Navora

Headless physics simulation system with USD-first, viewer-agnostic architecture. Generates time-sampled USD files for visualization in Blender and Omniverse-compatible tools.

Architecture

Navora follows a headless simulation → USD authoring → external viewer pipeline:

┌─────────────────┐
│  Python Sim     │
│  (Headless)     │
│  - Physics      │
│  - Time steps   │
└────────┬────────┘
         │
         │ Writes time-sampled USD
         │
    ┌────┴────┐
    │         │
    ▼         ▼
┌────────┐ ┌──────────┐
│ Blender│ │Omniverse │
│ Viewer │ │  Tools   │
└────────┘ └──────────┘

Core Principles

1. Simulation is headless: No rendering, no GPU dependencies
2. USD is authoritative: All scene data written to USD files
3. Viewer-agnostic: Blender, Omniverse, or any USD-capable tool can open outputs
4. Time-sampled: Transforms are keyframed for timeline scrubbing

Why Decouple Rendering?

• Hardware independence: Works on AMD GPUs, no CUDA/RTX required
• Flexibility: Use any USD viewer (Blender, Omniverse, Houdini, etc.)
• Reproducibility: USD files are deterministic and portable
• Performance: Simulation runs independently of visualization

Blender as Viewer

Blender serves as a viewer only:

• Import USD files (File → Import → Universal Scene Description)
• Inspect geometry and hierarchy
• Scrub timeline to view animation
• No rendering logic in simulation
• Rendering intentionally decoupled
• Not used as an editor - simulation is authoritative

Omniverse Compatibility

Outputs remain Omniverse-compatible:

• Standard USD schemas (UsdGeom, UsdPhysics)
• Z-up coordinate system (USD and Blender standard)
• Time-sampled transforms
• Proper stage metadata

Quick Start

Installation

pip install -r requirements.txt
pip install usd-core

Run Example

python examples/moving_cube.py

Generates output/moving_cube.usda - a 5-second animation of a cube falling under gravity.

View in Blender

1. Install Blender 4.0 or later
2. Open Blender
3. File → Import → Universal Scene Description (.usd/.usda)
4. Select output/moving_cube.usda
5. Press Home to frame the scene
6. Scrub timeline to view animation

Expected Result:

• Horizontal gray plane (ground)
• Blue sphere floating above the plane
• Sphere falls when scrubbing timeline
• No manual rotation or repositioning required

Note: The USD world is pre-rotated +90° around X for Blender compatibility. Blender is used strictly as a viewer - import preserves hierarchy and animation for timeline scrubbing.

Debug UI

cd frontend/debug_ui
python app.py

Open http://localhost:5000 for browser-based controls:

• Start/stop simulation
• Spawn entities
• Inspect scene metadata
• Export USD files

Project Structure

navora/
├── sim/              # Simulation engine
│   ├── engine.py     # Main simulation loop
│   ├── physics.py    # Physics rules (gravity, collisions)
│   └── entities.py   # Scene objects and state
├── usd/              # USD authoring
│   ├── stage.py      # Stage setup (Z-up, units)
│   ├── writer.py     # Time-sampled USD writing
│   └── schemas.py    # UsdGeom/UsdPhysics helpers
├── frontend/
│   └── debug_ui/     # Browser controls (no rendering)
├── examples/
│   └── moving_cube.py  # Minimal demo
└── requirements.txt

USD Requirements

• Z-up coordinate system: Standard for USD and Blender
• metersPerUnit = 1.0: Standard unit scale
• Time-sampled transforms: Enables timeline scrubbing
• Standard schemas: UsdGeom, UsdPhysics for compatibility

Installing OpenUSD

Install via pip:

pip install usd-core

No source build required. Blender's bundled USD can be used as fallback, but pip installation is recommended.

Viewing in Blender

Workflow

1. Generate USD file: python examples/moving_cube.py
2. Open Blender 4.0+
3. File → Import → Universal Scene Description (.usd/.usda) → select .usda file
4. Press Home to frame the scene
5. Scrub timeline to view animation

What Success Looks Like

• Objects visible in viewport (floor plane, falling cube)
• Animation plays when scrubbing timeline
• Outliner shows /World hierarchy with entities
• Timeline shows correct frame range (0-300 for 5s at 60fps)

Important Notes

• Use File → Import → Universal Scene Description to import USD files
• Import preserves hierarchy and animation for timeline scrubbing
• The USD world is pre-rotated +90° around X for Blender compatibility
• Blender is viewer only - simulation runs independently
• No manual rotation or repositioning required

Development

Creating a Simulation

from sim.engine import SimulationEngine
from sim.entities import Entity, Vector3
from usd.writer import USDWriter

engine = SimulationEngine()

# Create entities
floor = engine.create_entity("floor")
floor.body.is_static = True
floor.shape_type = "plane"

cube = engine.create_entity("cube")
cube.transform.position = Vector3(0, 0, 10)

# Run simulation
engine.start()
for frame in range(300):
    engine.tick()

# Write USD
writer = USDWriter("output.usda")
for frame in range(300):
    time = frame / 60.0
    writer.write_frame(engine.get_all_entities(), time)
writer.save()

Non-Goals

This project explicitly does NOT include:

• Isaac Sim integration
• Omniverse RTX rendering
• CUDA acceleration
• Browser-based rendering
• Building OpenUSD from source (use pip install usd-core)

Dependencies

• usd-core: OpenUSD Python API (install via pip)
• flask: Debug UI server
• flask-cors: CORS support

License

[Your License Here]