pyforge3d 2.2.0

Pure-Python 3D physics game engine — own dynamics, own rules, no compromises.

forge3d

Pure-Python 3D physics game engine — own dynamics, own rules, no compromises.

forge3d is a batteries-included 3D physics and game engine written entirely in Python — no external physics engines (no MuJoCo, PyBullet, or Bullet). Dynamics, collision, and contact are all solved by forge3d's own code, backed by NumPy and optional JAX acceleration.

┌──────────────────────────────────────────────────────────────┐
│                     Public API (Facade)                       │
│  App · World · Body · Shape · Material · Viewer · Recorder    │
│         Input · Key · OrbitCamera · FollowCamera              │
└──────────────┬──────────────────────────┬────────────────────┘
     ┌──────────▼──────────┐   ┌──────────▼───────────────────┐
     │  Physics core        │   │   Rendering layer             │
     │  RNEA · CRBA · ABA   │   │   RealtimeRenderer (OpenGL)  │
     │  SAT · GJK/EPA       │   │   HQRenderer (ray-tracer)    │
     │  Impulse contact     │   │   SceneSnapshot contract      │
     └─────────────────────┘   └──────────────────────────────┘

---

Features

Category	Details
Game loop	App class — @on_start / @on_update / @on_render decorators
Input	Input snapshot — key_held, key_pressed, mouse_pos, scroll_delta
Camera	OrbitCamera, FollowCamera — orbit, zoom, pan, smooth follow
Physics	Rigid-body dynamics (RNEA / CRBA / ABA), semi-implicit Euler integrator
Collision	SAT OBB-OBB (15-axis), sphere, capsule, GJK/EPA convex-mesh; AABB broad-phase
Contact	Impulse solver, Coulomb friction, Baumgarte correction, warm-starting
Grasping	weld / release kinematic constraints; friction-based pinch grasp
Robots	UR5 6-DOF FK/IK, DH parameters, Jacobian
Rendering	Real-time PBR (Cook-Torrance, PCF shadows, albedo/normal textures); HQ software ray-tracer
RL	Gymnasium-compatible ReachEnv / PickPlaceEnv
Performance	JAX JIT+vmap: 2 000× throughput vs. NumPy; AABB broad-phase O(n log n)
Testing	215+ automated tests; PyBullet baseline comparison
Typed	Fully annotated with py.typed marker

---

Installation

# Core library (physics + rendering)
pip install pyforge3d

# With rendering dependencies
pip install "pyforge3d[render]"

# With RL dependencies
pip install "pyforge3d[rl]"

# Everything
pip install "pyforge3d[all]"

# Development install
git clone https://github.com/iruki-dev/forge3d
cd forge3d
pip install -e ".[dev]"

Install name vs import name: pip install pyforge3d — then import forge3d in your code.

Requirements: Python 3.12+, NumPy, SciPy, JAX (CPU wheel)

---

Quick start (15 lines)

import forge3d as f3d

world = f3d.World(gravity=(0, 0, -9.81))
world.add_ground()
box = world.add_box(size=(1, 1, 1), position=(0, 0, 5), mass=1.0)

viewer = f3d.Viewer(world, max_frames=90)
while viewer.is_open:
    world.step(dt=1 / 60)
    viewer.draw()

print(f"Box landed at z = {box.position[2]:.3f} m")

---

App-style game loop

The App class wraps the game loop into a decorator-driven flow — just like popular game frameworks, but with full 3D physics built in.

import forge3d as f3d

app = f3d.App("Physics Sandbox", width=1280, height=720, fps=60)
ball = None  # filled in on_start

@app.on_start
def setup(world: f3d.World) -> None:
    global ball
    world.add_ground()
    ball = world.add_sphere(radius=0.4, position=(0, 0, 6),
                             material=f3d.Material(color="orange"))

@app.on_update
def update(world: f3d.World, dt: float, inp: f3d.Input) -> None:
    # Jump on space
    if inp.key_pressed(f3d.Key.SPACE):
        world.apply_impulse(ball, (0, 0, 8))
    # Nudge with arrow keys
    if inp.key_held(f3d.Key.RIGHT):
        world.apply_impulse(ball, (3 * dt, 0, 0))
    if inp.key_held(f3d.Key.LEFT):
        world.apply_impulse(ball, (-3 * dt, 0, 0))

app.run()

---

Recording a high-quality video

import forge3d as f3d

world = f3d.World(gravity=(0, 0, -9.81))
world.add_ground(material=f3d.Material(color="ground", roughness=0.8))
world.add_sphere(radius=0.4, position=(0, 0, 4.4), mass=1.0,
                  restitution=0.8, material=f3d.Material(color="orange"))
world.set_camera(position=(4, -7, 3), target=(0, 0, 1))

rec = f3d.Recorder(world, mode="hq", resolution=(1920, 1080),
                   samples=16, output="bounce.mp4")
rec.run(duration=3.0, dt=1 / 240, fps=60)

The same World code — only the renderer changes. That is the SceneSnapshot contract working.

---

Camera controls

import forge3d as f3d

world = f3d.World()
world.add_ground()
ball = world.add_sphere(radius=0.5, position=(0, 0, 3))

# Orbit camera starts 10 m back, 30° elevation
cam = f3d.OrbitCamera(target=(0, 0, 1), distance=10, elevation=30)

viewer = f3d.Viewer(world, max_frames=300)
while viewer.is_open:
    inp = viewer.input          # per-frame Input snapshot
    cam.rotate(d_azimuth=inp.scroll_delta() * 5)
    if inp.mouse_button(1):     # right-drag to orbit
        dx, dy = inp.mouse_delta()
        cam.rotate(d_azimuth=dx * 0.5, d_elevation=-dy * 0.5)
    viewer.set_camera(cam.to_snapshot())
    world.step()
    viewer.draw()

---

Robot arm control

import numpy as np
import forge3d as f3d
import forge3d.robot as f3r

world = f3d.World()
world.add_ground()

arm = f3r.load("ur5", base_position=(0, 0, 0))
world.add(arm)

arm.set_joints([0.0, -np.pi/2, np.pi/2, -np.pi/2, -np.pi/2, 0.0])
world.step()

ee_pos, ee_rot = arm.ee_pose()
print(f"End-effector: {ee_pos.round(4)}")

---

Reinforcement learning

from apps.robot_rl.envs.reach_env import ReachEnv
from stable_baselines3 import PPO

env  = ReachEnv(render_mode=None)          # headless, fast
model = PPO("MlpPolicy", env, verbose=1)
model.learn(total_timesteps=200_000)
model.save("reach_policy")

JAX batch stepping — 2 000× throughput:

import jax, jax.numpy as jnp
from forge3d.sim.jax_batch import batch_reach_reset, batch_reach_step

key = jax.random.PRNGKey(42)
q, tgt, obs = batch_reach_reset(key, n_envs=256)
q, obs, rew, done = batch_reach_step(q, tgt, jnp.zeros((256, 6)))

---

API reference

forge3d.App

Member	Description
App(title, width, height, fps, gravity)	Create application
@app.on_start	fn(world) — called once before the loop
@app.on_update	fn(world, dt, inp) — called every frame before step()
@app.on_render	fn(world, viewer) — called after draw()
app.world	The managed World
app.run(max_frames)	Start the game loop

forge3d.World

Member	Description
World(gravity)	Create world; default gravity (0, 0, -9.81)
add_ground(material, size, height)	Static ground plane
add_box(size, position, mass, …)	Dynamic box body
add_sphere(radius, position, mass, …)	Dynamic sphere body
add_capsule(radius, half_length, …)	Dynamic capsule body
add_mesh(mesh_data, …)	Dynamic convex-hull body
remove(body)	Remove a body from simulation
clear(keep_statics)	Remove all (or all dynamic) bodies
get_body(name)	Find body by name
bodies	list[Body] — all current bodies
step(dt)	Advance physics by dt s (default 1/60)
snapshot()	Build SceneSnapshot for rendering
apply_impulse(body, impulse)	Δv = impulse / mass
teleport(body, position, quat)	Instantly move a body
weld(body, anchor, local_offset)	Kinematic attachment
release(body)	Remove weld constraint
set_camera(position, target, …)	Default camera pose
time	Elapsed simulation time in seconds

forge3d.Body

Member	Description
position	(3,) world-frame position
velocity	(3,) linear velocity m/s
orientation	(4,) quaternion [w, x, y, z]
angular_velocity	(3,) angular velocity rad/s
name	String label
is_static	bool
mass	float, kg
apply_force(force)	Accumulate force for next step()
apply_torque(torque)	Accumulate torque for next step()
set_position(pos)	Teleport shortcut
set_velocity(vel)	Velocity override

forge3d.Input

Member	Description
key_held(key)	bool — key currently pressed
key_pressed(key)	bool — key just went down this frame
key_released(key)	bool — key just went up this frame
mouse_pos()	(x, y) pixels
mouse_delta()	(dx, dy) pixels since last frame
mouse_button(n)	bool — mouse button 0/1/2
scroll_delta()	float — mouse wheel tick this frame

forge3d.Key — key name constants

f3d.Key.SPACE, Key.ESCAPE, Key.ENTER, Key.BACKSPACE, Key.TAB
Key.UP, Key.DOWN, Key.LEFT, Key.RIGHT
Key.W, Key.A, Key.S, Key.D   # also Key.Q … Key.Z
Key.N0 … Key.N9
Key.F1 … Key.F12
Key.SHIFT, Key.CTRL, Key.ALT

forge3d.OrbitCamera

Member	Description
OrbitCamera(target, distance, azimuth, elevation, fov_deg)	Create camera
rotate(d_azimuth, d_elevation)	Orbit around target
zoom(delta)	Multiply distance; delta > 0 → zoom in
pan(dx, dy)	Translate target in screen space
position	Current world-space eye position
to_snapshot()	CameraSnapshot for viewer.set_camera()

forge3d.Shape

Shape.box(size=(1, 1, 1))
Shape.sphere(radius=0.5)
Shape.capsule(radius=0.2, half_length=0.5)
Shape.convex_mesh(mesh_data)          # from forge3d.io.load_obj()

forge3d.Material

Material(color="red")                 # built-in preset
Material(color=(0.9, 0.4, 0.1))       # RGB tuple in [0, 1]
Material(color="default", roughness=0.3, metallic=0.7)
Material(texture_path="wall.png")

Built-in colour presets: "default", "red", "blue", "green", "orange", "ground", "gold", "white".

forge3d.Viewer

viewer = f3d.Viewer(world, width=1280, height=720, max_frames=None)
viewer.is_open          # False when window closed or max_frames reached
viewer.draw()           # render one frame → ndarray (H×W×3 uint8)
viewer.input            # current-frame Input snapshot
viewer.set_camera(cam)  # override camera (CameraSnapshot or OrbitCamera)
viewer.run(dt, max_frames, collect_frames)
viewer.close()

forge3d.Recorder

rec = f3d.Recorder(world, mode="realtime",        # or "hq"
                   resolution=(1920, 1080),
                   samples=64,                     # HQ only
                   output="sim.mp4")
rec.run(duration=5.0, dt=1/240, fps=60)
rec.run_policy(policy, env, duration=5.0)          # SB3-compatible

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Architecture

forge3d is designed around one principle: physics and rendering never know about each other.

world.step()                     # pure physics, no renderer import
snap = world.snapshot()          # SceneSnapshot — pure data
frame = renderer.render(snap)    # renderer consumes data only

The SceneSnapshot is the sole bridge. Swap the renderer without touching the physics.

Physics core        → SceneSnapshot →  RealtimeRenderer (OpenGL)
(RNEA/CRBA/ABA)                    →  HQRenderer       (ray-tracer)
                                   →  headless / training (no snapshot)

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Project structure

forge3d/
├── src/forge3d/
│   ├── __init__.py          # Public API: World, App, Body, Shape, Material…
│   ├── app.py               # App — game-loop abstraction
│   ├── input.py             # Input, Key, _InputBuilder
│   ├── camera.py            # OrbitCamera, FollowCamera
│   ├── facade.py            # World, Body, Shape, Material facades
│   ├── viewer.py            # Viewer (realtime render loop)
│   ├── recorder.py          # Recorder (video capture)
│   ├── backend.py           # NumPy ↔ JAX backend switch
│   ├── math/                # SE3, quaternion, spatial algebra
│   ├── dynamics/            # RNEA, CRBA, ABA
│   ├── collision/
│   │   ├── detection.py     # SAT + AABB broad-phase
│   │   ├── gjk.py           # GJK distance / intersection
│   │   └── epa.py           # EPA penetration depth
│   ├── contact/
│   │   └── solver.py        # Impulse solver (PGS + Coulomb friction)
│   ├── model/               # RigidBodyModel, DH joints, kinematics
│   ├── sim/
│   │   ├── world.py         # PhysicsWorld (step, snapshot, CRUD)
│   │   ├── jax_batch.py     # JAX JIT+vmap batch physics
│   │   └── domain_rand.py   # Domain randomisation
│   ├── robot/               # Robot, UR5 preset, FK/IK
│   ├── render/
│   │   ├── snapshot.py      # SceneSnapshot, Transform, Material…
│   │   ├── base.py          # Renderer ABC
│   │   ├── realtime/        # OpenGL rasteriser (PBR, PCF shadow)
│   │   └── hq/              # Software ray-tracer (Blinn-Phong, AO, AA)
│   ├── io/
│   │   ├── obj_loader.py    # Pure-Python OBJ parser
│   │   └── mesh_data.py     # MeshData, convex_hull_inertia
│   └── py.typed             # PEP 561 type marker
├── apps/robot_rl/            # RL application (Gymnasium envs, training)
├── examples/                 # Self-contained examples (≤15 lines each)
├── tests/                    # 215+ automated tests
├── validation/               # PyBullet / MuJoCo baseline comparison
├── assets/                   # 3D models, textures
├── CHANGELOG.md
├── CONTRIBUTING.md
├── LICENSE
└── pyproject.toml

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Validation

Check	Result
PyBullet acceleration comparison (50 pairs)	max_abs < 2e-11 ✅
Energy conservation (torque-free, no damping)	deviation < 0.1 % ✅
Pendulum period vs. closed-form	error < 0.01 % ✅
JAX ↔ NumPy FK consistency	max_diff < 1e-16 ✅
Restitution coefficient vs. theory	error < 1.5 % ✅
Coulomb friction threshold	✅

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Backend switching

ENGINE_BACKEND=numpy python my_sim.py   # NumPy (default, CPU)
ENGINE_BACKEND=jax   python my_sim.py   # JAX JIT+vmap

The physics core is identical under both backends. JAX enables JIT compilation and vmap for batched multi-environment rollouts.

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Testing

# Single file (recommended for iteration)
pytest tests/test_collision.py -q

# Full suite (skips slow training tests)
pytest tests/ --ignore=tests/test_p9_training.py -q

# With coverage
pytest --cov=forge3d tests/ -q

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Contributing

See CONTRIBUTING.md. In short:

1. Fork → feature branch → PR
2. ruff check . && ruff format . must pass
3. mypy src/ must pass
4. New physics code needs a conservation-law or analytical-solution test
5. New public API needs an example in examples/

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License

MIT — see LICENSE.