independent of other OVPhysX asset specs

Estimated Scope

• Base class extraction: ~500 lines of refactoring (separate PR)
• deformable_object.py: ~500 lines
• deformable_object_data.py: ~300 lines
• kernels.py: ~100 lines
• Tests: ~200 lines of adaptations
• ovphysx-side work: very significant — FEM support is new