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unisim.backend.drake.backend.DrakeBackend

class unisim.backend.drake.backend.DrakeBackend

Bases: SimBackend

UniLab SimBackend implementation backed by DrakeUni batch runtime.

The backend keeps the public UniLab API stable while delegating model construction, integration, and raw sensor evaluation to DrakeUni.

Parameters:

• scene (SceneCfg)

• num_envs (int)

• sim_dt (float)

• drake_backend_mode (str)

• nthread (int)

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_interval_randomization(plan)	Apply a scheduled interval randomization plan.
bind_height_scanner(*, hfield_geom_id, ...)	Create a reusable height-field scanner on the init/cold path.
bind_host_bridge_io(spec)	Compile persistent Drake staging and packed device layouts.
bind_mocap_pose(body_name)	Resolve a mocap body once; unavailable capabilities fail at binding.
bind_packed_reset(*[, device])	Begin a backend-owned packed reset transaction.
bind_renderer([spacing, offset_mode, ...])	Initialize a backend-native renderer.
bind_sensor_data(names)	Materialize a validated view over named tensor sensors.
capture_video_frame()	Capture one RGB frame through a backend-native renderer.
cleanup_scene_assets()	Release cold-path scene artifacts owned by the backend.
close()
diagnostics()
get_actuator_ctrl_range()	Return actuator control ranges.
get_actuator_gains()	Return per-joint (kp, kd) arrays from the backend model.
get_actuator_joint_names()	Return each actuator's target single-DoF joint in control-vector order.
get_actuator_names()	Return actuator names in control-vector order on the cold path.
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([env_ids])	Return body center-of-mass offsets in each body's local frame, in meters.
get_body_mass()	Return the backend body-mass table.
get_body_subtree_ids(root_body_id)	Return body ids in the subtree rooted at root_body_id.
get_capabilities(*[, profile])	Query semantic declarations plus authoritative DR/play/variant support.
get_default_dof_pos()	Return default joint positions in canonical non-root qpos order.
get_default_geom_sizes()	Return default geometry sizes, shape (ngeom, 3).
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_dr_capabilities()	Return supported domain-randomization capabilities for this backend.
get_entity_default_state(entity[, env_ids])	Detached construction/keyframe defaults in selected environment order.
get_entity_names()	Return materialized physical entity names in the frozen public order.
get_entity_state(entity)	Return detached root_pose/root_velocity/joint_positions/joint_velocities.
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 in backend geom-name order.
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_import_report()	Return a detached construction/materialization configuration snapshot.
get_init_qvel()	Return a zero-initialized qvel vector compatible with set_state_tensor.
get_joint_dof_indices(names)	Resolve joint names to absolute DoF indices in velocity space.
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 joint-section DoF indices in velocity space.
get_joint_range(*[, names])	Return joint position limits, excluding the floating base.
get_joint_state_qpos_indices(names)	Resolve single-DoF joints to full set_state_tensor qpos columns.
get_joint_state_qvel_indices(names)	Resolve single-DoF joints to full set_state_tensor qvel columns.
get_keyframe_qpos(name)	Return the full qpos for a named keyframe, including the floating base.
get_motion_body_ids(names)	Resolve body IDs used by motion datasets.
get_physics_state()	Return a physics snapshot suitable for offline playback/video export.
get_physics_state_layout()	Return the [time, qpos, qvel] packet layout (no mocap bodies).
get_play_capabilities()	Return backend-native play/render capabilities.
get_playback_mocap_state([env_index])	Return copied (mocap_pos, mocap_quat) arrays for detached playback.
get_playback_model([env_index])	Return the playback model for a specific env when variants exist.
get_public_state_widths()	Return canonical qpos/qvel widths for packed tensor reset layout.
get_reset_term_default(term)	Return the authoritative default table for a curated reset term.
get_root_state_layout(root_body_name)	Resolve one body's floating-root columns on the cold path.
get_scene_layout()	Return the immutable materialized public addresses, never native handles.
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_inventory()	Return the complete public named-sensor inventory and widths.
get_sensor_names()	Return the complete public named-sensor namespace.
get_sensor_view(name[, device])	Copy one authoritative CPU sensor block to a Torch device.
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_views([fields, device])	Copy authoritative CPU state to an explicitly selected Torch device.
get_tensor_capabilities()	Return the deliberately narrow initial packed host-bridge profile.
get_tensor_execution()	Declare Drake's CPU-authoritative tensor execution profile.
get_tensor_runtime_diagnostics()	Return runtime-selected diagnostics for optional tensor optimizations.
get_terrain_spawn_data()	Return backend-materialized terrain metadata on the cold path.
get_tracked_body_views([body_names, device])	Return all tracked-body fields in one public backend read.
materialize()	Finalize cold-path backend resources before reset/step.
render()	Render one frame through a backend-native interactive renderer.
reset_entities(request)	Validate the complete selected-entity request, then commit it once.
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_mocap_pose_tensor(body_name, ...)	Write selected mocap poses through the declared tensor lifecycle.
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_tensor(env_indices, qpos, qvel[, ...])	Bridge selected accelerator reset state to CPU Drake physics.
set_state_tensor_mask(reset_mask, qpos, qvel)	Set state selected by a fixed-width boolean mask.
step_tensor(ctrl[, nsteps])	Bridge one accelerator control tensor to CPU Drake physics.

Attributes

backend_type
capability_flags	Coarse capability labels for clients that need a cheap feature check.
model	Underlying physics model.
nthread
num_actuators	Number of actuators.
num_dof_vel	Number of joint velocity DoFs, excluding the floating base.
num_envs	Number of vectorized environments.
scene_model_file

backend_type: str = 'drake'

__init__(scene, num_envs, sim_dt, *, drake_backend_mode='batch', nthread=0)

Parameters:

• scene (SceneCfg)

• num_envs (int)

• sim_dt (float)

• drake_backend_mode (str)

• nthread (int)

property scene_model_file: str

property num_envs: int

Number of vectorized environments.

property nthread: int

property model: _DrakeUniModelView

Underlying physics model.

property num_actuators: int

Number of actuators.

property num_dof_vel: int

Number of joint velocity DoFs, excluding the floating base.

get_actuator_ctrl_range()

Return actuator control ranges.

Return type:

ndarray

Returns:

Array with shape (num_actuators, 2) and columns [low, high].

get_actuator_names()

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

Return type:

tuple[str, ...]

get_actuator_joint_names()

Return each actuator’s target single-DoF joint in control-vector order.

Backends must fail closed when an actuator does not target exactly one hinge/slide joint. Manager action terms use this cold-path metadata to map community joint selectors onto the backend control vector without inspecting backend-private model objects.

Return type:

tuple[str, ...]

get_scene_model_file()

Return the materialized scene path for diagnostics, when available.

Return type:

str | None

get_scene_layout()

Return the immutable materialized public addresses, never native handles.

Return type:

CompiledSceneLayout

get_entity_names()

Return materialized physical entity names in the frozen public order.

Return type:

tuple[str, ...]

get_entity_default_state(entity, env_ids=None)

Detached construction/keyframe defaults in selected environment order.

Fields and frames match get_entity_state. Defaults follow immutable variant assignment and never reflect current reset-time randomization. This query does not reset, step or reparse the scene.

Parameters:

• entity (str)

• env_ids (Sequence[int] | ndarray | None)

Return type:

Mapping[str, ndarray]

get_entity_state(entity)

Return detached root_pose/root_velocity/joint_positions/joint_velocities.

Root fields follow EntityStatePatch’s link-origin/world-frame contract. Non-root joint fields use the frozen entity joint order and native generalized widths. Unavailable fields must fail, never return old data as if current. State freshness follows the adapter’s declared profile.

Parameters:

entity (str)

Return type:

Mapping[str, ndarray]

get_joint_range(*, names=None)

Return joint position limits, excluding the floating base.

Parameters:

names (Sequence[str] | None) – Optional joint names in requested return order. Adapters that support named scalar joints resolve the model mapping internally.

Return type:

ndarray | None

Returns:

Array with shape (num_dof, 2) and columns [low, high], or None when the backend does not expose limits.

When names is provided by a supporting adapter, the result has shape (len(names), 2). Hinge limits are radians, slide limits are meters, and joints without enabled limits return infinities.

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_default_qpos()

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

Return type:

ndarray

get_default_dof_pos()

Return default joint positions in canonical non-root qpos order.

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_init_qvel()

Return a zero-initialized qvel vector compatible with set_state_tensor.

Return type:

ndarray

Returns:

Zero-filled qvel array.

get_actuator_gains()

Return per-joint (kp, kd) arrays from the backend model.

Return type:

tuple[ndarray, ndarray]

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_motion_body_ids(names)

Resolve body IDs used by motion datasets.

Motion datasets are generated from MuJoCo, so the returned ids follow the MJCF body order with worldbody as id 0, regardless of the backend-native indexing used by get_body_ids.

Parameters:

names (Sequence[str])

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_joint_dof_indices(names)

Resolve joint names to absolute DoF indices in velocity space.

Parameters:

names (Sequence[str]) – Joint names.

Return type:

ndarray

Returns:

int32 index array with shape (len(names),) addressing the complete qvel vector, including any root coordinates.

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 joint-section DoF indices in velocity space.

Unlike get_joint_dof_indices(), the returned indices exclude any root/free-joint velocity columns. They address the same joint section used by get_joint_dof_pos_indices().

Parameters:

names (Sequence[str])

Return type:

ndarray

get_joint_state_qpos_indices(names)

Resolve single-DoF joints to full set_state_tensor qpos columns.

Unlike get_joint_dof_pos_indices(), these indices address the complete qpos vector accepted by set_state_tensor(), 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_tensor qvel columns.

Parameters:

names (Sequence[str])

Return type:

ndarray

reset_entities(request)

Validate the complete selected-entity request, then commit it once.

Validation failure leaves all state unchanged. A native partial commit failure must fault the backend unless the adapter can actually roll back. Unselected entities/environments and fixed identity remain unchanged.

Parameters:

request (SceneResetRequest)

Return type:

None

get_dr_capabilities()

Return supported domain-randomization capabilities for this backend.

Return type:

DomainRandomizationCapabilities

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(). Op payloads are torch-first: Torch tensors or TensorIntervalPayload values produced by the caller; host adapters convert tensors at their private boundary through unisim.dr._host, and a missing producer-sampled payload fails closed. 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

get_play_capabilities()

Return backend-native play/render capabilities.

Return type:

PlayCapabilities

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:

PlayRenderPlan

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 (Callable[[], Any])

• step (Callable[[Any], 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 (Callable[[], np.ndarray] | None)

• camera_kwargs (CameraCfg | Mapping[str, Any] | None)

• debug_overlay_getter (DebugOverlayGetter | None)

• on_frame (Callable[[int, np.ndarray], np.ndarray | None] | None)

Return type:

str | None

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

Initialize a backend-native renderer.

headless controls whether a native window is opened. capture controls whether capture_video_frame is valid for the renderer. camera_kwargs is normalized into CameraCfg at this boundary; unknown mapping keys fail closed with an error naming them.

Parameters:

• spacing (float)

• offset_mode (str)

• headless (bool)

• capture (bool)

• width (int)

• height (int)

• camera_kwargs (CameraCfg | Mapping[str, Any] | None)

Return type:

None

render()

Render one frame through a backend-native interactive renderer.

Raises:

RenderClosedError – If the user closed the render window.

Return type:

None

capture_video_frame()

Capture one RGB frame through a backend-native renderer.

Raises:

RenderClosedError – If the user closed the render window.

Return type:

ndarray

get_physics_state_layout()

Return the [time, qpos, qvel] packet layout (no mocap bodies).

Return type:

PhysicsStateLayout

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. Consumers must decode snapshots through get_physics_state_layout().split_state rather than hardcoding column slices.

Return type:

ndarray

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:

str

Returns:

The backend model object used by playback tooling.

diagnostics()

Return type:

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.

get_tensor_execution()

Declare Drake’s CPU-authoritative tensor execution profile.

Return type:

TensorExecution

get_tensor_capabilities()

Return the deliberately narrow initial packed host-bridge profile.

Return type:

TensorLifecycleCapabilities

bind_host_bridge_io(spec)

Compile persistent Drake staging and packed device layouts.

Parameters:

spec (TensorIOSpec)

Return type:

HostBridgeTransferPlan

get_state_views(fields=None, device=None)

Copy authoritative CPU state to an explicitly selected Torch device.

Parameters:

• fields (tuple[str, ...] | str | None)

• device (Any | None)

Return type:

Mapping[str, Any]

get_sensor_view(name, device=None)

Copy one authoritative CPU sensor block to a Torch device.

Parameters:

• name (str)

• device (Any | None)

Return type:

Any

step_tensor(ctrl, nsteps=1)

Bridge one accelerator control tensor to CPU Drake physics.

Parameters:

• ctrl (Any)

• nsteps (int)

Return type:

dict | None

set_state_tensor(env_indices, qpos, qvel, randomization=None)

Bridge selected accelerator reset state to CPU Drake physics.

Parameters:

• env_indices (Any)

• qpos (Any)

• qvel (Any)

• randomization (TensorResetRandomizationPayload | None)

Return type:

dict | None

cleanup_scene_assets()

Release cold-path scene artifacts owned by the backend.

Return type:

None

close()

Return type:

None

bind_height_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:

HeightScanner

bind_mocap_pose(body_name)

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

Parameters:

body_name (str)

Return type:

MocapPoseBinding

bind_packed_reset(*, device=None)

Begin a backend-owned packed reset transaction.

Parameters:

device (Any | None)

Return type:

Any

bind_sensor_data(names)

Materialize a validated view over named tensor sensors.

This cold-path binding records the flattened public view width and delegates execution to the backend-owned tensor sensor reader. It never falls back to a NumPy named-sensor getter.

Parameters:

names (Sequence[str])

Return type:

SensorView

property capability_flags

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.

get_body_id(name)

Resolve one body/link name through the backend contract.

Parameters:

name (str)

Return type:

int

get_body_ipos(env_ids=None)

Return body center-of-mass offsets in each body’s local frame, in meters.

body_ipos[b] is the position of body b’s center of mass in that body’s own local coordinate frame; it is neither an inertia tensor nor a whole-subtree COM.

Without env_ids the canonical model default table is returned with shape (nbody, 3) in backend body-id order. It never changes with reset randomization; fixed-variant backends expose their per-environment default baselines through get_reset_term_default() instead.

With env_ids the current effective per-environment values are returned with shape (len(env_ids), nbody, 3), in env_ids order. The values reflect every reset randomization applied so far, including composition with base_com_offset; an environment untouched by a partial reset keeps its previous values. Backends that do not track per-environment inertial offsets fail closed with NotImplementedError for this form.

Parameters:

env_ids (Sequence[int] | ndarray | None)

Return type:

ndarray

get_body_mass()

Return the backend body-mass table.

Return type:

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_capabilities(*, profile='default')

Query semantic declarations plus authoritative DR/play/variant support.

This cold-path query does not discover SDKs or verify runtime behavior. Materialized configuration readback is exposed by get_import_report.

Parameters:

profile (str)

Return type:

CapabilityReport

get_default_geom_sizes()

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

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_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 in backend geom-name order.

get_default_geom_sizes returns the complete table of default sizes, while this selector resolves one geom by name.

Parameters:

name (str)

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_import_report()

Return a detached construction/materialization configuration snapshot.

This cached report never parses assets, starts workers, or reflects reset-time randomization. Use current-property queries for live values.

Return type:

ImportReport

get_playback_mocap_state(env_index=0)

Return copied (mocap_pos, mocap_quat) arrays for detached playback.

Shapes are (nmocap, 3) and (nmocap, 4) for the selected environment. Backends exposing this declare get_play_capabilities().supports_mocap_playback.

Parameters:

env_index (int)

Return type:

tuple[ndarray, ndarray]

get_public_state_widths()

Return canonical qpos/qvel widths for packed tensor reset layout.

Return type:

PublicStateWidths

get_reset_term_default(term)

Return the authoritative default table for a curated reset term.

Without fixed variants the tail shape is the canonical model table, for example (nbody,) for body_mass. With fixed variants the returned table is per-environment, for example (num_envs, nbody). Callers must treat the result as read-only; adapters return detached copies.

Parameters:

term (str)

Return type:

ndarray

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:

RootStateLayout

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_inventory()

Return the complete public named-sensor inventory and widths.

Return type:

tuple[SensorDescriptor, ...]

get_sensor_names()

Return the complete public named-sensor namespace.

Return type:

tuple[str, ...]

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_tensor_runtime_diagnostics()

Return runtime-selected diagnostics for optional tensor optimizations.

Unlike capability negotiation, these values describe actual cold-path initialization results and may change when a backend falls back or closes. The default empty mapping means the backend declares no optional tensor-runtime optimization.

Return type:

Mapping[str, TensorRuntimeDiagnostic]

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:

TerrainSpawnData | None

get_tracked_body_views(body_names=None, device=None)

Return all tracked-body fields in one public backend read.

body_names selects and orders the returned body axis. None requests every tracked body in backend insertion order. This aggregate contract avoids one Python projection boundary per body/field sensor.

Parameters:

• body_names (Sequence[str] | None)

• device (Any | None)

Return type:

TrackedBodyStateViews

materialize()

Finalize cold-path backend resources before reset/step.

Return type:

None

set_mocap_pose_tensor(body_name, env_indices, poses)

Write selected mocap poses through the declared tensor lifecycle.

Parameters:

• body_name (str)

• env_indices (Any)

• poses (Any)

Return type:

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)

Register an env-owned policy-control to physics-control converter.

The callback receives (backend, ctrl) so owner code can read the backend’s freshly-updated sensor contract before every physics substep. It must return either backend-native actuator control with the same shape, or a PreStepControlOutput carrying that control plus an optional per-substep body wrench. A returned wrench is recomposed from scratch every substep and cleared when the step() call finishes. Position-actuator envs leave this unset and keep the direct control path.

Parameters:

fn (Callable[[Any, ndarray], ndarray | PreStepControlOutput] | None)

Return type:

None

set_state_tensor_mask(reset_mask, qpos, qvel, randomization=None, *, full_refresh=False)

Set state selected by a fixed-width boolean mask.

reset_mask is a contiguous one-dimensional boolean Torch tensor with shape (num_envs,). qpos and qvel are full-width contiguous float32 tensors with shapes (num_envs, nq) and (num_envs, nv). All three share one accepted Torch device and contain finite values. The adapter changes qpos/qvel/time only for true rows and preserves every false row. It publishes authoritative selected state before returning; any row materialization required by the engine belongs behind this backend boundary.

randomization is the unified torch-first TensorResetRandomizationPayload (full-width tables on the mask’s plane); the adapter must preserve every false row. full_refresh=True requests an eager equivalent full-batch derived-state/publication refresh. It is valid only where TensorLifecycleCapabilities.mask_selected_reset_full_refresh is declared.

Parameters:

• reset_mask (Any)

• qpos (Any)

• qvel (Any)

• randomization (TensorResetRandomizationPayload | None)

• full_refresh (bool)

Return type:

dict | None