Culverin Physics

Culverin is a middleware bridge between the Jolt Physics engine and the Python Virtual Machine. It is designed for 3D games and simulations that require high performance and multi-threaded execution, for the Python game engine developers.

Key Concepts

• Free-Threading Support: Designed for Python 3.13t and 3.14t. The engine releases the Global Interpreter Lock (GIL) during physics updates and raycast batches.
• Shadow Buffers: All body positions, rotations, and velocities are stored in contiguous C-arrays. You can access this data via memoryview, NumPy or any dependency that supports the buffer protocol without the overhead of creating Python objects for every body.
• Thread-Safe API: The engine uses a priority-based locking system. Simulation steps, state mutations, and queries can run on different threads without causing deadlocks or memory corruption.
• Generational Handles: Bodies are referenced by 64-bit handles rather than pointers. This ensures that using a handle for a deleted object will not crash the program.
• Double-Precision Positions: Uses double-precision floats (float64) for world positions to prevent physics jitter in massive open worlds, while using float32 for rotations and velocities to save memory and computing resources.

Features

• Standard Primitives: Box, Sphere, Capsule, Cylinder, and Plane shapes.
• Complex Shapes: Support for Convex Hulls, Heightfields (Terrain), and static Meshes.
• Compound Bodies: Create single bodies composed of multiple child shapes.
• Character Controller: A virtual character controller with built-in support for climbing stairs, sliding down slopes, and pushing objects.
• Vehicles: Support for wheeled vehicles and tracked vehicles (tanks) with physical treads and skid-steering.
• Ragdolls & Skeletons: Multi-body articulated physics with active motorized poses.
• Allowed Degrees of Freedom: Restrict rigid bodies to specific world-space translation and rotation axes, including 2D-style motion.
• Constraints: Fixed, Point, Hinge, Slider, Distance, Swing-Twist, and Cone constraints.
• Queries: Efficient single and batch Raycasting, Shapecasting (sweeps), and Overlap queries.
• Collision Events: Native event buffer for contact added, persisted, and removed events.
• Soft Bodies: Support for soft bodies from Jolt Physics, with fine-grained configurations.

Installation

pip install culverin

📚 Documentation

Detailed API references for every class and method are available:

• Online Docs: View the Interactive API Reference
• In-Engine: Use the standard Python help() system: help(culverin.PhysicsWorld.create_body) or help(culverin)

Quick Start

import numpy as np

import culverin

# Initialize the world with a capacity limit
world = culverin.PhysicsWorld(settings={"max_bodies": 1000})

# Create a static ground plane
# a plane normal of default (0.577, 0.577, 0.577) represents an infinite 45-degree tilted ramp.
world.create_body(pos=(0, 0, 0), shape=culverin.SHAPE_PLANE, motion=culverin.MOTION_STATIC)

# Create a dynamic box
handle = world.create_body(
    pos=(0, 10, 0), size=(1, 1, 1), shape=culverin.SHAPE_BOX, motion=culverin.MOTION_DYNAMIC
)

# Simulation loop
for _ in range(1000):
    world.step(1 / 60)

    # Zero-Copy Data Access
    # Wrap the internal engine memory in NumPy without copying a single byte.
    # This gives you O(1) access to all 1,000+ bodies at once.
    positions = np.frombuffer(world.positions, dtype=np.float64).reshape(-1, 4)

    # Print the Y position of our box
    idx = world.get_index(handle)
    print(f"Box Height: {positions[idx, 1]:.2f}m")

Technical Specifications

Spec	Standard
Units	Metric (1.0 = 1 meter)
Coordinate System	Right-Handed (Y-Up)
Angle Units	Radians
Quaternion Format	(x, y, z, w)
Position Buffer	Float64 (Stride 4: x, y, z, pad)
Rotation/Velocity Buffers	Float32 (Stride 4: x, y, z, w/pad)
Minimum Python	3.12 (3.13t+ recommended for multi-threading)

Performance & Rendering Note

For maximum performance when updating a renderer (like OpenGL or Vulkan), do not loop through individual handles in Python. Instead, use the interpolating export method:

# Returns a single, tightly packed bytes object of Float32s 
# formatted as [px, py, pz, rx, ry, rz, rw] for every active body.
# The 'alpha' parameter (0.0 to 1.0) interpolates between the previous 
# and current physics steps for buttery-smooth rendering.
render_data = world.get_render_state(alpha=0.5)

To read data for gameplay logic, use numpy.frombuffer(world.positions, dtype=np.float64) and numpy.frombuffer(world.rotations, dtype=np.float32) to wrap the internal engine memory without making copies.