Quick start

A stack of three boxes. Steel steps State.joint_q and State.joint_qd; add_body gives each box a free joint.

import warp as wp
import newton

builder = newton.ModelBuilder()
builder.add_ground_plane()
for i in range(3):
    body = builder.add_body(xform=wp.transform((0.0, 0.0, 0.11 + 0.21 * i), wp.quat_identity()))
    builder.add_shape_box(body, hx=0.1, hy=0.1, hz=0.1)
model = builder.finalize()

solver = newton.solvers.SolverSteel(model, iterations=12, row_watermark=True)
pipeline = newton.CollisionPipeline(model)
contacts = pipeline.contacts()

state_0, state_1 = model.state(), model.state()
control = model.control()
dt = 1.0 / 240.0

for _ in range(480):
    state_0.clear_forces()
    pipeline.collide(state_0, contacts)
    solver.step(state_0, state_1, control, contacts, dt)
    state_0, state_1 = state_1, state_0

solver.check_constraint_capacity()      # raises if any row or contact was dropped
print(state_0.body_q.numpy()[:, 2])     # about [0.1, 0.3, 0.5]
print(solver.constraint_row_watermarks())

Tutorials Hello Steel · Shape types · Joint types

Many worlds and a CUDA graph

Replicate the scene into worlds, capture one frame of substeps, and replay it. Capture once, after construction; the solver’s buffers have fixed sizes.

scene = newton.ModelBuilder()
scene.add_ground_plane()
# ... add the bodies of one world to scene ...

builder = newton.ModelBuilder()
builder.replicate(scene, 1024)
model = builder.finalize()

solver = newton.solvers.SolverSteel(model)
pipeline = newton.CollisionPipeline(model)
contacts = pipeline.contacts()
state_0, state_1 = model.state(), model.state()
control = model.control()
fps, substeps = 60, 4
dt = 1.0 / (fps * substeps)

def simulate():
    global state_0, state_1
    for _ in range(substeps):      # even, so the captured swaps return to state_0
        state_0.clear_forces()
        pipeline.collide(state_0, contacts)
        solver.step(state_0, state_1, control, contacts, dt)
        state_0, state_1 = state_1, state_0

with wp.ScopedCapture() as capture:
    simulate()

for frame in range(600):
    wp.capture_launch(capture.graph)

solver.check_constraint_capacity()  # outside capture

Bundled examples run with python -m newton.examples <name>: steel_sleeping and steel_determinism_arms are in Newton 1.8; the integration branch adds steel_magnetic_door, steel_wrecking_ball, steel_plate_rack and steel_bolt_sweep.

Examples

The examples page has more scenes, each with a preset for Steel and for the other solvers that run it. From a clone of skild-ai/steel, run one with:

cd examples
uv sync
uv run shelf play jenga                  # its default preset
uv run shelf play jenga --solver steel   # a named preset
uv run shelf play                        # browse them all