//--------------------------------//
//  This file is part MuJoCo      //
//  Copyright © 2018, Roboti LLC  //
//--------------------------------//


#pragma once


//---------------------------- floating-point definitions -------------------------------

// compile-time configuration options
#define mjUSEDOUBLE                 // single or double precision for mjtNum
#define mjUSEAVX                    // C or AVX intrinsics for custom BLAS


// floating point data type and minval
#ifdef mjUSEDOUBLE
    typedef double mjtNum;
    #define mjMINVAL    1E-15       // minimum value in any denominator
#else
    typedef float mjtNum;
    #define mjMINVAL    1E-15f
#endif


// global constants
#define mjPI            3.14159265358979323846
#define mjMAXVAL        1E+10       // maximum value in qpos, qvel, qacc
#define mjMINMU         1E-5        // minimum friction coefficient
#define mjMINIMP        0.0001      // minimum constraint impedance
#define mjMAXIMP        0.9999      // maximum constraint impedance
#define mjMAXCONPAIR    50          // maximum number of contacts per geom pair
#define mjMAXVFS        200         // maximum number of files in virtual file system
#define mjMAXVFSNAME    100         // maximum filename size in virtual file system


//---------------------------- sizes ----------------------------------------------------

#define mjNEQDATA       7           // number of eq_data fields
#define mjNDYN          10          // number of actuator dynamics parameters
#define mjNGAIN         10          // number of actuator gain parameters
#define mjNBIAS         10          // number of actuator bias parameters
#define mjNREF          2           // number of solver reference parameters
#define mjNIMP          5           // number of solver impedance parameters
#define mjNSOLVER       1000        // size of mjData.solver_XXX arrays


//---------------------------- primitive types (mjt) ------------------------------------
    
typedef unsigned char mjtByte;      // used for true/false


typedef enum _mjtDisableBit         // disable default feature bitflags
{
    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;


typedef enum _mjtEnableBit          // enable optional feature bitflags
{
    mjENBL_OVERRIDE     = 1<<0,     // override contact parameters
    mjENBL_ENERGY       = 1<<1,     // energy computation
    mjENBL_FWDINV       = 1<<2,     // record solver statistics
    mjENBL_SENSORNOISE  = 1<<3,     // add noise to sensor data

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


typedef enum _mjtJoint              // type of degree of freedom
{
    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;


typedef enum _mjtGeom               // type of geometric shape
{
    // 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;


typedef enum _mjtCamLight           // tracking mode for camera and light
{
    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;


typedef enum _mjtTexture            // type of texture
{
    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;


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


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;


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


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


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


typedef enum _mjtEq                 // type of equality constraint
{
    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;


typedef enum _mjtWrap               // type of tendon wrap object
{
    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;


typedef enum _mjtTrn                // type of actuator transmission
{
    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;


typedef enum _mjtDyn                // type of actuator dynamics
{
    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;


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


typedef enum _mjtBias               // type of actuator bias
{
    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;


typedef enum _mjtObj                // type of MujoCo object
{
    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;


typedef enum _mjtConstraint         // type of constraint
{
    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;


typedef enum _mjtConstraintState    // constraint state
{
    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)
} mjtConstraintState;


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;


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


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;


typedef enum _mjtLRMode             // mode for actuator length range computation
{
    mjLRMODE_NONE   = 0,            // do not process any actuators
    mjLRMODE_MUSCLE,                // process muscle actuators
    mjLRMODE_MUSCLEUSER,            // process muscle and user actuators
    mjLRMODE_ALL                    // process all actuators
} mjtLRMode;


//------------------------------ mjLROpt ------------------------------------------------

struct _mjLROpt                     // options for mj_setLengthRange()
{
    // flags
    int mode;                       // which actuators to process (mjtLRMode)
    int useexisting;                // use existing length range if available
    int uselimit;                   // use joint and tendon limits if available

    // algorithm parameters
    mjtNum accel;                   // target acceleration used to compute force
    mjtNum maxforce;                // maximum force; 0: no limit
    mjtNum timeconst;               // time constant for velocity reduction; min 0.01
    mjtNum timestep;                // simulation timestep; 0: use mjOption.timestep
    mjtNum inttotal;                // total simulation time interval
    mjtNum inteval;                 // evaluation time interval (at the end)
    mjtNum tolrange;                // convergence tolerance (relative to range)
};
typedef struct _mjLROpt mjLROpt;


//------------------------------ 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;


//------------------------------ 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;


//------------------------------ 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;


//------------------------------ 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;


//---------------------------------- 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;
