[Newton] Decouples OV to enable OV-optional code paths

[kellyguo11]

Description

Decouples core code paths from OV modules such that we can run training/non-OV visualization without launching the OV app. If visualizer is selected as newton and/or rerun, or no visualizers are specified, the OV app will not run and no OV modules will be available. To enable OV paths, --visualizers omniverse must be set.

Main changes:

• Removed isaac sim SimulationContext and SimulationManager references
• Assumed no support for in-memory OV stages, non-OV stages are in-memory by default
• All omni.ui dependencies are lazy loaded
• Decoupling prims and stage utils from OV modules - fabric is still required for OV visualization
• Alternative way for carb settings is done through a SettingsManager
• XFormPrim class is re-implemented in Isaac Lab
• omni.kit.commands are either lazy imported or replaced (replacements should be verified)
• omni.timeline callbacks are removed (commented out for now)
• PhysicsScene is created by the SimulationContext, which also holds configurations for the scene

Limitations:

• Semantics are not supported
• VisualizationMarkers can only be run with OV visualizer

Type of change

• New feature (non-breaking change which adds functionality)
• Breaking change (existing functionality will not work without user modification)

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[greptile-apps]

Greptile Overview

Greptile Summary

This PR decouples Isaac Lab's core code paths from Omniverse (OV) modules to enable training and non-OV visualization without launching the OV app. When using Newton and/or Rerun visualizers (or no visualizers), the OV app will not run.

Key Changes:

• SimulationContext no longer inherits from Isaac Sim's SimulationContext base class - implements its own singleton pattern
• New SettingsManager provides a carb.settings-like interface that works in both Omniverse and standalone modes
• AppLauncher conditionally launches SimulationApp only when Omniverse is needed (visualizer, cameras, or livestreaming)
• New pure USD XFormPrim implementation replaces Isaac Sim dependency
• Cloner utilities refactored to support Newton physics backend alongside PhysX
• omni.timeline callbacks removed/commented out in favor of NewtonManager callbacks
• Lazy imports for omni.ui, omni.kit.commands, and other OV-specific modules

Breaking Changes:

• SimulationContext.get_version() method is commented out
• Timeline event subscriptions are disabled
• Some features raise NotImplementedError in Newton mode (deformable objects, rigid objects, surface grippers)

Confidence Score: 3/5

• This is a large architectural refactoring with potential runtime issues that need addressing before merge.
• The PR introduces significant architectural changes with two identified bugs: (1) get_current_stage() will crash if SimulationContext is not initialized, and (2) newton_params may be undefined when used. The extensive use of commented-out code suggests work in progress. Many timeline callbacks are disabled which could affect OV mode behavior.
• Pay close attention to source/isaaclab/isaaclab/sim/utils/stage.py and source/isaaclab/isaaclab/sim/simulation_context.py which have the identified issues.

Important Files Changed

File Analysis

Filename	Score	Overview
source/isaaclab/isaaclab/app/app_launcher.py	4/5	Major refactoring to conditionally launch SimulationApp only when Omniverse is needed (based on visualizer, cameras, or livestreaming). Adds standalone mode for Newton/Rerun-only usage. Adds SettingsManager integration and proper signal handling.
source/isaaclab/isaaclab/app/settings_manager.py	5/5	New settings manager singleton that provides carb.settings-like interface for both Omniverse and standalone modes. Clean implementation with proper singleton pattern stored in sys.modules to survive reloads.
source/isaaclab/isaaclab/sim/simulation_context.py	3/5	Major refactoring to decouple from Isaac Sim's SimulationContext base class. Now standalone with own singleton implementation, SettingsManager integration, and Newton physics backend. Several methods commented out during transition.
source/isaaclab/isaaclab/sim/prims/xform_prim.py	5/5	New pure USD implementation of XFormPrim replacing Isaac Sim dependency. Clean implementation with proper transform handling, regex path resolution, and numpy/torch conversion utilities.
source/isaaclab/isaaclab/sim/_impl/newton_manager.py	4/5	Newton physics backend manager. Static class managing physics simulation state, solver initialization, and physics stepping. Key integration point for Newton physics.
source/isaaclab/isaaclab/sim/utils/stage.py	4/5	Refactored stage utilities to use pure USD core APIs instead of omni APIs. Functions like add_reference_to_stage now support remote files and have fallback for non-Omniverse mode.
source/isaaclab/isaaclab/scene/interactive_scene.py	4/5	Updated to use new cloner API. Raises NotImplementedError for unsupported Newton features (deformable objects, rigid objects, surface grippers). Handles Newton-specific cloning path.

Sequence Diagram

sequenceDiagram
    participant User
    participant AppLauncher
    participant SettingsManager
    participant SimulationApp
    participant SimulationContext
    participant NewtonManager

    User->>AppLauncher: Initialize with args
    AppLauncher->>AppLauncher: _check_if_omniverse_required()
    
    alt Omniverse Required (cameras, livestream, or OV visualizer)
        AppLauncher->>SimulationApp: Create SimulationApp
        AppLauncher->>SettingsManager: initialize_carb_settings()
        SettingsManager->>SettingsManager: Use carb.settings
    else Standalone Mode (Newton/Rerun only)
        AppLauncher->>SettingsManager: _store_settings_standalone()
        SettingsManager->>SettingsManager: Use Python dict
    end
    
    User->>SimulationContext: Create SimulationContext
    SimulationContext->>SettingsManager: Get/Set settings
    SimulationContext->>NewtonManager: set_simulation_dt()
    SimulationContext->>NewtonManager: set_solver_settings()
    
    User->>SimulationContext: reset()
    SimulationContext->>NewtonManager: start_simulation()
    SimulationContext->>NewtonManager: initialize_solver()
    
    loop Simulation Loop
        User->>SimulationContext: step()
        SimulationContext->>NewtonManager: step()
    end

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[greptile-apps]

Additional Comments (2)

1. source/isaaclab/isaaclab/sim/utils/stage.py, line 206 (link)

   logic: SimulationContext.instance() can return None if no instance exists yet. This will cause an AttributeError when accessing .stage.

2. source/isaaclab/isaaclab/sim/simulation_context.py, line 312-316 (link)

   logic: newton_params used at line 362 but may be undefined if sim_params is None or doesn't contain "newton_cfg". Initialize with a default value.

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