This is legacy documentation covering MuJoCo versions 2.0 and earlier. Updated documentation is available from DeepMind at www.mujoco.org

Chapter 6:  API Reference

Introduction

This chapter is the reference manual for MuJoCo Pro. It is generated from the header files included with MuJoCo, but also contains additional text not available in the headers.

Type definitions

Primitive types

MuJoCo defines a large number of primitive types described here. Except for mjtNum and mjtByte, all other primitive types are C enums used to define various integer constants. Note that the rest of the API does not use these enum types directly. Instead it uses ints, and only the documentation/comments state that certain ints correspond to certain enum types. This is because we want the API to be compiler-independent, and the C standard does not dictate how many bytes must be used to represent an enum type. Nevertheless we recommend using these types when calling the API functions (and letting the compiler do the enum-to-int type cast.)

mjtNum

#ifdef mjUSEDOUBLE
    typedef double mjtNum;
#else
    typedef float mjtNum;
#endif

Defined in mjmodel.h

This is the floating-point type used throughout the simulator. If the symbol mjUSEDOUBLE is defined in mjmodel.h, this type is defined as double, otherwise it is defined as float. Currently only the double-precision version of MuJoCo is distributed, although the entire code base works with single-precision as well. We may release the single-precision version in the future for efficiency reasons, but the double-precision version will always be available. Thus it is safe to write user code assuming double precision. However, our preference is to write code that works with either single or double precision. To this end we provide math utility functions that are always defined with the correct floating-point type.

Note that changing mjUSEDOUBLE in mjmodel.h will not change how the library was compiled, and instead will result in numerous link errors. In general, the header files distributed with MuJoCo Pro should never be changed by the user.

mjtByte

typedef unsigned char mjtByte;

Defined in mjmodel.h

Byte type used to represent boolean variables.

mjtDisableBit

typedef enum _mjtDisableBit
{
    mjDSBL_CONSTRAINT   = 1<<0,     // entire constraint solver
    mjDSBL_EQUALITY     = 1<<1,     // equality constraints
    mjDSBL_FRICTIONLOSS = 1<<2,     // joint and tendon frictionloss constraints
    mjDSBL_LIMIT        = 1<<3,     // joint and tendon limit constraints
    mjDSBL_CONTACT      = 1<<4,     // contact constraints
    mjDSBL_PASSIVE      = 1<<5,     // passive forces
    mjDSBL_GRAVITY      = 1<<6,     // gravitational forces
    mjDSBL_CLAMPCTRL    = 1<<7,     // clamp control to specified range
    mjDSBL_WARMSTART    = 1<<8,     // warmstart constraint solver
    mjDSBL_FILTERPARENT = 1<<9,     // remove collisions with parent body
    mjDSBL_ACTUATION    = 1<<10,    // apply actuation forces
    mjDSBL_REFSAFE      = 1<<11,    // integrator safety: make ref[0]>=2*timestep

    mjNDISABLE          = 12        // number of disable flags
} mjtDisableBit;

Defined in mjmodel.h

Constants which are powers of 2. They are used as bitmasks for the field disableflags of mjOption. At runtime this field is m->opt.disableflags. The number of these constants is given by mjNDISABLE which is also the length of the global string array mjDISABLESTRING with text descriptions of these flags.

mjtEnableBit

typedef enum _mjtEnableBit
{
    mjENBL_OVERRIDE     = 1<<0,     // override contact parameters
    mjENBL_ENERGY       = 1<<1,     // energy computation
    mjENBL_FWDINV       = 1<<2,     // compare forward and inverse dynamics
    mjENBL_SENSORNOISE  = 1<<3,     // add noise to sensor data

    mjNENABLE           = 4         // number of enable flags
} mjtEnableBit;

Defined in mjmodel.h

Constants which are powers of 2. They are used as bitmasks for the field enableflags of mjOption. At runtime this field is m->opt.enableflags. The number of these constants is given by mjNENABLE which is also the length of the global string array mjENABLESTRING with text descriptions of these flags.

mjtJoint

typedef enum _mjtJoint
{
    mjJNT_FREE          = 0,        // global position and orientation (quat)       (7)
    mjJNT_BALL,                     // orientation (quat) relative to parent        (4)
    mjJNT_SLIDE,                    // sliding distance along body-fixed axis       (1)
    mjJNT_HINGE                     // rotation angle (rad) around body-fixed axis  (1)
} mjtJoint;

Defined in mjmodel.h

Primitive joint types. These values are used in m->jnt_type. The numbers in the comments indicate how many positional coordinates each joint type has. Note that ball joints and rotational components of free joints are represented as unit quaternions - which have 4 positional coordinates but 3 degrees of freedom each.

mjtGeom

typedef enum _mjtGeom
{
    // regular geom types
    mjGEOM_PLANE        = 0,        // plane
    mjGEOM_HFIELD,                  // height field
    mjGEOM_SPHERE,                  // sphere
    mjGEOM_CAPSULE,                 // capsule
    mjGEOM_ELLIPSOID,               // ellipsoid
    mjGEOM_CYLINDER,                // cylinder
    mjGEOM_BOX,                     // box
    mjGEOM_MESH,                    // mesh

    mjNGEOMTYPES,                   // number of regular geom types

    // rendering-only geom types: not used in mjModel, not counted in mjNGEOMTYPES
    mjGEOM_ARROW        = 100,      // arrow
    mjGEOM_ARROW1,                  // arrow without wedges
    mjGEOM_ARROW2,                  // arrow in both directions
    mjGEOM_LINE,                    // line
    mjGEOM_SKIN,                    // skin
    mjGEOM_LABEL,                   // text label

    mjGEOM_NONE         = 1001      // missing geom type
} mjtGeom;

Defined in mjmodel.h

Geometric types supported by MuJoCo. The first group are "official" geom types that can be used in the model. The second group are geom types that cannot be used in the model but are used by the visualizer to add decorative elements. These values are used in m->geom_type and m->site_type.

mjtCamLight

typedef enum _mjtCamLight
{
    mjCAMLIGHT_FIXED    = 0,        // pos and rot fixed in body
    mjCAMLIGHT_TRACK,               // pos tracks body, rot fixed in global
    mjCAMLIGHT_TRACKCOM,            // pos tracks subtree com, rot fixed in body
    mjCAMLIGHT_TARGETBODY,          // pos fixed in body, rot tracks target body
    mjCAMLIGHT_TARGETBODYCOM        // pos fixed in body, rot tracks target subtree com
} mjtCamLight;

Defined in mjmodel.h

Dynamic modes for cameras and lights, specifying how the camera/light position and orientation are computed. These values are used in m->cam_mode and m->light_mode.

mjtTexture

typedef enum _mjtTexture
{
    mjTEXTURE_2D        = 0,        // 2d texture, suitable for planes and hfields
    mjTEXTURE_CUBE,                 // cube texture, suitable for all other geom types
    mjTEXTURE_SKYBOX                // cube texture used as skybox
} mjtTexture;

Defined in mjmodel.h

Texture types, specifying how the texture will be mapped. These values are used in m->tex_type.

mjtIntegrator

typedef enum _mjtIntegrator         // integrator mode
{
    mjINT_EULER         = 0,        // semi-implicit Euler
    mjINT_RK4                       // 4th-order Runge Kutta
} mjtIntegrator;

Defined in mjmodel.h

Numerical integrator types. These values are used in m->opt.integrator.

mjtCollision

typedef enum _mjtCollision          // collision mode for selecting geom pairs
{
    mjCOL_ALL           = 0,        // test precomputed and dynamic pairs
    mjCOL_PAIR,                     // test predefined pairs only
    mjCOL_DYNAMIC                   // test dynamic pairs only
} mjtCollision;

Defined in mjmodel.h

Collision modes specifying how candidate geom pair are generated for near-phase collision checking. These values are used in m->opt.collision.

mjtCone

typedef enum _mjtCone               // type of friction cone
{
    mjCONE_PYRAMIDAL     = 0,       // pyramidal
    mjCONE_ELLIPTIC                 // elliptic
} mjtCone;

Defined in mjmodel.h

Available friction cone types. These values are used in m->opt.cone.

mjtJacobian

typedef enum _mjtJacobian           // type of constraint Jacobian
{
    mjJAC_DENSE          = 0,       // dense
    mjJAC_SPARSE,                   // sparse
    mjJAC_AUTO                      // dense if nv<=60, sparse otherwise
} mjtJacobian;

Defined in mjmodel.h

Available Jacobian types. These values are used in m->opt.jacobian.

mjtSolver

typedef enum _mjtSolver             // constraint solver algorithm
{
    mjSOL_PGS            = 0,       // PGS    (dual)
    mjSOL_CG,                       // CG     (primal)
    mjSOL_NEWTON                    // Newton (primal)
} mjtSolver;

Defined in mjmodel.h

Available constraint solver algorithms. These values are used in m->opt.solver.

mjtEq

typedef enum _mjtEq
{
    mjEQ_CONNECT        = 0,        // connect two bodies at a point (ball joint)
    mjEQ_WELD,                      // fix relative position and orientation of two bodies
    mjEQ_JOINT,                     // couple the values of two scalar joints with cubic
    mjEQ_TENDON,                    // couple the lengths of two tendons with cubic
    mjEQ_DISTANCE                   // fix the contact distance betweent two geoms
} mjtEq;

Defined in mjmodel.h

Equality constraint types. These values are used in m->eq_type.

mjtWrap

typedef enum _mjtWrap
{
    mjWRAP_NONE         = 0,        // null object
    mjWRAP_JOINT,                   // constant moment arm
    mjWRAP_PULLEY,                  // pulley used to split tendon
    mjWRAP_SITE,                    // pass through site
    mjWRAP_SPHERE,                  // wrap around sphere
    mjWRAP_CYLINDER                 // wrap around (infinite) cylinder
} mjtWrap;

Defined in mjmodel.h

Tendon wrapping object types. These values are used in m->wrap_type.

mjtTrn

typedef enum _mjtTrn
{
    mjTRN_JOINT         = 0,        // force on joint
    mjTRN_JOINTINPARENT,            // force on joint, expressed in parent frame
    mjTRN_SLIDERCRANK,              // force via slider-crank linkage
    mjTRN_TENDON,                   // force on tendon
    mjTRN_SITE,                     // force on site

    mjTRN_UNDEFINED     = 1000      // undefined transmission type
} mjtTrn;

Defined in mjmodel.h

Actuator transmission types. These values are used in m->actuator_trntype.

mjtDyn

typedef enum _mjtDyn
{
    mjDYN_NONE          = 0,        // no internal dynamics; ctrl specifies force
    mjDYN_INTEGRATOR,               // integrator: da/dt = u
    mjDYN_FILTER,                   // linear filter: da/dt = (u-a) / tau
    mjDYN_MUSCLE,                   // piece-wise linear filter with two time constants
    mjDYN_USER                      // user-defined dynamics type
} mjtDyn;

Defined in mjmodel.h

Actuator dynamics types. These values are used in m->actuator_dyntype.

mjtGain

typedef enum _mjtGain
{
    mjGAIN_FIXED        = 0,        // fixed gain
    mjGAIN_MUSCLE,                  // muscle FLV curve computed by mju_muscleGain()
    mjGAIN_USER                     // user-defined gain type
} mjtGain;

Defined in mjmodel.h

Actuator gain types. These values are used in m->actuator_gaintype.

mjtBias

typedef enum _mjtBias
{
    mjBIAS_NONE         = 0,        // no bias
    mjBIAS_AFFINE,                  // const + kp*length + kv*velocity
    mjBIAS_MUSCLE,                  // muscle passive force computed by mju_muscleBias()
    mjBIAS_USER                     // user-defined bias type
} mjtBias;

Defined in mjmodel.h

Actuator bias types. These values are used in m->actuator_biastype.

mjtObj

typedef enum _mjtObj
{
    mjOBJ_UNKNOWN       = 0,        // unknown object type
    mjOBJ_BODY,                     // body
    mjOBJ_XBODY,                    // body, used to access regular frame instead of i-frame
    mjOBJ_JOINT,                    // joint
    mjOBJ_DOF,                      // dof
    mjOBJ_GEOM,                     // geom
    mjOBJ_SITE,                     // site
    mjOBJ_CAMERA,                   // camera
    mjOBJ_LIGHT,                    // light
    mjOBJ_MESH,                     // mesh
    mjOBJ_SKIN,                     // skin
    mjOBJ_HFIELD,                   // heightfield
    mjOBJ_TEXTURE,                  // texture
    mjOBJ_MATERIAL,                 // material for rendering
    mjOBJ_PAIR,                     // geom pair to include
    mjOBJ_EXCLUDE,                  // body pair to exclude
    mjOBJ_EQUALITY,                 // equality constraint
    mjOBJ_TENDON,                   // tendon
    mjOBJ_ACTUATOR,                 // actuator
    mjOBJ_SENSOR,                   // sensor
    mjOBJ_NUMERIC,                  // numeric
    mjOBJ_TEXT,                     // text
    mjOBJ_TUPLE,                    // tuple
    mjOBJ_KEY                       // keyframe
} mjtObj;

Defined in mjmodel.h

MuJoCo object types. These values are used in the support functions mj_name2id and mj_id2name to convert between object names and integer ids.

mjtConstraint

typedef enum _mjtConstraint
{
    mjCNSTR_EQUALITY    = 0,        // equality constraint
    mjCNSTR_FRICTION_DOF,           // dof friction
    mjCNSTR_FRICTION_TENDON,        // tendon friction
    mjCNSTR_LIMIT_JOINT,            // joint limit
    mjCNSTR_LIMIT_TENDON,           // tendon limit
    mjCNSTR_CONTACT_FRICTIONLESS,   // frictionless contact
    mjCNSTR_CONTACT_PYRAMIDAL,      // frictional contact, pyramidal friction cone
    mjCNSTR_CONTACT_ELLIPTIC        // frictional contact, elliptic friction cone
} mjtConstraint;

Defined in mjmodel.h

Constraint types. These values are not used in mjModel, but are used in the mjData field d->efc_type when the list of active constraints is constructed at each simulation time step.

mjtConstraintState

typedef enum _mjtConstraint
{
    mjCNSTRSTATE_SATISFIED = 0,     // constraint satisfied, zero cost (limit, contact)
    mjCNSTRSTATE_QUADRATIC,         // quadratic cost (equality, friction, limit, contact)
    mjCNSTRSTATE_LINEARNEG,         // linear cost, negative side (friction)
    mjCNSTRSTATE_LINEARPOS,         // linear cost, positive side (friction)
    mjCNSTRSTATE_CONE               // squared distance to cone cost (elliptic contact)
} mjtConstraint;

Defined in mjmodel.h

These values are used by the solver internally to keep track of the constraint states.

mjtSensor

typedef enum _mjtSensor             // type of sensor
{
    // common robotic sensors, attached to a site
    mjSENS_TOUCH        = 0,        // scalar contact normal forces summed over sensor zone
    mjSENS_ACCELEROMETER,           // 3D linear acceleration, in local frame
    mjSENS_VELOCIMETER,             // 3D linear velocity, in local frame
    mjSENS_GYRO,                    // 3D angular velocity, in local frame
    mjSENS_FORCE,                   // 3D force between site's body and its parent body
    mjSENS_TORQUE,                  // 3D torque between site's body and its parent body
    mjSENS_MAGNETOMETER,            // 3D magnetometer
    mjSENS_RANGEFINDER,             // scalar distance to nearest geom or site along z-axis

    // sensors related to scalar joints, tendons, actuators
    mjSENS_JOINTPOS,                // scalar joint position (hinge and slide only)
    mjSENS_JOINTVEL,                // scalar joint velocity (hinge and slide only)
    mjSENS_TENDONPOS,               // scalar tendon position
    mjSENS_TENDONVEL,               // scalar tendon velocity
    mjSENS_ACTUATORPOS,             // scalar actuator position
    mjSENS_ACTUATORVEL,             // scalar actuator velocity
    mjSENS_ACTUATORFRC,             // scalar actuator force

    // sensors related to ball joints
    mjSENS_BALLQUAT,                // 4D ball joint quaterion
    mjSENS_BALLANGVEL,              // 3D ball joint angular velocity

    // joint and tendon limit sensors, in constraint space
    mjSENS_JOINTLIMITPOS,           // joint limit distance-margin
    mjSENS_JOINTLIMITVEL,           // joint limit velocity
    mjSENS_JOINTLIMITFRC,           // joint limit force
    mjSENS_TENDONLIMITPOS,          // tendon limit distance-margin
    mjSENS_TENDONLIMITVEL,          // tendon limit velocity
    mjSENS_TENDONLIMITFRC,          // tendon limit force

    // sensors attached to an object with spatial frame: (x)body, geom, site, camera
    mjSENS_FRAMEPOS,                // 3D position
    mjSENS_FRAMEQUAT,               // 4D unit quaternion orientation
    mjSENS_FRAMEXAXIS,              // 3D unit vector: x-axis of object's frame
    mjSENS_FRAMEYAXIS,              // 3D unit vector: y-axis of object's frame
    mjSENS_FRAMEZAXIS,              // 3D unit vector: z-axis of object's frame
    mjSENS_FRAMELINVEL,             // 3D linear velocity
    mjSENS_FRAMEANGVEL,             // 3D angular velocity
    mjSENS_FRAMELINACC,             // 3D linear acceleration
    mjSENS_FRAMEANGACC,             // 3D angular acceleration

    // sensors related to kinematic subtrees; attached to a body (which is the subtree root)
    mjSENS_SUBTREECOM,              // 3D center of mass of subtree
    mjSENS_SUBTREELINVEL,           // 3D linear velocity of subtree
    mjSENS_SUBTREEANGMOM,           // 3D angular momentum of subtree

    // user-defined sensor
    mjSENS_USER                     // sensor data provided by mjcb_sensor callback
} mjtSensor;

Defined in mjmodel.h

Sensor types. These values are used in m->sensor_type.

mjtStage

typedef enum _mjtStage
{
    mjSTAGE_NONE        = 0,        // no computations
    mjSTAGE_POS,                    // position-dependent computations
    mjSTAGE_VEL,                    // velocity-dependent computations
    mjSTAGE_ACC                     // acceleration/force-dependent computations
} mjtStage;

Defined in mjmodel.h

These are the compute stages for the skipstage parameters of mj_forwardSkip and mj_inverseSkip.

mjtDataType

typedef enum _mjtDataType           // data type for sensors
{
    mjDATATYPE_REAL     = 0,        // real values, no constraints
    mjDATATYPE_POSITIVE,            // positive values; 0 or negative: inactive
    mjDATATYPE_AXIS,                // 3D unit vector
    mjDATATYPE_QUATERNION           // unit quaternion
} mjtDataType;

Defined in mjmodel.h

These are the possible sensor data types, used in mjData.sensor_datatype.

mjtWarning

typedef enum _mjtWarning            // warning types
{
    mjWARN_INERTIA      = 0,        // (near) singular inertia matrix
    mjWARN_CONTACTFULL,             // too many contacts in contact list
    mjWARN_CNSTRFULL,               // too many constraints
    mjWARN_VGEOMFULL,               // too many visual geoms
    mjWARN_BADQPOS,                 // bad number in qpos
    mjWARN_BADQVEL,                 // bad number in qvel
    mjWARN_BADQACC,                 // bad number in qacc
    mjWARN_BADCTRL,                 // bad number in ctrl

    mjNWARNING                      // number of warnings
} mjtWarning;

Defined in mjdata.h

Warning types. The number of warning types is given by mjNWARNING which is also the length of the array mjData.warning.

mjtTimer

typedef enum _mjtTimer
{
    // main api
    mjTIMER_STEP        = 0,        // step
    mjTIMER_FORWARD,                // forward
    mjTIMER_INVERSE,                // inverse

    // breakdown of step/forward
    mjTIMER_POSITION,               // fwdPosition
    mjTIMER_VELOCITY,               // fwdVelocity
    mjTIMER_ACTUATION,              // fwdActuation
    mjTIMER_ACCELERATION,           // fwdAcceleration
    mjTIMER_CONSTRAINT,             // fwdConstraint

    // breakdown of fwdPosition
    mjTIMER_POS_KINEMATICS,         // kinematics, com, tendon, transmission
    mjTIMER_POS_INERTIA,            // inertia computations
    mjTIMER_POS_COLLISION,          // collision detection
    mjTIMER_POS_MAKE,               // make constraints
    mjTIMER_POS_PROJECT,            // project constraints

    mjNTIMER                        // number of timers
} mjtTimer;

Defined in mjdata.h

Timer types. The number of timer types is given by mjNTIMER which is also the length of the array mjData.timer, as well as the length of the string array mjTIMERSTRING with timer names.

mjtCatBit

typedef enum _mjtCatBit
{
    mjCAT_STATIC        = 1,        // model elements in body 0
    mjCAT_DYNAMIC       = 2,        // model elements in all other bodies
    mjCAT_DECOR         = 4,        // decorative geoms
    mjCAT_ALL           = 7         // select all categories
} mjtCatBit;

Defined in mjvisualize.h

These are the available categories of geoms in the abstract visualizer. The bitmask can be used in the function mjr_render to specify which categories should be rendered.

mjtMouse

typedef enum _mjtMouse
{
    mjMOUSE_NONE         = 0,       // no action
    mjMOUSE_ROTATE_V,               // rotate, vertical plane
    mjMOUSE_ROTATE_H,               // rotate, horizontal plane
    mjMOUSE_MOVE_V,                 // move, vertical plane
    mjMOUSE_MOVE_H,                 // move, horizontal plane
    mjMOUSE_ZOOM,                   // zoom
    mjMOUSE_SELECT                  // selection
} mjtMouse;

Defined in mjvisualize.h

These are the mouse actions that the abstract visualizer recognizes. It is up to the user to intercept mouse events and translate them into these actions, as illustrated in simulate.cpp.

mjtPertBit

typedef enum _mjtPertBit
{
    mjPERT_TRANSLATE    = 1,        // translation
    mjPERT_ROTATE       = 2         // rotation
} mjtPertBit;

Defined in mjvisualize.h

These bitmasks enable the translational and rotational components of the mouse perturbation. For the regular mouse, only one can be enabled at a time. For the 3D mouse (SpaceNavigator) both can be enabled simultaneously. Tehy are used in mjvPerturb.active.

mjtCamera

typedef enum _mjtCamera
{
    mjCAMERA_FREE        = 0,       // free camera
    mjCAMERA_TRACKING,              // tracking camera; uses trackbodyid 
    mjCAMERA_FIXED,                 // fixed camera; uses fixedcamid
    mjCAMERA_USER                   // user is responsible for setting OpenGL camera
} mjtCamera;

Defined in mjvisualize.h

These are the possible camera types, used in mjvCamera.type.

mjtLabel

typedef enum _mjtLabel
{
    mjLABEL_NONE        = 0,        // nothing
    mjLABEL_BODY,                   // body labels
    mjLABEL_JOINT,                  // joint labels
    mjLABEL_GEOM,                   // geom labels
    mjLABEL_SITE,                   // site labels
    mjLABEL_CAMERA,                 // camera labels
    mjLABEL_LIGHT,                  // light labels
    mjLABEL_TENDON,                 // tendon labels
    mjLABEL_ACTUATOR,               // actuator labels
    mjLABEL_CONSTRAINT,             // constraint labels
    mjLABEL_SKIN,                   // skin labels
    mjLABEL_SELECTION,              // selected object
    mjLABEL_SELPNT,                 // coordinates of selection point
    mjLABEL_CONTACTFORCE,           // magnitude of contact force

    mjNLABEL                        // number of label types
} mjtLabel;

Defined in mjvisualize.h

These are the abstract visualization elements that can have text labels. Used in mjvOption.label.

mjtFrame

typedef enum _mjtFrame
{
    mjFRAME_NONE        = 0,        // no frames
    mjFRAME_BODY,                   // body frames
    mjFRAME_GEOM,                   // geom frames
    mjFRAME_SITE,                   // site frames
    mjFRAME_CAMERA,                 // camera frames
    mjFRAME_LIGHT,                  // light frames
    mjFRAME_WORLD,                  // world frame

    mjNFRAME                        // number of visualization frames
} mjtFrame;

Defined in mjvisualize.h

These are the MuJoCo objects whose spatial frames can be rendered. Used in mjvOption.frame.

mjtVisFlag

typedef enum _mjtVisFlag
{
    mjVIS_CONVEXHULL    = 0,        // mesh convex hull
    mjVIS_TEXTURE,                  // textures
    mjVIS_JOINT,                    // joints
    mjVIS_ACTUATOR,                 // actuators
    mjVIS_CAMERA,                   // cameras
    mjVIS_LIGHT,                    // lights
    mjVIS_TENDON,                   // tendons
    mjVIS_RANGEFINDER,              // rangefinder sensors
    mjVIS_CONSTRAINT,               // point constraints
    mjVIS_INERTIA,                  // equivalent inertia boxes
    mjVIS_SCLINERTIA,               // scale equivalent inertia boxes with mass
    mjVIS_PERTFORCE,                // perturbation force
    mjVIS_PERTOBJ,                  // perturbation object
    mjVIS_CONTACTPOINT,             // contact points
    mjVIS_CONTACTFORCE,             // contact force
    mjVIS_CONTACTSPLIT,             // split contact force into normal and tanget
    mjVIS_TRANSPARENT,              // make dynamic geoms more transparent
    mjVIS_AUTOCONNECT,              // auto connect joints and body coms
    mjVIS_COM,                      // center of mass
    mjVIS_SELECT,                   // selection point
    mjVIS_STATIC,                   // static bodies
    mjVIS_SKIN,                     // skin

    mjNVISFLAG                      // number of visualization flags
} mjtVisFlag;

Defined in mjvisualize.h

These are indices in the array mjvOption.flags, whose elements enable/disable the visualization of the corresponding model or decoration element.

mjtRndFlag

typedef enum _mjtRndFlag
{
    mjRND_SHADOW        = 0,        // shadows
    mjRND_WIREFRAME,                // wireframe
    mjRND_REFLECTION,               // reflections
    mjRND_ADDITIVE,                 // additive transparency
    mjRND_SKYBOX,                   // skybox
    mjRND_FOG,                      // fog
    mjRND_HAZE,                     // haze
    mjRND_SEGMENT,                  // segmentation with random color
    mjRND_IDCOLOR,                  // segmentation with segid color

    mjNRNDFLAG                      // number of rendering flags
} mjtRndFlag;

Defined in mjvisualize.h

These are indices in the array mjvScene.flags, whose elements enable/disable OpenGL rendering effects.

mjtStereo

typedef enum _mjtStereo 
{
    mjSTEREO_NONE       = 0,        // no stereo; use left eye only
    mjSTEREO_QUADBUFFERED,          // quad buffered; revert to side-by-side if no hardware support
    mjSTEREO_SIDEBYSIDE             // side-by-side
} mjtStereo;

Defined in mjvisualize.h

These are the possible stereo rendering types. They are used in mjvScene.stereo.

mjtGridPos

typedef enum _mjtGridPos
{
    mjGRID_TOPLEFT      = 0,        // top left
    mjGRID_TOPRIGHT,                // top right
    mjGRID_BOTTOMLEFT,              // bottom left
    mjGRID_BOTTOMRIGHT              // bottom right
} mjtGridPos;

Defined in mjrender.h

These are the possible grid positions for text overlays. They are used as an argument to the function mjr_overlay.

mjtFramebuffer

typedef enum _mjtFramebuffer
{
    mjFB_WINDOW         = 0,        // default/window buffer
    mjFB_OFFSCREEN                  // offscreen buffer
} mjtFramebuffer;

Defined in mjrender.h

These are the possible framebuffers. They are used as an argument to the function mjr_setBuffer.

mjtFontScale

typedef enum _mjtFontScale
{
    mjFONTSCALE_50      = 50,       // 50% scale, suitable for low-res rendering
    mjFONTSCALE_100     = 100,      // normal scale, suitable in the absence of DPI scaling
    mjFONTSCALE_150     = 150,      // 150% scale
    mjFONTSCALE_200     = 200,      // 200% scale
    mjFONTSCALE_250     = 250,      // 250% scale
    mjFONTSCALE_300     = 300       // 300% scale
} mjtFontScale;

Defined in mjrender.h

These are the possible font sizes. The fonts are predefined bitmaps stored in the dynamic library at three different sizes.

mjtFont

typedef enum _mjtFont
{
    mjFONT_NORMAL       = 0,        // normal font
    mjFONT_SHADOW,                  // normal font with shadow (for higher contrast)
    mjFONT_BIG                      // big font (for user alerts)
} mjtFont;

Defined in mjrender.h

These are the possible font types.

mjtButton

typedef enum _mjtButton         // mouse button
{
    mjBUTTON_NONE = 0,          // no button
    mjBUTTON_LEFT,              // left button
    mjBUTTON_RIGHT,             // right button
    mjBUTTON_MIDDLE             // middle button
} mjtButton;

Defined in mjui.h

Mouse button IDs used in the UI framework.

mjtEvent

typedef enum _mjtEvent          // mouse and keyboard event type
{
    mjEVENT_NONE = 0,           // no event
    mjEVENT_MOVE,               // mouse move
    mjEVENT_PRESS,              // mouse button press
    mjEVENT_RELEASE,            // mouse button release
    mjEVENT_SCROLL,             // scroll
    mjEVENT_KEY,                // key press
    mjEVENT_RESIZE              // resize
} mjtEvent;

Defined in mjui.h

Event types used in the UI framework.

mjtItem

typedef enum _mjtItem           // UI item type
{
    mjITEM_END = -2,            // end of definition list (not an item)
    mjITEM_SECTION = -1,        // section (not an item)
    mjITEM_SEPARATOR = 0,       // separator
    mjITEM_STATIC,              // static text
    mjITEM_BUTTON,              // button

    // the rest have data pointer
    mjITEM_CHECKINT,            // check box, int value
    mjITEM_CHECKBYTE,           // check box, mjtByte value
    mjITEM_RADIO,               // radio group
    mjITEM_SELECT,              // selection box
    mjITEM_SLIDERINT,           // slider, int value
    mjITEM_SLIDERNUM,           // slider, mjtNum value
    mjITEM_EDITINT,             // editable array, int values
    mjITEM_EDITNUM,             // editable array, mjtNum values
    mjITEM_EDITTXT,             // editable text

    mjNITEM                     // number of item types
} mjtItem;

Defined in mjui.h

Item types used in the UI framework.

Function types

MuJoCo callbacks have corresponding function types. They are defined in mjdata.h and in mjui.h. The actual callback functions are documented later.

mjfGeneric

typedef void (*mjfGeneric)(const mjModel* m, mjData* d);

This is the function type of the callbacks mjcb_passive and mjcb_control.

mjfConFilt

typedef int (*mjfConFilt)(const mjModel* m, mjData* d, int geom1, int geom2);

This is the function type of the callback mjcb_contactfilter. The return value is 1: discard, 0: proceed with collision check.

mjfSensor

typedef void (*mjfSensor)(const mjModel* m, mjData* d, int stage);

This is the function type of the callback mjcb_sensor.

mjfTime

typedef mjtNum (*mjfTime)(void);  

This is the function type of the callback mjcb_time.

mjfAct

typedef mjtNum (*mjfAct)(const mjModel* m, const mjData* d, int id);

This is the function type of the callbacks mjcb_act_dyn, mjcb_act_gain and mjcb_act_bias.

mjfCollision

typedef int (*mjfCollision)(const mjModel* m, const mjData* d, 
                            mjContact* con, int g1, int g2, mjtNum margin);

This is the function type of the callbacks in the collision table mjCOLLISIONFUNC.

mjfItemEnable

typedef int (*mjfItemEnable)(int category, void* data);

This is the function type of the predicate function used by the UI framework to determine if each item is enabled or disabled.

Data structures

MuJoCo uses several data structures shown below. They are taken directly from the header files which contain comments for each field.

mjVFS

struct _mjVFS                       // virtual file system for loading from memory
{
    int   nfile;                    // number of files present
    char  filename[mjMAXVFS][mjMAXVFSNAME]; // file name without path
    int   filesize[mjMAXVFS];       // file size in bytes   
    void* filedata[mjMAXVFS];       // buffer with file data
};
typedef struct _mjVFS mjVFS;

Defined in mjmodel.h

This is the data structure with the virtual file system. It can only be constructed programmatically, and does not have an analog in MJCF.

mjOption

struct _mjOption                    // physics options
{
    // timing parameters
    mjtNum timestep;                // timestep
    mjtNum apirate;                 // update rate for remote API (Hz)

    // solver parameters
    mjtNum impratio;                // ratio of friction-to-normal contact impedance
    mjtNum tolerance;               // main solver tolerance
    mjtNum noslip_tolerance;        // noslip solver tolerance
    mjtNum mpr_tolerance;           // MPR solver tolerance

    // physical constants
    mjtNum gravity[3];              // gravitational acceleration
    mjtNum wind[3];                 // wind (for lift, drag and viscosity)
    mjtNum magnetic[3];             // global magnetic flux
    mjtNum density;                 // density of medium
    mjtNum viscosity;               // viscosity of medium

    // override contact solver parameters (if enabled)
    mjtNum o_margin;                // margin
    mjtNum o_solref[mjNREF];        // solref
    mjtNum o_solimp[mjNIMP];        // solimp

    // discrete settings
    int integrator;                 // integration mode (mjtIntegrator)
    int collision;                  // collision mode (mjtCollision)
    int cone;                       // type of friction cone (mjtCone)
    int jacobian;                   // type of Jacobian (mjtJacobian)
    int solver;                     // solver algorithm (mjtSolver)
    int iterations;                 // maximum number of main solver iterations
    int noslip_iterations;          // maximum number of noslip solver iterations
    int mpr_iterations;             // maximum number of MPR solver iterations
    int disableflags;               // bit flags for disabling standard features
    int enableflags;                // bit flags for enabling optional features
};
typedef struct _mjOption mjOption;

Defined in mjmodel.h

This is the data structure with simulation options. It corresponds to the MJCF element option. One instance of it is embedded in mjModel.

mjVisual

struct _mjVisual                    // visualization options
{
    struct                          // global parameters
    {
        float fovy;                 // y-field of view (deg) for free camera
        float ipd;                  // inter-pupilary distance for free camera
        float linewidth;            // line width for wireframe and ray rendering
        float glow;                 // glow coefficient for selected body
        int offwidth;               // width of offscreen buffer
        int offheight;              // height of offscreen buffer
    } global;

    struct                          // rendering quality
    {
        int   shadowsize;           // size of shadowmap texture
        int   offsamples;           // number of multisamples for offscreen rendering
        int   numslices;            // number of slices for builtin geom drawing
        int   numstacks;            // number of stacks for builtin geom drawing
        int   numquads;             // number of quads for box rendering
    } quality;

    struct                          // head light
    {
        float ambient[3];           // ambient rgb (alpha=1)
        float diffuse[3];           // diffuse rgb (alpha=1)
        float specular[3];          // specular rgb (alpha=1)
        int   active;               // is headlight active
    } headlight;

    struct                          // mapping
    {
        float stiffness;            // mouse perturbation stiffness (space->force)
        float stiffnessrot;         // mouse perturbation stiffness (space->torque)
        float force;                // from force units to space units
        float torque;               // from torque units to space units
        float alpha;                // scale geom alphas when transparency is enabled
        float fogstart;             // OpenGL fog starts at fogstart * mjModel.stat.extent
        float fogend;               // OpenGL fog ends at fogend * mjModel.stat.extent
        float znear;                // near clipping plane = znear * mjModel.stat.extent
        float zfar;                 // far clipping plane = zfar * mjModel.stat.extent
        float haze;                 // haze ratio
        float shadowclip;           // directional light: shadowclip * mjModel.stat.extent
        float shadowscale;          // spot light: shadowscale * light.cutoff
        float actuatortendon;       // scale tendon width
    } map;

    struct                          // scale of decor elements relative to mean body size
    {
        float forcewidth;           // width of force arrow
        float contactwidth;         // contact width
        float contactheight;        // contact height
        float connect;              // autoconnect capsule width
        float com;                  // com radius
        float camera;               // camera object
        float light;                // light object
        float selectpoint;          // selection point
        float jointlength;          // joint length
        float jointwidth;           // joint width
        float actuatorlength;       // actuator length
        float actuatorwidth;        // actuator width
        float framelength;          // bodyframe axis length
        float framewidth;           // bodyframe axis width
        float constraint;           // constraint width
        float slidercrank;          // slidercrank width
    } scale;

    struct                          // color of decor elements
    {
        float fog[4];               // fog
        float haze[4];              // haze
        float force[4];             // external force
        float inertia[4];           // inertia box
        float joint[4];             // joint
        float actuator[4];          // actuator, neutral
        float actuatornegative[4];  // actuator, negative limit
        float actuatorpositive[4];  // actuator, positive limit
        float com[4];               // center of mass
        float camera[4];            // camera object
        float light[4];             // light object
        float selectpoint[4];       // selection point
        float connect[4];           // auto connect
        float contactpoint[4];      // contact point
        float contactforce[4];      // contact force
        float contactfriction[4];   // contact friction force
        float contacttorque[4];     // contact torque
        float contactgap[4];        // contact point in gap
        float rangefinder[4];       // rangefinder ray
        float constraint[4];        // constraint
        float slidercrank[4];       // slidercrank
        float crankbroken[4];       // used when crank must be stretched/broken
    } rgba;
};
typedef struct _mjVisual mjVisual;

Defined in mjmodel.h

This is the data structure with abstract visualization options. It corresponds to the MJCF element visual. One instance of it is embedded in mjModel.

mjStatistic

struct _mjStatistic                 // model statistics (in qpos0)
{
    mjtNum meaninertia;             // mean diagonal inertia
    mjtNum meanmass;                // mean body mass
    mjtNum meansize;                // mean body size
    mjtNum extent;                  // spatial extent
    mjtNum center[3];               // center of model
};
typedef struct _mjStatistic mjStatistic;

Defined in mjmodel.h

This is the data structure with model statistics precomputed by the compiler or set by the user. It corresponds to the MJCF element statistic. One instance of it is embedded in mjModel.

mjModel

struct _mjModel
{
    // ------------------------------- sizes

    // sizes needed at mjModel construction
    int nq;                         // number of generalized coordinates = dim(qpos)
    int nv;                         // number of degrees of freedom = dim(qvel)
    int nu;                         // number of actuators/controls = dim(ctrl)
    int na;                         // number of activation states = dim(act)
    int nbody;                      // number of bodies
    int njnt;                       // number of joints
    int ngeom;                      // number of geoms
    int nsite;                      // number of sites
    int ncam;                       // number of cameras
    int nlight;                     // number of lights
    int nmesh;                      // number of meshes
    int nmeshvert;                  // number of vertices in all meshes
    int nmeshtexvert;               // number of vertices with texcoords in all meshes
    int nmeshface;                  // number of triangular faces in all meshes
    int nmeshgraph;                 // number of ints in mesh auxiliary data
    int nskin;                      // number of skins
    int nskinvert;                  // number of vertices in all skins
    int nskintexvert;               // number of vertiex with texcoords in all skins
    int nskinface;                  // number of triangular faces in all skins
    int nskinbone;                  // number of bones in all skins
    int nskinbonevert;              // number of vertices in all skin bones
    int nhfield;                    // number of heightfields
    int nhfielddata;                // number of data points in all heightfields
    int ntex;                       // number of textures
    int ntexdata;                   // number of bytes in texture rgb data
    int nmat;                       // number of materials
    int npair;                      // number of predefined geom pairs
    int nexclude;                   // number of excluded geom pairs
    int neq;                        // number of equality constraints
    int ntendon;                    // number of tendons
    int nwrap;                      // number of wrap objects in all tendon paths
    int nsensor;                    // number of sensors
    int nnumeric;                   // number of numeric custom fields
    int nnumericdata;               // number of mjtNums in all numeric fields
    int ntext;                      // number of text custom fields
    int ntextdata;                  // number of mjtBytes in all text fields
    int ntuple;                     // number of tuple custom fields
    int ntupledata;                 // number of objects in all tuple fields
    int nkey;                       // number of keyframes
    int nuser_body;                 // number of mjtNums in body_user
    int nuser_jnt;                  // number of mjtNums in jnt_user
    int nuser_geom;                 // number of mjtNums in geom_user
    int nuser_site;                 // number of mjtNums in site_user
    int nuser_cam;                  // number of mjtNums in cam_user
    int nuser_tendon;               // number of mjtNums in tendon_user
    int nuser_actuator;             // number of mjtNums in actuator_user
    int nuser_sensor;               // number of mjtNums in sensor_user
    int nnames;                     // number of chars in all names

    // sizes set after mjModel construction (only affect mjData)
    int nM;                         // number of non-zeros in sparse inertia matrix
    int nemax;                      // number of potential equality-constraint rows
    int njmax;                      // number of available rows in constraint Jacobian
    int nconmax;                    // number of potential contacts in contact list
    int nstack;                     // number of fields in mjData stack
    int nuserdata;                  // number of extra fields in mjData
    int nmocap;                     // number of mocap bodies
    int nsensordata;                // number of fields in sensor data vector

    int nbuffer;                    // number of bytes in buffer

    // ------------------------------- options and statistics

    mjOption opt;                   // physics options
    mjVisual vis;                   // visualization options
    mjStatistic stat;               // model statistics

    // ------------------------------- buffers

    // main buffer
    void*     buffer;               // main buffer; all pointers point in it    (nbuffer)

    // default generalized coordinates
    mjtNum*   qpos0;                // qpos values at default pose              (nq x 1)
    mjtNum*   qpos_spring;          // reference pose for springs               (nq x 1)

    // bodies
    int*      body_parentid;        // id of body's parent                      (nbody x 1)
    int*      body_rootid;          // id of root above body                    (nbody x 1)
    int*      body_weldid;          // id of body that this body is welded to   (nbody x 1)
    int*      body_mocapid;         // id of mocap data; -1: none               (nbody x 1)
    int*      body_jntnum;          // number of joints for this body           (nbody x 1)
    int*      body_jntadr;          // start addr of joints; -1: no joints      (nbody x 1)
    int*      body_dofnum;          // number of motion degrees of freedom      (nbody x 1)
    int*      body_dofadr;          // start addr of dofs; -1: no dofs          (nbody x 1)
    int*      body_geomnum;         // number of geoms                          (nbody x 1)
    int*      body_geomadr;         // start addr of geoms; -1: no geoms        (nbody x 1)
    mjtByte*  body_simple;          // body is simple (has diagonal M)          (nbody x 1)
    mjtByte*  body_sameframe;       // inertial frame is same as body frame     (nbody x 1)
    mjtNum*   body_pos;             // position offset rel. to parent body      (nbody x 3)
    mjtNum*   body_quat;            // orientation offset rel. to parent body   (nbody x 4)
    mjtNum*   body_ipos;            // local position of center of mass         (nbody x 3)
    mjtNum*   body_iquat;           // local orientation of inertia ellipsoid   (nbody x 4)
    mjtNum*   body_mass;            // mass                                     (nbody x 1)
    mjtNum*   body_subtreemass;     // mass of subtree starting at this body    (nbody x 1)
    mjtNum*   body_inertia;         // diagonal inertia in ipos/iquat frame     (nbody x 3)
    mjtNum*   body_invweight0;      // mean inv inert in qpos0 (trn, rot)       (nbody x 2)
    mjtNum*   body_user;            // user data                                (nbody x nuser_body)

    // joints
    int*      jnt_type;             // type of joint (mjtJoint)                 (njnt x 1)
    int*      jnt_qposadr;          // start addr in 'qpos' for joint's data    (njnt x 1)
    int*      jnt_dofadr;           // start addr in 'qvel' for joint's data    (njnt x 1)
    int*      jnt_bodyid;           // id of joint's body                       (njnt x 1)
    int*      jnt_group;            // group for visibility                     (njnt x 1)
    mjtByte*  jnt_limited;          // does joint have limits                   (njnt x 1)
    mjtNum*   jnt_solref;           // constraint solver reference: limit       (njnt x mjNREF)
    mjtNum*   jnt_solimp;           // constraint solver impedance: limit       (njnt x mjNIMP)
    mjtNum*   jnt_pos;              // local anchor position                    (njnt x 3)
    mjtNum*   jnt_axis;             // local joint axis                         (njnt x 3)
    mjtNum*   jnt_stiffness;        // stiffness coefficient                    (njnt x 1)
    mjtNum*   jnt_range;            // joint limits                             (njnt x 2)
    mjtNum*   jnt_margin;           // min distance for limit detection         (njnt x 1)
    mjtNum*   jnt_user;             // user data                                (njnt x nuser_jnt)

    // dofs
    int*      dof_bodyid;           // id of dof's body                         (nv x 1)
    int*      dof_jntid;            // id of dof's joint                        (nv x 1)
    int*      dof_parentid;         // id of dof's parent; -1: none             (nv x 1)
    int*      dof_Madr;             // dof address in M-diagonal                (nv x 1)
    int*      dof_simplenum;        // number of consecutive simple dofs        (nv x 1)
    mjtNum*   dof_solref;           // constraint solver reference:frictionloss (nv x mjNREF)
    mjtNum*   dof_solimp;           // constraint solver impedance:frictionloss (nv x mjNIMP)
    mjtNum*   dof_frictionloss;     // dof friction loss                        (nv x 1)
    mjtNum*   dof_armature;         // dof armature inertia/mass                (nv x 1)
    mjtNum*   dof_damping;          // damping coefficient                      (nv x 1)
    mjtNum*   dof_invweight0;       // diag. inverse inertia in qpos0           (nv x 1)
    mjtNum*   dof_M0;               // diag. inertia in qpos0                   (nv x 1)

    // geoms
    int*      geom_type;            // geometric type (mjtGeom)                 (ngeom x 1)
    int*      geom_contype;         // geom contact type                        (ngeom x 1)
    int*      geom_conaffinity;     // geom contact affinity                    (ngeom x 1)
    int*      geom_condim;          // contact dimensionality (1, 3, 4, 6)      (ngeom x 1)
    int*      geom_bodyid;          // id of geom's body                        (ngeom x 1)
    int*      geom_dataid;          // id of geom's mesh/hfield (-1: none)      (ngeom x 1)
    int*      geom_matid;           // material id for rendering                (ngeom x 1)
    int*      geom_group;           // group for visibility                     (ngeom x 1)
    int*      geom_priority;        // geom contact priority                    (ngeom x 1)
    mjtByte*  geom_sameframe;       // same as body frame (1) or iframe (2)     (ngeom x 1)
    mjtNum*   geom_solmix;          // mixing coef for solref/imp in geom pair  (ngeom x 1)
    mjtNum*   geom_solref;          // constraint solver reference: contact     (ngeom x mjNREF)
    mjtNum*   geom_solimp;          // constraint solver impedance: contact     (ngeom x mjNIMP)
    mjtNum*   geom_size;            // geom-specific size parameters            (ngeom x 3)
    mjtNum*   geom_rbound;          // radius of bounding sphere                (ngeom x 1)
    mjtNum*   geom_pos;             // local position offset rel. to body       (ngeom x 3)
    mjtNum*   geom_quat;            // local orientation offset rel. to body    (ngeom x 4)
    mjtNum*   geom_friction;        // friction for (slide, spin, roll)         (ngeom x 3)
    mjtNum*   geom_margin;          // detect contact if dist<margin            (ngeom x 1)
    mjtNum*   geom_gap;             // include in solver if dist<margin-gap     (ngeom x 1)
    mjtNum*   geom_user;            // user data                                (ngeom x nuser_geom)
    float*    geom_rgba;            // rgba when material is omitted            (ngeom x 4)

    // sites
    int*      site_type;            // geom type for rendering (mjtGeom)        (nsite x 1)
    int*      site_bodyid;          // id of site's body                        (nsite x 1)
    int*      site_matid;           // material id for rendering                (nsite x 1)
    int*      site_group;           // group for visibility                     (nsite x 1)
    mjtByte*  site_sameframe;       // same as body frame (1) or iframe (2)     (nsite x 1)
    mjtNum*   site_size;            // geom size for rendering                  (nsite x 3)
    mjtNum*   site_pos;             // local position offset rel. to body       (nsite x 3)
    mjtNum*   site_quat;            // local orientation offset rel. to body    (nsite x 4)
    mjtNum*   site_user;            // user data                                (nsite x nuser_site)
    float*    site_rgba;            // rgba when material is omitted            (nsite x 4)

    // cameras
    int*      cam_mode;             // camera tracking mode (mjtCamLight)       (ncam x 1)
    int*      cam_bodyid;           // id of camera's body                      (ncam x 1)
    int*      cam_targetbodyid;     // id of targeted body; -1: none            (ncam x 1)
    mjtNum*   cam_pos;              // position rel. to body frame              (ncam x 3)
    mjtNum*   cam_quat;             // orientation rel. to body frame           (ncam x 4)
    mjtNum*   cam_poscom0;          // global position rel. to sub-com in qpos0 (ncam x 3)
    mjtNum*   cam_pos0;             // global position rel. to body in qpos0    (ncam x 3)
    mjtNum*   cam_mat0;             // global orientation in qpos0              (ncam x 9)
    mjtNum*   cam_fovy;             // y-field of view (deg)                    (ncam x 1)
    mjtNum*   cam_ipd;              // inter-pupilary distance                  (ncam x 1)
    mjtNum*   cam_user;             // user data                                (ncam x nuser_cam)

    // lights
    int*      light_mode;           // light tracking mode (mjtCamLight)        (nlight x 1)
    int*      light_bodyid;         // id of light's body                       (nlight x 1)
    int*      light_targetbodyid;   // id of targeted body; -1: none            (nlight x 1)
    mjtByte*  light_directional;    // directional light                        (nlight x 1)
    mjtByte*  light_castshadow;     // does light cast shadows                  (nlight x 1)
    mjtByte*  light_active;         // is light on                              (nlight x 1)
    mjtNum*   light_pos;            // position rel. to body frame              (nlight x 3)
    mjtNum*   light_dir;            // direction rel. to body frame             (nlight x 3)
    mjtNum*   light_poscom0;        // global position rel. to sub-com in qpos0 (nlight x 3)
    mjtNum*   light_pos0;           // global position rel. to body in qpos0    (nlight x 3)
    mjtNum*   light_dir0;           // global direction in qpos0                (nlight x 3)
    float*    light_attenuation;    // OpenGL attenuation (quadratic model)     (nlight x 3)
    float*    light_cutoff;         // OpenGL cutoff                            (nlight x 1)
    float*    light_exponent;       // OpenGL exponent                          (nlight x 1)
    float*    light_ambient;        // ambient rgb (alpha=1)                    (nlight x 3)
    float*    light_diffuse;        // diffuse rgb (alpha=1)                    (nlight x 3)
    float*    light_specular;       // specular rgb (alpha=1)                   (nlight x 3)

    // meshes
    int*      mesh_vertadr;         // first vertex address                     (nmesh x 1)
    int*      mesh_vertnum;         // number of vertices                       (nmesh x 1)
    int*      mesh_texcoordadr;     // texcoord data address; -1: no texcoord   (nmesh x 1)
    int*      mesh_faceadr;         // first face address                       (nmesh x 1)
    int*      mesh_facenum;         // number of faces                          (nmesh x 1)
    int*      mesh_graphadr;        // graph data address; -1: no graph         (nmesh x 1)
    float*    mesh_vert;            // vertex positions for all meshe           (nmeshvert x 3)
    float*    mesh_normal;          // vertex normals for all meshes            (nmeshvert x 3)
    float*    mesh_texcoord;        // vertex texcoords for all meshes          (nmeshtexvert x 2)
    int*      mesh_face;            // triangle face data                       (nmeshface x 3)
    int*      mesh_graph;           // convex graph data                        (nmeshgraph x 1)

    // skins
    int*      skin_matid;           // skin material id; -1: none               (nskin x 1)
    float*    skin_rgba;            // skin rgba                                (nskin x 4)
    float*    skin_inflate;         // inflate skin in normal direction         (nskin x 1)
    int*      skin_vertadr;         // first vertex address                     (nskin x 1)
    int*      skin_vertnum;         // number of vertices                       (nskin x 1)
    int*      skin_texcoordadr;     // texcoord data address; -1: no texcoord   (nskin x 1)
    int*      skin_faceadr;         // first face address                       (nskin x 1)
    int*      skin_facenum;         // number of faces                          (nskin x 1)
    int*      skin_boneadr;         // first bone in skin                       (nskin x 1)
    int*      skin_bonenum;         // number of bones in skin                  (nskin x 1)
    float*    skin_vert;            // vertex positions for all skin meshes     (nskinvert x 3)
    float*    skin_texcoord;        // vertex texcoords for all skin meshes     (nskintexvert x 2)
    int*      skin_face;            // triangle faces for all skin meshes       (nskinface x 3)
    int*      skin_bonevertadr;     // first vertex in each bone                (nskinbone x 1)
    int*      skin_bonevertnum;     // number of vertices in each bone          (nskinbone x 1)
    float*    skin_bonebindpos;     // bind pos of each bone                    (nskinbone x 3)
    float*    skin_bonebindquat;    // bind quat of each bone                   (nskinbone x 4)
    int*      skin_bonebodyid;      // body id of each bone                     (nskinbone x 1)
    int*      skin_bonevertid;      // mesh ids of vertices in each bone        (nskinbonevert x 1)
    float*    skin_bonevertweight;  // weights of vertices in each bone         (nskinbonevert x 1)

    // height fields
    mjtNum*   hfield_size;          // (x, y, z_top, z_bottom)                  (nhfield x 4)
    int*      hfield_nrow;          // number of rows in grid                   (nhfield x 1)
    int*      hfield_ncol;          // number of columns in grid                (nhfield x 1)
    int*      hfield_adr;           // address in hfield_data                   (nhfield x 1)
    float*    hfield_data;          // elevation data                           (nhfielddata x 1)

    // textures
    int*      tex_type;             // texture type (mjtTexture)                (ntex x 1)
    int*      tex_height;           // number of rows in texture image          (ntex x 1)
    int*      tex_width;            // number of columns in texture image       (ntex x 1)
    int*      tex_adr;              // address in rgb                           (ntex x 1)
    mjtByte*  tex_rgb;              // rgb (alpha = 1)                          (ntexdata x 1)

    // materials
    int*      mat_texid;            // texture id; -1: none                     (nmat x 1)
    mjtByte*  mat_texuniform;       // make texture cube uniform                (nmat x 1)
    float*    mat_texrepeat;        // texture repetition for 2d mapping        (nmat x 2)
    float*    mat_emission;         // emission (x rgb)                         (nmat x 1)
    float*    mat_specular;         // specular (x white)                       (nmat x 1)
    float*    mat_shininess;        // shininess coef                           (nmat x 1)
    float*    mat_reflectance;      // reflectance (0: disable)                 (nmat x 1)
    float*    mat_rgba;             // rgba                                     (nmat x 4)

    // predefined geom pairs for collision detection; has precedence over exclude
    int*      pair_dim;             // contact dimensionality                   (npair x 1)
    int*      pair_geom1;           // id of geom1                              (npair x 1)
    int*      pair_geom2;           // id of geom2                              (npair x 1)
    int*      pair_signature;       // (body1+1)<<16 + body2+1                  (npair x 1)
    mjtNum*   pair_solref;          // constraint solver reference: contact     (npair x mjNREF)
    mjtNum*   pair_solimp;          // constraint solver impedance: contact     (npair x mjNIMP)
    mjtNum*   pair_margin;          // detect contact if dist<margin            (npair x 1)
    mjtNum*   pair_gap;             // include in solver if dist<margin-gap     (npair x 1)
    mjtNum*   pair_friction;        // tangent1, 2, spin, roll1, 2              (npair x 5)

    // excluded body pairs for collision detection
    int*      exclude_signature;    // (body1+1)<<16 + body2+1                  (nexclude x 1)

    // equality constraints
    int*      eq_type;              // constraint type (mjtEq)                  (neq x 1)
    int*      eq_obj1id;            // id of object 1                           (neq x 1)
    int*      eq_obj2id;            // id of object 2                           (neq x 1)
    mjtByte*  eq_active;            // enable/disable constraint                (neq x 1)
    mjtNum*   eq_solref;            // constraint solver reference              (neq x mjNREF)
    mjtNum*   eq_solimp;            // constraint solver impedance              (neq x mjNIMP)
    mjtNum*   eq_data;              // numeric data for constraint              (neq x mjNEQDATA)

    // tendons
    int*      tendon_adr;           // address of first object in tendon's path (ntendon x 1)
    int*      tendon_num;           // number of objects in tendon's path       (ntendon x 1)
    int*      tendon_matid;         // material id for rendering                (ntendon x 1)
    int*      tendon_group;         // group for visibility                     (ntendon x 1)
    mjtByte*  tendon_limited;       // does tendon have length limits           (ntendon x 1)
    mjtNum*   tendon_width;         // width for rendering                      (ntendon x 1)
    mjtNum*   tendon_solref_lim;    // constraint solver reference: limit       (ntendon x mjNREF)
    mjtNum*   tendon_solimp_lim;    // constraint solver impedance: limit       (ntendon x mjNIMP)
    mjtNum*   tendon_solref_fri;    // constraint solver reference: friction    (ntendon x mjNREF)
    mjtNum*   tendon_solimp_fri;    // constraint solver impedance: friction    (ntendon x mjNIMP)
    mjtNum*   tendon_range;         // tendon length limits                     (ntendon x 2)
    mjtNum*   tendon_margin;        // min distance for limit detection         (ntendon x 1)
    mjtNum*   tendon_stiffness;     // stiffness coefficient                    (ntendon x 1)
    mjtNum*   tendon_damping;       // damping coefficient                      (ntendon x 1)
    mjtNum*   tendon_frictionloss;  // loss due to friction                     (ntendon x 1)
    mjtNum*   tendon_lengthspring;  // tendon length in qpos_spring             (ntendon x 1)
    mjtNum*   tendon_length0;       // tendon length in qpos0                   (ntendon x 1)
    mjtNum*   tendon_invweight0;    // inv. weight in qpos0                     (ntendon x 1)
    mjtNum*   tendon_user;          // user data                                (ntendon x nuser_tendon)
    float*    tendon_rgba;          // rgba when material is omitted            (ntendon x 4)

    // list of all wrap objects in tendon paths
    int*      wrap_type;            // wrap object type (mjtWrap)               (nwrap x 1)
    int*      wrap_objid;           // object id: geom, site, joint             (nwrap x 1)
    mjtNum*   wrap_prm;             // divisor, joint coef, or site id          (nwrap x 1)

    // actuators
    int*      actuator_trntype;     // transmission type (mjtTrn)               (nu x 1)
    int*      actuator_dyntype;     // dynamics type (mjtDyn)                   (nu x 1)
    int*      actuator_gaintype;    // gain type (mjtGain)                      (nu x 1)
    int*      actuator_biastype;    // bias type (mjtBias)                      (nu x 1)
    int*      actuator_trnid;       // transmission id: joint, tendon, site     (nu x 2)
    int*      actuator_group;       // group for visibility                     (nu x 1)
    mjtByte*  actuator_ctrllimited; // is control limited                       (nu x 1)
    mjtByte*  actuator_forcelimited;// is force limited                         (nu x 1)
    mjtNum*   actuator_dynprm;      // dynamics parameters                      (nu x mjNDYN)
    mjtNum*   actuator_gainprm;     // gain parameters                          (nu x mjNGAIN)
    mjtNum*   actuator_biasprm;     // bias parameters                          (nu x mjNBIAS)
    mjtNum*   actuator_ctrlrange;   // range of controls                        (nu x 2)
    mjtNum*   actuator_forcerange;  // range of forces                          (nu x 2)
    mjtNum*   actuator_gear;        // scale length and transmitted force       (nu x 6)
    mjtNum*   actuator_cranklength; // crank length for slider-crank            (nu x 1)
    mjtNum*   actuator_acc0;        // acceleration from unit force in qpos0    (nu x 1)
    mjtNum*   actuator_length0;     // actuator length in qpos0                 (nu x 1)
    mjtNum*   actuator_lengthrange; // feasible actuator length range           (nu x 2)
    mjtNum*   actuator_user;        // user data                                (nu x nuser_actuator)

    // sensors
    int*      sensor_type;          // sensor type (mjtSensor)                  (nsensor x 1)
    int*      sensor_datatype;      // numeric data type (mjtDataType)          (nsensor x 1)
    int*      sensor_needstage;     // required compute stage (mjtStage)        (nsensor x 1)
    int*      sensor_objtype;       // type of sensorized object (mjtObj)       (nsensor x 1)
    int*      sensor_objid;         // id of sensorized object                  (nsensor x 1)
    int*      sensor_dim;           // number of scalar outputs                 (nsensor x 1)
    int*      sensor_adr;           // address in sensor array                  (nsensor x 1)
    mjtNum*   sensor_cutoff;        // cutoff for real and positive; 0: ignore  (nsensor x 1)
    mjtNum*   sensor_noise;         // noise standard deviation                 (nsensor x 1)
    mjtNum*   sensor_user;          // user data                                (nsensor x nuser_sensor)

    // custom numeric fields
    int*      numeric_adr;          // address of field in numeric_data         (nnumeric x 1)
    int*      numeric_size;         // size of numeric field                    (nnumeric x 1)
    mjtNum*   numeric_data;         // array of all numeric fields              (nnumericdata x 1)

    // custom text fields
    int*      text_adr;             // address of text in text_data             (ntext x 1)
    int*      text_size;            // size of text field (strlen+1)            (ntext x 1)
    char*     text_data;            // array of all text fields (0-terminated)  (ntextdata x 1)

    // custom tuple fields
    int*      tuple_adr;            // address of text in text_data             (ntuple x 1)
    int*      tuple_size;           // number of objects in tuple               (ntuple x 1)
    int*      tuple_objtype;        // array of object types in all tuples      (ntupledata x 1)
    int*      tuple_objid;          // array of object ids in all tuples        (ntupledata x 1)
    mjtNum*   tuple_objprm;         // array of object params in all tuples     (ntupledata x 1)

    // keyframes
    mjtNum*   key_time;             // key time                                 (nkey x 1)
    mjtNum*   key_qpos;             // key position                             (nkey x nq)
    mjtNum*   key_qvel;             // key velocity                             (nkey x nv)
    mjtNum*   key_act;              // key activation                           (nkey x na)

    // names
    int*      name_bodyadr;         // body name pointers                       (nbody x 1)
    int*      name_jntadr;          // joint name pointers                      (njnt x 1)
    int*      name_geomadr;         // geom name pointers                       (ngeom x 1)
    int*      name_siteadr;         // site name pointers                       (nsite x 1)
    int*      name_camadr;          // camera name pointers                     (ncam x 1)
    int*      name_lightadr;        // light name pointers                      (nlight x 1)
    int*      name_meshadr;         // mesh name pointers                       (nmesh x 1)
    int*      name_skinadr;         // skin name pointers                       (nskin x 1)
    int*      name_hfieldadr;       // hfield name pointers                     (nhfield x 1)
    int*      name_texadr;          // texture name pointers                    (ntex x 1)
    int*      name_matadr;          // material name pointers                   (nmat x 1)
    int*      name_pairadr;         // geom pair name pointers                  (npair x 1)
    int*      name_excludeadr;      // exclude name pointers                    (nexclude x 1)
    int*      name_eqadr;           // equality constraint name pointers        (neq x 1)
    int*      name_tendonadr;       // tendon name pointers                     (ntendon x 1)
    int*      name_actuatoradr;     // actuator name pointers                   (nu x 1)
    int*      name_sensoradr;       // sensor name pointers                     (nsensor x 1)
    int*      name_numericadr;      // numeric name pointers                    (nnumeric x 1)
    int*      name_textadr;         // text name pointers                       (ntext x 1)
    int*      name_tupleadr;        // tuple name pointers                      (ntuple x 1)
    int*      name_keyadr;          // keyframe name pointers                   (nkey x 1)
    char*     names;                // names of all objects, 0-terminated       (nnames x 1)
};
typedef struct _mjModel mjModel;

Defined in mjmodel.h

This is the main data structure holding the MuJoCo model. It is treated as constant by the simulator.

mjContact

struct _mjContact                   // result of collision detection functions
{
    // contact parameters set by geom-specific collision detector
    mjtNum dist;                    // distance between nearest points; neg: penetration
    mjtNum pos[3];                  // position of contact point: midpoint between geoms
    mjtNum frame[9];                // normal is in [0-2]

    // contact parameters set by mj_collideGeoms
    mjtNum includemargin;           // include if dist<includemargin=margin-gap
    mjtNum friction[5];             // tangent1, 2, spin, roll1, 2
    mjtNum solref[mjNREF];          // constraint solver reference
    mjtNum solimp[mjNIMP];          // constraint solver impedance

    // internal storage used by solver
    mjtNum mu;                      // friction of regularized cone, set by mj_makeR
    mjtNum H[36];                   // cone Hessian, set by mj_updateConstraint

    // contact descriptors set by mj_collideGeoms
    int dim;                        // contact space dimensionality: 1, 3, 4 or 6
    int geom1;                      // id of geom 1
    int geom2;                      // id of geom 2

    // flag set by mj_fuseContact or mj_instantianteEquality
    int exclude;                    // 0: include, 1: in gap, 2: fused, 3: equality

    // address computed by mj_instantiateContact
    int efc_address;                // address in efc; -1: not included, -2-i: distance constraint i
};
typedef struct _mjContact mjContact;

Defined in mjdata.h

This is the data structure holding information about one contact. mjData.contact is a preallocated array of mjContact data structures, populated at runtime with the contacts found by the collision detector. Additional contact information is then filled-in by the simulator.

mjWarningStat

struct _mjWarningStat               // warning statistics
{
    int lastinfo;                   // info from last warning
    int number;                     // how many times was warning raised
};
typedef struct _mjWarningStat mjWarningStat;

Defined in mjdata.h

This is the data structure holding information about one warning type. mjData.warning is a preallocated array of mjWarningStat data structures, one for each warning type.

mjTimerStat

struct _mjTimerStat                 // timer statistics
{
    mjtNum duration;                // cumulative duration
    int number;                     // how many times was timer called
};
typedef struct _mjTimerStat mjTimerStat;

Defined in mjdata.h

This is the data structure holding information about one timer. mjData.timer is a preallocated array of mjTimerStat data structures, one for each timer type.

mjSolverStat

struct _mjSolverStat                // per-iteration solver statistics
{
    mjtNum improvement;             // cost reduction, scaled by 1/trace(M(qpos0))
    mjtNum gradient;                // gradient norm (primal only, scaled)
    mjtNum lineslope;               // slope in linesearch
    int nactive;                    // number of active constraints
    int nchange;                    // number of constraint state changes
    int neval;                      // number of cost evaluations in line search
    int nupdate;                    // number of Cholesky updates in line search
};
typedef struct _mjSolverStat mjSolverStat;

Defined in mjdata.h

This is the data structure holding information about one solver iteration. mjData.solver is a preallocated array of mjSolverStat data structures, one for each iteration of the solver, up to a maximum of mjNSOLVER. The actual number of solver iterations is given by mjData.solver_iter.

mjData

struct _mjData
{
    // constant sizes
    int nstack;                     // number of mjtNums that can fit in stack
    int nbuffer;                    // size of main buffer in bytes

    // stack pointer
    int pstack;                     // first available mjtNum address in stack

    // memory utilization stats
    int maxuse_stack;               // maximum stack allocation
    int maxuse_con;                 // maximum number of contacts
    int maxuse_efc;                 // maximum number of scalar constraints

    // diagnostics
    mjWarningStat warning[mjNWARNING]; // warning statistics
    mjTimerStat timer[mjNTIMER];       // timer statistics
    mjSolverStat solver[mjNSOLVER];    // solver statistics per iteration
    int solver_iter;                // number of solver iterations
    int solver_nnz;                 // number of non-zeros in Hessian or efc_AR
    mjtNum solver_fwdinv[2];        // forward-inverse comparison: qfrc, efc

    // variable sizes
    int ne;                         // number of equality constraints
    int nf;                         // number of friction constraints
    int nefc;                       // number of constraints
    int ncon;                       // number of detected contacts

    // global properties
    mjtNum time;                    // simulation time
    mjtNum energy[2];               // potential, kinetic energy

    //-------------------------------- end of info header

    // buffers
    void*     buffer;               // main buffer; all pointers point in it    (nbuffer bytes)
    mjtNum*   stack;                // stack buffer                             (nstack mjtNums)

    //-------------------------------- main inputs and outputs of the computation

    // state
    mjtNum*   qpos;                 // position                                 (nq x 1)
    mjtNum*   qvel;                 // velocity                                 (nv x 1)
    mjtNum*   act;                  // actuator activation                      (na x 1)
    mjtNum*   qacc_warmstart;       // acceleration used for warmstart          (nv x 1)

    // control
    mjtNum*   ctrl;                 // control                                  (nu x 1)
    mjtNum*   qfrc_applied;         // applied generalized force                (nv x 1)
    mjtNum*   xfrc_applied;         // applied Cartesian force/torque           (nbody x 6)

    // dynamics
    mjtNum*   qacc;                 // acceleration                             (nv x 1)
    mjtNum*   act_dot;              // time-derivative of actuator activation   (na x 1)

    // mocap data
    mjtNum*  mocap_pos;             // positions of mocap bodies                (nmocap x 3)
    mjtNum*  mocap_quat;            // orientations of mocap bodies             (nmocap x 4)

    // user data
    mjtNum*  userdata;              // user data, not touched by engine         (nuserdata x 1)

    // sensors
    mjtNum*  sensordata;            // sensor data array                        (nsensordata x 1)

    //-------------------------------- POSITION dependent

    // computed by mj_fwdPosition/mj_kinematics
    mjtNum*   xpos;                 // Cartesian position of body frame         (nbody x 3)
    mjtNum*   xquat;                // Cartesian orientation of body frame      (nbody x 4)
    mjtNum*   xmat;                 // Cartesian orientation of body frame      (nbody x 9)
    mjtNum*   xipos;                // Cartesian position of body com           (nbody x 3)
    mjtNum*   ximat;                // Cartesian orientation of body inertia    (nbody x 9)
    mjtNum*   xanchor;              // Cartesian position of joint anchor       (njnt x 3)
    mjtNum*   xaxis;                // Cartesian joint axis                     (njnt x 3)
    mjtNum*   geom_xpos;            // Cartesian geom position                  (ngeom x 3)
    mjtNum*   geom_xmat;            // Cartesian geom orientation               (ngeom x 9)
    mjtNum*   site_xpos;            // Cartesian site position                  (nsite x 3)
    mjtNum*   site_xmat;            // Cartesian site orientation               (nsite x 9)
    mjtNum*   cam_xpos;             // Cartesian camera position                (ncam x 3)
    mjtNum*   cam_xmat;             // Cartesian camera orientation             (ncam x 9)
    mjtNum*   light_xpos;           // Cartesian light position                 (nlight x 3)
    mjtNum*   light_xdir;           // Cartesian light direction                (nlight x 3)

    // computed by mj_fwdPosition/mj_comPos
    mjtNum*   subtree_com;          // center of mass of each subtree           (nbody x 3)
    mjtNum*   cdof;                 // com-based motion axis of each dof        (nv x 6)
    mjtNum*   cinert;               // com-based body inertia and mass          (nbody x 10)

    // computed by mj_fwdPosition/mj_tendon
    int*      ten_wrapadr;          // start address of tendon's path           (ntendon x 1)
    int*      ten_wrapnum;          // number of wrap points in path            (ntendon x 1)
    int*      ten_J_rownnz;         // number of non-zeros in Jacobian row      (ntendon x 1)
    int*      ten_J_rowadr;         // row start address in colind array        (ntendon x 1)
    int*      ten_J_colind;         // column indices in sparse Jacobian        (ntendon x nv)
    mjtNum*   ten_length;           // tendon lengths                           (ntendon x 1)
    mjtNum*   ten_J;                // tendon Jacobian                          (ntendon x nv)
    int*      wrap_obj;             // geom id; -1: site; -2: pulley            (nwrap*2 x 1)
    mjtNum*   wrap_xpos;            // Cartesian 3D points in all path          (nwrap*2 x 3)

    // computed by mj_fwdPosition/mj_transmission
    mjtNum*   actuator_length;      // actuator lengths                         (nu x 1)
    mjtNum*   actuator_moment;      // actuator moments                         (nu x nv)

    // computed by mj_fwdPosition/mj_crb
    mjtNum*   crb;                  // com-based composite inertia and mass     (nbody x 10)
    mjtNum*   qM;                   // total inertia                            (nM x 1)

    // computed by mj_fwdPosition/mj_factorM
    mjtNum*   qLD;                  // L'*D*L factorization of M                (nM x 1)
    mjtNum*   qLDiagInv;            // 1/diag(D)                                (nv x 1)
    mjtNum*   qLDiagSqrtInv;        // 1/sqrt(diag(D))                          (nv x 1)

    // computed by mj_fwdPosition/mj_collision
    mjContact* contact;             // list of all detected contacts            (nconmax x 1)

    // computed by mj_fwdPosition/mj_makeConstraint
    int*      efc_type;             // constraint type (mjtConstraint)          (njmax x 1)
    int*      efc_id;               // id of object of specified type           (njmax x 1)
    int*      efc_J_rownnz;         // number of non-zeros in Jacobian row      (njmax x 1)
    int*      efc_J_rowadr;         // row start address in colind array        (njmax x 1)
    int*      efc_J_rowsuper;       // number of subsequent rows in supernode   (njmax x 1)
    int*      efc_J_colind;         // column indices in Jacobian               (njmax x nv)
    int*      efc_JT_rownnz;        // number of non-zeros in Jacobian row    T (nv x 1)
    int*      efc_JT_rowadr;        // row start address in colind array      T (nv x 1)
    int*      efc_JT_rowsuper;      // number of subsequent rows in supernode T (nv x 1)
    int*      efc_JT_colind;        // column indices in Jacobian             T (nv x njmax)
    mjtNum*   efc_J;                // constraint Jacobian                      (njmax x nv)
    mjtNum*   efc_JT;               // constraint Jacobian transposed           (nv x njmax)
    mjtNum*   efc_pos;              // constraint position (equality, contact)  (njmax x 1)
    mjtNum*   efc_margin;           // inclusion margin (contact)               (njmax x 1)
    mjtNum*   efc_frictionloss;     // frictionloss (friction)                  (njmax x 1)
    mjtNum*   efc_diagApprox;       // approximation to diagonal of A           (njmax x 1)
    mjtNum*   efc_KBIP;             // stiffness, damping, impedance, imp'      (njmax x 4)
    mjtNum*   efc_D;                // constraint mass                          (njmax x 1)
    mjtNum*   efc_R;                // inverse constraint mass                  (njmax x 1)

    // computed by mj_fwdPosition/mj_projectConstraint
    int*      efc_AR_rownnz;        // number of non-zeros in AR                (njmax x 1)
    int*      efc_AR_rowadr;        // row start address in colind array        (njmax x 1)
    int*      efc_AR_colind;        // column indices in sparse AR              (njmax x njmax)
    mjtNum*   efc_AR;               // J*inv(M)*J' + R                          (njmax x njmax)

    //-------------------------------- POSITION, VELOCITY dependent

    // computed by mj_fwdVelocity
    mjtNum*   ten_velocity;         // tendon velocities                        (ntendon x 1)
    mjtNum*   actuator_velocity;    // actuator velocities                      (nu x 1)

    // computed by mj_fwdVelocity/mj_comVel
    mjtNum*   cvel;                 // com-based velocity [3D rot; 3D tran]     (nbody x 6)
    mjtNum*   cdof_dot;             // time-derivative of cdof                  (nv x 6)

    // computed by mj_fwdVelocity/mj_rne (without acceleration)
    mjtNum*   qfrc_bias;            // C(qpos,qvel)                             (nv x 1)

    // computed by mj_fwdVelocity/mj_passive
    mjtNum*   qfrc_passive;         // passive force                            (nv x 1)

    // computed by mj_fwdVelocity/mj_referenceConstraint
    mjtNum*   efc_vel;              // velocity in constraint space: J*qvel     (njmax x 1)
    mjtNum*   efc_aref;             // reference pseudo-acceleration            (njmax x 1)

    // computed by mj_sensorVel/mj_subtreeVel if needed
    mjtNum*   subtree_linvel;       // linear velocity of subtree com           (nbody x 3)
    mjtNum*   subtree_angmom;       // angular momentum about subtree com       (nbody x 3)

    //-------------------------------- POSITION, VELOCITY, CONTROL/ACCELERATION dependent

    // computed by mj_fwdActuation
    mjtNum*   actuator_force;       // actuator force in actuation space        (nu x 1)
    mjtNum*   qfrc_actuator;        // actuator force                           (nv x 1)

    // computed by mj_fwdAcceleration
    mjtNum*   qfrc_unc;             // net unconstrained force                  (nv x 1)
    mjtNum*   qacc_unc;             // unconstrained acceleration               (nv x 1)

    // computed by mj_fwdConstraint/mj_inverse
    mjtNum*   efc_b;                // linear cost term: J*qacc_unc - aref      (njmax x 1)
    mjtNum*   efc_force;            // constraint force in constraint space     (njmax x 1)
    int*      efc_state;            // constraint state (mjtConstraintState)    (njmax x 1)
    mjtNum*   qfrc_constraint;      // constraint force                         (nv x 1)

    // computed by mj_inverse
    mjtNum*   qfrc_inverse;         // net external force; should equal:        (nv x 1)
                                    //  qfrc_applied + J'*xfrc_applied + qfrc_actuator 

    // computed by mj_sensorAcc/mj_rnePostConstraint if needed; rotation:translation format
    mjtNum*   cacc;                 // com-based acceleration                   (nbody x 6)
    mjtNum*   cfrc_int;             // com-based interaction force with parent  (nbody x 6)
    mjtNum*   cfrc_ext;             // com-based external force on body         (nbody x 6)
};
typedef struct _mjData mjData;

Defined in mjdata.h

This is the main data structure holding the simulation state. It is the workspace where all functions read their modifiable inputs and write their outputs.

mjvPerturb

struct _mjvPerturb                  // object selection and perturbation
{
    int      select;                // selected body id; non-positive: none
    int      skinselect;            // selected skin id; non-positive: none
    int      active;                // perturbation bitmask (mjtPertBit)
    mjtNum   refpos[3];             // desired position for selected object
    mjtNum   refquat[4];            // desired orientation for selected object
    mjtNum   localpos[3];           // selection point in object coordinates
    mjtNum   scale;                 // relative mouse motion-to-space scaling (set by initPerturb)
};
typedef struct _mjvPerturb mjvPerturb;

Defined in mjvisualize.h

This is the data structure holding information about mouse perturbations.

mjvCamera

struct _mjvCamera                   // abstract camera
{
    // type and ids
    int      type;                  // camera type (mjtCamera)
    int      fixedcamid;            // fixed camera id
    int      trackbodyid;           // body id to track

    // abstract camera pose specification
    mjtNum   lookat[3];             // lookat point
    mjtNum   distance;              // distance to lookat point or tracked body
    mjtNum   azimuth;               // camera azimuth (deg)
    mjtNum   elevation;             // camera elevation (deg)
};
typedef struct _mjvCamera mjvCamera;

Defined in mjvisualize.h

This is the data structure describing one abstract camera.

mjvGLCamera

struct _mjvGLCamera                 // OpenGL camera
{
    // camera frame
    float    pos[3];                // position
    float    forward[3];            // forward direction
    float    up[3];                 // up direction

    // camera projection
    float    frustum_center;        // hor. center (left,right set to match aspect)
    float    frustum_bottom;        // bottom
    float    frustum_top;           // top
    float    frustum_near;          // near
    float    frustum_far;           // far
};
typedef struct _mjvGLCamera mjvGLCamera;

Defined in mjvisualize.h

This is the data structure describing one OpenGL camera.

mjvGeom

struct _mjvGeom                     // abstract geom
{
    // type info
    int      type;                  // geom type (mjtGeom)
    int      dataid;                // mesh, hfield or plane id; -1: none
    int      objtype;               // mujoco object type; mjOBJ_UNKNOWN for decor
    int      objid;                 // mujoco object id; -1 for decor
    int      category;              // visual category
    int      texid;                 // texture id; -1: no texture
    int      texuniform;            // uniform cube mapping
    int      texcoord;              // mesh geom has texture coordinates
    int      segid;                 // segmentation id; -1: not shown

    // OpenGL info
    float    texrepeat[2];          // texture repetition for 2D mapping
    float    size[3];               // size parameters
    float    pos[3];                // Cartesian position
    float    mat[9];                // Cartesian orientation
    float    rgba[4];               // color and transparency
    float    emission;              // emission coef
    float    specular;              // specular coef
    float    shininess;             // shininess coef
    float    reflectance;           // reflectance coef
    char     label[100];            // text label

    // transparency rendering (set internally)
    float    camdist;               // distance to camera (used by sorter)
    float    modelrbound;           // geom rbound from model, 0 if not model geom
    mjtByte  transparent;           // treat geom as transparent
};
typedef struct _mjvGeom mjvGeom;

Defined in mjvisualize.h

This is the data structure describing one abstract visualization geom - which could correspond to a model geom or to a decoration element constructed by the visualizer.

mjvLight

struct _mjvLight                    // OpenGL light
{
    float    pos[3];                // position rel. to body frame              
    float    dir[3];                // direction rel. to body frame             
    float    attenuation[3];        // OpenGL attenuation (quadratic model)     
    float    cutoff;                // OpenGL cutoff                            
    float    exponent;              // OpenGL exponent                          
    float    ambient[3];            // ambient rgb (alpha=1)                    
    float    diffuse[3];            // diffuse rgb (alpha=1)                    
    float    specular[3];           // specular rgb (alpha=1)
    mjtByte  headlight;             // headlight
    mjtByte  directional;           // directional light                        
    mjtByte  castshadow;            // does light cast shadows                  
};
typedef struct _mjvLight mjvLight;

Defined in mjvisualize.h

This is the data structure describing one OpenGL light.

mjvOption

struct _mjvOption                   // abstract visualization options
{
    int      label;                 // what objects to label (mjtLabel)
    int      frame;                 // which frame to show (mjtFrame)
    mjtByte  geomgroup[mjNGROUP];   // geom visualization by group
    mjtByte  sitegroup[mjNGROUP];   // site visualization by group
    mjtByte  jointgroup[mjNGROUP];  // joint visualization by group
    mjtByte  tendongroup[mjNGROUP];    // tendon visualization by group
    mjtByte  actuatorgroup[mjNGROUP];  // actuator visualization by group
    mjtByte  flags[mjNVISFLAG];     // visualization flags (indexed by mjtVisFlag)
};
typedef struct _mjvOption mjvOption;

Defined in mjvisualize.h

This structure contains options that enable and disable the visualization of various elements.

mjvScene

struct _mjvScene                    // abstract scene passed to OpenGL renderer
{
    // abstract geoms
    int      maxgeom;               // size of allocated geom buffer
    int      ngeom;                 // number of geoms currently in buffer
    mjvGeom* geoms;                 // buffer for geoms
    int*     geomorder;             // buffer for ordering geoms by distance to camera

    // skin data
    int      nskin;                 // number of skins
    int*     skinfacenum;           // number of faces in skin
    int*     skinvertadr;           // address of skin vertices
    int*     skinvertnum;           // number of vertices in skin
    float*   skinvert;              // skin vertex data
    float*   skinnormal;            // skin normal data

    // OpenGL lights
    int      nlight;                // number of lights currently in buffer
    mjvLight lights[8];             // buffer for lights

    // OpenGL cameras
    mjvGLCamera camera[2];          // left and right camera

    // OpenGL model transformation
    mjtByte  enabletransform;       // enable model transformation
    float    translate[3];          // model translation
    float    rotate[4];             // model quaternion rotation
    float    scale;                 // model scaling

    // OpenGL rendering effects
    int      stereo;                // stereoscopic rendering (mjtStereo)
    mjtByte  flags[mjNRNDFLAG];     // rendering flags (indexed by mjtRndFlag)
};
typedef struct _mjvScene mjvScene;

Defined in mjvisualize.h

This structure contains everything needed to render the 3D scene in OpenGL.

mjvFigure

struct _mjvFigure                   // abstract 2D figure passed to OpenGL renderer
{
    // enable/disable flags
    int     flg_legend;             // show legend
    int     flg_ticklabel[2];       // show grid tick labels (x,y)
    int     flg_extend;             // automatically extend axis ranges to fit data
    int     flg_barplot;            // isolated line segments (i.e. GL_LINES)
    int     flg_selection;          // vertical selection line
    int     flg_symmetric;          // symmetric y-axis

    // figure options
    int     legendoff;              // number of lines to offset legend
    int     gridsize[2];            // number of grid points in (x,y)
    int     selection;              // selection line x-value
    int     highlight[2];           // if point is in legend rect, highlight line
    float   gridrgb[3];             // grid line rgb
    float   gridwidth;              // grid line width
    float   figurergba[4];          // figure color and alpha
    float   panergba[4];            // pane color and alpha
    float   legendrgba[4];          // legend color and alpha
    float   textrgb[3];             // text color
    float   range[2][2];            // axis ranges; (min>=max) automatic
    char    xlabel[100];            // x-axis label
    char    title[100];             // figure title
    char    xformat[20];            // x-tick label format for sprintf
    char    yformat[20];            // y-tick label format for sprintf
    char    minwidth[20];           // string used to determine min y-tick width

    // line data
    int     linepnt[mjMAXLINE];                   // number of points in line; (0) disable
    float   linergb[mjMAXLINE][3];                // line color
    float   linewidth[mjMAXLINE];                 // line width
    float   linedata[mjMAXLINE][2*mjMAXLINEPNT];  // line data (x,y)
    char    linename[mjMAXLINE][100];             // line name for legend

    // output from renderer
    int     xaxispixel[2];          // range of x-axis in pixels
    int     yaxispixel[2];          // range of y-axis in pixels
    float   xaxisdata[2];           // range of x-axis in data units
    float   yaxisdata[2];           // range of y-axis in data units
};
typedef struct _mjvFigure mjvFigure;

Defined in mjvisualize.h

This structure contains everything needed to render a 2D plot in OpenGL. The buffers for line points etc. are preallocated, and the user has to populate them before calling the function mjr_figure with this data structure as an argument.

mjrRect

struct _mjrRect                     // OpenGL rectangle
{
    int left;                       // left (usually 0)
    int bottom;                     // bottom (usually 0)
    int width;                      // width (usually buffer width)
    int height;                     // height (usually buffer height)
};
typedef struct _mjrRect mjrRect;

Defined in mjrender.h

This structure specifies a rectangle.

mjrContext

struct _mjrContext                  // custom OpenGL context
{
    // parameters copied from mjVisual
    float lineWidth;                // line width for wireframe rendering
    float shadowClip;               // clipping radius for directional lights
    float shadowScale;              // fraction of light cutoff for spot lights
    float fogStart;                 // fog start = stat.extent * vis.map.fogstart
    float fogEnd;                   // fog end = stat.extent * vis.map.fogend
    float fogRGBA[4];               // fog rgba
    int shadowSize;                 // size of shadow map texture
    int offWidth;                   // width of offscreen buffer
    int offHeight;                  // height of offscreen buffer
    int offSamples;                 // number of offscreen buffer multisamples

    // parameters specified at creation
    int fontScale;                  // font scale
    int auxWidth[mjNAUX];           // auxiliary buffer width
    int auxHeight[mjNAUX];          // auxiliary buffer height
    int auxSamples[mjNAUX];         // auxiliary buffer multisamples

    // offscreen rendering objects
    unsigned int offFBO;            // offscreen framebuffer object
    unsigned int offFBO_r;          // offscreen framebuffer for resolving multisamples
    unsigned int offColor;          // offscreen color buffer
    unsigned int offColor_r;        // offscreen color buffer for resolving multisamples
    unsigned int offDepthStencil;   // offscreen depth and stencil buffer
    unsigned int offDepthStencil_r; // offscreen depth and stencil buffer for resolving multisamples

    // shadow rendering objects
    unsigned int shadowFBO;         // shadow map framebuffer object
    unsigned int shadowTex;         // shadow map texture

    // auxiliary buffers
    unsigned int auxFBO[mjNAUX];    // auxiliary framebuffer object
    unsigned int auxFBO_r[mjNAUX];  // auxiliary framebuffer object for resolving
    unsigned int auxColor[mjNAUX];  // auxiliary color buffer
    unsigned int auxColor_r[mjNAUX];// auxiliary color buffer for resolving

    // texture objects and info
    int ntexture;                   // number of allocated textures
    int textureType[100];           // type of texture (mjtTexture)
    unsigned int texture[100];      // texture names

    // displaylist starting positions
    unsigned int basePlane;         // all planes from model
    unsigned int baseMesh;          // all meshes from model
    unsigned int baseHField;        // all hfields from model
    unsigned int baseBuiltin;       // all buildin geoms, with quality from model
    unsigned int baseFontNormal;    // normal font
    unsigned int baseFontShadow;    // shadow font
    unsigned int baseFontBig;       // big font

    // displaylist ranges
    int     rangePlane;             // all planes from model
    int     rangeMesh;              // all meshes from model
    int     rangeHField;            // all hfields from model
    int     rangeBuiltin;           // all builtin geoms, with quality from model
    int     rangeFont;              // all characters in font

    // skin VBOs
    int      nskin;                 // number of skins
    unsigned int* skinvertVBO;      // skin vertex position VBOs
    unsigned int* skinnormalVBO;    // skin vertex normal VBOs
    unsigned int* skintexcoordVBO;  // skin vertex texture coordinate VBOs
    unsigned int* skinfaceVBO;      // skin face index VBOs

    // character info
    int     charWidth[127];         // character widths: normal and shadow
    int     charWidthBig[127];      // chacarter widths: big
    int     charHeight;             // character heights: normal and shadow
    int     charHeightBig;          // character heights: big

    // capabilities
    int     glewInitialized;        // is glew initialized
    int     windowAvailable;        // is default/window framebuffer available
    int     windowSamples;          // number of samples for default/window framebuffer
    int     windowStereo;           // is stereo available for default/window framebuffer
    int     windowDoublebuffer;     // is default/window framebuffer double buffered

    // framebuffer
    int     currentBuffer;          // currently active framebuffer: mjFB_WINDOW or mjFB_OFFSCREEN
};
typedef struct _mjrContext mjrContext;

Defined in mjrender.h

This structure contains the custom OpenGL rendering context, with the ids of all OpenGL resources uploaded to the GPU.

mjuiState

struct _mjuiState               // mouse and keyboard state
{
    // constants set by user
    int nrect;                  // number of rectangles used
    mjrRect rect[mjMAXUIRECT];  // rectangles (index 0: entire window)
    void* userdata;             // pointer to user data (for callbacks)

    // event type
    int type;                   // (type mjtEvent)

    // mouse buttons
    int left;                   // is left button down
    int right;                  // is right button down
    int middle;                 // is middle button down
    int doubleclick;            // is last press a double click
    int button;                 // which button was pressed (mjtButton)
    double buttontime;          // time of last button press

    // mouse position
    double x;                   // x position
    double y;                   // y position
    double dx;                  // x displacement
    double dy;                  // y displacement
    double sx;                  // x scroll
    double sy;                  // y scroll

    // keyboard
    int control;                // is control down
    int shift;                  // is shift down
    int alt;                    // is alt down
    int key;                    // which key was pressed
    double keytime;             // time of last key press

    // rectangle ownership and dragging
    int mouserect;              // which rectangle contains mouse
    int dragrect;               // which rectangle is dragged with mouse
    int dragbutton;             // which button started drag (mjtButton)
};
typedef struct _mjuiState mjuiState;

Defined in mjui.h

This structure contains the keyboard and mouse state used by the UI framework.

mjuiThemeSpacing

struct _mjuiThemeSpacing        // UI visualization theme spacing
{
        int total;              // total width
        int scroll;             // scrollbar width
        int label;              // label width
        int section;            // section gap
        int itemside;           // item side gap
        int itemmid;            // item middle gap
        int itemver;            // item vertical gap
        int texthor;            // text horizontal gap
        int textver;            // text vertical gap
        int linescroll;         // number of pixels to scroll
        int samples;            // number of multisamples
};
typedef struct _mjuiThemeSpacing mjuiThemeSpacing;

Defined in mjui.h

This structure defines the spacing of UI items in the theme.

mjuiThemeColor

struct _mjuiThemeColor          // UI visualization theme color
{
    float master[3];            // master background
    float thumb[3];             // scrollbar thumb
    float secttitle[3];         // section title
    float sectfont[3];          // section font
    float sectsymbol[3];        // section symbol
    float sectpane[3];          // section pane
    float shortcut[3];          // shortcut background
    float fontactive[3];        // font active
    float fontinactive[3];      // font inactive
    float decorinactive[3];     // decor inactive
    float decorinactive2[3];    // inactive slider color 2
    float button[3];            // button
    float check[3];             // check
    float radio[3];             // radio
    float select[3];            // select
    float select2[3];           // select pane
    float slider[3];            // slider
    float slider2[3];           // slider color 2
    float edit[3];              // edit
    float edit2[3];             // edit invalid
    float cursor[3];            // edit cursor
};
typedef struct _mjuiThemeColor mjuiThemeColor;	

Defined in mjui.h

This structure defines the colors of UI items in the theme.

mjuiItem

struct _mjuiItem                // UI item
{
    // common properties
    int type;                   // type (mjtItem)
    char name[mjMAXUINAME];     // name
    int state;                  // 0: disable, 1: enable, 2+: use predicate
    void *pdata;                // data pointer (type-specific)
    int sectionid;              // id of section containing item
    int itemid;                 // id of item within section

    // type-specific properties
    union
    {
        // check and button-related
        struct
        {
            int modifier;       // 0: none, 1: control, 2: shift; 4: alt
            int shortcut;       // shortcut key; 0: undefined
        } single;

        // static, radio and select-related
        struct
        {
            int nelem;          // number of elements in group
            char name[mjMAXUIMULTI][mjMAXUINAME]; // element names
        } multi;

        // slider-related
        struct
        {
            double range[2];    // slider range
            double divisions;   // number of range divisions
        } slider;

        // edit-related
        struct
        {
            int nelem;          // number of elements in list
            double range[mjMAXUIEDIT][2]; // element range (min>=max: ignore)
        } edit;
    };

    // internal
    mjrRect rect;               // rectangle occupied by item
};
typedef struct _mjuiItem mjuiItem;	

Defined in mjui.h

This structure defines one UI item.

Defined in mjui.h

This structure

mjuiSection

struct _mjuiSection             // UI section
{
    // properties
    char name[mjMAXUINAME];     // name
    int state;                  // 0: closed, 1: open
    int modifier;               // 0: none, 1: control, 2: shift; 4: alt
    int shortcut;               // shortcut key; 0: undefined
    int nitem;                  // number of items in use
    mjuiItem item[mjMAXUIITEM];// preallocated array of items

    // internal
    mjrRect rtitle;             // rectangle occupied by title
    mjrRect rcontent;           // rectangle occupied by content
};
typedef struct _mjuiSection mjuiSection;	

Defined in mjui.h

This structure defines one section of the UI.

mjUI

struct _mjUI                    // entire UI
{
    // constants set by user
    mjuiThemeSpacing spacing;   // UI theme spacing
    mjuiThemeColor color;       // UI theme color
    mjfItemEnable predicate;    // callback to set item state programmatically
    void* userdata;             // pointer to user data (passed to predicate)
    int rectid;                 // index of this ui rectangle in mjuiState
    int auxid;                  // aux buffer index of this ui
    int radiocol;               // number of radio columns (0 defaults to 2)

    // UI sizes (framebuffer units)
    int width;                  // width
    int height;                 // current heigth
    int maxheight;              // height when all sections open
    int scroll;                 // scroll from top of UI

    // mouse focus
    int mousesect;              // 0: none, -1: scroll, otherwise 1+section
    int mouseitem;              // item within section
    int mousehelp;              // help button down: print shortcuts

    // keyboard focus and edit
    int editsect;               // 0: none, otherwise 1+section
    int edititem;               // item within section
    int editcursor;             // cursor position
    int editscroll;             // horizontal scroll
    char edittext[mjMAXUITEXT]; // current text
    mjuiItem* editchanged;      // pointer to changed edit in last mjui_event

    // sections
    int nsect;                  // number of sections in use
    mjuiSection sect[mjMAXUISECT];  // preallocated array of sections
};
typedef struct _mjUI mjUI;

Defined in mjui.h

This structure defines the entire UI.

mjuiDef

struct _mjuiDef
{
    int type;                   // type (mjtItem); -1: section
    char name[mjMAXUINAME];     // name
    int state;                  // state
    void* pdata;                // pointer to data
    char other[mjMAXUITEXT];    // string with type-specific properties
};
typedef struct _mjuiDef mjuiDef;

Defined in mjui.h

This structure defines one entry in the definition table used for simplified UI construction.

X Macros

The X Macros are not needed in most user projects. They are used internally to allocate the model, and are also available for users who know how to use this programming technique. See the header file mjxmacro.h for the actual definitions. They are particularly useful in writing MuJoCo wrappers for scripting languages, where dynamic structures matching the MuJoCo data structures need to be constructed programmatically.

MJOPTION_SCALARS

Scalar fields of mjOption.

MJOPTION_VECTORS

Vector fields of mjOption.

MJMODEL_INTS

Int fields of mjModel.

MJMODEL_POINTERS

Pointer fields of mjModel.

MJDATA_SCALAR

Scalar fields of mjData.

MJDATA_VECTOR

Vector fields of mjData.

MJDATA_POINTERS

Pointer fields of mjData.

Global variables

Error callbacks

All user callbacks (i.e. global function pointers whose name starts with 'mjcb') are initially set to NULL, which disables them and allows the default processing to take place. To install a callback, simply set the corresponding global pointer to a user function of the correct type. Keep in mind that these are global and not model-specific. So if you are simulating multiple models in parallel, they use the same set of callbacks.

mju_user_error

extern void (*mju_user_error)(const char*);

This is called from within the main error function mju_error. When installed, this function overrides the default error processing. Once it prints error mesages (or whatever else the user wants to do), it must exit the program. MuJoCo is written with the assumption that mju_error will not return. If it does, the behavior of the software is undefined.

mju_user_warning

extern void (*mju_user_warning)(const char*);

This is called from within the main warning function mju_warning. It is similar to the error handler, but instead it must return without exiting the program.

Memory callbacks

The purpose of the memory callbacks is to allow the user to install custom memory allocation and deallocation mechanisms. One example where we have found this to be useful is a MATLAB wrapper for MuJoCo, where mex files are expected to use MATLAB's memory mechanism for permanent memory allocation.

mju_user_malloc

extern void* (*mju_user_malloc)(size_t);

If this is installed, the MuJoCo runtime will use it to allocate all heap memory it needs (instead of using aligned malloc). The user allocator must allocate memory aligned on 8-byte boundaries. Note that the parser and compiler are written in C++ and sometimes allocate memory with the "new" operator which bypasses this mechanism.

mju_user_free

extern void (*mju_user_free)(void*);

If this is installed, MuJoCo will free any heap memory it allocated by calling this function (instead of using aligned free).

Physics callbacks

The physics callbacks are the main mechanism for modifying the behavior of the simulator, beyond setting various options. The options control the operation of the default pipeline, while callbacks extend the pipeline at well-defined places. This enables advanced users to implement many interesting functions which we have not thought of, while still taking advantage of the default pipeline. As with all other callbacks, there is no automated error checking - instead we assume that the authors of callback functions know what they are doing.

Custom physics callbacks will often need parameters that are not standard in MJCF. This is largely why we have provided custom fields as well as user data arrays in MJCF. The idea is to "instrument" the MJCF model by entering the necessary user parameters, and then write callbacks that look for those parameters and perform the corresponding computations. We strongly encourage users to write callbacks that check the model for the presence of user parameters before accessing them - so that when a regular model is loaded, the callback disables itself automatically instead of causing the software to crash.

mjcb_passive

extern mjfGeneric mjcb_passive;

This is used to implement a custom passive force in joint space; if the force is more naturally defined in Cartesian space, use the end-effector Jacobian to map it to joint space. By "passive" we do not mean a force that does no positive work (as in physics), but simply a force that depends only on position and velocity but not on control. There are standard passive forces in MuJoCo arising from springs, dampers, viscosity and desnity of the medium. They are computed in mjData.qfrc_passive before mjcb_passive is called. The user callback should add to this vector instead of overwriting it (otherwise the standard passive forces will be lost).

mjcb_control

extern mjfGeneric mjcb_control;

This is the most commonly used callback. It implements a control law, by writing in the vector of controls mjData.ctrl. It can also write in mjData.qfrc_applied and mjData.xfrc_applied. The values written in these vectors can depend on position, velocity and all other quantities derived from them, but cannot depend on contact forces and other quantities that are computed after the control is specified. If the callback accesses the latter fields, their values do not correspond to the current time step.

The control callback is called from within mj_forward and mj_step, just before the controls and applied forces are needed. When using the RK integrator, it will be called 4 times per step. The alternative way of specifying controls and applied forces is to set them before mj_step, or use mj_step1 and mj_step2. The latter approach allows setting the controls after the position and velocity computations have been performed by mj_step1, allowing these results to be utilized in computing the control (similar to using mjcb_control). However, the only way to change the controls between sub-steps of the RK integrator is to define the control callback.

mjcb_contactfilter

extern mjfConFilt mjcb_contactfilter;

This callback can be used to replace MuJoCo's default collision filtering. When installed, this function is called for each pair of geoms that have passed the broad-phase test (or are predefined geom pairs in the MJCF) and are candidates for near-phase collision. The default processing uses the contype and conaffinity masks, the parent-child filter and some other considerations related to welded bodies to decide if collision should be allowed. This callback replaces the default processing, but keep in mind that the entire mechanism is being replaced. So for example if you still want to take advantage of contype/conaffinity, you have to re-implement it in the callback.

mjcb_sensor

extern mjfSensor mjcb_sensor;

This callback populates fields of mjData.sensordata corresponding to user-defined sensors. It is called if it is installed and the model contains user-defined sensors. It is called once per compute stage (mjSTAGE_POS, mjSTAGE_VEL, mjSTAGE_ACC) and must fill in all user sensor values for that stage. The user-defined sensors have dimensionality and data types defined in the MJCF model which must be respected by the callback.

mjcb_time

extern mjfTime mjcb_time;

Installing this callback enables the built-in profiler, and keeps timing statistics in mjData.timer. The return type is mjtNum, while the time units are up to the user. simulate.cpp assumes the unit is 1 millisecond. In order to be useful, the callback should use high-resolution timers with at least microsecond precision. This is because the computations being timed are very fast.

mjcb_act_dyn

extern mjfAct mjcb_act_dyn;

This callback implements custom activation dynamics: it must return the value of mjData.act_dot for the specified actuator. This is the time-derivative of the activation state vector mjData.act. It is called for model actuators with user dynamics (mjDYN_USER). If such actuators exist in the model but the callback is not installed, their time-derivative is set to 0.

mjcb_act_gain

extern mjfAct mjcb_act_gain;

This callback implements custom actuator gains: it must return the gain for the specified actuator with mjModel.actuator_gaintype set to mjGAIN_USER. If such actuators exist in the model and this callback is not installed, their gains are set to 1.

mjcb_act_bias

extern mjfAct mjcb_act_bias;

This callback implements custom actuator biases: it must return the bias for the specified actuator with mjModel.actuator_biastype set to mjBIAS_USER. If such actuators exist in the model and this callback is not installed, their biases are set to 0.

Collision table

mjCOLLISIONFUNC

extern mjfCollision mjCOLLISIONFUNC[mjNGEOMTYPES][mjNGEOMTYPES];

Table of pairwise collision functions indexed by geom types. Only the upper-right triangle is used. The user can replace these function pointers with custom routines, replacing MuJoCo's collision mechanism. If a given entry is NULL, the corresponding pair of geom types cannot be collided. Note that these functions apply only to near-phase collisions. The broadphase mechanism is built-in and cannot be modified.

String constants

The string constants described here are provided for user convenience. They correspond to the English names of lists of options, and can be displayed in menus or dialogs in a GUI. The code sample simulate.cpp illustrates how they can be used.

mjDISABLESTRING

extern const char* mjDISABLESTRING[mjNDISABLE];

Names of the disable bits defined by mjtDisableBit.

mjENABLESTRING

extern const char* mjENABLESTRING[mjNENABLE];

Names of the enable bits defined by mjtEnableBit.

mjTIMERSTRING

extern const char* mjTIMERSTRING[mjNTIMER];

Names of the mjData timers defined by mjtTimer.

mjLABELSTRING

extern const char* mjLABELSTRING[mjNLABEL];

Names of the visual labeling modes defined by mjtLabel.

mjFRAMESTRING

extern const char* mjFRAMESTRING[mjNFRAME];

Names of the frame visualization modes defined by mjtFrame.

mjVISSTRING

extern const char* mjVISSTRING[mjNVISFLAG][3];

Descriptions of the abstract visualization flags defined by mjtVisFlag. For each flag there are three strings, with the following meaning:

[0]: flag name;
[1]: the string "0" or "1" indicating if the flag is on or off by default, as set by mjv_defaultOption;
[2]: one-character string with a suggested keyboard shortcut, used in simulate.cpp and MuJoCo HAPTIX.

mjRNDSTRING

extern const char* mjRNDSTRING[mjNRNDFLAG][3];

Descriptions of the OpenGL rendering flags defined by mjtRndFlag. The three strings for each flag have the same format as above, except the defaults here are set by mjv_makeScene.

Numeric constants

Many integer constants were already documented in the primitive types above. In addition, the header files define several other constants documented here. Unless indicated otherwise, each entry in the table below is defined in mjmodel.h. Note that some extended key codes are defined in mjui.h which are not shown in the table below. Their names are in the format mjKEY_XXX. They correspond to GLFW key codes.

symbol	value	description
mjMINVAL	1E-15	The minimal value allowed in any denominator, and in general any mathematical operation where 0 is not allowed. In almost all cases, MuJoCo silently clamps smaller values to mjMINVAL.
mjPI	pi	The value of pi. This is used in various trigonometric functions, and also for conversion from degrees to radians in the compiler.
mjMAXVAL	1E+10	The maximal absolute value allowed in mjData.qpos, mjData.qvel, mjData.qacc. The API functions mj_checkPos, mj_checkVel, mj_checkAcc use this constant to detect instability.
mjMINMU	1E-5	The minimal value allowed in any friction coefficient. Recall that MuJoCo's contact model allows different number of friction dimensions to be included, as specified by the condim attribute. If however a given friction dimension is included, its friction is not allowed to be smaller than this constant. Smaller values are automatically clamped to this constant.
mjMINIMP	0.0001	The minimal value allowed in any constraint impedance. Smaller values are automatically clamped to this constant.
mjMAXIMP	0.9999	The maximal value allowed in any constraint impedance. Larger values are automatically clamped to this constant.
mjMAXCONPAIR	50	The maximal number of contacts points that can be generated per geom pair. MuJoCo's built-in collision functions respect this limit, and user-defined functions should also respect it. Such functions are called with a return buffer of size mjMAXCONPAIR; attempting to write more contacts in the buffer can cause unpredictable behavior.
mjMAXVFS	200	The maximal number of files in the virtual file system.
mjMAXVFSNAME	100	The maximal number of characters in the name of each file in the virtual file system.
mjNEQDATA	7	The maximal number of real-valued parameters used to define each equality constraint. Determines the size of mjModel.eq_data. This and the next five constants correspond to array sizes which we have not fully settled. There may be reasons to increase them in the future, so as to accommodate extra parameters needed for more elaborate computations. This is why we maintain them as symbolic constants that can be easily changed, as opposed to the array size for representing quaterions for example - which has no reason to change.
mjNDYN	10	The maximal number of real-valued parameters used to define the activation dynamics of each actuator. Determines the size of mjModel.actuator_dynprm.
mjNGAIN	10	The maximal number of real-valued parameters used to define the gain of each actuator. Determines the size of mjModel.actuator_gainprm.
mjNBIAS	10	The maximal number of real-valued parameters used to define the bias of each actuator. Determines the size of mjModel.actuator_biasprm.
mjNREF	2	The maximal number of real-valued parameters used to define the reference acceleration of each scalar constraint. Determines the size of all mjModel.XXX_solref fields.
mjNIMP	5	The maximal number of real-valued parameters used to define the impedance of each scalar constraint. Determines the size of all mjModel.XXX_solimp fields.
mjNSOLVER	1000	The size of the preallocated array mjData.solver. This is used to store diagnostic information about each iteration of the constraint solver. The actual number of iterations is given by mjData.solver_iter.
mjNGROUP	6	The number of geom, site, joint, tendon and actuator groups whose rendering can be enabled and disabled via mjvOption. Defined in mjvisualize.h.
mjMAXOVERLAY	500	The maximal number of characters in overlay text for rendering. Defined in mjvisualize.h.
mjMAXLINE	100	The maximal number of lines per 2D figure (mjvFigure). Defined in mjvisualize.h.
mjMAXLINEPNT	1000	The maximal number of points in each line in a 2D figure. Note that the buffer mjvFigure.linepnt has length 2*mjMAXLINEPNT because each point has X and Y coordinates. Defined in mjvisualize.h.
mjMAXPLANEGRID	200	The maximal number of grid lines in each dimension for rendering planes. Defined in mjvisualize.h.
mjNAUX	10	Number of auxiliary buffers that can be allocated in mjrContext. Defined in mjrender.h.
mjMAXTEXTURE	1000	Maximum number of textures allowed. Defined in mjrender.h.
mjMAXUISECT	10	Maximum number of UI sections. Defined in mjui.h.
mjMAXUIITEM	80	Maximum number of items per UI section. Defined in mjui.h.
mjMAXUITEXT	500	Maximum number of characters in UI fiels 'edittext' and 'other'. Defined in mjui.h.
mjMAXUINAME	40	Maximum number of characters in any UI name. Defined in mjui.h.
mjMAXUIMULTI	20	Maximum number of radio and select items in UI group. Defined in mjui.h.
mjMAXUIEDIT	5	Maximum number of elements in UI edit list. Defined in mjui.h.
mjMAXUIRECT	15	Maximum number of UI rectangles. Defined in mjui.h.
mjVERSION_HEADER	200	The version of the MuJoCo headers; changes with every release. This is an integer equal to 100x the software version, so 200 corresponds to version 2.0. Defined in mujoco.h. The API function mj_version returns a number with the same meaning but for the compiled library.

API functions

The main header mujoco.h exposes a very large number of functions. However the functions that most users are likely to need are a small fraction. For example, simulate.cpp which is as elaborate as a MuJoCo application is likely to get, calls around 40 of these functions, while basic.cpp calls around 20. The rest are explosed just in case someone has a use for them. This includes us as users of MuJoCo - we do our own work with the public library instead of relying on internal builds.

A drawback of this liberal function exposure policy is that documenting of all them properly is not realistic. Of course we can always add documentation, and we encourage users to ask questions on the Forum about functions they would like to use but do not find sufficiently documented. The documentation below contains the comments from the header file, with some additional comments regarding groups of functions or commonly used functions.

Activation

The functions in this section expose the license manager. The main function that all applications need to call is mj_activate. Calling mj_deactivate before closing the program is good style but not really needed. The rest of the functions support a client-server model where the owner of the server has license to run MuJoCo simulations on behalf of clients who already have a valid MuJoCo license.

mj_activate

int mj_activate(const char* filename);

This function activates the MuJoCo license for the session. Activation is required by all major simulation functions. It should be called with the path and name of the plain-text activation key, usually called mjkey.txt. It returns 1 on success, and calls mju_error on failure. Do not bother to replace mju_error with a user error handler and try to bypass the termination; the license manager is smarter than that :)

mj_deactivate

void mj_deactivate(void);

Deactivate license, free memory.

mj_certQuestion

void mj_certQuestion(mjtNum question[16]);

Server side: generate certificate question.

mj_certAnswer

void mj_certAnswer(const mjtNum question[16], mjtNum answer[16]);

Client side: generate certificate answer given question.

mj_certCheck

int mj_certCheck(const mjtNum question[16], const mjtNum answer[16]);

Server side: check certificate question-answer pair; return 1 if match, 0 if mismatch.

Virtual file system

Virtual file system (VFS) functionality was introduced in MuJoCo 1.50. It enables the user to load all necessary files in memory, including MJB binary model files, XML files (MJCF, URDF and included files), STL meshes, PNGs for textures and height fields, and HF files in our custom height field format. Model and resource files in the VFS can also be constructed programmatically (say using an XML library that writes to memory). Once all desired files are in the VFS, the user can call mj_loadModel or mj_loadXML with a pointer to the VFS. When this pointer is not NULL, the loaders will first check the VFS for any file they are about to load, and only access the disk if the file is not found in the VFS. The file names stored in the VFS have their name and extension but the path information is stripped; this can be bypassed however by using a custom path symbol in the file names, say "mydir_myfile.xml".

The entire VFS is contained in the data structure mjVFS. All utility functions for maintaining the VFS operate on this data structure. The common usage pattern is to first clear it with mj_defaultVFS, then add disk files to it with mj_addFileVFS (which allocates memory buffers and loads the file content in memory), then call mj_loadXML or mj_loadModel, and then clear everything with mj_deleteVFS.

mj_defaultVFS

void mj_defaultVFS(mjVFS* vfs);

Initialize VFS to empty (no deallocation).

mj_addFileVFS

int mj_addFileVFS(mjVFS* vfs, const char* directory, const char* filename);

Add file to VFS, return 0: success, 1: full, 2: repeated name, -1: not found on disk.

mj_makeEmptyFileVFS

int mj_makeEmptyFileVFS(mjVFS* vfs, const char* filename, int filesize);

Make empty file in VFS, return 0: success, 1: full, 2: repeated name.

mj_findFileVFS

int mj_findFileVFS(const mjVFS* vfs, const char* filename);

Return file index in VFS, or -1 if not found in VFS.

mj_deleteFileVFS

int mj_deleteFileVFS(mjVFS* vfs, const char* filename);

Delete file from VFS, return 0: success, -1: not found in VFS.

mj_deleteVFS

void mj_deleteVFS(mjVFS* vfs);

Delete all files from VFS.

Parse and compile

The key function here is mj_loadXML. It invokes the built-in parser and compiler, and either returns a pointer to a valid mjModel, or NULL - in which case the user should check the error information in the user-provided string. The model and all files referenced in it can be loaded from disk or from a VFS when provided.

mj_loadXML

mjModel* mj_loadXML(const char* filename, const mjVFS* vfs,
                    char* error, int error_sz);

Parse XML file in MJCF or URDF format, compile it, return low-level model. If vfs is not NULL, look up files in vfs before reading from disk. If error is not NULL, it must have size error_sz.

mj_saveLastXML

int mj_saveLastXML(const char* filename, const mjModel* m,
                   char* error, int error_sz);

Update XML data structures with info from low-level model, save as MJCF. If error is not NULL, it must have size error_sz.

mj_freeLastXML

void mj_freeLastXML(void);

Free last XML model if loaded. Called internally at each load.

mj_printSchema

int mj_printSchema(const char* filename, char* buffer, int buffer_sz,
                   int flg_html, int flg_pad);

Print internal XML schema as plain text or HTML, with style-padding or  .

Main simulation

These are the main entry points to the simulator. Most users will only need to call mj_step, which computes everything and advanced the simulation state by one time step. Controls and applied forces must either be set in advance (in mjData.ctrl, qfrc_applied and xfrc_applied), or a control callback mjcb_control must be installed which will be called just before the controls and applied forces are needed. Alternatively, one can use mj_step1 and mj_step2 which break down the simulation pipeline into computations that are executed before and after the controls are needed; in this way one can set controls that depend on the results from mj_step1. Keep in mind though that the RK4 solver does not work with mj_step1/2.

mj_forward performs the same computations as mj_step but without the integration. It is useful after loading or resetting a model (to put the entire mjData in a valid state), and also for out-of-order computations that involve sampling or finite-difference approximations.

mj_inverse runs the inverse dynamics, and writes its output in mjData.qfrc_inverse. Note that mjData.qacc must be set before calling this function. Given the state (qpos, qvel, act), mj_forward maps from force to acceleration, while mj_inverse maps from acceleration to force. Mathematically these functions are inverse of each other, but numerically this may not always be the case because the forward dynamics rely on a constraint optimization algorithm which is usually terminated early. The difference between the results of forward and inverse dynamics can be computed with the function mj_compareFwdInv, which can be though of as another solver accuracy check (as well as a general sanity check).

The skip version of mj_forward and mj_inverse are useful for example when qpos was unchanged but qvel was changed (usually in the context of finite differencing). Then there is no point repeating the computations that only depend on qpos. Calling the dynamics with skipstage = mjSTAGE_POS will achieve these savings.

mj_step

void mj_step(const mjModel* m, mjData* d);

Advance simulation, use control callback to obtain external force and control.

mj_step1

void mj_step1(const mjModel* m, mjData* d);

Advance simulation in two steps: before external force and control is set by user.

mj_step2

void mj_step2(const mjModel* m, mjData* d);

Advance simulation in two steps: after external force and control is set by user.

mj_forward

void mj_forward(const mjModel* m, mjData* d);

Forward dynamics: same as mj_step but do not integrate in time.

mj_inverse

void mj_inverse(const mjModel* m, mjData* d);

Inverse dynamics: qacc must be set before calling.

mj_forwardSkip

void mj_forwardSkip(const mjModel* m, mjData* d,
                    int skipstage, int skipsensor);

Forward dynamics with skip; skipstage is mjtStage.

mj_inverseSkip

void mj_inverseSkip(const mjModel* m, mjData* d,
                    int skipstage, int skipsensor);

Inverse dynamics with skip; skipstage is mjtStage.

Initialization

This section contains functions that load/initialize the model or other data structures. Their use is well illustrated in the code samples.

mj_defaultLROpt

void mj_defaultLROpt(mjLROpt* opt);

Set default options for length range computation.

mj_defaultSolRefImp

void mj_defaultSolRefImp(mjtNum* solref, mjtNum* solimp);

Set solver parameters to default values.

mj_defaultOption

void mj_defaultOption(mjOption* opt);

Set physics options to default values.

mj_defaultVisual

void mj_defaultVisual(mjVisual* vis);

Set visual options to default values.

mj_copyModel

mjModel* mj_copyModel(mjModel* dest, const mjModel* src);

Copy mjModel, allocate new if dest is NULL.

mj_saveModel

void mj_saveModel(const mjModel* m, const char* filename, void* buffer, int buffer_sz);

Save model to binary MJB file or memory buffer; buffer has precedence when given.

mj_loadModel

mjModel* mj_loadModel(const char* filename, const mjVFS* vfs);

Load model from binary MJB file. If vfs is not NULL, look up file in vfs before reading from disk.

mj_deleteModel

void mj_deleteModel(mjModel* m);

Free memory allocation in model.

mj_sizeModel

int mj_sizeModel(const mjModel* m);

Return size of buffer needed to hold model.

mj_makeData

mjData* mj_makeData(const mjModel* m);

Allocate mjData correponding to given model.

mj_copyData

mjData* mj_copyData(mjData* dest, const mjModel* m, const mjData* src);

Copy mjData.

mj_resetData

void mj_resetData(const mjModel* m, mjData* d);

Reset data to defaults.

mj_resetDataDebug

void mj_resetDataDebug(const mjModel* m, mjData* d, unsigned char debug_value);

Reset data to defaults, fill everything else with debug_value.

mj_resetDataKeyframe

void mj_resetDataKeyframe(const mjModel* m, mjData* d, int key);

Reset data, set fields from specified keyframe.

mj_stackAlloc

mjtNum* mj_stackAlloc(mjData* d, int size);

Allocate array of specified size on mjData stack. Call mju_error on stack overflow.

mj_deleteData

void mj_deleteData(mjData* d);

Free memory allocation in mjData.

mj_resetCallbacks

void mj_resetCallbacks(void);

Reset all callbacks to NULL pointers (NULL is the default).

mj_setConst

void mj_setConst(mjModel* m, mjData* d);

Set constant fields of mjModel, corresponding to qpos0 configuration.

mj_setLengthRange

int mj_setLengthRange(mjModel* m, mjData* d, int index,
                      const mjLROpt* opt, char* error, int error_sz);

Set actuator_lengthrange for specified actuator; return 1 if ok, 0 if error.

Printing

These functions can be used to print various quantities to the screen for debugging purposes.

mj_printModel

void mj_printModel(const mjModel* m, const char* filename);

Print model to text file.

mj_printData

void mj_printData(const mjModel* m, mjData* d, const char* filename);

Print data to text file.

mju_printMat

void mju_printMat(const mjtNum* mat, int nr, int nc);

Print matrix to screen.

mju_printMatSparse

void mju_printMatSparse(const mjtNum* mat, int nr,
                        const int* rownnz, const int* rowadr,
                        const int* colind);

Print sparse matrix to screen.

Components

These are components of the simulation pipeline, called internally from mj_step, mj_forward and mj_inverse. It is unlikely that the user will need to call them.

mj_fwdPosition

void mj_fwdPosition(const mjModel* m, mjData* d);

Run position-dependent computations.

mj_fwdVelocity

void mj_fwdVelocity(const mjModel* m, mjData* d);

Run velocity-dependent computations.

mj_fwdActuation

void mj_fwdActuation(const mjModel* m, mjData* d);

Compute actuator force qfrc_actuation.

mj_fwdAcceleration

void mj_fwdAcceleration(const mjModel* m, mjData* d);

Add up all non-constraint forces, compute qacc_unc.

mj_fwdConstraint

void mj_fwdConstraint(const mjModel* m, mjData* d);

Run selected constraint solver.

mj_Euler

void mj_Euler(const mjModel* m, mjData* d);

Euler integrator, semi-implicit in velocity.

mj_RungeKutta

void mj_RungeKutta(const mjModel* m, mjData* d, int N);

Runge-Kutta explicit order-N integrator.

mj_invPosition

void mj_invPosition(const mjModel* m, mjData* d);

Run position-dependent computations in inverse dynamics.

mj_invVelocity

void mj_invVelocity(const mjModel* m, mjData* d);

Run velocity-dependent computations in inverse dynamics.

mj_invConstraint

void mj_invConstraint(const mjModel* m, mjData* d);

Apply the analytical formula for inverse constraint dynamics.

mj_compareFwdInv

void mj_compareFwdInv(const mjModel* m, mjData* d);

Compare forward and inverse dynamics, save results in fwdinv.

Sub components

These are sub-components of the simulation pipeline, called internally from the components above. It is very unlikely that the user will need to call them.

mj_sensorPos

void mj_sensorPos(const mjModel* m, mjData* d);

Evaluate position-dependent sensors.

mj_sensorVel

void mj_sensorVel(const mjModel* m, mjData* d);

Evaluate velocity-dependent sensors.

mj_sensorAcc

void mj_sensorAcc(const mjModel* m, mjData* d);

Evaluate acceleration and force-dependent sensors.

mj_energyPos

void mj_energyPos(const mjModel* m, mjData* d);

Evaluate position-dependent energy (potential).

mj_energyVel

void mj_energyVel(const mjModel* m, mjData* d);

Evaluate velocity-dependent energy (kinetic).

mj_checkPos

void mj_checkPos(const mjModel* m, mjData* d);

Check qpos, reset if any element is too big or nan.

mj_checkVel

void mj_checkVel(const mjModel* m, mjData* d);

Check qvel, reset if any element is too big or nan.

mj_checkAcc

void mj_checkAcc(const mjModel* m, mjData* d);

Check qacc, reset if any element is too big or nan.

mj_kinematics

void mj_kinematics(const mjModel* m, mjData* d);

Run forward kinematics.

mj_comPos

void mj_comPos(const mjModel* m, mjData* d);

Map inertias and motion dofs to global frame centered at CoM.

mj_camlight

void mj_camlight(const mjModel* m, mjData* d);

Compute camera and light positions and orientations.

mj_tendon

void mj_tendon(const mjModel* m, mjData* d);

Compute tendon lengths, velocities and moment arms.

mj_transmission

void mj_transmission(const mjModel* m, mjData* d);

Compute actuator transmission lengths and moments.

mj_crb

void mj_crb(const mjModel* m, mjData* d);

Run composite rigid body inertia algorithm (CRB).

mj_factorM

void mj_factorM(const mjModel* m, mjData* d);

Compute sparse L'*D*L factorizaton of inertia matrix.

mj_solveM

void mj_solveM(const mjModel* m, mjData* d, mjtNum* x, const mjtNum* y, int n);

Solve linear system M * x = y using factorization: x = inv(L'*D*L)*y

mj_solveM2

void mj_solveM2(const mjModel* m, mjData* d, mjtNum* x, const mjtNum* y, int n);

Half of linear solve: x = sqrt(inv(D))*inv(L')*y

mj_comVel

void mj_comVel(const mjModel* m, mjData* d);

Compute cvel, cdof_dot.

mj_passive

void mj_passive(const mjModel* m, mjData* d);

Compute qfrc_passive from spring-dampers, viscosity and density.

mj_subtreeVel

void mj_subtreeVel(const mjModel* m, mjData* d);

subtree linear velocity and angular momentum

mj_rne

void mj_rne(const mjModel* m, mjData* d, int flg_acc, mjtNum* result);

RNE: compute M(qpos)*qacc + C(qpos,qvel); flg_acc=0 removes inertial term.

mj_rnePostConstraint

void mj_rnePostConstraint(const mjModel* m, mjData* d);

RNE with complete data: compute cacc, cfrc_ext, cfrc_int.

mj_collision

void mj_collision(const mjModel* m, mjData* d);

Run collision detection.

mj_makeConstraint

void mj_makeConstraint(const mjModel* m, mjData* d);

Construct constraints.

mj_projectConstraint

void mj_projectConstraint(const mjModel* m, mjData* d);

Compute inverse constaint inertia efc_AR.

mj_referenceConstraint

void mj_referenceConstraint(const mjModel* m, mjData* d);

Compute efc_vel, efc_aref.

mj_constraintUpdate

void mj_constraintUpdate(const mjModel* m, mjData* d, const mjtNum* jar,
                         mjtNum* cost, int flg_coneHessian);

Compute efc_state, efc_force, qfrc_constraint, and (optionally) cone Hessians. If cost is not NULL, set *cost = s(jar) where jar = Jac*qacc-aref.

Support

These are support functions that need access to mjModel and mjData, unlike the utility functions which do not need such access. Support functions are called within the simulator but some of them can also be useful for custom computations, and are documented in more detail below.

mj_addContact

int mj_addContact(const mjModel* m, mjData* d, const mjContact* con);

Add contact to d->contact list; return 0 if success; 1 if buffer full.

mj_isPyramidal

int mj_isPyramidal(const mjModel* m);

Determine type of friction cone.

mj_isSparse

int mj_isSparse(const mjModel* m);

Determine type of constraint Jacobian.

mj_isDual

int mj_isDual(const mjModel* m);

Determine type of solver (PGS is dual, CG and Newton are primal).

mj_mulJacVec

void mj_mulJacVec(const mjModel* m, mjData* d,
                  mjtNum* res, const mjtNum* vec);

This function multiplies the constraint Jacobian mjData.efc_J by a vector. Note that the Jacobian can be either dense or sparse; the function is aware of this setting. Multiplication by J maps velocities from joint space to constraint space.

mj_mulJacTVec

void mj_mulJacTVec(const mjModel* m, mjData* d, mjtNum* res, const mjtNum* vec);

Same as mj_mulJacVec but multiplies by the transpose of the Jacobian. This maps forces from constraint space to joint space.

mj_jac

void mj_jac(const mjModel* m, const mjData* d,
            mjtNum* jacp, mjtNum* jacr, const mjtNum point[3], int body);

This function computes an "end-effector" Jacobian, which is unrelated to the constraint Jacobian above. Any MuJoCo body can be treated as end-effector, and the point for which the Jacobian is computed can be anywhere in space (it is treated as attached to the body). The Jacobian has translational (jacp) and rotational (jacr) components. Passing NULL for either pointer will skip part of the computation. Each component is a 3-by-nv matrix. Each row of this matrix is the gradient of the corresponding 3D coordinate of the specified point with respect to the degrees of freedom. The ability to compute end-effector Jacobians analytically is one of the advantages of working in minimal coordinates - so use it!

mj_jacBody

void mj_jacBody(const mjModel* m, const mjData* d,
                mjtNum* jacp, mjtNum* jacr, int body);

This and the remaining variants of the Jacobian function call mj_jac internally, with the center of the body, geom or site. They are just shortcuts; the same can be achieved by calling mj_jac directly.

mj_jacBodyCom

void mj_jacBodyCom(const mjModel* m, const mjData* d,
                   mjtNum* jacp, mjtNum* jacr, int body);

Compute body center-of-mass end-effector Jacobian.

mj_jacGeom

void mj_jacGeom(const mjModel* m, const mjData* d,
                mjtNum* jacp, mjtNum* jacr, int geom);

Compute geom end-effector Jacobian.

mj_jacSite

void mj_jacSite(const mjModel* m, const mjData* d,
                mjtNum* jacp, mjtNum* jacr, int site);

Compute site end-effector Jacobian.

mj_jacPointAxis

void mj_jacPointAxis(const mjModel* m, mjData* d,
                     mjtNum* jacPoint, mjtNum* jacAxis,
                     const mjtNum point[3], const mjtNum axis[3], int body);

Compute translation end-effector Jacobian of point, and rotation Jacobian of axis.

mj_name2id

int mj_name2id(const mjModel* m, int type, const char* name);

Get id of object with specified name, return -1 if not found; type is mjtObj.

mj_id2name

const char* mj_id2name(const mjModel* m, int type, int id);

Get name of object with specified id, return 0 if invalid type or id; type is mjtObj.

mj_fullM

void mj_fullM(const mjModel* m, mjtNum* dst, const mjtNum* M);

Convert sparse inertia matrix M into full (i.e. dense) matrix.

mj_mulM

void mj_mulM(const mjModel* m, const mjData* d, mjtNum* res, const mjtNum* vec);

This function multiplies the joint-space inertia matrix stored in mjData.qM by a vector. qM has a custom sparse format that the user should not attempt to manipulate directly. Alternatively one can convert qM to a dense matrix with mj_fullM and then user regular matrix-vector multiplication, but this is slower because it no longer benefits from sparsity.

mj_mulM2

void mj_mulM2(const mjModel* m, const mjData* d, mjtNum* res, const mjtNum* vec);

Multiply vector by (inertia matrix)^(1/2).

mj_addM

void mj_addM(const mjModel* m, mjData* d, mjtNum* dst,
             int* rownnz, int* rowadr, int* colind);

Add inertia matrix to destination matrix. Destination can be sparse uncompressed, or dense when all int* are NULL

mj_applyFT

void mj_applyFT(const mjModel* m, mjData* d,
                const mjtNum* force, const mjtNum* torque,
                const mjtNum* point, int body, mjtNum* qfrc_target);

This function can be used to apply a Cartesian force and torque to a point on a body, and add the result to the vector mjData.qfrc_applied of all applied forces. Note that the function requires a pointer to this vector, because sometimes we want to add the result to a different vector.

mj_objectVelocity

void mj_objectVelocity(const mjModel* m, const mjData* d,
                       int objtype, int objid, mjtNum* res, int flg_local);

Compute object 6D velocity in object-centered frame, world/local orientation.

mj_objectAcceleration

void mj_objectAcceleration(const mjModel* m, const mjData* d,
                           int objtype, int objid, mjtNum* res, int flg_local);

Compute object 6D acceleration in object-centered frame, world/local orientation.

mj_contactForce

void mj_contactForce(const mjModel* m, const mjData* d, int id, mjtNum* result);

Extract 6D force:torque for one contact, in contact frame.

mj_differentiatePos

void mj_differentiatePos(const mjModel* m, mjtNum* qvel, mjtNum dt,
                         const mjtNum* qpos1, const mjtNum* qpos2);

This function subtracts two vectors in the format of qpos (and divides the result by dt), while respecting the properties of quaternions. Recall that unit quaternions represent spatial orientations. They are points on the unit sphere in 4D. The tangent to that sphere is a 3D plane of rotational velocities. Thus when we subtract two quaternions in the right way, the result is a 3D vector and not a 4D vector. This the output qvel has dimensionality nv while the inputs have dimensionality nq.

mj_integratePos

void mj_integratePos(const mjModel* m, mjtNum* qpos, const mjtNum* qvel, mjtNum dt);

This is the opposite of mj_differentiatePos. It adds a vector in the format of qvel (scaled by dt) to a vector in the format of qpos.

mj_normalizeQuat

void mj_normalizeQuat(const mjModel* m, mjtNum* qpos);

Normalize all quaterions in qpos-type vector.

mj_local2Global

void mj_local2Global(mjData* d, mjtNum* xpos, mjtNum* xmat,
                     const mjtNum* pos, const mjtNum* quat,
                     int body, mjtByte sameframe);

Map from body local to global Cartesian coordinates.

mj_getTotalmass

mjtNum mj_getTotalmass(const mjModel* m);

Sum all body masses.

mj_setTotalmass

void mj_setTotalmass(mjModel* m, mjtNum newmass);

Scale body masses and inertias to achieve specified total mass.

mj_version

int mj_version(void);

Return version number: 1.0.2 is encoded as 102.

Ray collisions

Ray collision functionality was added in MuJoCo 1.50. This is a new collision detection module that uses analytical formulas to intersect a ray (p + x*v, x>=0) with a geom, where p is the origin of the ray and v is the vector specifying the direction. All functions in this family return the distance to the nearest geom surface, or -1 if there is no intersection. Note that if p is inside a geom, the ray will intersect the surface from the inside which still counts as an intersection.

mj_ray

mjtNum mj_ray(const mjModel* m, const mjData* d, const mjtNum* pnt, const mjtNum* vec,
              const mjtByte* geomgroup, mjtByte flg_static, int bodyexclude,
              int* geomid);

Intersect ray (pnt+x*vec, x>=0) with visible geoms, except geoms in bodyexclude. Return geomid and distance (x) to nearest surface, or -1 if no intersection. geomgroup, flg_static are as in mjvOption; geomgroup==NULL skips group exclusion.

mj_rayHfield

mjtNum mj_rayHfield(const mjModel* m, const mjData* d, int geomid,
                    const mjtNum* pnt, const mjtNum* vec);

Interect ray with hfield, return nearest distance or -1 if no intersection.

mj_rayMesh

mjtNum mj_rayMesh(const mjModel* m, const mjData* d, int geomid,
                  const mjtNum* pnt, const mjtNum* vec);

Interect ray with mesh, return nearest distance or -1 if no intersection.

mju_rayGeom

mjtNum mju_rayGeom(const mjtNum* pos, const mjtNum* mat, const mjtNum* size,
                   const mjtNum* pnt, const mjtNum* vec, int geomtype);

Interect ray with pure geom, return nearest distance or -1 if no intersection.

mju_raySkin

mjtNum mju_raySkin(int nface, int nvert, const int* face, const float* vert,
                   const mjtNum* pnt, const mjtNum* vec, int* vertid);

Interect ray with skin, return nearest vertex id.

Interaction

These function implement abstract mouse interactions, allowing control over cameras and perturbations. Their use is well illustrated in simulate.cpp as well as mjvive.cpp.

mjv_defaultCamera

void mjv_defaultCamera(mjvCamera* cam);

Set default camera.

mjv_defaultPerturb

void mjv_defaultPerturb(mjvPerturb* pert);

Set default perturbation.

mjv_room2model

void mjv_room2model(mjtNum* modelpos, mjtNum* modelquat, const mjtNum* roompos,
                    const mjtNum* roomquat, const mjvScene* scn);

Transform pose from room to model space.

mjv_model2room

void mjv_model2room(mjtNum* roompos, mjtNum* roomquat, const mjtNum* modelpos,
                    const mjtNum* modelquat, const mjvScene* scn);

Transform pose from model to room space.

mjv_cameraInModel

void mjv_cameraInModel(mjtNum* headpos, mjtNum* forward, mjtNum* up,
                       const mjvScene* scn);

Get camera info in model space; average left and right OpenGL cameras.

mjv_cameraInRoom

void mjv_cameraInRoom(mjtNum* headpos, mjtNum* forward, mjtNum* up,
                      const mjvScene* scn);

Get camera info in room space; average left and right OpenGL cameras.

mjv_frustumHeight

mjtNum mjv_frustumHeight(const mjvScene* scn);

Get frustum height at unit distance from camera; average left and right OpenGL cameras.

mjv_alignToCamera

void mjv_alignToCamera(mjtNum* res, const mjtNum* vec, const mjtNum* forward);

Rotate 3D vec in horizontal plane by angle between (0,1) and (forward_x,forward_y).

mjv_moveCamera

void mjv_moveCamera(const mjModel* m, int action, mjtNum reldx, mjtNum reldy,
                    const mjvScene* scn, mjvCamera* cam);

Move camera with mouse; action is mjtMouse.

mjv_movePerturb

void mjv_movePerturb(const mjModel* m, const mjData* d, int action, mjtNum reldx,
                     mjtNum reldy, const mjvScene* scn, mjvPerturb* pert);

Move perturb object with mouse; action is mjtMouse.

mjv_moveModel

void mjv_moveModel(const mjModel* m, int action, mjtNum reldx, mjtNum reldy,
                   const mjtNum* roomup, mjvScene* scn);

Move model with mouse; action is mjtMouse.

mjv_initPerturb

void mjv_initPerturb(const mjModel* m, const mjData* d,
                     const mjvScene* scn, mjvPerturb* pert);

Copy perturb pos,quat from selected body; set scale for perturbation.

mjv_applyPerturbPose

void mjv_applyPerturbPose(const mjModel* m, mjData* d, const mjvPerturb* pert,
                          int flg_paused);

Set perturb pos,quat in d->mocap when selected body is mocap, and in d->qpos otherwise. Write d->qpos only if flg_paused and subtree root for selected body has free joint.

mjv_applyPerturbForce

void mjv_applyPerturbForce(const mjModel* m, mjData* d, const mjvPerturb* pert);

Set perturb force,torque in d->xfrc_applied, if selected body is dynamic.

mjv_averageCamera

mjvGLCamera mjv_averageCamera(const mjvGLCamera* cam1, const mjvGLCamera* cam2);

Return the average of two OpenGL cameras.

mjv_select

int mjv_select(const mjModel* m, const mjData* d, const mjvOption* vopt,
               mjtNum aspectratio, mjtNum relx, mjtNum rely,
               const mjvScene* scn, mjtNum* selpnt, int* geomid, int* skinid);

This function is used for mouse selection. Previously selection was done via OpenGL, but as of MuJoCo 1.50 it relies on ray intersections which are much more efficient. aspectratio is the viewport width/height. relx and rely are the relative coordinates of the 2D point of interest in the viewport (usually mouse cursor). The function returns the id of the geom under the specified 2D point, or -1 if there is no geom (note that they skybox if present is not a model geom). The 3D coordinates of the clicked point are returned in selpnt. See simulate.cpp for an illustration.

Visualization

The functions in this section implement abstract visualization. The results are used by the OpenGL rendered, and can also be used by users wishing to implement their own rendered, or hook up MuJoCo to advanced rendering tools such as Unity or Unreal Engine. See simulate.cpp for illustration of how to use these functions.

mjv_defaultOption

void mjv_defaultOption(mjvOption* opt);

Set default visualization options.

mjv_defaultFigure

void mjv_defaultFigure(mjvFigure* fig);

Set default figure.

mjv_initGeom

void mjv_initGeom(mjvGeom* geom, int type, const mjtNum* size,
                  const mjtNum* pos, const mjtNum* mat, const float* rgba);

Initialize given geom fields when not NULL, set the rest to their default values.

mjv_makeConnector

void mjv_makeConnector(mjvGeom* geom, int type, mjtNum width,
                       mjtNum a0, mjtNum a1, mjtNum a2,
                       mjtNum b0, mjtNum b1, mjtNum b2);

Set (type, size, pos, mat) for connector-type geom between given points. Assume that mjv_initGeom was already called to set all other properties.

mjv_defaultScene

void mjv_defaultScene(mjvScene* scn);

Set default abstract scene.

mjv_makeScene

void mjv_makeScene(const mjModel* m, mjvScene* scn, int maxgeom);

Allocate resources in abstract scene.

mjv_freeScene

void mjv_freeScene(mjvScene* scn);

Free abstract scene.

mjv_updateScene

void mjv_updateScene(const mjModel* m, mjData* d, const mjvOption* opt,
                     const mjvPerturb* pert, mjvCamera* cam, int catmask, mjvScene* scn);

Update entire scene given model state.

mjv_addGeoms

void mjv_addGeoms(const mjModel* m, mjData* d, const mjvOption* opt,
                  const mjvPerturb* pert, int catmask, mjvScene* scn);

Add geoms from selected categories.

mjv_makeLights

void mjv_makeLights(const mjModel* m, mjData* d, mjvScene* scn);

Make list of lights.

mjv_updateCamera

void mjv_updateCamera(const mjModel* m, mjData* d, mjvCamera* cam, mjvScene* scn);

Update camera.

mjv_updateSkin

void mjv_updateSkin(const mjModel* m, mjData* d, mjvScene* scn);

Update skins.

OpenGL rendering

These functions expose the OpenGL renderer. See simulate.cpp for illustration of how to use these functions.

mjr_defaultContext

void mjr_defaultContext(mjrContext* con);

Set default mjrContext.

mjr_makeContext

void mjr_makeContext(const mjModel* m, mjrContext* con, int fontscale);

Allocate resources in custom OpenGL context; fontscale is mjtFontScale.

mjr_changeFont

void mjr_changeFont(int fontscale, mjrContext* con);

Change font of existing context.

mjr_addAux

void mjr_addAux(int index, int width, int height, int samples, mjrContext* con);

Add Aux buffer with given index to context; free previous Aux buffer.

mjr_freeContext

void mjr_freeContext(mjrContext* con);

Free resources in custom OpenGL context, set to default.

mjr_uploadTexture

void mjr_uploadTexture(const mjModel* m, const mjrContext* con, int texid);

Upload texture to GPU, overwriting previous upload if any.

mjr_uploadMesh

void mjr_uploadMesh(const mjModel* m, const mjrContext* con, int meshid);

Upload mesh to GPU, overwriting previous upload if any.

mjr_uploadHField

void mjr_uploadHField(const mjModel* m, const mjrContext* con, int hfieldid);

Upload height field to GPU, overwriting previous upload if any.

mjr_restoreBuffer

void mjr_restoreBuffer(const mjrContext* con);

Make con->currentBuffer current again.

mjr_setBuffer

void mjr_setBuffer(int framebuffer, mjrContext* con);

Set OpenGL framebuffer for rendering: mjFB_WINDOW or mjFB_OFFSCREEN. If only one buffer is available, set that buffer and ignore framebuffer argument.

mjr_readPixels

void mjr_readPixels(unsigned char* rgb, float* depth,
                    mjrRect viewport, const mjrContext* con);

Read pixels from current OpenGL framebuffer to client buffer. Viewport is in OpenGL framebuffer; client buffer starts at (0,0).

mjr_drawPixels

void mjr_drawPixels(const unsigned char* rgb, const float* depth,
                    mjrRect viewport, const mjrContext* con);

Draw pixels from client buffer to current OpenGL framebuffer. Viewport is in OpenGL framebuffer; client buffer starts at (0,0).

mjr_blitBuffer

void mjr_blitBuffer(mjrRect src, mjrRect dst,
                    int flg_color, int flg_depth, const mjrContext* con);

Blit from src viewpoint in current framebuffer to dst viewport in other framebuffer. If src, dst have different size and flg_depth==0, color is interpolated with GL_LINEAR.

mjr_setAux

void mjr_setAux(int index, const mjrContext* con);

Set Aux buffer for custom OpenGL rendering (call restoreBuffer when done).

mjr_blitAux

void mjr_blitAux(int index, mjrRect src, int left, int bottom,
                 const mjrContext* con);

Blit from Aux buffer to con->currentBuffer.

mjr_text

void mjr_text(int font, const char* txt, const mjrContext* con,
              float x, float y, float r, float g, float b);

Draw text at (x,y) in relative coordinates; font is mjtFont.

mjr_overlay

void mjr_overlay(int font, int gridpos, mjrRect viewport,
                 const char* overlay, const char* overlay2, const mjrContext* con);

Draw text overlay; font is mjtFont; gridpos is mjtGridPos.

mjr_maxViewport

mjrRect mjr_maxViewport(const mjrContext* con);

Get maximum viewport for active buffer.

mjr_rectangle

void mjr_rectangle(mjrRect viewport, float r, float g, float b, float a);

Draw rectangle.

mjr_figure

void mjr_figure(mjrRect viewport, mjvFigure* fig, const mjrContext* con);

Draw 2D figure.

mjr_render

void mjr_render(mjrRect viewport, mjvScene* scn, const mjrContext* con);

Render 3D scene.

mjr_finish

void mjr_finish(void);

Call glFinish.

mjr_getError

int mjr_getError(void);

Call glGetError and return result.

mjr_findRect

int mjr_findRect(int x, int y, int nrect, const mjrRect* rect);

Find first rectangle containing mouse, -1: not found.

UI framework

mjui_themeSpacing

mjuiThemeSpacing mjui_themeSpacing(int ind);

Get builtin UI theme spacing (ind: 0-1).

mjui_themeColor

mjuiThemeColor mjui_themeColor(int ind);

Get builtin UI theme color (ind: 0-3).

mjui_add

void mjui_add(mjUI* ui, const mjuiDef* def);

Add definitions to UI.

mjui_resize

void mjui_resize(mjUI* ui, const mjrContext* con);

Compute UI sizes.

mjui_update

void mjui_update(int section, int item, const mjUI* ui,
                 const mjuiState* state, const mjrContext* con);

Update specific section/item; -1: update all.

mjui_event

mjuiItem* mjui_event(mjUI* ui, mjuiState* state, const mjrContext* con);

Handle UI event, return pointer to changed item, NULL if no change.

mjui_render

void mjui_render(mjUI* ui, const mjuiState* state, const mjrContext* con);

Copy UI image to current buffer.

Error and memory

mju_error

void mju_error(const char* msg);

Main error function; does not return to caller.

mju_error_i

void mju_error_i(const char* msg, int i);

Error function with int argument; msg is a printf format string.

mju_error_s

void mju_error_s(const char* msg, const char* text);

Error function with string argument.

mju_warning

void mju_warning(const char* msg);

Main warning function; returns to caller.

mju_warning_i

void mju_warning_i(const char* msg, int i);

Warning function with int argument.

mju_warning_s

void mju_warning_s(const char* msg, const char* text);

Warning function with string argument.

mju_clearHandlers

void mju_clearHandlers(void);

Clear user error and memory handlers.

mju_malloc

void* mju_malloc(size_t size);

Allocate memory; byte-align on 8; pad size to multiple of 8.

mju_free

void mju_free(void* ptr);

Free memory, using free() by default.

mj_warning

void mj_warning(mjData* d, int warning, int info);

High-level warning function: count warnings in mjData, print only the first.

mju_writeLog

void mju_writeLog(const char* type, const char* msg);

Write [datetime, type: message] to MUJOCO_LOG.TXT.

Standard math

The "functions" in this section are preprocessor macros replaced with the corresponding C standard library math functions. When MuJoCo is compiled with single precision (which is not currently available to the public, but we sometimes use it internally) these macros are replaced with the corresponding single-precision functions (not shown here). So one can think of them as having inputs and outputs of type mjtNum, where mjtNum is defined as double or float depending on how MuJoCo is compiled. We will not document these functions here; see the C standard library specification.

mju_sqrt

#define mju_sqrt    sqrt

mju_exp

#define mju_exp     exp

mju_sin

#define mju_sin     sin

mju_cos

#define mju_cos     cos

mju_tan

#define mju_tan     tan

mju_asin

#define mju_asin    asin

mju_acos

#define mju_acos    acos

mju_atan2

#define mju_atan2   atan2

mju_tanh

#define mju_tanh    tanh

mju_pow

#define mju_pow     pow

mju_abs

#define mju_abs     fabs

mju_log

#define mju_log     log

mju_log10

#define mju_log10   log10

mju_floor

#define mju_floor   floor

mju_ceil

#define mju_ceil    ceil

Vector math

mju_zero3

void mju_zero3(mjtNum res[3]);

Set res = 0.

mju_copy3

void mju_copy3(mjtNum res[3], const mjtNum data[3]);

Set res = vec.

mju_scl3

void mju_scl3(mjtNum res[3], const mjtNum vec[3], mjtNum scl);

Set res = vec*scl.

mju_add3

void mju_add3(mjtNum res[3], const mjtNum vec1[3], const mjtNum vec2[3]);

Set res = vec1 + vec2.

mju_sub3

void mju_sub3(mjtNum res[3], const mjtNum vec1[3], const mjtNum vec2[3]);

Set res = vec1 - vec2.

mju_addTo3

void mju_addTo3(mjtNum res[3], const mjtNum vec[3]);

Set res = res + vec.

mju_subFrom3

void mju_subFrom3(mjtNum res[3], const mjtNum vec[3]);

Set res = res - vec.

mju_addToScl3

void mju_addToScl3(mjtNum res[3], const mjtNum vec[3], mjtNum scl);

Set res = res + vec*scl.

mju_addScl3

void mju_addScl3(mjtNum res[3], const mjtNum vec1[3], const mjtNum vec2[3], mjtNum scl);

Set res = vec1 + vec2*scl.

mju_normalize3

mjtNum mju_normalize3(mjtNum res[3]);

Normalize vector, return length before normalization.

mju_norm3

mjtNum mju_norm3(const mjtNum vec[3]);

Return vector length (without normalizing the vector).

mju_dot3

mjtNum mju_dot3(const mjtNum vec1[3], const mjtNum vec2[3]);

Return dot-product of vec1 and vec2.

mju_dist3

mjtNum mju_dist3(const mjtNum pos1[3], const mjtNum pos2[3]);

Return Cartesian distance between 3D vectors pos1 and pos2.

mju_rotVecMat

void mju_rotVecMat(mjtNum res[3], const mjtNum vec[3], const mjtNum mat[9]);

Multiply vector by 3D rotation matrix: res = mat * vec.

mju_rotVecMatT

void mju_rotVecMatT(mjtNum res[3], const mjtNum vec[3], const mjtNum mat[9]);

Multiply vector by transposed 3D rotation matrix: res = mat' * vec.

mju_cross

void mju_cross(mjtNum res[3], const mjtNum a[3], const mjtNum b[3]);

Compute cross-product: res = cross(a, b).

mju_zero4

void mju_zero4(mjtNum res[4]);

Set res = 0.

mju_unit4

void mju_unit4(mjtNum res[4]);

Set res = (1,0,0,0).

mju_copy4

void mju_copy4(mjtNum res[4], const mjtNum data[4]);

Set res = vec.

mju_normalize4

mjtNum mju_normalize4(mjtNum res[4]);

Normalize vector, return length before normalization.

mju_zero

void mju_zero(mjtNum* res, int n);

Set res = 0.

mju_copy

void mju_copy(mjtNum* res, const mjtNum* data, int n);

Set res = vec.

mju_sum

mjtNum mju_sum(const mjtNum* vec, int n);

Return sum(vec).

mju_L1

mjtNum mju_L1(const mjtNum* vec, int n);

Return L1 norm: sum(abs(vec)).

mju_scl

void mju_scl(mjtNum* res, const mjtNum* vec, mjtNum scl, int n);

Set res = vec*scl.

mju_add

void mju_add(mjtNum* res, const mjtNum* vec1, const mjtNum* vec2, int n);

Set res = vec1 + vec2.

mju_sub

void mju_sub(mjtNum* res, const mjtNum* vec1, const mjtNum* vec2, int n);

Set res = vec1 - vec2.

mju_addTo

void mju_addTo(mjtNum* res, const mjtNum* vec, int n);

Set res = res + vec.

mju_subFrom

void mju_subFrom(mjtNum* res, const mjtNum* vec, int n);

Set res = res - vec.

mju_addToScl

void mju_addToScl(mjtNum* res, const mjtNum* vec, mjtNum scl, int n);

Set res = res + vec*scl.

mju_addScl

void mju_addScl(mjtNum* res, const mjtNum* vec1, const mjtNum* vec2, mjtNum scl, int n);

Set res = vec1 + vec2*scl.

mju_normalize

mjtNum mju_normalize(mjtNum* res, int n);

Normalize vector, return length before normalization.

mju_norm

mjtNum mju_norm(const mjtNum* res, int n);

Return vector length (without normalizing vector).

mju_dot

mjtNum mju_dot(const mjtNum* vec1, const mjtNum* vec2, const int n);

Return dot-product of vec1 and vec2.

mju_mulMatVec

void mju_mulMatVec(mjtNum* res, const mjtNum* mat, const mjtNum* vec,
                   int nr, int nc);

Multiply matrix and vector: res = mat * vec.

mju_mulMatTVec

void mju_mulMatTVec(mjtNum* res, const mjtNum* mat, const mjtNum* vec,
                    int nr, int nc);

Multiply transposed matrix and vector: res = mat' * vec.

mju_transpose

void mju_transpose(mjtNum* res, const mjtNum* mat, int nr, int nc);

Transpose matrix: res = mat'.

mju_mulMatMat

void mju_mulMatMat(mjtNum* res, const mjtNum* mat1, const mjtNum* mat2,
                   int r1, int c1, int c2);

Multiply matrices: res = mat1 * mat2.

mju_mulMatMatT

void mju_mulMatMatT(mjtNum* res, const mjtNum* mat1, const mjtNum* mat2,
                    int r1, int c1, int r2);

Multiply matrices, second argument transposed: res = mat1 * mat2'.

mju_mulMatTMat

void mju_mulMatTMat(mjtNum* res, const mjtNum* mat1, const mjtNum* mat2,
                    int r1, int c1, int c2);

Multiply matrices, first argument transposed: res = mat1' * mat2.

mju_sqrMatTD

void mju_sqrMatTD(mjtNum* res, const mjtNum* mat, const mjtNum* diag, int nr, int nc);

Set res = mat' * diag * mat if diag is not NULL, and res = mat' * mat otherwise.

mju_transformSpatial

void mju_transformSpatial(mjtNum res[6], const mjtNum vec[6], int flg_force,
                          const mjtNum newpos[3], const mjtNum oldpos[3],
                          const mjtNum rotnew2old[9]);

Coordinate transform of 6D motion or force vector in rotation:translation format. rotnew2old is 3-by-3, NULL means no rotation; flg_force specifies force or motion type.

Quaternions

mju_rotVecQuat

void mju_rotVecQuat(mjtNum res[3], const mjtNum vec[3], const mjtNum quat[4]);

Rotate vector by quaternion.

mju_negQuat

void mju_negQuat(mjtNum res[4], const mjtNum quat[4]);

Negate quaternion.

mju_mulQuat

void mju_mulQuat(mjtNum res[4], const mjtNum quat1[4], const mjtNum quat2[4]);

Muiltiply quaternions.

mju_mulQuatAxis

void mju_mulQuatAxis(mjtNum res[4], const mjtNum quat[4], const mjtNum axis[3]);

Muiltiply quaternion and axis.

mju_axisAngle2Quat

void mju_axisAngle2Quat(mjtNum res[4], const mjtNum axis[3], mjtNum angle);

Convert axisAngle to quaternion.

mju_quat2Vel

void mju_quat2Vel(mjtNum res[3], const mjtNum quat[4], mjtNum dt);

Convert quaternion (corresponding to orientation difference) to 3D velocity.

mju_subQuat

void mju_subQuat(mjtNum res[3], const mjtNum qa[4], const mjtNum qb[4]);

Subtract quaternions, express as 3D velocity: qb*quat(res) = qa.

mju_quat2Mat

void mju_quat2Mat(mjtNum res[9], const mjtNum quat[4]);

Convert quaternion to 3D rotation matrix.

mju_mat2Quat

void mju_mat2Quat(mjtNum quat[4], const mjtNum mat[9]);

Convert 3D rotation matrix to quaterion.

mju_derivQuat

void mju_derivQuat(mjtNum res[4], const mjtNum quat[4], const mjtNum vel[3]);

Compute time-derivative of quaternion, given 3D rotational velocity.

mju_quatIntegrate

void mju_quatIntegrate(mjtNum quat[4], const mjtNum vel[3], mjtNum scale);

Integrate quaterion given 3D angular velocity.

mju_quatZ2Vec

void mju_quatZ2Vec(mjtNum quat[4], const mjtNum vec[3]);

Construct quaternion performing rotation from z-axis to given vector.

Poses

mju_mulPose

void mju_mulPose(mjtNum posres[3], mjtNum quatres[4],
                 const mjtNum pos1[3], const mjtNum quat1[4],
                 const mjtNum pos2[3], const mjtNum quat2[4]);

Multiply two poses.

mju_negPose

void mju_negPose(mjtNum posres[3], mjtNum quatres[4],
                 const mjtNum pos[3], const mjtNum quat[4]);

Negate pose.

mju_trnVecPose

void mju_trnVecPose(mjtNum res[3], const mjtNum pos[3], const mjtNum quat[4],
                    const mjtNum vec[3]);

Transform vector by pose.

Decompositions

mju_cholFactor

int mju_cholFactor(mjtNum* mat, int n, mjtNum mindiag);

Cholesky decomposition: mat = L*L'; return rank.

mju_cholSolve

void mju_cholSolve(mjtNum* res, const mjtNum* mat, const mjtNum* vec, int n);

Solve mat * res = vec, where mat is Cholesky-factorized

mju_cholUpdate

int mju_cholUpdate(mjtNum* mat, mjtNum* x, int n, int flg_plus);

Cholesky rank-one update: L*L' +/- x*x'; return rank.

mju_eig3

int mju_eig3(mjtNum* eigval, mjtNum* eigvec, mjtNum* quat, const mjtNum* mat);

Eigenvalue decomposition of symmetric 3x3 matrix.

Miscellaneous

mju_muscleGain

mjtNum mju_muscleGain(mjtNum len, mjtNum vel, const mjtNum lengthrange[2],
                      mjtNum acc0, const mjtNum prm[9]);

Muscle active force, prm = (range[2], force, scale, lmin, lmax, vmax, fpmax, fvmax).

mju_muscleBias

mjtNum mju_muscleBias(mjtNum len, const mjtNum lengthrange[2],
                      mjtNum acc0, const mjtNum prm[9]);

Muscle passive force, prm = (range[2], force, scale, lmin, lmax, vmax, fpmax, fvmax).

mju_muscleDynamics

mjtNum mju_muscleDynamics(mjtNum ctrl, mjtNum act, const mjtNum prm[2]);

Muscle activation dynamics, prm = (tau_act, tau_deact).

mju_encodePyramid

void mju_encodePyramid(mjtNum* pyramid, const mjtNum* force,
                       const mjtNum* mu, int dim);

Convert contact force to pyramid representation.

mju_decodePyramid

void mju_decodePyramid(mjtNum* force, const mjtNum* pyramid,
                       const mjtNum* mu, int dim);

Convert pyramid representation to contact force.

mju_springDamper

mjtNum mju_springDamper(mjtNum pos0, mjtNum vel0, mjtNum Kp, mjtNum Kv, mjtNum dt);

Integrate spring-damper analytically, return pos(dt).

mju_min

mjtNum mju_min(mjtNum a, mjtNum b);

Return min(a,b) with single evaluation of a and b.

mju_max

mjtNum mju_max(mjtNum a, mjtNum b);

Return max(a,b) with single evaluation of a and b.

mju_sign

mjtNum mju_sign(mjtNum x);

Return sign of x: +1, -1 or 0.

mju_round

int mju_round(mjtNum x);

Round x to nearest integer.

mju_type2Str

const char* mju_type2Str(int type);

Convert type id (mjtObj) to type name.

mju_str2Type

int mju_str2Type(const char* str);

Convert type name to type id (mjtObj).

mju_warningText

const char* mju_warningText(int warning, int info);

Construct a warning message given the warning type and info.

mju_isBad

int mju_isBad(mjtNum x);

Return 1 if nan or abs(x)>mjMAXVAL, 0 otherwise. Used by check functions.

mju_isZero

int mju_isZero(mjtNum* vec, int n);

Return 1 if all elements are 0.

mju_standardNormal

mjtNum mju_standardNormal(mjtNum* num2);

Standard normal random number generator (optional second number).

mju_f2n

void mju_f2n(mjtNum* res, const float* vec, int n);

Convert from float to mjtNum.

mju_n2f

void mju_n2f(float* res, const mjtNum* vec, int n);

Convert from mjtNum to float.

mju_d2n

void mju_d2n(mjtNum* res, const double* vec, int n);

Convert from double to mjtNum.

mju_n2d

void mju_n2d(double* res, const mjtNum* vec, int n);

Convert from mjtNum to double.

mju_insertionSort

void mju_insertionSort(mjtNum* list, int n);

Insertion sort, resulting list is in increasing order.

mju_Halton

mjtNum mju_Halton(int index, int base);

Generate Halton sequence.

mju_strncpy

char* mju_strncpy(char *dst, const char *src, int n);

Call strncpy, then set dst[n-1] = 0.

Macros

mjMARKSTACK

#define mjMARKSTACK int _mark = d->pstack;

This macro is helpful when using the MuJoCo stack in custom computations. It works together with the next macro and the mj_stackAlloc funcion, and assumes that mjData* d is defined. The use pattern is this:

    mjMARKSTACK
    mjtNum* temp = mj_stackAlloc(d, 100);
    // ... use temp as needed
    mjFREESTACK

mjFREESTACK

#define mjFREESTACK d->pstack = _mark;

Reset the MuJoCo stack pointer to the variable _mark, normally saved by mjMARKSTACK.

mjDISABLED

#define mjDISABLED(x) (m->opt.disableflags & (x))

Check if a given standard feature has been disabled via the physics options, assuming mjModel* m is defined. x is of type mjtDisableBit.

mjENABLED

#define mjENABLED(x) (m->opt.enableflags & (x))

Check if a given optional feature has been enabled via the physics options, assuming mjModel* m is defined. x is of type mjtEnableBit.

mjMAX

#define mjMAX(a,b) (((a) > (b)) ? (a) : (b))

Return maximum value. To avoid repeated evaluation with mjtNum types, use the function mju_max.

mjMIN

#define mjMIN(a,b) (((a) < (b)) ? (a) : (b))

Return minimum value. To avoid repeated evaluation with mjtNum types, use the function mju_min.