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3.12.0

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@mmossg mmossg released this 20 Aug 11:11
3.12.0
13827e9

Version 3.12.0 (August 20, 2026)

General

  1. 3f8db4c1 The MJCF grammar is now defined in a single source of truth schema file, src/xml/mjcf.schema. The parser's grammar table, presence constraints, keyword maps, typed attribute bindings and save policies are generated from it and gated by tests, as are the schema's enum keywords and declared defaults against the C headers and default-constructors.

Warning

Breaking API changes
2. 6fe04aa8 Removed the custom binary texture format (image/vnd.mujoco.texture) and the automatic fallback to custom textures when loading files with unrecognized extensions. Textures can now only be loaded from PNG (image/png) and KTX (image/ktx) files.

Actuation

  1. 279df98c Added the pid actuator: a PID controller with real position and velocity setpoint inputs, optional integral action (ki, integrating the position error with imax anti-windup), setpoint rate limiting (slewmax), and an optional feedforward input. This subsumes the functionality of the mujoco.pid plugin with proper activation state: correct under all integrators and visible to keyframes and sensors. With a zero velocity setpoint it is identical to position. The input signature is any subset of [pos, vel, ff], selected by input; absent setpoint inputs are fixed at zero, so the control vector contains no inert entries.
  2. 2f1843f4 The dcmotor on-board controller is redesigned: the input attribute selects any subset of [pos, vel, ff, voltage], where pos and vel are setpoints for the controller, ff is a torque feedforward, and voltage is the raw terminal voltage (the default, a plain voltage-commanded motor). Controller gains are in torque space, as for pid, and the drive voltage compensates back-EMF as in a current-controlled driver: commanded torque is delivered exactly until a limit is reached. The keyword input="none" selects the empty signature: the actuator has no control inputs and is purely passive, so friction, cogging and back-EMF braking can be used as passive joint forces.

Warning

Breaking API changes
5. 2f1843f4 The mode-flag semantics of dcmotor/input ("voltage", "position", "velocity", selecting the interpretation of a single control) are replaced by input signatures, and the controller gains changed from voltage space to torque space. The old velocity mode's integral term (integrated-velocity tracking) is retired without replacement; the integrator always accumulates position error.

Migration: Voltage-commanded motors (the default) are unchanged. Replace input="position" with input="pos" and input="velocity" with input="vel", and multiply the controller gains by $K/R$ (torque per volt). The motor's back-EMF damping, previously felt in addition to the controller's damping, is now compensated: to preserve behavior when the velocity setpoint is zero, add $K^2/R$ to the converted kd.

Engine

  1. 83e621d7 Optimized large-mesh convex collision detection with up to 2x speedup in certain cases.
  2. 55d13aec Replaced the per-step sparse Cholesky factorization of the flex block of the implicit effective metric M + K with its prefactored per-vertex 3x3 diagonal blocks. The blocks precondition the CG constraint solver and drive an iterative solve for qacc_smooth, which now converges on tolerance rather than a fixed threshold. Flexes with elastic2d stretch stiffness step roughly twice as fast; bending-only flexes keep the exact constant factor and are unchanged.
  3. 86e98601 Rewrote cleaner box-box SAT collider.

Warning

Breaking API changes
9. 2a3554c8 Contacts of a flex with passive collisions are now integrated implicitly: their stiffness is carried by the effective metric rather than applied as an explicit spring, and can be far stiffer than the timestep would otherwise permit. Models using passive collisions should be re-checked: the feature now requires implicit or implicitfast with the CG solver, pyramidal cones and sleep disabled; passive handling covers flex-flex, self-, and static-geometry contact, while contact with a moving body stays on the constraint solver; and the stiffness is now a mass-scaled natural frequency rather than a fixed 1e4.
10. 55d13aec Removed mjData.efm_L_rownnz, mjData.efm_L_rowadr and mjData.efm_L_colind. They described the sparsity of the effective-metric Cholesky factor, which no longer exists; mjData.efm_L now holds dense 3x3 blocks, 9 numbers per covered vertex. mjData.efm_active no longer takes the value 2: nothing selects a solve path on preconditioner exactness, so it is now a plain 0/1 flag.
11. 1362a8bd Changed the default value of bvactive from "true" to "false". This avoids unnecessarily clearing bounding volume hierarchy visualization flags at every simulation step, which can be a bottleneck for models with large meshes.
12. ed13bf56 Mocap bodies and their dof-less descendants are now the root of their own weld group: mjModel.body_weldid of a mocap body equals its own id rather than 0. Consequences: dragging a mocap body into sleeping objects now wakes them; children of mocap bodies receive standard parent-child collision filtering; mocap bodies no longer count as static geometry for ray casting, and contact-matching sensors aggregate their contacts under the mocap body rather than the world; and geom pairs where neither body can move no longer generate contacts.

Models

  1. 2a3554c8 Added drape example model: three cloths draped over a sphere, demonstrating passive collisions. It replaces the sphere_passive model, which has been removed.
  2. 55d13aec Added bag example model: a cloth bag, held open by pinning the ring of vertices around its mouth, catching the standard humanoid dropped in from above. Unlike the poncho models, which are bending-only, this model exercises the 2D stretch elasticity of a flex.

Rendering

Warning

Breaking API changes

primitives_textured

  1. cc7fb98c Added explicit texture coordinates to built-in geometries (Plane, Box, Sphere, Ellipsoid, Capsule, Cylinder) in both the Classic renderer and Filament. 2D textures applied to primitive shapes will look different as textures are mapped using canonical UV parameterizations rather than projecting onto the $x,y$ plane.

    For finite planes, textures are now anchored to the bottom-left corner instead of the center. This will cause the most common visual breakage, as common procedural checker textures will be phase shifted. Infinite planes continue to be anchored at the origin with no visual changes.

    plane_uv_tiling

  2. f9a00bd5 Added light/softness: edge softness for spotlights under physically-based lighting models, given as the fraction of the cone over which intensity falls to zero. The default of 0.2 is a semi-soft cone which delivers the full intensity everywhere inside it, so that illuminance follows $E = I/d^2$ independent of the cutoff angle. Previously the filament renderer treated the entire cone as penumbra, dimming spotlights well below their rated intensity, increasingly so for narrow cutoffs.

    Migration: Set softness to 1 to reproduce the previous appearance of existing models.

MJX

Warning

Breaking API changes
17. 5e3464f4 mjx.render and mjx.render_with_segmentation now return the updated mjx.Data as the last element in their return tuple (i.e. (rgb, depth, d) and (rgb, depth, seg, d)). This ensures JAX/XLA strictly enforces causal scheduling between sequential refit_bvh and render calls.

**Migration:** Update unpacking calls from `pixels, depth = mjx.render(mx, d, rc)` to `pixels, depth, d = mjx.render(mx, d, rc)`.

Bug fixes

  1. 95539261 Fixed a bug where models with pinned interpolated flex nodes (e.g. a flexcomp with dof "trilinear" and pinned vertices) could not be reloaded after saving: node coordinates within their body frames were not saved, degenerating the interpolation grid. They are now saved in the new flex nodecoord attribute.
  2. 8655446f Fixed a bug in the box-box collider where near-degenerate face clipping could generate contacts with spuriously large penetration depth between nearly touching thin boxes with positive margin, causing resting stacks to explode.
  3. fb07a9ca Fixed a bug in the box-box collider where penetrations deeper than a box's smallest half-size could produce no contacts, letting boxes tunnel through thin boxes. Fixes #1800.
  4. 54979947 Fixed the flex stretch stiffness operator, which was the Gauss-Newton Hessian of the stretch force rather than its Jacobian: the geometric (stress-proportional) term was missing. Only the tensile part of that term is added, since it is positive semi-definite exactly when the edge is in tension, and its consumers require an SPD operator; the stretch force itself is unchanged. This affects the implicit integrators and the implicit effective metric, so flexes using elastic2d="stretch" integrate slightly differently. Bending-only flexes are unaffected.

OpenUSD

  1. 39e44588 Upgraded Newton USD schemas support to version 0.4.0:
    • NewtonJointAPI (newton:armature, newton:damping, newton:friction) deprecates the MjcJointAPI equivalent mjc:armature, mjc:damping, and mjc:frictionloss attributes.
    • NewtonMassAPI (newton:massModel, newton:inertia) deprecates the MjcCollisionAPI equivalent mjc:shellinertia and MjcMeshCollisionAPI mjc:inertia attributes. This completes the deprecation of all MjcMeshCollisionAPI attributes, slating it for removal in a future release.
    • Added support for NewtonSiteAPI to declare sites, MjcSiteAPI auto applies this schema, but remains as an extension for the mjc:group attribute.
    • Added support for NewtonMaterialAPI (newton:contactAdhesion, newton:torsionalFriction, newton:rollingFriction). This deprecates MjcMaterialAPI which will be removed in a future release.
    • Added support for NewtonMimicAPI (newton:mimicJoint, newton:mimicCoef0, newton:mimicCoef1) as a base for MjcEqualityJointAPI, this deprecates the mjc:coef0 and mjc:coef1 attributes and the mjc:target relationship.
    • Added support for NewtonArticulationRootAPI (newton:jointsAddMobility).

Caution

Breaking ABI changes
23. 279df98c mjsActuator gained velrange and ffrange fields, changing its size and layout. The mjtGain and mjtDyn enums gained pid members, shifting the values of mjGAIN_USER and mjDYN_USER.
24. 596b6f43 mjResource gained an args field (changing its size and layout), used to hold optional extra encoding and decoding arguments formatted as URI query parameters (separated by &).

Assets 10
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