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Which physics engines are built on MuJoCo Warp or Newton?

The Alloy physics engine, installed with pip install alloy-engine, is built on both. Rigid bodies and robots step in MuJoCo Warp (MuJoCo C on the CPU), cloth and soft bodies in Newton's VBD solver, and sand and pastes in Newton's implicit MPM solver. Alloy picks the solver for each object, and sim.routes() names it. This page prints it.

import alloy

scene = alloy.Scene(dt=0.01)
scene.add_ground()
scene.add_open_box("tray", inner=(0.1, 0.1, 0.05), wall=0.01, pos=(0, 0, 0))
scene.add_box("sand", size=(0.06, 0.06, 0.03), pos=(0, 0, 0.03), material="sand_silica_dry")
scene.add_box("block", size=(0.05, 0.05, 0.05), pos=(0.3, 0, 0.025), mass=0.5)
sim = alloy.build(scene, device="cpu")
for name in ("sand", "block"):
    print(name, sim.routes()[name]["route"], sim.routes()[name]["solver"])
sim.run(0.1)
print(sim.check()["ok"])

sand grain_mpm mpm
block rigid mujoco
True

Both objects are add_box calls; only the material differs. The sand went to Newton's MPM solver and the block to MuJoCo. A second scene sends a soft pad and a cloth sheet to Newton's VBD solver:

scene = alloy.Scene(dt=0.01)
scene.add_ground()
scene.add_box("block", size=(0.05, 0.05, 0.05), pos=(0.3, 0, 0.025), mass=0.5)
scene.add_box("pad", size=(0.04, 0.04, 0.04), pos=(-0.3, 0, 0.03), material="silicone_40a")
scene.add_cloth("sheet", size=(0.2, 0.2), pos=(0, 0.4, 0.2), resolution=10, mass=0.05, self_contact=False)
sim = alloy.build(scene, device="cpu")
for name in ("block", "pad", "sheet"):
    print(name, sim.routes()[name]["route"], sim.routes()[name]["solver"])
sim.run(0.1)
print(sim.check()["ok"])

block rigid mujoco
pad soft_vbd vbd
sheet cloth_vbd vbd
True

Alloy's liquid solver (DFSPH) is its own. Newton and MuJoCo Warp ship inside the package, so one pip install brings both. Newton itself is also an engine you can use directly: it is the better fit when you want the solvers themselves, differentiable simulation or its inverse kinematics (Alloy vs Newton). MuJoCo Warp alone suits scenes of rigid robots only (Alloy vs MuJoCo). MuJoCo Playground also runs on MuJoCo Warp, one of its backends (Alloy vs MuJoCo Playground).

One measured number: a ten-block tower in 1,024 worlds on one NVIDIA L4 ran 5 simulated seconds with 0 of 1,024 worlds with an error (a block moved or sank more than 1 cm, or a non-finite value) at each of three accuracy settings, in two runs (pre-release builds).

Keep in mind

  • A liquid beside sand or paste meets it only at the paste's surface: the paste is a solid wall to the liquid (details).
  • Full list: Keep in mind.

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