Language

unisim.backend.isaacgym.backend.IsaacGymBackend¶

class unisim.backend.isaacgym.backend.IsaacGymBackend[source]¶

Bases: MjcfSubprocessBackend

NumPy-facing SimBackend client for the IsaacGym worker.

Parameters:

scene (SceneCfg)
num_envs (int)
sim_dt (float)
base_name (str | None)
device_id (int | None)
worker_timeout_s (float | None)
worker_command (list[str] | None)
unexpected_kwargs (Any)

Methods

`__init__`(scene, num_envs, sim_dt, *[, ...])
`apply_body_force`(body_ids, force[, torque])	Apply a world-frame force (and optional torque) to bodies for the upcoming step.
`apply_init_randomization`(plan)	Apply cold-path model/materialization randomization.
`apply_interval_randomization`(plan)	Apply a scheduled interval randomization plan.
`bind_mocap_pose`(body_name)	Resolve a mocap body once; unavailable capabilities fail at binding.
`bind_sensor_data`(names)	Materialize a validated view over named sensors on the cold path.
`capture_video_frame`()	Capture one RGB frame from the worker's camera sensor.
`cleanup_scene_assets`()	Release all backend-owned resources, including the worker process.
`close`()	Shut down the worker and release shared memory.
`copy_body_state_w`(body_ids, out_pos, ...)	Copy selected world-frame body state into caller-owned buffers.
`create_hfield_scanner`(*, hfield_geom_id, ...)	Create a reusable height-field scanner on the init/cold path.
`get_actuator_ctrl_range`()	Position-target clamp per dof, from the MJCF `ctrlrange` attributes.
`get_actuator_gains`()	Per-dof (kp, kd) from the MJCF `<position>` actuators (pure XML).
`get_actuator_joint_names`()	The shared position-control profile drives one actuator per DoF.
`get_actuator_names`()	Return actuator names in control-vector order on the cold path.
`get_base_ang_vel`()	Return base angular velocity in the world frame.
`get_base_lin_vel`()	Return base linear velocity in the world frame.
`get_base_pos`()	Return base position in the world frame.
`get_base_quat`()	Return base quaternion in the world frame as `wxyz`.
`get_body_ang_vel_b`(body_ids)	Return selected body angular velocities expressed in each body's own frame.
`get_body_ang_vel_w`(body_ids)	Return selected body angular velocities in the world frame.
`get_body_ang_vel_w_rows`(env_ids, body_ids)	Get selected env rows of world-frame body angular velocity.
`get_body_id`(name)	Resolve one body/link name through the backend contract.
`get_body_ids`(names)	Resolve body/link names to backend integer IDs.
`get_body_ipos`()	Return the backend body inertial-position table.
`get_body_lin_vel_b`(body_ids)	Return selected body linear velocities expressed in each body's own frame.
`get_body_lin_vel_w`(body_ids)	Return selected body linear velocities in the world frame.
`get_body_lin_vel_w_rows`(env_ids, body_ids)	Get selected env rows of world-frame body linear velocity.
`get_body_mass`()	Return the backend body-mass table.
`get_body_pos_b`(body_ids)	Return selected body positions in the baselink frame.
`get_body_pos_w`(body_ids)	Return selected body positions in the world frame.
`get_body_pose_w`(body_ids)	Return selected body positions and quaternions in the world frame.
`get_body_pose_w_rows`(env_ids, body_ids)	Get selected env rows of world-frame body position and quaternion.
`get_body_quat_b`(body_ids)	Return selected body quaternions in the baselink frame as `wxyz`.
`get_body_quat_w`(body_ids)	Return selected body quaternions in the world frame as `wxyz`.
`get_body_state_w`(body_ids)	Get selected body position, quaternion, linear velocity, and angular velocity.
`get_body_subtree_ids`(root_body_id)	Return body ids in the subtree rooted at `root_body_id`.
`get_body_vel_w`(body_ids)	Return selected body linear and angular velocities in the world frame.
`get_default_dof_pos`()	Return default joint positions in the same column order as `get_dof_pos`.
`get_default_qpos`()	Return the backend/model default qpos through a stable contract.
`get_dof_armature`()	Return the backend dof-armature table.
`get_dof_damping`()	Return default joint damping, shape (nv,).
`get_dof_frictionloss`()	Return default joint friction loss, shape (nv,).
`get_dof_pos`()	Return joint positions, excluding the base.
`get_dof_vel`()	Return joint velocities, excluding the base.
`get_dr_capabilities`()	Advertise no DR until per-env model mutation is effect-tested.
`get_geom_body_ids`()	Return the owning body id for each geom.
`get_geom_contact_masks`()	Return per-geom contact type and affinity masks.
`get_geom_friction`()	Return the backend geom-friction table.
`get_geom_id`(name)	Resolve one geom name through the backend contract.
`get_geom_names`()	Return backend geom names in backend id order.
`get_geom_size`(name)	Return one geom size vector through the backend contract.
`get_geom_sizes`()	Return default geometry sizes, shape (ngeom, 3).
`get_geom_solimp`()	Return default contact impedance parameters, shape (ngeom, 5).
`get_geom_solref`()	Return default contact reference parameters, shape (ngeom, 2).
`get_gravity`()	Return the backend gravity vector.
`get_init_qvel`()	Return a zero-initialized qvel vector compatible with `set_state`.
`get_joint_dof_indices`(names)	Resolve named joints to absolute qvel indices (root 6 columns first).
`get_joint_dof_pos_indices`(names)	Resolve joint names to DoF indices in position space (qpos).
`get_joint_dof_vel_indices`(names)	Resolve joint names to DoF indices in velocity space (qvel).
`get_joint_range`()	Per-joint `range` from the MJCF (pure XML, available pre-materialize).
`get_joint_state_qpos_indices`(names)	Resolve single-DoF joints to full `set_state` qpos columns.
`get_joint_state_qvel_indices`(names)	Resolve single-DoF joints to full `set_state` qvel columns.
`get_keyframe_qpos`(name)	Return the full qpos for a named keyframe, including the floating base.
`get_motion_body_ids`(names)	Resolve backend-native body IDs used by motion datasets.
`get_physics_state`()	Return a physics snapshot suitable for offline playback/video export.
`get_play_capabilities`()	Return backend-native play/render capabilities.
`get_playback_model`([env_index])	Return the playback model for a specific env when variants exist.
`get_root_state_layout`(root_body_name)	Resolve one body's floating-root columns on the cold path.
`get_scene_model_file`()	Return the materialized scene path for diagnostics, when available.
`get_scene_visual_model_file`()	Return the scene visual model file on the cold path, when available.
`get_sensor_data`(name)	Compute one mapped scene sensor from the shm state caches.
`get_sensor_data_batch`(names)	Fetch multiple sensors and concatenate their flattened values.
`get_sensor_data_rows`(name, env_ids)	Get selected env rows of a sensor array.
`get_site_ids`(names)	Resolve site names to integer ID arrays.
`get_site_jacobian_w`(site_id, dof_indices)	Compute world-frame Jacobians for one site and selected DoF columns.
`get_state`([fields])	Return a detached, backend-neutral state snapshot.
`get_terrain_spawn_data`()	Return backend-materialized terrain metadata on the cold path.
`init_renderer`([spacing, offset_mode, ...])	Initialize the worker-side viewer and/or capture camera.
`materialize`()	Spawn the worker, run the handshake, and bind shared-memory slots.
`render`()	Draw one interactive viewer frame through the worker.
`reset`([env_ids])	Reset selected environments to the backend's default state.
`resolve_play_render_plan`(*, ...)	Resolve high-level playback mode into backend-owned render parameters.
`run_playback`(*, env, initialize, step, num_steps)	Execute backend-owned playback for an env wrapper.
`set_physics_state`(state)	Restore a snapshot produced by `get_physics_state`.
`set_pre_step_control`(fn)	Register an env-owned policy-control to physics-control converter.
`set_state`(env_indices, qpos, qvel[, ...])	Set physics state for selected environments.
`step`(ctrl[, nsteps])	Advance physics.

Attributes

`capabilities`	Coarse capability labels for clients that need a cheap feature check.
`model`	Return backend-owned model metadata; never a live physics object.
`num_actuators`	Number of actuators.
`num_dof_vel`	Number of joint velocity DoFs, excluding the floating base.
`num_envs`	Number of vectorized environments.
`backend_type`

__init__(scene, num_envs, sim_dt, *, base_name=None, device_id=None, worker_timeout_s=None, worker_command=None, **unexpected_kwargs)¶

Parameters:

scene (SceneCfg)
num_envs (int)
sim_dt (float)
base_name (str | None)
device_id (int | None)
worker_timeout_s (float | None)
worker_command (list[str] | None)
unexpected_kwargs (Any)

apply_body_force(body_ids, force, torque=None)¶

Apply a world-frame force (and optional torque) to bodies for the upcoming step.

Parameters:

body_ids (ndarray) – Body ids whose external forces should be perturbed.
force (ndarray) – Force values with shape (num_envs, len(body_ids), 3).
torque (ndarray | None) – Optional world-frame torque values with the same shape. Backends without a torque channel must fail closed when this is not None.

Return type:

None

Returns:

None. Backends that support this mutate their pending simulation state.

apply_init_randomization(plan)¶

Apply cold-path model/materialization randomization.

Parameters:: plan (InitRandomizationPlan)
Return type:: None

apply_interval_randomization(plan)¶

Apply a scheduled interval randomization plan.

Generic dispatch: each op yielded by plan.iter_ops() is validated against the builtin term specs (custom terms pass through) and routed to the backend-owned handler table returned by _interval_term_handlers(). A term without a handler fails closed with NotImplementedError naming the backend class and the term. Backends that need per-plan prologue/epilogue semantics (for example clearing staged external forces before the ops accumulate) keep a thin override that calls this base implementation.

Parameters:: plan (IntervalRandomizationPlan)
Return type:: None

bind_mocap_pose(body_name)¶

Resolve a mocap body once; unavailable capabilities fail at binding.

Parameters:: body_name (str)
Return type:: BackendMocapPoseBinding

bind_sensor_data(names)¶

Materialize a validated view over named sensors on the cold path.

The existing sensor getters remain the sole backend adapter surface. This method validates each requested sensor once, records its flattened width, and returns a stable view for manager terms. Backends override the protected reader hook when numeric slots or stable cache slices are available; callers do not depend on that implementation detail.

Parameters:: names (Sequence[str])
Return type:: BackendSensorView

property capabilities¶

Coarse capability labels for clients that need a cheap feature check.

The detailed contract is expressed by the methods on this class. The labels remain useful for benchmark/conformance metadata and are derived from the mandatory lifecycle methods rather than maintained separately by every adapter.

capture_video_frame()¶

Capture one RGB frame from the worker’s camera sensor.

Return type:: ndarray

cleanup_scene_assets()¶

Release all backend-owned resources, including the worker process.

NpEnv.close() deliberately depends on the base cleanup_scene_assets hook rather than a backend-specific close method. A subprocess backend must therefore bridge that lifecycle hook explicitly; otherwise closing a manager environment would leave the Python 3.8/3.11 worker and its shared-memory segments alive until interpreter teardown.

Return type:: None

close()¶

Shut down the worker and release shared memory. Idempotent.

Return type:: None

copy_body_state_w(body_ids, out_pos, out_quat, out_lin_vel, out_ang_vel)¶

Copy selected world-frame body state into caller-owned buffers.

Parameters:

body_ids (ndarray)
out_pos (ndarray)
out_quat (ndarray)
out_lin_vel (ndarray)
out_ang_vel (ndarray)

Return type:

tuple[ndarray, ndarray, ndarray, ndarray]

create_hfield_scanner(*, hfield_geom_id, offsets, frame_body_id, alignment='yaw', output='height')¶

Create a reusable height-field scanner on the init/cold path.

Backends that support height-field terrain scan must override this method.

Parameters:

hfield_geom_id (int)
offsets (ndarray)
frame_body_id (int)
alignment (str)
output (str)

Return type:

BackendHeightScanner

get_actuator_ctrl_range()¶

Position-target clamp per dof, from the MJCF ctrlrange attributes.

Pure XML metadata (available pre-materialize). Undeclared ctrlranges report (0, 0), matching the MuJoCo backend which returns the raw actuator_ctrlrange (ctrllimited=false → 0 0).

Return type:: ndarray

get_actuator_gains()¶

Per-dof (kp, kd) from the MJCF <position> actuators (pure XML).

Passive joints (no actuator) report zero gains. Returned in MJCF joint document order, which the INIT handshake pins to the worker’s dof order.

Return type:: tuple[ndarray, ndarray]

get_actuator_joint_names()¶

The shared position-control profile drives one actuator per DoF.

Return type:: tuple[str, ...]

get_actuator_names()¶

Return actuator names in control-vector order on the cold path.

Return type:: tuple[str, ...]

get_base_ang_vel()¶

Return base angular velocity in the world frame.

This is dimensions 3-5 of generalized velocity qvel, expressed in world coordinates. It differs from gyro readings: gyro sensors report angular velocity components in the body/sensor local frame, while this contract returns world-frame values. Use the matching sensor contract when body-frame angular velocity is required.

Return type:: ndarray
Returns:: (num_envs, 3)

get_base_lin_vel()¶

Return base linear velocity in the world frame.

This is the first three dimensions of generalized velocity qvel, expressed in world coordinates.

Return type:: ndarray
Returns:: (num_envs, 3)

get_base_pos()¶

Return base position in the world frame.

Return type:: ndarray
Returns:: (num_envs, 3)

get_base_quat()¶

Return base quaternion in the world frame as wxyz.

Return type:: ndarray
Returns:: (num_envs, 4)

get_body_ang_vel_b(body_ids)¶

Return selected body angular velocities expressed in each body’s own frame.

The value is the body’s world-frame angular velocity rotated by the inverse of the body’s world-frame orientation, i.e. quat_apply_inverse(quat_w, ang_vel_w) (mjlab/Isaac-style analytical definition). It is well-defined for every body — including the root body — and must NOT be implemented as the motion relative to the baselink frame (which degenerates to zero for the root body).

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_ang_vel_w(body_ids)¶

Return selected body angular velocities in the world frame.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_ang_vel_w_rows(env_ids, body_ids)¶

Get selected env rows of world-frame body angular velocity.

Parameters:

env_ids (ndarray)
body_ids (ndarray)

Return type:

ndarray

get_body_id(name)¶

Resolve one body/link name through the backend contract.

Parameters:: name (str)
Return type:: int

get_body_ids(names)¶

Resolve body/link names to backend integer IDs.

Parameters:: names (Sequence[str]) – Body/link names.
Return type:: ndarray
Returns:: int32 array with shape (len(names),).
Raises:: ValueError – If any name is not found.

get_body_ipos()¶

Return the backend body inertial-position table.

Return type:: ndarray

get_body_lin_vel_b(body_ids)¶

Return selected body linear velocities expressed in each body’s own frame.

The value is the body’s world-frame velocity rotated by the inverse of the body’s world-frame orientation, i.e. quat_apply_inverse(quat_w, lin_vel_w) (mjlab/Isaac-style analytical definition). It is well-defined for every body — including the root body — and must NOT be implemented as the motion relative to the baselink frame (which degenerates to zero for the root body).

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_lin_vel_w(body_ids)¶

Return selected body linear velocities in the world frame.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_lin_vel_w_rows(env_ids, body_ids)¶

Get selected env rows of world-frame body linear velocity.

Parameters:

env_ids (ndarray)
body_ids (ndarray)

Return type:

ndarray

get_body_mass()¶

Return the backend body-mass table.

Return type:: ndarray

get_body_pos_b(body_ids)¶

Return selected body positions in the baselink frame.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_pos_w(body_ids)¶

Return selected body positions in the world frame.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 3)

get_body_pose_w(body_ids)¶

Return selected body positions and quaternions in the world frame.

Parameters:: body_ids (ndarray)
Return type:: tuple[ndarray, ndarray]

get_body_pose_w_rows(env_ids, body_ids)¶

Get selected env rows of world-frame body position and quaternion.

Parameters:

env_ids (ndarray)
body_ids (ndarray)

Return type:

tuple[ndarray, ndarray]

get_body_quat_b(body_ids)¶

Return selected body quaternions in the baselink frame as wxyz.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 4)

get_body_quat_w(body_ids)¶

Return selected body quaternions in the world frame as wxyz.

Parameters:: body_ids (ndarray) – Body ID array.
Return type:: ndarray
Returns:: (num_envs, len(body_ids), 4)

get_body_state_w(body_ids)¶

Get selected body position, quaternion, linear velocity, and angular velocity.

Parameters:: body_ids (ndarray)
Return type:: tuple[ndarray, ndarray, ndarray, ndarray]

get_body_subtree_ids(root_body_id)¶

Return body ids in the subtree rooted at root_body_id.

Parameters:: root_body_id (int)
Return type:: ndarray

get_body_vel_w(body_ids)¶

Return selected body linear and angular velocities in the world frame.

Parameters:: body_ids (ndarray)
Return type:: tuple[ndarray, ndarray]

get_default_dof_pos()¶

Return default joint positions in the same column order as get_dof_pos.

The returned array is detached, one-dimensional, and excludes floating root coordinates. Backends whose DoF view is actuator-indexed must use that same actuator-target order here.

Return type:: ndarray

get_default_qpos()¶

Return the backend/model default qpos through a stable contract.

Return type:: ndarray

get_dof_armature()¶

Return the backend dof-armature table.

Return type:: ndarray

get_dof_damping()¶

Return default joint damping, shape (nv,).

Return type:: ndarray

get_dof_frictionloss()¶

Return default joint friction loss, shape (nv,).

Return type:: ndarray

get_dof_pos()¶

Return joint positions, excluding the base.

Return type:: ndarray
Returns:: (num_envs, num_dof)

get_dof_vel()¶

Return joint velocities, excluding the base.

Return type:: ndarray
Returns:: (num_envs, num_dof)

get_dr_capabilities()¶

Advertise no DR until per-env model mutation is effect-tested.

Return type:: DomainRandomizationCapabilities

get_geom_body_ids()¶

Return the owning body id for each geom.

Return type:: ndarray

get_geom_contact_masks()¶

Return per-geom contact type and affinity masks.

Return type:: tuple[ndarray, ndarray]

get_geom_friction()¶

Return the backend geom-friction table.

Return type:: ndarray

get_geom_id(name)¶

Resolve one geom name through the backend contract.

Parameters:: name (str)
Return type:: int

get_geom_names()¶

Return backend geom names in backend id order.

Return type:: tuple[str, ...]

get_geom_size(name)¶

Return one geom size vector through the backend contract.

Parameters:: name (str)
Return type:: ndarray

get_geom_sizes()¶

Return default geometry sizes, shape (ngeom, 3).

Return type:: ndarray

get_geom_solimp()¶

Return default contact impedance parameters, shape (ngeom, 5).

Return type:: ndarray

get_geom_solref()¶

Return default contact reference parameters, shape (ngeom, 2).

Return type:: ndarray

get_gravity()¶

Return the backend gravity vector.

Return type:: ndarray

get_init_qvel()¶

Return a zero-initialized qvel vector compatible with set_state.

Return type:: ndarray
Returns:: Zero-filled qvel array.

get_joint_dof_indices(names)¶

Resolve named joints to absolute qvel indices (root 6 columns first).

Parameters:: names (Sequence[str])
Return type:: ndarray

get_joint_dof_pos_indices(names)¶

Resolve joint names to DoF indices in position space (qpos).

Only single-DoF joints are supported; free joints are excluded.

Parameters:: names (Sequence[str]) – Joint names.
Return type:: ndarray
Returns:: int32 index array with shape (len(names),) relative to the joint section of qpos.

get_joint_dof_vel_indices(names)¶

Resolve joint names to DoF indices in velocity space (qvel).

Parameters:: names (Sequence[str]) – Joint names.
Return type:: ndarray
Returns:: int32 index array with shape (len(names),) relative to the joint section start.

get_joint_range()¶

Per-joint range from the MJCF (pure XML, available pre-materialize).

The XML is the cross-runtime source of truth for this contract. Joints without a range attribute report (-inf, inf).

Return type:: ndarray | None

get_joint_state_qpos_indices(names)¶

Resolve single-DoF joints to full set_state qpos columns.

Unlike get_joint_dof_pos_indices(), these indices address the complete qpos vector accepted by set_state(), including any root coordinates. Manager reset transactions resolve them on the cold path.

Parameters:: names (Sequence[str])
Return type:: ndarray

get_joint_state_qvel_indices(names)¶

Resolve single-DoF joints to full set_state qvel columns.

Parameters:: names (Sequence[str])
Return type:: ndarray

get_keyframe_qpos(name)¶

Return the full qpos for a named keyframe, including the floating base.

Parameters:: name (str) – Keyframe name such as "stand" or "home".
Return type:: ndarray
Returns:: Array with shape (nq,).

get_motion_body_ids(names)¶

Resolve backend-native body IDs used by motion datasets.

Parameters:: names (Sequence[str])
Return type:: ndarray

get_physics_state()¶

Return a physics snapshot suitable for offline playback/video export.

Rows use the [time, qpos, qvel] layout; backends whose model has mocap bodies append [mocap_pos(nmocap*3), mocap_quat(nmocap*4)] so offline rendering can replay mocap-driven geometry at its recorded pose.

Return type:: ndarray

get_play_capabilities()¶

Return backend-native play/render capabilities.

Return type:: BackendPlayCapabilities

get_playback_model(env_index=None)¶

Return the playback model for a specific env when variants exist.

Parameters:: env_index (int | None) – Optional vectorized environment index.
Return type:: Any
Returns:: The backend model object used by playback tooling.

get_root_state_layout(root_body_name)¶

Resolve one body’s floating-root columns on the cold path.

Backends must verify that root_body_name owns a free/floating joint; fixed bodies and runtimes without body-to-root metadata fail closed. Name/model lookup is forbidden on reset and step hot paths, so callers cache either the returned layout or the unsupported result during scene materialization.

Parameters:: root_body_name (str)
Return type:: BackendRootStateLayout

get_scene_model_file()¶

Return the materialized scene path for diagnostics, when available.

Return type:: str | None

get_scene_visual_model_file()¶

Return the scene visual model file on the cold path, when available.

Backends without a separate visual scene model return None.

Return type:: str | None

get_sensor_data(name)¶

Compute one mapped scene sensor from the shm state caches.

See sensors.py for the MJCF-sensor → tensor-quantity mapping table. Names that are not declared in the scene raise ValueError; declared but unmappable sensors fail closed with NotImplementedError.

Parameters:: name (str)
Return type:: ndarray

get_sensor_data_batch(names)¶

Fetch multiple sensors and concatenate their flattened values.

Parameters:: names (Sequence[str]) – Sensor names in output order.
Return type:: ndarray
Returns:: Array with shape (num_envs, total_sensor_values).

get_sensor_data_rows(name, env_ids)¶

Get selected env rows of a sensor array.

Parameters:

name (str)
env_ids (ndarray)

Return type:

ndarray

get_site_ids(names)¶

Resolve site names to integer ID arrays.

Parameters:: names (Sequence[str]) – Site names.
Return type:: ndarray
Returns:: int32 ID array with shape (len(names),).

get_site_jacobian_w(site_id, dof_indices)¶

Compute world-frame Jacobians for one site and selected DoF columns.

Parameters:

site_id (int) – Integer site ID.
dof_indices (ndarray) – DoF column indices to extract, with shape (n_dof,).

Return type:

tuple[ndarray, ndarray]

Returns:

(jacp, jacr) translation/rotation Jacobians, each with shape (num_envs, 3, n_dof).

get_state(fields=None)¶

Return a detached, backend-neutral state snapshot.

qpos and qvel are assembled from the public kinematic getters; adapters may override this to expose native fields such as ctrl. This convenience API keeps benchmark clients independent from private model/data objects while the full reset contract remains set_state.

get_terrain_spawn_data()¶

Return backend-materialized terrain metadata on the cold path.

Backends without generated terrain support return None. Callers should resolve this once during env initialization and cache the returned height-sampling callable for reset/reward hot paths.

Return type:: BackendTerrainSpawnData | None

init_renderer(spacing=1.0, *, offset_mode='grid', headless=False, capture=False, width=1280, height=720, camera_kwargs=None)¶

Initialize the worker-side viewer and/or capture camera.

spacing/offset_mode are accepted for contract parity and ignored: envs are already laid out on the worker sim’s grid.

Parameters:

spacing (float)
offset_mode (str)
headless (bool)
capture (bool)
width (int)
height (int)
camera_kwargs (CameraCfg | Mapping[str, Any] | None)

Return type:

None

materialize()¶

Spawn the worker, run the handshake, and bind shared-memory slots.

Idempotent. Called lazily by the first state/metadata access, so env constructors that read shapes before the explicit lifecycle point work like they do on the MuJoCo backend. A closed backend cannot be materialized again.

Return type:: None

property model: SubprocessModelInfo¶: Return backend-owned model metadata; never a live physics object.

property num_actuators: int¶: Number of actuators.

property num_dof_vel: int¶: Number of joint velocity DoFs, excluding the floating base.

property num_envs: int¶: Number of vectorized environments.

render()¶

Draw one interactive viewer frame through the worker.

Return type:: None

reset(env_ids=None)¶

Reset selected environments to the backend’s default state.

Parameters:: env_ids (ndarray | None)
Return type:: None

resolve_play_render_plan(*, play_render_mode, play_steps, output_video)¶

Resolve high-level playback mode into backend-owned render parameters.

Parameters:

play_render_mode (str | None)
play_steps (int | None)
output_video (str | PathLike[str] | None)

Return type:

BackendPlayRenderPlan

run_playback(*, env, initialize, step, num_steps, output_video=None, render_spacing=None, render_offset_mode=None, headless=None, record_video=None, frame_state_getter=None, camera_kwargs=None, debug_overlay_getter=None, on_frame=None)¶

Execute backend-owned playback for an env wrapper.

camera_kwargs is normalized into CameraCfg at this boundary; unknown mapping keys fail closed with an error naming them.

debug_overlay_getter is an optional per-frame callback returning a sequence with one entry per environment (len == num_envs); each entry is that env’s sequence of DebugPrimitive (None or empty marks an env without overlay) and returning None disables overlays for the frame. Primitive poses are env-local; the renderer applies grid offsets when composing multiple envs. Backends whose get_play_capabilities().supports_debug_overlay is False fail closed with NotImplementedError when this is not None. On the interactive rendering path only backends whose supports_interactive_debug_overlay is True consume it; the others fail closed with NotImplementedError.

on_frame is an optional per-frame video hook called by offline render pipelines before encoding: it receives (frame_index, frame) with the frame an (H, W, 3) uint8 array, and returns a replacement frame of the same shape/dtype or None to keep the original. Backends rendering through a native (non-offline) renderer fail closed with NotImplementedError when this is not None.

Known boundary: env is the owning env wrapper, not a physics-layer concept. Current playback implementations read env-level configuration (e.g. cfg.scene, cfg.ctrl_dt, cfg.render_spacing) and env-owned playback helpers (get_playback_model, get_physics_state_snapshot) that have no backend-native equivalent yet. The parameter stays on this contract until playback asset/config resolution moves onto backend-owned metadata; backends must only use it on the cold playback path.

Parameters:

env (Any)
initialize (Any)
step (Any)
num_steps (int | None)
output_video (str | PathLike[str] | None)
render_spacing (float | None)
render_offset_mode (str | None)
headless (bool | None)
record_video (bool | None)
frame_state_getter (Any)
camera_kwargs (CameraCfg | Mapping[str, Any] | None)
debug_overlay_getter (Any)
on_frame (Any)

Return type:

str | None

set_physics_state(state)¶

Restore a snapshot produced by get_physics_state.

Backends implementing this must refresh their host caches so state and sensor getters stay consistent with the restored physics state.

Parameters:: state (ndarray)
Return type:: None

set_pre_step_control(fn)¶

The callback receives (backend, ctrl) so owner code can read the backend’s freshly-updated sensor contract before every physics substep. It must return backend-native actuator control with the same shape. Position-actuator envs leave this unset and keep the direct control path.

Parameters:: fn (Any | None)
Return type:: None

set_state(env_indices, qpos, qvel, randomization=None)¶

Set physics state for selected environments.

Parameters:

env_indices (ndarray) – Environment indices.
qpos (ndarray) – Position state. Free-root columns exposed by get_root_state_layout() use world xyz and wxyz quaternion.
qvel (ndarray) – Velocity state. Free-root columns exposed by get_root_state_layout() use world linear velocity and body-frame angular velocity.
randomization (ResetRandomizationPayload | None) – Optional backend randomization payload.

Return type:

dict[str, dict[str, float]]

Returns:

Optional dictionary. Backends MAY include a "timing" key with per-substep timings in milliseconds (e.g. set_state_mask_ms, set_state_data_slice_ms, …). Callers MUST treat None or missing keys as “not reported” — the outer wall-clock measurement in DomainRandomizationManager.reset (dr_reset_set_state_ms) remains authoritative for total set_state time.

step(ctrl, nsteps=1)¶

Advance physics.

Parameters:

ctrl (ndarray) – Control input with shape (num_envs, nu).
nsteps (int) – Number of physics substeps.

Return type:

dict[str, dict[str, float]]

Returns:

Optional dictionary. Backends may include a "timing" key with per-phase timings in milliseconds.

backend_type: str¶