// Copyright 2021 DeepMind Technologies Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "simulate.h"

#include <algorithm>
#include <atomic>
#include <chrono>
#include <climits>
#include <cstdio>
#include <cstring>
#include <memory>
#include <optional>
#include <ratio>
#include <string>
#include <type_traits>
#include <utility>

#include "lodepng.h"
#include <mujoco/mjdata.h>
#include <mujoco/mjui.h>
#include <mujoco/mjvisualize.h>
#include <mujoco/mjxmacro.h>
#include <mujoco/mujoco.h>
#include "platform_ui_adapter.h"
#include "array_safety.h"

// When launched via an App Bundle on macOS, the working directory is the path to the App Bundle's
// resource directory. This causes files to be saved into the bundle, which is not the desired
// behavior. Instead, we open a save dialog box to ask the user where to put the file.
// Since the dialog box logic needs to be written in Objective-C, we separate it into a different
// source file.
#ifdef __APPLE__
std::string GetSavePath(const char* filename);
#else
static std::string GetSavePath(const char* filename) {
  return filename;
}
#endif

namespace {
namespace mj = ::mujoco;
namespace mju = ::mujoco::sample_util;

using Seconds = std::chrono::duration<double>;
using Milliseconds = std::chrono::duration<double, std::milli>;

template <typename T>
inline bool IsDifferent(const T& a, const T& b) {
  if constexpr (std::is_array_v<T>) {
    static_assert(std::rank_v<T> == 1);
    for (int i = 0; i < std::extent_v<T>; ++i) {
      if (a[i] != b[i]) {
        return true;
      }
    }
    return false;
  } else {
    return a != b;
  }
}

template <typename T>
inline void CopyScalar(T& dst, const T& src) {
  dst = src;
}

template <typename T, int N>
inline void CopyArray(T (&dst)[N], const T (&src)[N]) {
  for (int i = 0; i < N; ++i) {
    dst[i] = src[i];
  }
}

template <typename T>
inline void Copy(T& dst, const T& src) {
  if constexpr (std::is_array_v<T>) {
    CopyArray(dst, src);
  } else {
    CopyScalar(dst, src);
  }
}

//------------------------------------------- global -----------------------------------------------

const double zoom_increment = 0.02;  // ratio of one click-wheel zoom increment to vertical extent

// section ids
enum {
  // left ui
  SECT_FILE   = 0,
  SECT_OPTION,
  SECT_SIMULATION,
  SECT_WATCH,
  SECT_PHYSICS,
  SECT_RENDERING,
  SECT_VISUALIZATION,
  SECT_GROUP,
  NSECT0,

  // right ui
  SECT_JOINT = 0,
  SECT_CONTROL,
  NSECT1
};

// file section of UI
const mjuiDef defFile[] = {
  {mjITEM_SECTION,   "File",          mjPRESERVE, nullptr, "AF"},
  {mjITEM_BUTTON,    "Save xml",      2, nullptr, ""},
  {mjITEM_BUTTON,    "Save mjb",      2, nullptr, ""},
  {mjITEM_BUTTON,    "Print model",   2, nullptr, "CM"},
  {mjITEM_BUTTON,    "Print data",    2, nullptr, "CD"},
  {mjITEM_BUTTON,    "Quit",          1, nullptr, "CQ"},
  {mjITEM_BUTTON,    "Screenshot",    2, nullptr, "CP"},
  {mjITEM_END}
};

// help strings
const char help_content[] =
  "Space\n"
  "+  -\n"
  "Left / Right arrow\n"
  "Tab / Shift-Tab\n"
  "[  ]\n"
  "Esc\n"
  "Double-click\n"
  "Page Up\n"
  "Right double-click\n"
  "Ctrl Right double-click\n"
  "Scroll, middle drag\n"
  "Left drag\n"
  "[Shift] right drag\n"
  "Ctrl [Shift] drag\n"
  "Ctrl [Shift] right drag\n"
  "F1\n"
  "F2\n"
  "F3\n"
  "F4\n"
  "F5\n"
  "UI right-button hold\n"
  "UI title double-click";

const char help_title[] =
  "Play / Pause\n"
  "Speed Up / Down\n"
  "Step Back / Forward\n"
  "Toggle Left / Right UI\n"
  "Cycle cameras\n"
  "Free camera\n"
  "Select\n"
  "Select parent\n"
  "Center camera\n"
  "Tracking camera\n"
  "Zoom\n"
  "View Orbit\n"
  "View Pan\n"
  "Object Rotate\n"
  "Object Translate\n"
  "Help\n"
  "Info\n"
  "Profiler\n"
  "Sensors\n"
  "Full screen\n"
  "Show UI shortcuts\n"
  "Expand/collapse all";


//-------------------------------- profiler, sensor, info, watch -----------------------------------

// number of lines in the Constraint ("Counts") and Cost ("Convergence") figures
static constexpr int kConstraintNum = 5;
static constexpr int kCostNum = 3;

// init profiler figures
void InitializeProfiler(mj::Simulate* sim) {
  // set figures to default
  mjv_defaultFigure(&sim->figconstraint);
  mjv_defaultFigure(&sim->figcost);
  mjv_defaultFigure(&sim->figtimer);
  mjv_defaultFigure(&sim->figsize);

  // titles
  mju::strcpy_arr(sim->figconstraint.title, "Counts");
  mju::strcpy_arr(sim->figcost.title, "Convergence (log 10)");
  mju::strcpy_arr(sim->figsize.title, "Dimensions");
  mju::strcpy_arr(sim->figtimer.title, "CPU time (msec)");

  // x-labels
  mju::strcpy_arr(sim->figconstraint.xlabel, "Solver iteration");
  mju::strcpy_arr(sim->figcost.xlabel, "Solver iteration");
  mju::strcpy_arr(sim->figsize.xlabel, "Video frame");
  mju::strcpy_arr(sim->figtimer.xlabel, "Video frame");

  // y-tick number formats
  mju::strcpy_arr(sim->figconstraint.yformat, "%.0f");
  mju::strcpy_arr(sim->figcost.yformat, "%.1f");
  mju::strcpy_arr(sim->figsize.yformat, "%.0f");
  mju::strcpy_arr(sim->figtimer.yformat, "%.2f");

  // colors
  sim->figconstraint.figurergba[0] = 0.1f;
  sim->figcost.figurergba[2]       = 0.2f;
  sim->figsize.figurergba[0]       = 0.1f;
  sim->figtimer.figurergba[2]      = 0.2f;
  sim->figconstraint.figurergba[3] = 0.5f;
  sim->figcost.figurergba[3]       = 0.5f;
  sim->figsize.figurergba[3]       = 0.5f;
  sim->figtimer.figurergba[3]      = 0.5f;

  // repeat line colors for constraint and cost figures
  mjvFigure* fig = &sim->figcost;
  for (int i=kCostNum; i<mjMAXLINE; i++) {
    fig->linergb[i][0] = fig->linergb[i - kCostNum][0];
    fig->linergb[i][1] = fig->linergb[i - kCostNum][1];
    fig->linergb[i][2] = fig->linergb[i - kCostNum][2];
  }
  fig = &sim->figconstraint;
  for (int i=kConstraintNum; i<mjMAXLINE; i++) {
    fig->linergb[i][0] = fig->linergb[i - kConstraintNum][0];
    fig->linergb[i][1] = fig->linergb[i - kConstraintNum][1];
    fig->linergb[i][2] = fig->linergb[i - kConstraintNum][2];
  }

  // legends
  mju::strcpy_arr(sim->figconstraint.linename[0], "total");
  mju::strcpy_arr(sim->figconstraint.linename[1], "active");
  mju::strcpy_arr(sim->figconstraint.linename[2], "changed");
  mju::strcpy_arr(sim->figconstraint.linename[3], "evals");
  mju::strcpy_arr(sim->figconstraint.linename[4], "updates");
  mju::strcpy_arr(sim->figcost.linename[0], "improvement");
  mju::strcpy_arr(sim->figcost.linename[1], "gradient");
  mju::strcpy_arr(sim->figcost.linename[2], "lineslope");
  mju::strcpy_arr(sim->figsize.linename[0], "dof");
  mju::strcpy_arr(sim->figsize.linename[1], "body");
  mju::strcpy_arr(sim->figsize.linename[2], "constraint");
  mju::strcpy_arr(sim->figsize.linename[3], "sqrt(nnz)");
  mju::strcpy_arr(sim->figsize.linename[4], "contact");
  mju::strcpy_arr(sim->figsize.linename[5], "iteration");
  mju::strcpy_arr(sim->figtimer.linename[0], "total");
  mju::strcpy_arr(sim->figtimer.linename[1], "collision");
  mju::strcpy_arr(sim->figtimer.linename[2], "prepare");
  mju::strcpy_arr(sim->figtimer.linename[3], "solve");
  mju::strcpy_arr(sim->figtimer.linename[4], "other");

  // grid sizes
  sim->figconstraint.gridsize[0] = 5;
  sim->figconstraint.gridsize[1] = 5;
  sim->figcost.gridsize[0] = 5;
  sim->figcost.gridsize[1] = 5;
  sim->figsize.gridsize[0] = 3;
  sim->figsize.gridsize[1] = 5;
  sim->figtimer.gridsize[0] = 3;
  sim->figtimer.gridsize[1] = 5;

  // minimum ranges
  sim->figconstraint.range[0][0] = 0;
  sim->figconstraint.range[0][1] = 20;
  sim->figconstraint.range[1][0] = 0;
  sim->figconstraint.range[1][1] = 80;
  sim->figcost.range[0][0] = 0;
  sim->figcost.range[0][1] = 20;
  sim->figcost.range[1][0] = -15;
  sim->figcost.range[1][1] = 5;
  sim->figsize.range[0][0] = -200;
  sim->figsize.range[0][1] = 0;
  sim->figsize.range[1][0] = 0;
  sim->figsize.range[1][1] = 100;
  sim->figtimer.range[0][0] = -200;
  sim->figtimer.range[0][1] = 0;
  sim->figtimer.range[1][0] = 0;
  sim->figtimer.range[1][1] = 0.4f;

  // init x axis on history figures (do not show yet)
  for (int n=0; n<6; n++) {
    for (int i=0; i<mjMAXLINEPNT; i++) {
      sim->figtimer.linedata[n][2*i] = -i;
      sim->figsize.linedata[n][2*i] = -i;
    }
  }
}

// update profiler figures
void UpdateProfiler(mj::Simulate* sim, const mjModel* m, const mjData* d) {
  // reset lines in Constraint and Cost figures
  memset(sim->figconstraint.linepnt, 0, mjMAXLINE*sizeof(int));
  memset(sim->figcost.linepnt, 0, mjMAXLINE*sizeof(int));

  // number of islands that have diagnostics
  int nisland = mjMIN(d->solver_nisland, mjNISLAND);

  // iterate over islands
  for (int k=0; k < nisland; k++) {
    // ==== update Constraint ("Counts") figure

    // number of points to plot, starting line
    int npoints = mjMIN(mjMIN(d->solver_niter[k], mjNSOLVER), mjMAXLINEPNT);
    int start = kConstraintNum * k;

    sim->figconstraint.linepnt[start + 0] = npoints;
    for (int i=1; i < kConstraintNum; i++) {
      sim->figconstraint.linepnt[start + i] = npoints;
    }
    if (m->opt.solver == mjSOL_PGS) {
      sim->figconstraint.linepnt[start + 3] = 0;
      sim->figconstraint.linepnt[start + 4] = 0;
    }
    if (m->opt.solver == mjSOL_CG) {
      sim->figconstraint.linepnt[start + 4] = 0;
    }
    for (int i=0; i<npoints; i++) {
      // x
      sim->figconstraint.linedata[start + 0][2*i] = i;
      sim->figconstraint.linedata[start + 1][2*i] = i;
      sim->figconstraint.linedata[start + 2][2*i] = i;
      sim->figconstraint.linedata[start + 3][2*i] = i;
      sim->figconstraint.linedata[start + 4][2*i] = i;

      // y
      int nefc = nisland == 1 ? d->nefc : d->island_efcnum[k];
      sim->figconstraint.linedata[start + 0][2*i+1] = nefc;
      const mjSolverStat* stat = d->solver + k*mjNSOLVER + i;
      sim->figconstraint.linedata[start + 1][2*i+1] = stat->nactive;
      sim->figconstraint.linedata[start + 2][2*i+1] = stat->nchange;
      sim->figconstraint.linedata[start + 3][2*i+1] = stat->neval;
      sim->figconstraint.linedata[start + 4][2*i+1] = stat->nupdate;
    }

    // update cost figure
    start = kCostNum * k;
    sim->figcost.linepnt[start + 0] = npoints;
    for (int i=1; i<kCostNum; i++) {
      sim->figcost.linepnt[start + i] = npoints;
    }
    if (m->opt.solver==mjSOL_PGS) {
      sim->figcost.linepnt[start + 1] = 0;
      sim->figcost.linepnt[start + 2] = 0;
    }

    for (int i=0; i<sim->figcost.linepnt[0]; i++) {
      // x
      sim->figcost.linedata[start + 0][2*i] = i;
      sim->figcost.linedata[start + 1][2*i] = i;
      sim->figcost.linedata[start + 2][2*i] = i;

      // y
      const mjSolverStat* stat = d->solver + k*mjNSOLVER + i;
      sim->figcost.linedata[start + 0][2*i + 1] =
          mju_log10(mju_max(mjMINVAL, stat->improvement));
      sim->figcost.linedata[start + 1][2*i + 1] =
          mju_log10(mju_max(mjMINVAL, stat->gradient));
      sim->figcost.linedata[start + 2][2*i + 1] =
          mju_log10(mju_max(mjMINVAL, stat->lineslope));
    }
  }

  // get timers: total, collision, prepare, solve, other
  mjtNum total = d->timer[mjTIMER_STEP].duration;
  int number = d->timer[mjTIMER_STEP].number;
  if (!number) {
    total = d->timer[mjTIMER_FORWARD].duration;
    number = d->timer[mjTIMER_FORWARD].number;
  }

  if (number) {  // skip update if no measurements
    float tdata[5] = {
      static_cast<float>(total/number),
      static_cast<float>(d->timer[mjTIMER_POS_COLLISION].duration/number),
      static_cast<float>(d->timer[mjTIMER_POS_MAKE].duration/number) +
      static_cast<float>(d->timer[mjTIMER_POS_PROJECT].duration/number),
      static_cast<float>(d->timer[mjTIMER_CONSTRAINT].duration/number),
      0
    };
    tdata[4] = tdata[0] - tdata[1] - tdata[2] - tdata[3];

    // update figtimer
    int pnt = mjMIN(201, sim->figtimer.linepnt[0]+1);
    for (int n=0; n<5; n++) {
      // shift data
      for (int i=pnt-1; i>0; i--) {
        sim->figtimer.linedata[n][2*i+1] = sim->figtimer.linedata[n][2*i-1];
      }

      // assign new
      sim->figtimer.linepnt[n] = pnt;
      sim->figtimer.linedata[n][1] = tdata[n];
    }
  }

  // get total number of iterations and nonzeros
  mjtNum sqrt_nnz = 0;
  int solver_niter = 0;
  for (int island=0; island < nisland; island++) {
    sqrt_nnz += mju_sqrt(d->solver_nnz[island]);
    solver_niter += d->solver_niter[island];
  }

  // get sizes: nv, nbody, nefc, sqrt(nnz), ncont, iter
  float sdata[6] = {
    static_cast<float>(m->nv),
    static_cast<float>(m->nbody),
    static_cast<float>(d->nefc),
    static_cast<float>(sqrt_nnz),
    static_cast<float>(d->ncon),
    static_cast<float>(solver_niter)
  };

  // update figsize
  int pnt = mjMIN(201, sim->figsize.linepnt[0]+1);
  for (int n=0; n<6; n++) {
    // shift data
    for (int i=pnt-1; i>0; i--) {
      sim->figsize.linedata[n][2*i+1] = sim->figsize.linedata[n][2*i-1];
    }

    // assign new
    sim->figsize.linepnt[n] = pnt;
    sim->figsize.linedata[n][1] = sdata[n];
  }
}

// show profiler figures
void ShowProfiler(mj::Simulate* sim, mjrRect rect) {
  mjrRect viewport = {
    rect.left + rect.width - rect.width/4,
    rect.bottom,
    rect.width/4,
    rect.height/4
  };
  mjr_figure(viewport, &sim->figtimer, &sim->platform_ui->mjr_context());
  viewport.bottom += rect.height/4;
  mjr_figure(viewport, &sim->figsize, &sim->platform_ui->mjr_context());
  viewport.bottom += rect.height/4;
  mjr_figure(viewport, &sim->figcost, &sim->platform_ui->mjr_context());
  viewport.bottom += rect.height/4;
  mjr_figure(viewport, &sim->figconstraint, &sim->platform_ui->mjr_context());
}


// init sensor figure
void InitializeSensor(mj::Simulate* sim) {
  mjvFigure& figsensor = sim->figsensor;

  // set figure to default
  mjv_defaultFigure(&figsensor);
  figsensor.figurergba[3] = 0.5f;

  // set flags
  figsensor.flg_extend = 1;
  figsensor.flg_barplot = 1;
  figsensor.flg_symmetric = 1;

  // title
  mju::strcpy_arr(figsensor.title, "Sensor data");

  // y-tick nubmer format
  mju::strcpy_arr(figsensor.yformat, "%.1f");

  // grid size
  figsensor.gridsize[0] = 2;
  figsensor.gridsize[1] = 3;

  // minimum range
  figsensor.range[0][0] = 0;
  figsensor.range[0][1] = 0;
  figsensor.range[1][0] = -1;
  figsensor.range[1][1] = 1;
}

// update sensor figure
void UpdateSensor(mj::Simulate* sim, const mjModel* m, const mjData* d) {
  mjvFigure& figsensor = sim->figsensor;
  static const int maxline = 10;

  // clear linepnt
  for (int i=0; i<maxline; i++) {
    figsensor.linepnt[i] = 0;
  }

  // start with line 0
  int lineid = 0;

  // loop over sensors
  for (int n=0; n<m->nsensor; n++) {
    // go to next line if type is different
    if (n>0 && m->sensor_type[n]!=m->sensor_type[n-1]) {
      lineid = mjMIN(lineid+1, maxline-1);
    }

    // get info about this sensor
    mjtNum cutoff = (m->sensor_cutoff[n]>0 ? m->sensor_cutoff[n] : 1);
    int adr = m->sensor_adr[n];
    int dim = m->sensor_dim[n];

    // data pointer in line
    int p = figsensor.linepnt[lineid];

    // fill in data for this sensor
    for (int i=0; i<dim; i++) {
      // check size
      if ((p+2*i)>=mjMAXLINEPNT/2) {
        break;
      }

      // x
      figsensor.linedata[lineid][2*p+4*i] = adr+i;
      figsensor.linedata[lineid][2*p+4*i+2] = adr+i;

      // y
      figsensor.linedata[lineid][2*p+4*i+1] = 0;
      figsensor.linedata[lineid][2*p+4*i+3] = d->sensordata[adr+i]/cutoff;
    }

    // update linepnt
    figsensor.linepnt[lineid] = mjMIN(mjMAXLINEPNT-1, figsensor.linepnt[lineid]+2*dim);
  }
}

// show sensor figure
void ShowSensor(mj::Simulate* sim, mjrRect rect) {
  // constant width with and without profiler
  int width = sim->profiler ? rect.width/3 : rect.width/4;

  // render figure on the right
  mjrRect viewport = {
    rect.left + rect.width - width,
    rect.bottom,
    width,
    rect.height/3
  };
  mjr_figure(viewport, &sim->figsensor, &sim->platform_ui->mjr_context());
}

// load state from history buffer
static void LoadScrubState(mj::Simulate* sim) {
  // get index into circular buffer
  int i = (sim->scrub_index + sim->history_cursor_) % sim->nhistory_;
  i = (i + sim->nhistory_) % sim->nhistory_;

  // load state
  mjtNum* state = &sim->history_[i * sim->state_size_];
  mj_setState(sim->m_, sim->d_, state, mjSTATE_INTEGRATION);

  // call forward dynamics
  mj_forward(sim->m_, sim->d_);
}

// update an entire section of ui0
static void mjui0_update_section(mj::Simulate* sim, int section) {
  mjui_update(section, -1, &sim->ui0, &sim->uistate, &sim->platform_ui->mjr_context());
}

// prepare info text
void UpdateInfoText(mj::Simulate* sim, const mjModel* m, const mjData* d,
              char (&title)[mj::Simulate::kMaxFilenameLength],
              char (&content)[mj::Simulate::kMaxFilenameLength]) {
  char tmp[20];

  // number of islands with statistics
  int nisland = mjMIN(d->solver_nisland, mjNISLAND);

  // compute solver error (maximum over islands)
  mjtNum solerr = 0;
  for (int i=0; i < nisland; i++) {
    mjtNum solerr_i = 0;
    if (d->solver_niter[i]) {
      int ind = mjMIN(d->solver_niter[i], mjNSOLVER) - 1;
      const mjSolverStat* stat = d->solver + i*mjNSOLVER + ind;
      solerr_i = mju_min(stat->improvement, stat->gradient);
      if (solerr_i==0) {
        solerr_i = mju_max(stat->improvement, stat->gradient);
      }
    }
    solerr = mju_max(solerr, solerr_i);
  }
  solerr = mju_log10(mju_max(mjMINVAL, solerr));

  // format FPS text
  char fps[10];
  if (sim->fps_ < 1) {
    mju::sprintf_arr(fps, "%0.1f ", sim->fps_);
  } else {
    mju::sprintf_arr(fps, "%.0f ", sim->fps_);
  }

  // total iterations of all islands with statistics
  int solver_niter = 0;
  for (int i=0; i < nisland; i++) {
    solver_niter += d->solver_niter[i];
  }

  // prepare info text
  mju::strcpy_arr(title, "Time\nSize\nCPU\nSolver   \nFPS\nMemory");
  mju::sprintf_arr(content,
                   "%-9.3f\n%d  (%d con)\n%.3f\n%.1f  (%d it)\n%s\n%.1f%% of %s",
                   d->time,
                   d->nefc, d->ncon,
                   sim->run ?
                   d->timer[mjTIMER_STEP].duration / mjMAX(1, d->timer[mjTIMER_STEP].number) :
                   d->timer[mjTIMER_FORWARD].duration / mjMAX(1, d->timer[mjTIMER_FORWARD].number),
                   solerr, solver_niter,
                   fps,
                   100*d->maxuse_arena/(double)(d->narena),
                   mju_writeNumBytes(d->narena));

  // add Energy if enabled
  {
    if (mjENABLED(mjENBL_ENERGY)) {
      mju::sprintf_arr(tmp, "\n%.3f", d->energy[0]+d->energy[1]);
      mju::strcat_arr(content, tmp);
      mju::strcat_arr(title, "\nEnergy");
    }

    // add FwdInv if enabled
    if (mjENABLED(mjENBL_FWDINV)) {
      mju::sprintf_arr(tmp, "\n%.1f %.1f",
                       mju_log10(mju_max(mjMINVAL, d->solver_fwdinv[0])),
                       mju_log10(mju_max(mjMINVAL, d->solver_fwdinv[1])));
      mju::strcat_arr(content, tmp);
      mju::strcat_arr(title, "\nFwdInv");
    }

    // add islands if enabled
    if (mjENABLED(mjENBL_ISLAND)) {
      mju::sprintf_arr(tmp, "\n%d", d->nisland);
      mju::strcat_arr(content, tmp);
      mju::strcat_arr(title, "\nIslands");
    }
  }
}

// sprintf forwarding, to avoid compiler warning in x-macro
void PrintField(char (&str)[mjMAXUINAME], void* ptr) {
  mju::sprintf_arr(str, "%g", *static_cast<mjtNum*>(ptr));
}

// update watch
void UpdateWatch(mj::Simulate* sim, const mjModel* m, const mjData* d) {
  // clear
  sim->ui0.sect[SECT_WATCH].item[2].multi.nelem = 1;
  mju::strcpy_arr(sim->ui0.sect[SECT_WATCH].item[2].multi.name[0], "invalid field");

  // prepare symbols needed by xmacro
  MJDATA_POINTERS_PREAMBLE(m);

  // find specified field in mjData arrays, update value
  #define X(TYPE, NAME, NR, NC)                                                                  \
    if (!mju::strcmp_arr(#NAME, sim->field) &&                                                   \
        !mju::strcmp_arr(#TYPE, "mjtNum")) {                                                     \
      if (sim->index >= 0 && sim->index < m->NR * NC) {                                          \
        PrintField(sim->ui0.sect[SECT_WATCH].item[2].multi.name[0], d->NAME + sim->index);       \
      } else {                                                                                   \
        mju::strcpy_arr(sim->ui0.sect[SECT_WATCH].item[2].multi.name[0], "invalid index");       \
      }                                                                                          \
      return;                                                                                    \
    }

  MJDATA_POINTERS
#undef X
}


//---------------------------------- UI construction -----------------------------------------------

// make physics section of UI
void MakePhysicsSection(mj::Simulate* sim) {
  mjOption* opt = sim->is_passive_ ? &sim->scnstate_.model.opt : &sim->m_->opt;
  mjuiDef defPhysics[] = {
    {mjITEM_SECTION,   "Physics",       mjPRESERVE, nullptr,          "AP"},
    {mjITEM_SELECT,    "Integrator",    2, &(opt->integrator),        "Euler\nRK4\nimplicit\nimplicitfast"},
    {mjITEM_SELECT,    "Cone",          2, &(opt->cone),              "Pyramidal\nElliptic"},
    {mjITEM_SELECT,    "Jacobian",      2, &(opt->jacobian),          "Dense\nSparse\nAuto"},
    {mjITEM_SELECT,    "Solver",        2, &(opt->solver),            "PGS\nCG\nNewton"},
    {mjITEM_SEPARATOR, "Algorithmic Parameters", mjPRESERVE},
    {mjITEM_EDITNUM,   "Timestep",      2, &(opt->timestep),          "1 0 1"},
    {mjITEM_EDITINT,   "Iterations",    2, &(opt->iterations),        "1 0 1000"},
    {mjITEM_EDITNUM,   "Tolerance",     2, &(opt->tolerance),         "1 0 1"},
    {mjITEM_EDITINT,   "LS Iter",       2, &(opt->ls_iterations),     "1 0 100"},
    {mjITEM_EDITNUM,   "LS Tol",        2, &(opt->ls_tolerance),      "1 0 0.1"},
    {mjITEM_EDITINT,   "Noslip Iter",   2, &(opt->noslip_iterations), "1 0 1000"},
    {mjITEM_EDITNUM,   "Noslip Tol",    2, &(opt->noslip_tolerance),  "1 0 1"},
    {mjITEM_EDITINT,   "CCD Iter",      2, &(opt->ccd_iterations),    "1 0 1000"},
    {mjITEM_EDITNUM,   "CCD Tol",       2, &(opt->ccd_tolerance),     "1 0 1"},
    {mjITEM_EDITNUM,   "API Rate",      2, &(opt->apirate),           "1 0 1000"},
    {mjITEM_EDITINT,   "SDF Iter",      2, &(opt->sdf_iterations),    "1 1 20"},
    {mjITEM_EDITINT,   "SDF Init",      2, &(opt->sdf_initpoints),    "1 1 100"},
    {mjITEM_SEPARATOR, "Physical Parameters", mjPRESERVE},
    {mjITEM_EDITNUM,   "Gravity",       2, opt->gravity,              "3"},
    {mjITEM_EDITNUM,   "Wind",          2, opt->wind,                 "3"},
    {mjITEM_EDITNUM,   "Magnetic",      2, opt->magnetic,             "3"},
    {mjITEM_EDITNUM,   "Density",       2, &(opt->density),           "1"},
    {mjITEM_EDITNUM,   "Viscosity",     2, &(opt->viscosity),         "1"},
    {mjITEM_EDITNUM,   "Imp Ratio",     2, &(opt->impratio),          "1"},
    {mjITEM_SEPARATOR, "Disable Flags", mjPRESERVE},
    {mjITEM_END}
  };
  mjuiDef defEnableFlags[] = {
    {mjITEM_SEPARATOR, "Enable Flags", mjPRESERVE},
    {mjITEM_END}
  };
  mjuiDef defOverride[] = {
    {mjITEM_SEPARATOR, "Contact Override", mjPRESERVE},
    {mjITEM_EDITNUM,   "Margin",        2, &(opt->o_margin),          "1"},
    {mjITEM_EDITNUM,   "Sol Imp",       2, &(opt->o_solimp),          "5"},
    {mjITEM_EDITNUM,   "Sol Ref",       2, &(opt->o_solref),          "2"},
    {mjITEM_EDITNUM,   "Friction",      2, &(opt->o_friction),        "5"},
    {mjITEM_END}
  };
  mjuiDef defDisableActuator[] = {
    {mjITEM_SEPARATOR, "Actuator Group Enable", mjPRESERVE},
    {mjITEM_CHECKBYTE,  "Act Group 0",  2, sim->enableactuator+0,     ""},
    {mjITEM_CHECKBYTE,  "Act Group 1",  2, sim->enableactuator+1,     ""},
    {mjITEM_CHECKBYTE,  "Act Group 2",  2, sim->enableactuator+2,     ""},
    {mjITEM_CHECKBYTE,  "Act Group 3",  2, sim->enableactuator+3,     ""},
    {mjITEM_CHECKBYTE,  "Act Group 4",  2, sim->enableactuator+4,     ""},
    {mjITEM_CHECKBYTE,  "Act Group 5",  2, sim->enableactuator+5,     ""},
    {mjITEM_END}
  };

  // add physics
  mjui_add(&sim->ui0, defPhysics);

  // add flags programmatically
  mjuiDef defFlag[] = {
    {mjITEM_CHECKINT,  "", 2, nullptr, ""},
    {mjITEM_END}
  };
  for (int i=0; i<mjNDISABLE; i++) {
    mju::strcpy_arr(defFlag[0].name, mjDISABLESTRING[i]);
    defFlag[0].pdata = sim->disable + i;
    mjui_add(&sim->ui0, defFlag);
  }
  mjui_add(&sim->ui0, defEnableFlags);
  for (int i=0; i<mjNENABLE; i++) {
    mju::strcpy_arr(defFlag[0].name, mjENABLESTRING[i]);
    defFlag[0].pdata = sim->enable + i;
    mjui_add(&sim->ui0, defFlag);
  }
  // add contact override
  mjui_add(&sim->ui0, defOverride);

  // add actuator group enable/disable
  mjui_add(&sim->ui0, defDisableActuator);

  // make some subsections closed by default
  for (int i=0; i < sim->ui0.sect[SECT_PHYSICS].nitem; i++) {
    mjuiItem* it = sim->ui0.sect[SECT_PHYSICS].item + i;

    // close less useful subsections
    if (it->type == mjITEM_SEPARATOR) {
      if (mju::strcmp_arr(it->name, "Actuator Group Enable") &&
          mju::strcmp_arr(it->name, "Contact Override")  &&
          mju::strcmp_arr(it->name, "Physical Parameters")) {
        it->state = mjSEPCLOSED+1;
      }
    }
  }
}



// make rendering section of UI
void MakeRenderingSection(mj::Simulate* sim, const mjModel* m) {
  mjuiDef defRendering[] = {
    {mjITEM_SECTION, "Rendering", mjPRESERVE, nullptr, "AR"},
    {mjITEM_SELECT, "Camera", 2, &(sim->camera), "Free\nTracking"},
    {mjITEM_SELECT, "Label", 2, &(sim->opt.label),
      "None\nBody\nJoint\nGeom\nSite\nCamera\nLight\nTendon\n"
      "Actuator\nConstraint\nFlex\nSkin\nSelection\nSel Pnt\nContact\nForce\nIsland"
    },
    {mjITEM_SELECT, "Frame", 2, &(sim->opt.frame),
      "None\nBody\nGeom\nSite\nCamera\nLight\nContact\nWorld"
    },
    {mjITEM_BUTTON, "Copy camera", 2, nullptr, ""},
    {mjITEM_SEPARATOR, "Model Elements", 1},
    {mjITEM_END}
  };
  mjuiDef defOpenGL[] = {
    {mjITEM_SEPARATOR, "OpenGL Effects", 1},
    {mjITEM_END}
  };

  // add model cameras, up to UI limit
  for (int i=0; i<mjMIN(m->ncam, mjMAXUIMULTI-2); i++) {
    // prepare name
    char camname[mjMAXUINAME] = "\n";
    if (m->names[m->name_camadr[i]]) {
      mju::strcat_arr(camname, m->names+m->name_camadr[i]);
    } else {
      mju::sprintf_arr(camname, "\nCamera %d", i);
    }

    // check string length
    if (mju::strlen_arr(camname) + mju::strlen_arr(defRendering[1].other)>=mjMAXUITEXT-1) {
      break;
    }

    // add camera
    mju::strcat_arr(defRendering[1].other, camname);
  }

  // add rendering standard
  mjui_add(&sim->ui0, defRendering);

  // add flags programmatically
  mjuiDef defFlag[] = {
    {mjITEM_CHECKBYTE,  "", 2, nullptr, ""},
    {mjITEM_END}
  };
  for (int i=0; i<mjNVISFLAG; i++) {
    // set name
    mju::strcpy_arr(defFlag[0].name, mjVISSTRING[i][0]);

    // set shortcut and data
    if (mjVISSTRING[i][2][0]) {
      mju::sprintf_arr(defFlag[0].other, " %s", mjVISSTRING[i][2]);
    } else {
      mju::sprintf_arr(defFlag[0].other, "");
    }
    defFlag[0].pdata = sim->opt.flags + i;
    mjui_add(&sim->ui0, defFlag);
  }

  // create tree slider
  mjuiDef defTree[] = {
      {mjITEM_SLIDERINT, "Tree depth", 2, &sim->opt.bvh_depth, "0 20"},
      {mjITEM_SLIDERINT, "Flex layer", 2, &sim->opt.flex_layer, "0 10"},
      {mjITEM_END}
  };
  mjui_add(&sim->ui0, defTree);

  // add rendering flags
  mjui_add(&sim->ui0, defOpenGL);
  for (int i=0; i<mjNRNDFLAG; i++) {
    // set name
    mju::strcpy_arr(defFlag[0].name, mjRNDSTRING[i][0]);

    // set shortcut and data
    if (mjRNDSTRING[i][2][0]) {
      mju::sprintf_arr(defFlag[0].other, " %s", mjRNDSTRING[i][2]);
    } else {
      mju::sprintf_arr(defFlag[0].other, "");
    }
    defFlag[0].pdata = sim->scn.flags + i;
    mjui_add(&sim->ui0, defFlag);
  }
}

// make visualization section of UI
void MakeVisualizationSection(mj::Simulate* sim, const mjModel* m) {
  mjStatistic* stat = sim->is_passive_ ? &sim->scnstate_.model.stat : &sim->m_->stat;
  mjVisual* vis = sim->is_passive_ ? &sim->scnstate_.model.vis : &sim->m_->vis;

  mjuiDef defVisualization[] = {
    {mjITEM_SECTION,   "Visualization", mjPRESERVE, nullptr, "AV"},
    {mjITEM_SEPARATOR, "Headlight",  1},
    {mjITEM_RADIO,     "Active",          5, &(vis->headlight.active),     "Off\nOn"},
    {mjITEM_EDITFLOAT, "Ambient",         2, &(vis->headlight.ambient),    "3"},
    {mjITEM_EDITFLOAT, "Diffuse",         2, &(vis->headlight.diffuse),    "3"},
    {mjITEM_EDITFLOAT, "Specular",        2, &(vis->headlight.specular),   "3"},
    {mjITEM_SEPARATOR, "Free Camera", 1},
    {mjITEM_RADIO,     "Orthographic",    2, &(vis->global.orthographic),  "No\nYes"},
    {mjITEM_EDITFLOAT, "Field of view",   2, &(vis->global.fovy),          "1"},
    {mjITEM_EDITNUM,   "Center",          2, &(stat->center),              "3"},
    {mjITEM_EDITFLOAT, "Azimuth",         2, &(vis->global.azimuth),       "1"},
    {mjITEM_EDITFLOAT, "Elevation",       2, &(vis->global.elevation),     "1"},
    {mjITEM_BUTTON,    "Align",           2, nullptr,                      "CA"},
    {mjITEM_SEPARATOR, "Global",  1},
    {mjITEM_EDITNUM,   "Extent",          2, &(stat->extent),              "1"},
    {mjITEM_RADIO,     "Inertia",         5, &(vis->global.ellipsoidinertia), "Box\nEllipsoid"},
    {mjITEM_RADIO,     "BVH active",      5, &(vis->global.bvactive), "False\nTrue"},
    {mjITEM_SEPARATOR, "Map",  1},
    {mjITEM_EDITFLOAT, "Stiffness",       2, &(vis->map.stiffness),        "1"},
    {mjITEM_EDITFLOAT, "Rot stiffness",   2, &(vis->map.stiffnessrot),     "1"},
    {mjITEM_EDITFLOAT, "Force",           2, &(vis->map.force),            "1"},
    {mjITEM_EDITFLOAT, "Torque",          2, &(vis->map.torque),           "1"},
    {mjITEM_EDITFLOAT, "Alpha",           2, &(vis->map.alpha),            "1"},
    {mjITEM_EDITFLOAT, "Fog start",       2, &(vis->map.fogstart),         "1"},
    {mjITEM_EDITFLOAT, "Fog end",         2, &(vis->map.fogend),           "1"},
    {mjITEM_EDITFLOAT, "Z near",          2, &(vis->map.znear),            "1"},
    {mjITEM_EDITFLOAT, "Z far",           2, &(vis->map.zfar),             "1"},
    {mjITEM_EDITFLOAT, "Haze",            2, &(vis->map.haze),             "1"},
    {mjITEM_EDITFLOAT, "Shadow clip",     2, &(vis->map.shadowclip),       "1"},
    {mjITEM_EDITFLOAT, "Shadow scale",    2, &(vis->map.shadowscale),      "1"},
    {mjITEM_SEPARATOR, "Scale", mjPRESERVE},
    {mjITEM_EDITNUM,   "All (meansize)",  2, &(stat->meansize),            "1"},
    {mjITEM_EDITFLOAT, "Force width",     2, &(vis->scale.forcewidth),     "1"},
    {mjITEM_EDITFLOAT, "Contact width",   2, &(vis->scale.contactwidth),   "1"},
    {mjITEM_EDITFLOAT, "Contact height",  2, &(vis->scale.contactheight),  "1"},
    {mjITEM_EDITFLOAT, "Connect",         2, &(vis->scale.connect),        "1"},
    {mjITEM_EDITFLOAT, "Com",             2, &(vis->scale.com),            "1"},
    {mjITEM_EDITFLOAT, "Camera",          2, &(vis->scale.camera),         "1"},
    {mjITEM_EDITFLOAT, "Light",           2, &(vis->scale.light),          "1"},
    {mjITEM_EDITFLOAT, "Select point",    2, &(vis->scale.selectpoint),    "1"},
    {mjITEM_EDITFLOAT, "Joint length",    2, &(vis->scale.jointlength),    "1"},
    {mjITEM_EDITFLOAT, "Joint width",     2, &(vis->scale.jointwidth),     "1"},
    {mjITEM_EDITFLOAT, "Actuator length", 2, &(vis->scale.actuatorlength), "1"},
    {mjITEM_EDITFLOAT, "Actuator width",  2, &(vis->scale.actuatorwidth),  "1"},
    {mjITEM_EDITFLOAT, "Frame length",    2, &(vis->scale.framelength),    "1"},
    {mjITEM_EDITFLOAT, "Frame width",     2, &(vis->scale.framewidth),     "1"},
    {mjITEM_EDITFLOAT, "Constraint",      2, &(vis->scale.constraint),     "1"},
    {mjITEM_EDITFLOAT, "Slider-crank",    2, &(vis->scale.slidercrank),    "1"},
    {mjITEM_SEPARATOR, "RGBA", mjPRESERVE},
    {mjITEM_EDITFLOAT, "fog",             2, &(vis->rgba.fog),              "4"},
    {mjITEM_EDITFLOAT, "haze",            2, &(vis->rgba.haze),             "4"},
    {mjITEM_EDITFLOAT, "force",           2, &(vis->rgba.force),            "4"},
    {mjITEM_EDITFLOAT, "inertia",         2, &(vis->rgba.inertia),          "4"},
    {mjITEM_EDITFLOAT, "joint",           2, &(vis->rgba.joint),            "4"},
    {mjITEM_EDITFLOAT, "actuator",        2, &(vis->rgba.actuator),         "4"},
    {mjITEM_EDITFLOAT, "actnegative",     2, &(vis->rgba.actuatornegative), "4"},
    {mjITEM_EDITFLOAT, "actpositive",     2, &(vis->rgba.actuatorpositive), "4"},
    {mjITEM_EDITFLOAT, "com",             2, &(vis->rgba.com),              "4"},
    {mjITEM_EDITFLOAT, "camera",          2, &(vis->rgba.camera),           "4"},
    {mjITEM_EDITFLOAT, "light",           2, &(vis->rgba.light),            "4"},
    {mjITEM_EDITFLOAT, "selectpoint",     2, &(vis->rgba.selectpoint),      "4"},
    {mjITEM_EDITFLOAT, "connect",         2, &(vis->rgba.connect),          "4"},
    {mjITEM_EDITFLOAT, "contactpoint",    2, &(vis->rgba.contactpoint),     "4"},
    {mjITEM_EDITFLOAT, "contactforce",    2, &(vis->rgba.contactforce),     "4"},
    {mjITEM_EDITFLOAT, "contactfriction", 2, &(vis->rgba.contactfriction),  "4"},
    {mjITEM_EDITFLOAT, "contacttorque",   2, &(vis->rgba.contacttorque),    "4"},
    {mjITEM_EDITFLOAT, "contactgap",      2, &(vis->rgba.contactgap),       "4"},
    {mjITEM_EDITFLOAT, "rangefinder",     2, &(vis->rgba.rangefinder),      "4"},
    {mjITEM_EDITFLOAT, "constraint",      2, &(vis->rgba.constraint),       "4"},
    {mjITEM_EDITFLOAT, "slidercrank",     2, &(vis->rgba.slidercrank),      "4"},
    {mjITEM_EDITFLOAT, "crankbroken",     2, &(vis->rgba.crankbroken),      "4"},
    {mjITEM_EDITFLOAT, "frustum",         2, &(vis->rgba.frustum),          "4"},
    {mjITEM_EDITFLOAT, "bv",              2, &(vis->rgba.bv),               "4"},
    {mjITEM_EDITFLOAT, "bvactive",        2, &(vis->rgba.bvactive),         "4"},
    {mjITEM_END}
  };

  // add visualization section
  mjui_add(&sim->ui0, defVisualization);
}

// make group section of UI
void MakeGroupSection(mj::Simulate* sim) {
  mjuiDef defGroup[] = {
    {mjITEM_SECTION,    "Group enable",     mjPRESERVE, nullptr,            "AG"},
    {mjITEM_SEPARATOR,  "Geom groups",  1},
    {mjITEM_CHECKBYTE,  "Geom 0",           2, sim->opt.geomgroup,          " 0"},
    {mjITEM_CHECKBYTE,  "Geom 1",           2, sim->opt.geomgroup+1,        " 1"},
    {mjITEM_CHECKBYTE,  "Geom 2",           2, sim->opt.geomgroup+2,        " 2"},
    {mjITEM_CHECKBYTE,  "Geom 3",           2, sim->opt.geomgroup+3,        " 3"},
    {mjITEM_CHECKBYTE,  "Geom 4",           2, sim->opt.geomgroup+4,        " 4"},
    {mjITEM_CHECKBYTE,  "Geom 5",           2, sim->opt.geomgroup+5,        " 5"},
    {mjITEM_SEPARATOR,  "Site groups",  1},
    {mjITEM_CHECKBYTE,  "Site 0",           2, sim->opt.sitegroup,          "S0"},
    {mjITEM_CHECKBYTE,  "Site 1",           2, sim->opt.sitegroup+1,        "S1"},
    {mjITEM_CHECKBYTE,  "Site 2",           2, sim->opt.sitegroup+2,        "S2"},
    {mjITEM_CHECKBYTE,  "Site 3",           2, sim->opt.sitegroup+3,        "S3"},
    {mjITEM_CHECKBYTE,  "Site 4",           2, sim->opt.sitegroup+4,        "S4"},
    {mjITEM_CHECKBYTE,  "Site 5",           2, sim->opt.sitegroup+5,        "S5"},
    {mjITEM_SEPARATOR,  "Joint groups", 1},
    {mjITEM_CHECKBYTE,  "Joint 0",          2, sim->opt.jointgroup,         ""},
    {mjITEM_CHECKBYTE,  "Joint 1",          2, sim->opt.jointgroup+1,       ""},
    {mjITEM_CHECKBYTE,  "Joint 2",          2, sim->opt.jointgroup+2,       ""},
    {mjITEM_CHECKBYTE,  "Joint 3",          2, sim->opt.jointgroup+3,       ""},
    {mjITEM_CHECKBYTE,  "Joint 4",          2, sim->opt.jointgroup+4,       ""},
    {mjITEM_CHECKBYTE,  "Joint 5",          2, sim->opt.jointgroup+5,       ""},
    {mjITEM_SEPARATOR,  "Tendon groups",    1},
    {mjITEM_CHECKBYTE,  "Tendon 0",         2, sim->opt.tendongroup,        ""},
    {mjITEM_CHECKBYTE,  "Tendon 1",         2, sim->opt.tendongroup+1,      ""},
    {mjITEM_CHECKBYTE,  "Tendon 2",         2, sim->opt.tendongroup+2,      ""},
    {mjITEM_CHECKBYTE,  "Tendon 3",         2, sim->opt.tendongroup+3,      ""},
    {mjITEM_CHECKBYTE,  "Tendon 4",         2, sim->opt.tendongroup+4,      ""},
    {mjITEM_CHECKBYTE,  "Tendon 5",         2, sim->opt.tendongroup+5,      ""},
    {mjITEM_SEPARATOR,  "Actuator groups", 1},
    {mjITEM_CHECKBYTE,  "Actuator 0",       2, sim->opt.actuatorgroup,      ""},
    {mjITEM_CHECKBYTE,  "Actuator 1",       2, sim->opt.actuatorgroup+1,    ""},
    {mjITEM_CHECKBYTE,  "Actuator 2",       2, sim->opt.actuatorgroup+2,    ""},
    {mjITEM_CHECKBYTE,  "Actuator 3",       2, sim->opt.actuatorgroup+3,    ""},
    {mjITEM_CHECKBYTE,  "Actuator 4",       2, sim->opt.actuatorgroup+4,    ""},
    {mjITEM_CHECKBYTE,  "Actuator 5",       2, sim->opt.actuatorgroup+5,    ""},
    {mjITEM_SEPARATOR,  "Flex groups", 1},
    {mjITEM_CHECKBYTE,  "Flex 0",           2, sim->opt.flexgroup,          ""},
    {mjITEM_CHECKBYTE,  "Flex 1",           2, sim->opt.flexgroup+1,        ""},
    {mjITEM_CHECKBYTE,  "Flex 2",           2, sim->opt.flexgroup+2,        ""},
    {mjITEM_CHECKBYTE,  "Flex 3",           2, sim->opt.flexgroup+3,        ""},
    {mjITEM_CHECKBYTE,  "Flex 4",           2, sim->opt.flexgroup+4,        ""},
    {mjITEM_CHECKBYTE,  "Flex 5",           2, sim->opt.flexgroup+5,        ""},
    {mjITEM_SEPARATOR,  "Skin groups", 1},
    {mjITEM_CHECKBYTE,  "Skin 0",           2, sim->opt.skingroup,          ""},
    {mjITEM_CHECKBYTE,  "Skin 1",           2, sim->opt.skingroup+1,        ""},
    {mjITEM_CHECKBYTE,  "Skin 2",           2, sim->opt.skingroup+2,        ""},
    {mjITEM_CHECKBYTE,  "Skin 3",           2, sim->opt.skingroup+3,        ""},
    {mjITEM_CHECKBYTE,  "Skin 4",           2, sim->opt.skingroup+4,        ""},
    {mjITEM_CHECKBYTE,  "Skin 5",           2, sim->opt.skingroup+5,        ""},
    {mjITEM_END}
  };

  // add section
  mjui_add(&sim->ui0, defGroup);
}

// make joint section of UI
void MakeJointSection(mj::Simulate* sim) {
  mjuiDef defJoint[] = {
    {mjITEM_SECTION, "Joint", mjPRESERVE, nullptr, "AJ"},
    {mjITEM_END}
  };
  mjuiDef defSlider[] = {
    {mjITEM_SLIDERNUM, "", 2, nullptr, "0 1"},
    {mjITEM_END}
  };

  // add section
  mjui_add(&sim->ui1, defJoint);
  defSlider[0].state = 4;

  // add scalar joints, exit if UI limit reached
  int itemcnt = 0;
  for (int i=0; i < sim->jnt_type_.size() && itemcnt<mjMAXUIITEM; i++) {
    if ((sim->jnt_type_[i]==mjJNT_HINGE || sim->jnt_type_[i]==mjJNT_SLIDE)) {
      // skip if joint group is disabled
      if (!sim->opt.jointgroup[mjMAX(0, mjMIN(mjNGROUP-1, sim->jnt_group_[i]))]) {
        continue;
      }

      // set data and name
      if (!sim->is_passive_) {
        defSlider[0].pdata = &sim->d_->qpos[sim->m_->jnt_qposadr[i]];
      } else {
        defSlider[0].pdata = &sim->qpos_[sim->jnt_qposadr_[i]];
      }
      if (!sim->jnt_names_[i].empty()) {
        mju::strcpy_arr(defSlider[0].name, sim->jnt_names_[i].c_str());
      } else {
        mju::sprintf_arr(defSlider[0].name, "joint %d", i);
      }

      // set range
      if (sim->jnt_range_[i].has_value())
        mju::sprintf_arr(defSlider[0].other, "%.4g %.4g",
                         sim->jnt_range_[i]->first, sim->jnt_range_[i]->second);
      else if (sim->jnt_type_[i]==mjJNT_SLIDE) {
        mju::strcpy_arr(defSlider[0].other, "-1 1");
      } else {
        mju::strcpy_arr(defSlider[0].other, "-3.1416 3.1416");
      }

      // add and count
      mjui_add(&sim->ui1, defSlider);
      itemcnt++;
    }
  }
}

// make control section of UI
void MakeControlSection(mj::Simulate* sim) {
  mjuiDef defControl[] = {
    {mjITEM_SECTION, "Control", mjPRESERVE, nullptr, "AC"},
    {mjITEM_BUTTON,  "Clear all", 2},
    {mjITEM_END}
  };
  mjuiDef defSlider[] = {
    {mjITEM_SLIDERNUM, "", 2, nullptr, "0 1"},
    {mjITEM_END}
  };

  // add section
  mjui_add(&sim->ui1, defControl);

  // add controls, exit if UI limit reached (Clear button already added)
  int itemcnt = 1;
  for (int i=0; i < sim->actuator_ctrlrange_.size() && itemcnt<mjMAXUIITEM; i++) {
    // skip if actuator vis group is disabled
    int group = sim->actuator_group_[i];
    if (!sim->opt.actuatorgroup[mjMAX(0, mjMIN(mjNGROUP-1, group))]) {
      continue;
    }
    // grey out if actuator group is disabled
    if (group >= 0 && group <= 30 && sim->m_->opt.disableactuator & (1 << group)) {
      defSlider[0].state = 0;
    } else {
      defSlider[0].state = 2;
    }

    // set data and name
    if (!sim->is_passive_) {
      defSlider[0].pdata = &sim->d_->ctrl[i];
    } else {
      defSlider[0].pdata = &sim->ctrl_[i];
    }
    if (!sim->actuator_names_[i].empty()) {
      mju::strcpy_arr(defSlider[0].name, sim->actuator_names_[i].c_str());
    } else {
      mju::sprintf_arr(defSlider[0].name, "control %d", i);
    }

    // set range
    if (sim->actuator_ctrlrange_[i].has_value())
      mju::sprintf_arr(defSlider[0].other, "%.4g %.4g",
                       sim->actuator_ctrlrange_[i]->first, sim->actuator_ctrlrange_[i]->second);
    else {
      mju::strcpy_arr(defSlider[0].other, "-1 1");
    }

    // add and count
    mjui_add(&sim->ui1, defSlider);
    itemcnt++;
  }
}

// make model-dependent UI sections
void MakeUiSections(mj::Simulate* sim, const mjModel* m, const mjData* d) {
  // clear model-dependent sections of UI
  sim->ui0.nsect = SECT_PHYSICS;
  sim->ui1.nsect = 0;

  // make
  MakePhysicsSection(sim);
  MakeRenderingSection(sim, m);
  MakeVisualizationSection(sim, m);
  MakeGroupSection(sim);
  MakeJointSection(sim);
  MakeControlSection(sim);
}

//---------------------------------- utility functions ---------------------------------------------

// align and scale view
void AlignAndScaleView(mj::Simulate* sim, const mjModel* m) {
  // use default free camera parameters
  mjv_defaultFreeCamera(m, &sim->cam);
}


// copy qpos to clipboard as key
void CopyPose(mj::Simulate* sim, const mjModel* m, const mjData* d) {
  char clipboard[5000] = "<key qpos='";
  char buf[200];

  // prepare string
  for (int i=0; i<m->nq; i++) {
    mju::sprintf_arr(buf, i==m->nq-1 ? "%g" : "%g ", d->qpos[i]);
    mju::strcat_arr(clipboard, buf);
  }
  mju::strcat_arr(clipboard, "'/>");

  // copy to clipboard
  sim->platform_ui->SetClipboardString(clipboard);
}

// millisecond timer, for MuJoCo built-in profiler
mjtNum Timer() {
  static auto start = mj::Simulate::Clock::now();
  auto elapsed = Milliseconds(mj::Simulate::Clock::now() - start);
  return elapsed.count();
}

// clear all times
void ClearTimers(mjData* d) {
  for (int i=0; i<mjNTIMER; i++) {
    d->timer[i].duration = 0;
    d->timer[i].number = 0;
  }
}

// copy current camera to clipboard as MJCF specification
void CopyCamera(mj::Simulate* sim) {
  mjvGLCamera* camera = sim->scn.camera;

  char clipboard[500];
  mjtNum cam_right[3];
  mjtNum cam_forward[3];
  mjtNum cam_up[3];

  // get camera spec from the GLCamera
  mju_f2n(cam_forward, camera[0].forward, 3);
  mju_f2n(cam_up, camera[0].up, 3);
  mju_cross(cam_right, cam_forward, cam_up);

  // make MJCF camera spec
  mju::sprintf_arr(clipboard,
                   "<camera pos=\"%.3f %.3f %.3f\" xyaxes=\"%.3f %.3f %.3f %.3f %.3f %.3f\"/>\n",
                   (camera[0].pos[0] + camera[1].pos[0]) / 2,
                   (camera[0].pos[1] + camera[1].pos[1]) / 2,
                   (camera[0].pos[2] + camera[1].pos[2]) / 2,
                   cam_right[0], cam_right[1], cam_right[2],
                   camera[0].up[0], camera[0].up[1], camera[0].up[2]);

  // copy spec into clipboard
  sim->platform_ui->SetClipboardString(clipboard);
}

// update UI 0 when MuJoCo structures change (except for joint sliders)
void UpdateSettings(mj::Simulate* sim, const mjModel* m) {
  // physics flags
  for (int i=0; i<mjNDISABLE; i++) {
    int new_value = ((m->opt.disableflags & (1<<i)) != 0);
    if (sim->disable[i] != new_value) {
      sim->disable[i] = new_value;
      sim->pending_.ui_update_physics = true;
    }
  }
  for (int i=0; i<mjNENABLE; i++) {
    int new_value = ((m->opt.enableflags & (1<<i)) != 0);
    if (sim->enable[i] != new_value) {
      sim->enable[i] = new_value;
      sim->pending_.ui_update_physics = true;
    }
  }
  for (int i=0; i<mjNGROUP; i++) {
    int enabled = ((m->opt.disableactuator & (1<<i)) == 0);
    if (sim->enableactuator[i] != enabled) {
      sim->enableactuator[i] = enabled;
      sim->pending_.ui_update_physics = true;
      sim->pending_.ui_remake_ctrl = true;
    }
  }

  // camera
  int old_camera = sim->camera;
  if (sim->cam.type==mjCAMERA_FIXED) {
    sim->camera = 2 + sim->cam.fixedcamid;
  } else if (sim->cam.type==mjCAMERA_TRACKING) {
    sim->camera = 1;
  } else {
    sim->camera = 0;
  }
  if (old_camera != sim->camera) {
    sim->pending_.ui_update_rendering = true;
  }
}

// Compute suitable font scale.
int ComputeFontScale(const mj::PlatformUIAdapter& platform_ui) {
  // compute framebuffer-to-window ratio
  auto [buf_width, buf_height] = platform_ui.GetFramebufferSize();
  auto [win_width, win_height] = platform_ui.GetWindowSize();
  double b2w = static_cast<double>(buf_width) / win_width;

  // compute PPI
  double PPI = b2w * platform_ui.GetDisplayPixelsPerInch();

  // estimate font scaling, guard against unrealistic PPI
  int fs;
  if (buf_width > win_width) {
    fs = mju_round(b2w * 100);
  } else if (PPI>50 && PPI<350) {
    fs = mju_round(PPI);
  } else {
    fs = 150;
  }
  fs = mju_round(fs * 0.02) * 50;
  fs = mjMIN(300, mjMAX(100, fs));

  return fs;
}


//---------------------------------- UI handlers ---------------------------------------------------

// determine enable/disable item state given category
int UiPredicate(int category, void* userdata) {
  mj::Simulate* sim = static_cast<mj::Simulate*>(userdata);

  switch (category) {
  case 2:                 // require model
    return sim->m_ || sim->is_passive_;

  case 3:                 // require model and nkey
    return (sim->m_ || sim->is_passive_) && sim->nkey_;

  case 4:                 // require model and paused
    return sim->m_ && !sim->run;

  case 5:                 // require model and fully managed mode
    return !sim->is_passive_ && sim->m_;

  default:
    return 1;
  }
}

// set window layout
void UiLayout(mjuiState* state) {
  mj::Simulate* sim = static_cast<mj::Simulate*>(state->userdata);
  mjrRect* rect = state->rect;

  // set number of rectangles
  state->nrect = 4;

  // rect 1: UI 0
  rect[1].left = 0;
  rect[1].width = sim->ui0_enable ? sim->ui0.width : 0;
  rect[1].bottom = 0;
  rect[1].height = rect[0].height;

  // rect 2: UI 1
  rect[2].width = sim->ui1_enable ? sim->ui1.width : 0;
  rect[2].left = mjMAX(0, rect[0].width - rect[2].width);
  rect[2].bottom = 0;
  rect[2].height = rect[0].height;

  // rect 3: 3D plot (everything else is an overlay)
  rect[3].left = rect[1].width;
  rect[3].width = mjMAX(0, rect[0].width - rect[1].width - rect[2].width);
  rect[3].bottom = 0;
  rect[3].height = rect[0].height;
}

// modify UI
void UiModify(mjUI* ui, mjuiState* state, mjrContext* con) {
  mjui_resize(ui, con);

  // remake aux buffer only if missing or different
  int id = ui->auxid;
  if (con->auxFBO[id] == 0 ||
      con->auxFBO_r[id] == 0 ||
      con->auxColor[id] == 0 ||
      con->auxColor_r[id] == 0 ||
      con->auxWidth[id] != ui->width ||
      con->auxHeight[id] != ui->maxheight ||
      con->auxSamples[id] != ui->spacing.samples) {
    mjr_addAux(id, ui->width, ui->maxheight, ui->spacing.samples, con);
  }

  UiLayout(state);
  mjui_update(-1, -1, ui, state, con);
}

// handle UI event
void UiEvent(mjuiState* state) {
  mj::Simulate* sim = static_cast<mj::Simulate*>(state->userdata);

  // call UI 0 if event is directed to it
  if ((state->dragrect==sim->ui0.rectid) ||
      (state->dragrect==0 && state->mouserect==sim->ui0.rectid) ||
      state->type==mjEVENT_KEY) {
    // process UI event
    mjuiItem* it = mjui_event(&sim->ui0, state, &sim->platform_ui->mjr_context());

    // file section
    if (it && it->sectionid==SECT_FILE) {
      switch (it->itemid) {
      case 0:             // Save xml
        sim->pending_.save_xml = GetSavePath("mjmodel.xml");
        break;

      case 1:             // Save mjb
        sim->pending_.save_mjb = GetSavePath("mjmodel.mjb");
        break;

      case 2:             // Print model
        sim->pending_.print_model = GetSavePath("MJMODEL.TXT");
        break;

      case 3:             // Print data
        sim->pending_.print_data = GetSavePath("MJDATA.TXT");
        break;

      case 4:             // Quit
        sim->exitrequest.store(1);
        break;

      case 5:             // Screenshot
        sim->screenshotrequest.store(true);
        break;
      }
    }

    // option section
    else if (it && it->sectionid==SECT_OPTION) {
      if (it->pdata == &sim->spacing) {
        sim->ui0.spacing = mjui_themeSpacing(sim->spacing);
        sim->ui1.spacing = mjui_themeSpacing(sim->spacing);
      } else if (it->pdata == &sim->color) {
        sim->ui0.color = mjui_themeColor(sim->color);
        sim->ui1.color = mjui_themeColor(sim->color);
      } else if (it->pdata == &sim->font) {
        mjr_changeFont(50*(sim->font+1), &sim->platform_ui->mjr_context());
      } else if (it->pdata == &sim->fullscreen) {
        sim->platform_ui->ToggleFullscreen();
      } else if (it->pdata == &sim->vsync) {
        sim->platform_ui->SetVSync(sim->vsync);
      }

      // modify UI
      UiModify(&sim->ui0, state, &sim->platform_ui->mjr_context());
      UiModify(&sim->ui1, state, &sim->platform_ui->mjr_context());
    }

    // simulation section
    else if (it && it->sectionid==SECT_SIMULATION) {
      switch (it->itemid) {
      case 1:             // Reset
        sim->pending_.reset = true;
        break;

      case 2:             // Reload
        sim->uiloadrequest.fetch_add(1);
        break;

      case 3:             // Align
        sim->pending_.align = true;
        break;

      case 4:             // Copy pose
        sim->pending_.copy_pose = true;
        break;

      case 5:             // Adjust key
      case 6:             // Load key
        sim->pending_.load_key = true;
        break;

      case 7:             // Save key
        sim->pending_.save_key = true;
        break;

      case 11:            // History scrubber
        sim->run = 0;
        sim->pending_.load_from_history = true;
        mjui0_update_section(sim, SECT_SIMULATION);
        break;
      }
    }

    // physics section
    else if (it && it->sectionid==SECT_PHYSICS && sim->m_) {
      mjOption* opt = sim->is_passive_ ? &sim->scnstate_.model.opt : &sim->m_->opt;

      // update disable flags in mjOption
      opt->disableflags = 0;
      for (int i=0; i<mjNDISABLE; i++) {
        if (sim->disable[i]) {
          opt->disableflags |= (1<<i);
        }
      }

      // update enable flags in mjOption
      opt->enableflags = 0;
      for (int i=0; i<mjNENABLE; i++) {
        if (sim->enable[i]) {
          opt->enableflags |= (1<<i);
        }
      }

      // update disableactuator bitflag in mjOption
      bool group_changed = false;
      for (int i=0; i<mjNGROUP; i++) {
        if ((!sim->enableactuator[i]) != (opt->disableactuator & (1<<i))) {
          group_changed = true;
          if (!sim->enableactuator[i]) {
            // disable actuator group i
            opt->disableactuator |= (1<<i);
          } else {
            // enable actuator group i
            opt->disableactuator &= ~(1<<i);
          }
        }
      }

      // remake control section if actuator disable group changed
      if (group_changed) {
        sim->pending_.ui_remake_ctrl = true;
      }
    }

    // rendering section
    else if (it && it->sectionid==SECT_RENDERING) {
      // set camera in mjvCamera
      if (sim->camera==0) {
        sim->cam.type = mjCAMERA_FREE;
      } else if (sim->camera==1) {
        if (sim->pert.select>0) {
          sim->cam.type = mjCAMERA_TRACKING;
          sim->cam.trackbodyid = sim->pert.select;
          sim->cam.fixedcamid = -1;
        } else {
          sim->cam.type = mjCAMERA_FREE;
          sim->camera = 0;
          mjui0_update_section(sim, SECT_RENDERING);
        }
      } else {
        sim->cam.type = mjCAMERA_FIXED;
        sim->cam.fixedcamid = sim->camera - 2;
      }
      // copy camera spec to clipboard (as MJCF element)
      if (it->itemid == 3) {
        CopyCamera(sim);
      }
    }

    // visualization section
    else if (it && it->sectionid==SECT_VISUALIZATION) {
      if (!mju::strcmp_arr(it->name, "Align")) {
        sim->pending_.align = true;
      }
    }

    // group section
    else if (it && it->sectionid==SECT_GROUP) {
      // remake joint section if joint group changed
      if (it->name[0]=='J' && it->name[1]=='o') {
        sim->ui1.nsect = SECT_JOINT;
        MakeJointSection(sim);
        sim->ui1.nsect = NSECT1;
        UiModify(&sim->ui1, state, &sim->platform_ui->mjr_context());
      }

      // remake control section if actuator group changed
      if (it->name[0]=='A' && it->name[1]=='c') {
        sim->pending_.ui_remake_ctrl = true;
      }
    }

    // stop if UI processed event
    if (it!=nullptr || (state->type==mjEVENT_KEY && state->key==0)) {
      return;
    }
  }

  // call UI 1 if event is directed to it
  if ((state->dragrect==sim->ui1.rectid) ||
      (state->dragrect==0 && state->mouserect==sim->ui1.rectid) ||
      state->type==mjEVENT_KEY) {
    // process UI event
    mjuiItem* it = mjui_event(&sim->ui1, state, &sim->platform_ui->mjr_context());

    // control section
    if (it && it->sectionid==SECT_CONTROL) {
      // clear controls
      if (it->itemid==0) {
        sim->pending_.zero_ctrl = true;
      }
    }

    // stop if UI processed event
    if (it!=nullptr || (state->type==mjEVENT_KEY && state->key==0)) {
      return;
    }
  }

  // shortcut not handled by UI
  if (state->type==mjEVENT_KEY && state->key!=0) {
    switch (state->key) {
    case ' ':                   // Mode
      if (!sim->is_passive_ && sim->m_) {
        sim->run = 1 - sim->run;
        sim->pert.active = 0;

        if (sim->run) sim->scrub_index = 0;  // reset scrubber

        mjui0_update_section(sim, -1);
      }
      break;

    case mjKEY_RIGHT:           // step forward
      if (!sim->is_passive_ && sim->m_ && !sim->run) {
        ClearTimers(sim->d_);

        // currently in scrubber: increment scrub, load state, update slider UI
        if (sim->scrub_index < 0) {
          sim->scrub_index++;
          sim->pending_.load_from_history = true;
          mjui0_update_section(sim, SECT_SIMULATION);
        }

        // not in scrubber: step, add to history buffer
        else {
          mj_step(sim->m_, sim->d_);
          sim->AddToHistory();
        }

        UpdateProfiler(sim, sim->m_, sim->d_);
        UpdateSensor(sim, sim->m_, sim->d_);
        UpdateSettings(sim, sim->m_);
      }
      break;

    case mjKEY_LEFT:           // step backward
      if (!sim->is_passive_ && sim->m_) {
        sim->run = 0;
        ClearTimers(sim->d_);

        // decrement scrub, load state
        sim->scrub_index = mjMAX(sim->scrub_index - 1, 1 - sim->nhistory_);
        sim->pending_.load_from_history = true;

        // update slider UI, profiler, sensor
        mjui0_update_section(sim, SECT_SIMULATION);
        UpdateProfiler(sim, sim->m_, sim->d_);
        UpdateSensor(sim, sim->m_, sim->d_);
      }
      break;

    case mjKEY_PAGE_UP:         // select parent body
      if ((sim->m_ || sim->is_passive_) && sim->pert.select > 0) {
        sim->pert.select = sim->body_parentid_[sim->pert.select];
        sim->pert.flexselect = -1;
        sim->pert.skinselect = -1;

        // stop perturbation if world reached
        if (sim->pert.select<=0) {
          sim->pert.active = 0;
        }
      }

      break;

    case ']':                   // cycle up fixed cameras
      if ((sim->m_ || !sim->is_passive_) && sim->ncam_) {
        sim->cam.type = mjCAMERA_FIXED;
        // camera = {0 or 1} are reserved for the free and tracking cameras
        if (sim->camera < 2 || sim->camera == 2 + sim->ncam_ - 1) {
          sim->camera = 2;
        } else {
          sim->camera += 1;
        }
        sim->cam.fixedcamid = sim->camera - 2;
        mjui0_update_section(sim, SECT_RENDERING);
      }
      break;

    case '[':                   // cycle down fixed cameras
      if ((sim->m_ || sim->is_passive_) && sim->ncam_) {
        sim->cam.type = mjCAMERA_FIXED;
        // camera = {0 or 1} are reserved for the free and tracking cameras
        if (sim->camera <= 2) {
          sim->camera = 2 + sim->ncam_-1;
        } else {
          sim->camera -= 1;
        }
        sim->cam.fixedcamid = sim->camera - 2;
        mjui0_update_section(sim, SECT_RENDERING);
      }
      break;

    case mjKEY_F6:                   // cycle frame visualisation
      if (sim->m_ || sim->is_passive_) {
        sim->opt.frame = (sim->opt.frame + 1) % mjNFRAME;
        mjui0_update_section(sim, SECT_RENDERING);
      }
      break;

    case mjKEY_F7:                   // cycle label visualisation
      if (sim->m_ || sim->is_passive_) {
        sim->opt.label = (sim->opt.label + 1) % mjNLABEL;
        mjui0_update_section(sim, SECT_RENDERING);
      }
      break;

    case mjKEY_ESCAPE:          // free camera
      sim->cam.type = mjCAMERA_FREE;
      sim->camera = 0;
      mjui0_update_section(sim, SECT_RENDERING);
      break;

    case '-':                   // slow down
      if (!sim->is_passive_) {
        int numclicks = sizeof(sim->percentRealTime) / sizeof(sim->percentRealTime[0]);
        if (sim->real_time_index < numclicks-1 && !state->shift) {
          sim->real_time_index++;
          sim->speed_changed = true;
        }
      }
      break;

    case '=':                   // speed up
      if (!sim->is_passive_ && sim->real_time_index > 0 && !state->shift) {
        sim->real_time_index--;
        sim->speed_changed = true;
      }
      break;

    case mjKEY_TAB:             // toggle left/right UI
      if (!state->shift) {
        // toggle left UI
        sim->ui0_enable = !sim->ui0_enable;
        UiModify(&sim->ui0, state, &sim->platform_ui->mjr_context());
      } else {
        // toggle right UI
        sim->ui1_enable = !sim->ui1_enable;
        UiModify(&sim->ui1, state, &sim->platform_ui->mjr_context());
      }
      break;
    }

    return;
  }

  // 3D scroll
  if (state->type==mjEVENT_SCROLL && state->mouserect==3) {
    // emulate vertical mouse motion = 2% of window height
    if (sim->m_ && !sim->is_passive_) {
      mjv_moveCamera(sim->m_, mjMOUSE_ZOOM, 0, -zoom_increment*state->sy, &sim->scn, &sim->cam);
    } else {
      mjv_moveCameraFromState(
          &sim->scnstate_, mjMOUSE_ZOOM, 0, -zoom_increment*state->sy, &sim->scn, &sim->cam);
    }
    return;
  }

  // 3D press
  if (state->type==mjEVENT_PRESS && state->mouserect==3) {
    // set perturbation
    int newperturb = 0;
    if (state->control && sim->pert.select>0 && (sim->m_ || sim->is_passive_)) {
      // right: translate;  left: rotate
      if (state->right) {
        newperturb = mjPERT_TRANSLATE;
      } else if (state->left) {
        newperturb = mjPERT_ROTATE;
      }
      if (newperturb && !sim->pert.active) {
        sim->pending_.newperturb = newperturb;
      }
    }

    // handle double-click
    if (state->doubleclick && (sim->m_ || sim->is_passive_)) {
      sim->pending_.select = true;
      std::memcpy(&sim->pending_.select_state, state, sizeof(sim->pending_.select_state));

      // stop perturbation on select
      sim->pert.active = 0;
      sim->pending_.newperturb = 0;
    }

    return;
  }

  // 3D release
  if (state->type==mjEVENT_RELEASE && state->dragrect==3 && (sim->m_ || sim->is_passive_)) {
    // stop perturbation
    sim->pert.active = 0;
    sim->pending_.newperturb = 0;
    return;
  }

  // 3D move
  if (state->type==mjEVENT_MOVE && state->dragrect==3 && (sim->m_ || sim->is_passive_)) {
    // determine action based on mouse button
    mjtMouse action;
    if (state->right) {
      action = state->shift ? mjMOUSE_MOVE_H : mjMOUSE_MOVE_V;
    } else if (state->left) {
      action = state->shift ? mjMOUSE_ROTATE_H : mjMOUSE_ROTATE_V;
    } else {
      action = mjMOUSE_ZOOM;
    }

    // move perturb or camera
    mjrRect r = state->rect[3];
    if (sim->pert.active) {
      if (!sim->is_passive_) {
        mjv_movePerturb(
            sim->m_, sim->d_, action, state->dx / r.height, -state->dy / r.height,
            &sim->scn, &sim->pert);
      } else {
        mjv_movePerturbFromState(
            &sim->scnstate_, action, state->dx / r.height, -state->dy / r.height,
            &sim->scn, &sim->pert);
      }
    } else {
      if (!sim->is_passive_) {
        mjv_moveCamera(
            sim->m_, action, state->dx / r.height, -state->dy / r.height,
            &sim->scn, &sim->cam);
      } else {
        mjv_moveCameraFromState(
            &sim->scnstate_, action, state->dx / r.height, -state->dy / r.height,
            &sim->scn, &sim->cam);
      }
    }
    return;
  }

  // Dropped files
  if (state->type == mjEVENT_FILESDROP && state->dropcount > 0 && !sim->is_passive_) {
    while (sim->droploadrequest.load()) {}
    mju::strcpy_arr(sim->dropfilename, state->droppaths[0]);
    sim->droploadrequest.store(true);
    return;
  }

  // Redraw
  if (state->type == mjEVENT_REDRAW) {
    sim->Render();
    return;
  }
}
}  // namespace

namespace mujoco {
namespace mju = ::mujoco::sample_util;

Simulate::Simulate(std::unique_ptr<PlatformUIAdapter> platform_ui,
                   mjvCamera* cam, mjvOption* opt, mjvPerturb* pert,
                   bool is_passive)
    : is_passive_(is_passive),
      cam(*cam),
      opt(*opt),
      pert(*pert),
      platform_ui(std::move(platform_ui)),
      uistate(this->platform_ui->state()) {
  mjv_defaultScene(&scn);
  mjv_defaultSceneState(&scnstate_);
}

// synchronize model and data
// operations which require holding the mutex, prevents racing with physics thread
void Simulate::Sync() {
  MutexLock lock(this->mtx);

  if (!m_) {
    return;
  }
  if (this->exitrequest.load()) {
    return;
  }

  bool update_profiler = this->profiler && (this->pause_update || this->run);
  bool update_sensor = this->sensor && (this->pause_update || this->run);

  for (int i = 0; i < m_->njnt; ++i) {
    std::optional<std::pair<mjtNum, mjtNum>> range;
    if (m_->jnt_limited[i]) {
      range.emplace(m_->jnt_range[2*i], m_->jnt_range[2*i + 1]);
    }
    if (jnt_range_[i] != range) {
      pending_.ui_update_joint = true;
      jnt_range_[i].swap(range);
    }
  }

  for (int i = 0; i < m_->nu; ++i) {
    std::optional<std::pair<mjtNum, mjtNum>> range;
    if (m_->actuator_ctrllimited[i]) {
      range.emplace(m_->actuator_ctrlrange[2*i], m_->actuator_ctrlrange[2*i + 1]);
    }
    if (actuator_ctrlrange_[i] != range) {
      pending_.ui_remake_ctrl = true;
      actuator_ctrlrange_[i].swap(range);
    }
  }

  for (int i = 0; i < m_->nq; ++i) {
    if (qpos_[i] != qpos_prev_[i]) {
      d_->qpos[i] = qpos_[i];
    } else {
      qpos_[i] = d_->qpos[i];
    }
    if (qpos_prev_[i] != qpos_[i]) {
      pending_.ui_update_joint = true;
      qpos_prev_[i] = qpos_[i];
    }
  }

  for (int i = 0; i < m_->nu; ++i) {
    if (ctrl_[i] != ctrl_prev_[i]) {
      d_->ctrl[i] = ctrl_[i];
    } else {
      ctrl_[i] = d_->ctrl[i];
    }
    if (ctrl_prev_[i] != ctrl_[i]) {
      pending_.ui_update_ctrl = true;
      ctrl_prev_[i] = ctrl_[i];
    }
  }

  if (is_passive_) {
    // synchronize m_->opt with changes made via the UI
#define X(name)                                                  \
  if (IsDifferent(scnstate_.model.opt.name, mjopt_prev_.name)) { \
    pending_.ui_update_physics = true;                           \
    Copy(m_->opt.name, scnstate_.model.opt.name);                \
  }

    X(timestep);
    X(apirate);
    X(impratio);
    X(tolerance);
    X(noslip_tolerance);
    X(ccd_tolerance);
    X(gravity);
    X(wind);
    X(magnetic);
    X(density);
    X(viscosity);
    X(o_margin);
    X(o_solref);
    X(o_solimp);
    X(o_friction);
    X(integrator);
    X(cone);
    X(jacobian);
    X(solver);
    X(iterations);
    X(noslip_iterations);
    X(ccd_iterations);
    X(disableflags);
    X(enableflags);
    X(disableactuator);
    X(sdf_initpoints);
    X(sdf_iterations);

  #undef X

    // synchronize number of mjWARN_VGEOMFULL warnings
    if (scnstate_.data.warning[mjWARN_VGEOMFULL].number > warn_vgeomfull_prev_) {
      d_->warning[mjWARN_VGEOMFULL].number +=
          scnstate_.data.warning[mjWARN_VGEOMFULL].number - warn_vgeomfull_prev_;
    }
  }

  if (pending_.save_xml) {
    char err[200];
    if (!pending_.save_xml->empty() && !mj_saveLastXML(pending_.save_xml->c_str(), m_, err, 200)) {
      std::printf("Save XML error: %s", err);
    }
    pending_.save_xml = std::nullopt;
  }

  if (pending_.save_mjb) {
    if (!pending_.save_mjb->empty()) {
      mj_saveModel(m_, pending_.save_mjb->c_str(), nullptr, 0);
    }
    pending_.save_mjb = std::nullopt;
  }

  if (pending_.print_model) {
    if (!pending_.print_model->empty()) {
      mj_printModel(m_, pending_.print_model->c_str());
    }
    pending_.print_model = std::nullopt;
  }

  if (pending_.print_data) {
    if (!pending_.print_data->empty()) {
      mj_printData(m_, d_, pending_.print_data->c_str());
    }
    pending_.print_data = std::nullopt;
  }

  if (pending_.reset) {
    mj_resetData(m_, d_);
    mj_forward(m_, d_);
    load_error[0] = '\0';
    update_profiler = true;
    update_sensor = true;
    scrub_index = 0;
    pending_.ui_update_simulation = true;
    pending_.reset = false;
  }

  if (pending_.align) {
    AlignAndScaleView(this, m_);
    pending_.align = false;
  }

  if (pending_.copy_pose) {
    CopyPose(this, m_, d_);
    pending_.copy_pose = false;
  }

  if (pending_.load_from_history) {
    LoadScrubState(this);
    update_profiler = true;
    update_sensor = true;
    pending_.load_from_history = false;
  }

  if (pending_.load_key) {
    mj_resetDataKeyframe(m_, d_, this->key);
    mj_forward(m_, d_);
    update_profiler = true;
    update_sensor = true;
    pending_.load_key = false;
  }

  if (pending_.save_key) {
    mj_setKeyframe(m_, d_, this->key);
    pending_.save_key = false;
  }

  if (pending_.zero_ctrl) {
    mju_zero(d_->ctrl, m_->nu);
    pending_.zero_ctrl = false;
  }

  // perturbation onset: reset reference
  if (pending_.newperturb) {
    mjv_initPerturb(m_, d_, &this->scn, &this->pert);
    this->pert.active = pending_.newperturb;
    pending_.newperturb = 0;
  }

  if (pending_.select) {
    // determine selection mode
    int selmode;
    if (pending_.select_state.button==mjBUTTON_LEFT) {
      selmode = 1;
    } else if (pending_.select_state.control) {
      selmode = 3;
    } else {
      selmode = 2;
    }

    // find geom and 3D click point, get corresponding body
    mjrRect r = pending_.select_state.rect[3];
    mjtNum selpnt[3];
    int selgeom, selflex, selskin;
    int selbody = mjv_select(m_, d_, &this->opt,
                             static_cast<mjtNum>(r.width) / r.height,
                             (pending_.select_state.x - r.left) / r.width,
                             (pending_.select_state.y - r.bottom) / r.height,
                             &this->scn, selpnt, &selgeom, &selflex, &selskin);

    // set lookat point, start tracking is requested
    if (selmode==2 || selmode==3) {
      // copy selpnt if anything clicked
      if (selbody>=0) {
        mju_copy3(this->cam.lookat, selpnt);
      }

      // switch to tracking camera if dynamic body clicked
      if (selmode==3 && selbody>0) {
        // mujoco camera
        this->cam.type = mjCAMERA_TRACKING;
        this->cam.trackbodyid = selbody;
        this->cam.fixedcamid = -1;

        // UI camera
        this->camera = 1;
        pending_.ui_update_rendering = true;
      }
    }

    // set body selection
    else {
      if (selbody>=0) {
        // record selection
        this->pert.select = selbody;
        this->pert.flexselect = selflex;
        this->pert.skinselect = selskin;

        // compute localpos
        mjtNum tmp[3];
        mju_sub3(tmp, selpnt, d_->xpos + 3*this->pert.select);
        mju_mulMatTVec(this->pert.localpos, d_->xmat + 9*this->pert.select, tmp, 3, 3);
      } else {
        this->pert.select = 0;
        this->pert.flexselect = -1;
        this->pert.skinselect = -1;
      }
    }
    pending_.select = false;
  }

  // update scene
  if (!is_passive_) {
    mjv_updateScene(m_, d_, &this->opt, &this->pert, &this->cam, mjCAT_ALL, &this->scn);
  } else {
    mjv_updateSceneState(m_, d_, &this->opt, &scnstate_);

    // append geoms from user_scn to scnstate_ scratch space
    if (user_scn) {
      int ngeom = user_scn->ngeom;
      int maxgeom = scnstate_.scratch.maxgeom - scnstate_.scratch.ngeom;
      if (ngeom > maxgeom) {
        mj_warning(d_, mjWARN_VGEOMFULL, scnstate_.scratch.maxgeom);
        ngeom = maxgeom;
      }
      if (ngeom > 0) {
        std::memcpy(scnstate_.scratch.geoms + scnstate_.scratch.ngeom,
                    user_scn->geoms,
                    sizeof(mjvGeom) * ngeom);
        scnstate_.scratch.ngeom += ngeom;
      }
    }

    // pick up rendering flags changed via user_scn
    if (user_scn) {
      for (int i = 0; i < mjNRNDFLAG; ++i) {
        if (user_scn->flags[i] != user_scn_flags_prev_[i]) {
          scn.flags[i] = user_scn->flags[i];
          pending_.ui_update_rendering = true;
        }
      }
      Copy(user_scn->flags, scn.flags);
      Copy(user_scn_flags_prev_, user_scn->flags);
    }

    mjopt_prev_ = scnstate_.model.opt;
    warn_vgeomfull_prev_ = scnstate_.data.warning[mjWARN_VGEOMFULL].number;
  }

  // update settings
  UpdateSettings(this, m_);

  // update watch
  if (this->ui0_enable && this->ui0.sect[SECT_WATCH].state) {
    UpdateWatch(this, m_, d_);
  }

  // update info text
  if (this->info) {
    UpdateInfoText(this, m_, d_, this->info_title, this->info_content);
  }
  if (update_profiler) { UpdateProfiler(this, m_, d_); }
  if (update_sensor) { UpdateSensor(this, m_, d_); }

  // clear timers once profiler info has been copied
  ClearTimers(d_);

  if (this->run || this->is_passive_) {
    // clear old perturbations, apply new
    mju_zero(d_->xfrc_applied, 6*m_->nbody);
    mjv_applyPerturbPose(m_, d_, &this->pert, 0);  // mocap bodies only
    mjv_applyPerturbForce(m_, d_, &this->pert);
  } else {
    mjv_applyPerturbPose(m_, d_, &this->pert, 1);  // mocap and dynamic bodies
  }
}

//------------------------- Tell the render thread to load a file and wait -------------------------
void Simulate::LoadMessage(const char* displayed_filename) {
  mju::strcpy_arr(this->filename, displayed_filename);

  {
    MutexLock lock(mtx);
    this->loadrequest = 3;
  }
}

void Simulate::Load(mjModel* m, mjData* d, const char* displayed_filename) {
  this->mnew_ = m;
  this->dnew_ = d;
  mju::strcpy_arr(this->filename, displayed_filename);

  {
    MutexLock lock(mtx);
    this->loadrequest = 2;

    // Wait for the render thread to be done loading
    // so that we know the old model and data's memory can
    // be free'd by the other thread (sometimes python)
    cond_loadrequest.wait(lock, [this]() { return this->loadrequest == 0; });
  }
}

void Simulate::LoadMessageClear(void) {
  {
    MutexLock lock(mtx);
    this->loadrequest = 0;
  }
}



//------------------------------------- load mjb or xml model --------------------------------------
void Simulate::LoadOnRenderThread() {
  this->m_ = this->mnew_;
  this->d_ = this->dnew_;

  ncam_ = this->m_->ncam;
  nkey_ = this->m_->nkey;
  body_parentid_.resize(this->m_->nbody);
  std::memcpy(body_parentid_.data(), this->m_->body_parentid,
              sizeof(this->m_->body_parentid[0]) * this->m_->nbody);

  jnt_type_.resize(this->m_->njnt);
  std::memcpy(jnt_type_.data(), this->m_->jnt_type,
              sizeof(this->m_->jnt_type[0]) * this->m_->njnt);

  jnt_group_.resize(this->m_->njnt);
  std::memcpy(jnt_group_.data(), this->m_->jnt_group,
              sizeof(this->m_->jnt_group[0]) * this->m_->njnt);

  jnt_qposadr_.resize(this->m_->njnt);
  std::memcpy(jnt_qposadr_.data(), this->m_->jnt_qposadr,
              sizeof(this->m_->jnt_qposadr[0]) * this->m_->njnt);

  jnt_range_.clear();
  jnt_range_.reserve(this->m_->njnt);
  for (int i = 0; i < this->m_->njnt; ++i) {
    if (this->m_->jnt_limited[i]) {
      jnt_range_.push_back(
          std::make_pair(this->m_->jnt_range[2 * i], this->m_->jnt_range[2 * i + 1]));
    } else {
      jnt_range_.push_back(std::nullopt);
    }
  }

  jnt_names_.clear();
  jnt_names_.reserve(this->m_->njnt);
  for (int i = 0; i < this->m_->njnt; ++i) {
    jnt_names_.emplace_back(this->m_->names + this->m_->name_jntadr[i]);
  }

  actuator_group_.resize(this->m_->nu);
  std::memcpy(actuator_group_.data(), this->m_->actuator_group,
              sizeof(this->m_->actuator_group[0]) * this->m_->nu);

  actuator_ctrlrange_.clear();
  actuator_ctrlrange_.reserve(this->m_->nu);
  for (int i = 0; i < this->m_->nu; ++i) {
    if (this->m_->actuator_ctrllimited[i]) {
      actuator_ctrlrange_.push_back(std::make_pair(
          this->m_->actuator_ctrlrange[2 * i], this->m_->actuator_ctrlrange[2 * i + 1]));
    } else {
      actuator_ctrlrange_.push_back(std::nullopt);
    }
  }

  actuator_names_.clear();
  actuator_names_.reserve(this->m_->nu);
  for (int i = 0; i < this->m_->nu; ++i) {
    actuator_names_.emplace_back(this->m_->names + this->m_->name_actuatoradr[i]);
  }

  qpos_.resize(this->m_->nq);
  std::memcpy(qpos_.data(), this->d_->qpos, sizeof(this->d_->qpos[0]) * this->m_->nq);
  qpos_prev_ = qpos_;

  ctrl_.resize(this->m_->nu);
  std::memcpy(ctrl_.data(), this->d_->ctrl, sizeof(this->d_->ctrl[0]) * this->m_->nu);
  ctrl_prev_ = ctrl_;

  // allocate history buffer: smaller of {2000 states, 100 MB}
  if (!this->is_passive_) {
    constexpr int kMaxHistoryBytes = 1e8;

    // get state size, size of history buffer
    state_size_ = mj_stateSize(this->m_, mjSTATE_INTEGRATION);
    int state_bytes = state_size_ * sizeof(mjtNum);
    int history_length = mjMIN(INT_MAX / state_bytes, 2000);
    int history_bytes = mjMIN(state_bytes * history_length, kMaxHistoryBytes);
    nhistory_ = history_bytes / state_bytes;

    // allocate history buffer, reset cursor and UI slider
    history_.clear();
    history_.resize(nhistory_ * state_size_);
    history_cursor_ = 0;
    scrub_index = 0;

    // fill buffer with initial state
    mj_getState(this->m_, this->d_, history_.data(), mjSTATE_INTEGRATION);
    for (int i = 1; i < nhistory_; ++i) {
      mju_copy(&history_[i * state_size_], history_.data(), state_size_);
    }
  }

  // re-create scene and context
  mjv_makeScene(this->m_, &this->scn, kMaxGeom);
  if (this->is_passive_) {
    mjopt_prev_ = m_->opt;
    opt_prev_ = opt;
    cam_prev_ = cam;
    warn_vgeomfull_prev_ = d_->warning[mjWARN_VGEOMFULL].number;
    mjv_makeSceneState(this->m_, this->d_, &this->scnstate_, kMaxGeom);
  }

  this->platform_ui->RefreshMjrContext(this->m_, 50*(this->font+1));
  UiModify(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
  UiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());

  if (!this->platform_ui->IsGPUAccelerated()) {
    this->scn.flags[mjRND_SHADOW] = 0;
    this->scn.flags[mjRND_REFLECTION] = 0;
  }

  if (this->user_scn) {
    Copy(this->user_scn->flags, this->scn.flags);
    Copy(this->user_scn_flags_prev_, this->scn.flags);
  }

  // clear perturbation state
  this->pert.active = 0;
  this->pert.select = 0;
  this->pert.flexselect = -1;
  this->pert.skinselect = -1;

  // align and scale view unless reloading the same file
  if (this->filename[0] &&
      mju::strcmp_arr(this->filename, this->previous_filename)) {
    AlignAndScaleView(this, this->m_);
    mju::strcpy_arr(this->previous_filename, this->filename);
  }

  // update scene
  if (!is_passive_) {
    mjv_updateScene(this->m_, this->d_,
                    &this->opt, &this->pert, &this->cam, mjCAT_ALL, &this->scn);
  } else {
    mjv_updateSceneState(this->m_, this->d_, &this->opt, &this->scnstate_);
  }

  // set window title to model name
  if (this->m_->names) {
    char title[200] = "MuJoCo : ";
    mju::strcat_arr(title, this->m_->names);
    platform_ui->SetWindowTitle(title);
  }

  // set keyframe range and divisions
  this->ui0.sect[SECT_SIMULATION].item[5].slider.range[0] = 0;
  this->ui0.sect[SECT_SIMULATION].item[5].slider.range[1] = mjMAX(0, this->m_->nkey - 1);
  this->ui0.sect[SECT_SIMULATION].item[5].slider.divisions = mjMAX(1, this->m_->nkey - 1);

  // set scrubber range and divisions
  this->ui0.sect[SECT_SIMULATION].item[11].slider.range[0] = 1 - nhistory_;
  this->ui0.sect[SECT_SIMULATION].item[11].slider.divisions = nhistory_;

  // rebuild UI sections
  MakeUiSections(this, this->m_, this->d_);

  // full ui update
  UiModify(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
  UiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
  UpdateSettings(this, this->m_);

  // clear request
  this->loadrequest = 0;
  cond_loadrequest.notify_all();

  // set real time index
  int numclicks = sizeof(this->percentRealTime) / sizeof(this->percentRealTime[0]);
  float min_error = 1e6;
  float desired = mju_log(100*this->m_->vis.global.realtime);
  for (int click=0; click<numclicks; click++) {
    float error = mju_abs(mju_log(this->percentRealTime[click]) - desired);
    if (error < min_error) {
      min_error = error;
      this->real_time_index = click;
    }
  }

  this->mnew_ = nullptr;
  this->dnew_ = nullptr;
}


//------------------------------------------- rendering --------------------------------------------

// render the ui to the window
void Simulate::Render() {
  // update rendering context buffer size if required
  if (this->platform_ui->EnsureContextSize()) {
    UiModify(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
    UiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
  }

  // get 3D rectangle and reduced for profiler
  mjrRect rect = this->uistate.rect[3];
  mjrRect smallrect = rect;
  if (this->profiler) {
    smallrect.width = rect.width - rect.width/4;
  }

  // no model
  if (!this->is_passive_ && !this->m_) {
    // blank screen
    mjr_rectangle(rect, 0.2f, 0.3f, 0.4f, 1);

    // label
    if (this->loadrequest) {
      mjr_overlay(mjFONT_BIG, mjGRID_TOP, smallrect, "LOADING...", nullptr,
                  &this->platform_ui->mjr_context());
    } else {
      char intro_message[Simulate::kMaxFilenameLength];
      mju::sprintf_arr(intro_message,
                       "MuJoCo version %s\nDrag-and-drop model file here", mj_versionString());
      mjr_overlay(mjFONT_NORMAL, mjGRID_TOPLEFT, rect, intro_message, 0,
                  &this->platform_ui->mjr_context());
    }

    // show last loading error
    if (this->load_error[0]) {
      mjr_overlay(mjFONT_NORMAL, mjGRID_BOTTOMLEFT, rect, this->load_error, 0,
                  &this->platform_ui->mjr_context());
    }

    // render uis
    if (this->ui0_enable) {
      mjui_render(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
    }
    if (this->ui1_enable) {
      mjui_render(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
    }

    // finalize
    this->platform_ui->SwapBuffers();

    return;
  }

  // update UI sections from last sync
  if (pending_.ui_update_simulation) {
    if (this->ui0_enable && this->ui0.sect[SECT_SIMULATION].state) {
      mjui0_update_section(this, SECT_SIMULATION);
    }
    pending_.ui_update_simulation = false;
  }

  if (this->ui0_enable && this->ui0.sect[SECT_WATCH].state) {
    mjui0_update_section(this, SECT_WATCH);
  }

  if (pending_.ui_update_physics) {
    if (this->ui0_enable && this->ui0.sect[SECT_PHYSICS].state) {
      mjui0_update_section(this, SECT_PHYSICS);
    }
    pending_.ui_update_physics = false;
  }

  if (is_passive_) {
    if (this->ui0_enable && this->ui0.sect[SECT_RENDERING].state &&
        (cam_prev_.type != cam.type ||
         cam_prev_.fixedcamid != cam.fixedcamid ||
         cam_prev_.trackbodyid != cam.trackbodyid ||
         opt_prev_.label != opt.label || opt_prev_.frame != opt.frame ||
         IsDifferent(opt_prev_.flags, opt.flags))) {
      pending_.ui_update_rendering = true;
    }

    if (this->ui0_enable && this->ui0.sect[SECT_RENDERING].state &&
        (IsDifferent(opt_prev_.geomgroup, opt.geomgroup) ||
         IsDifferent(opt_prev_.sitegroup, opt.sitegroup) ||
         IsDifferent(opt_prev_.jointgroup, opt.jointgroup) ||
         IsDifferent(opt_prev_.tendongroup, opt.tendongroup) ||
         IsDifferent(opt_prev_.actuatorgroup, opt.actuatorgroup) ||
         IsDifferent(opt_prev_.flexgroup, opt.flexgroup) ||
         IsDifferent(opt_prev_.skingroup, opt.skingroup))) {
      mjui0_update_section(this, SECT_GROUP);
    }

    opt_prev_ = opt;
    cam_prev_ = cam;
  }

  if (pending_.ui_update_rendering) {
    if (this->ui0_enable && this->ui0.sect[SECT_RENDERING].state) {
      mjui0_update_section(this, SECT_RENDERING);
    }
    pending_.ui_update_rendering = false;
  }

  if (pending_.ui_update_joint) {
    if (this->ui1_enable && this->ui1.sect[SECT_JOINT].state) {
      mjui_update(SECT_JOINT, -1, &this->ui1, &this->uistate, &this->platform_ui->mjr_context());
    }
    pending_.ui_update_joint = false;
  }

  if (pending_.ui_remake_ctrl) {
    if (this->ui1_enable && this->ui1.sect[SECT_CONTROL].state) {
      this->ui1.nsect = SECT_CONTROL;
      MakeControlSection(this);
      this->ui1.nsect = NSECT1;
      UiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
    }
    pending_.ui_remake_ctrl = false;
  }

  if (pending_.ui_update_ctrl) {
    if (this->ui1_enable && this->ui1.sect[SECT_CONTROL].state) {
      mjui_update(SECT_CONTROL, -1, &this->ui1, &this->uistate, &this->platform_ui->mjr_context());
    }
    pending_.ui_update_ctrl = false;
  }

  // render scene
  mjr_render(rect, &this->scn, &this->platform_ui->mjr_context());

  // show last loading error
  if (this->load_error[0]) {
    mjr_overlay(mjFONT_NORMAL, mjGRID_BOTTOMLEFT, rect, this->load_error, 0,
                &this->platform_ui->mjr_context());
  }

  // show pause/loading label
  if (!this->run || this->loadrequest) {
    char label[30] = {'\0'};
    if (this->loadrequest) {
      std::snprintf(label, sizeof(label), "LOADING...");
    } else if (this->scrub_index == 0) {
      std::snprintf(label, sizeof(label), "PAUSE");
    } else {
      std::snprintf(label, sizeof(label), "PAUSE (%d)", this->scrub_index);
    }
    mjr_overlay(mjFONT_BIG, mjGRID_TOP, smallrect, label, nullptr,
                &this->platform_ui->mjr_context());
  }

  // get desired and actual percent-of-real-time
  float desiredRealtime = this->percentRealTime[this->real_time_index];
  float actualRealtime = 100 / this->measured_slowdown;

  // if running, check for misalignment of more than 10%
  float realtime_offset = mju_abs(actualRealtime - desiredRealtime);
  bool misaligned = this->run && realtime_offset > 0.1 * desiredRealtime;

  // make realtime overlay label
  char rtlabel[30] = {'\0'};
  if (desiredRealtime != 100.0 || misaligned) {
    // print desired realtime
    int labelsize = std::snprintf(rtlabel, sizeof(rtlabel), "%g%%", desiredRealtime);

    // if misaligned, append to label
    if (misaligned) {
      std::snprintf(rtlabel+labelsize, sizeof(rtlabel)-labelsize, " (%-4.1f%%)", actualRealtime);
    }
  }

  // show real-time overlay
  if (rtlabel[0]) {
    mjr_overlay(mjFONT_BIG, mjGRID_TOPLEFT, smallrect, rtlabel, nullptr,
                &this->platform_ui->mjr_context());
  }

  // show ui 0
  if (this->ui0_enable) {
    mjui_render(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
  }

  // show ui 1
  if (this->ui1_enable) {
    mjui_render(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());
  }

  // show help
  if (this->help) {
    mjr_overlay(mjFONT_NORMAL, mjGRID_TOPLEFT, rect, help_title, help_content,
                &this->platform_ui->mjr_context());
  }

  // show info
  if (this->info) {
    mjr_overlay(mjFONT_NORMAL, mjGRID_BOTTOMLEFT, rect, this->info_title, this->info_content,
                &this->platform_ui->mjr_context());
  }

  // show profiler
  if (this->profiler) {
    ShowProfiler(this, rect);
  }

  // show sensor
  if (this->sensor) {
    ShowSensor(this, smallrect);
  }

  // take screenshot, save to file
  if (this->screenshotrequest.exchange(false)) {
    const unsigned int h = uistate.rect[0].height;
    const unsigned int w = uistate.rect[0].width;
    std::unique_ptr<unsigned char[]> rgb(new unsigned char[3*w*h]);
    if (!rgb) {
      mju_error("could not allocate buffer for screenshot");
    }
    mjr_readPixels(rgb.get(), nullptr, uistate.rect[0], &this->platform_ui->mjr_context());

    // flip up-down
    for (int r = 0; r < h/2; ++r) {
      unsigned char* top_row = &rgb[3*w*r];
      unsigned char* bottom_row = &rgb[3*w*(h-1-r)];
      std::swap_ranges(top_row, top_row+3*w, bottom_row);
    }

    // save as PNG
    // TODO(b/241577466): Parse the stem of the filename and use a .PNG extension.
    // Unfortunately, if we just yank ".xml"/".mjb" from the filename and append .PNG, the macOS
    // file dialog does not automatically open that location. Thus, we defer to a default
    // "screenshot.png" for now.
    const std::string path = GetSavePath("screenshot.png");
    if (!path.empty()) {
      if (lodepng::encode(path, rgb.get(), w, h, LCT_RGB)) {
        mju_error("could not save screenshot");
      } else {
        std::printf("saved screenshot: %s\n", path.c_str());
      }
    }
  }

  // finalize
  this->platform_ui->SwapBuffers();
}



void Simulate::RenderLoop() {
  // Set timer callback (milliseconds)
  mjcb_time = Timer;

  // init abstract visualization
  mjv_defaultCamera(&this->cam);
  mjv_defaultOption(&this->opt);
  InitializeProfiler(this);
  InitializeSensor(this);

  // make empty scene
  if (!is_passive_) {
    mjv_defaultScene(&this->scn);
    mjv_makeScene(nullptr, &this->scn, kMaxGeom);
  }

  if (!this->platform_ui->IsGPUAccelerated()) {
    this->scn.flags[mjRND_SHADOW] = 0;
    this->scn.flags[mjRND_REFLECTION] = 0;
  }

  // select default font
  int fontscale = ComputeFontScale(*this->platform_ui);
  this->font = fontscale/50 - 1;

  // make empty context
  this->platform_ui->RefreshMjrContext(nullptr, fontscale);

  // init state and uis
  std::memset(&this->uistate, 0, sizeof(mjuiState));
  std::memset(&this->ui0, 0, sizeof(mjUI));
  std::memset(&this->ui1, 0, sizeof(mjUI));

  auto [buf_width, buf_height] = this->platform_ui->GetFramebufferSize();
  this->uistate.nrect = 1;
  this->uistate.rect[0].width = buf_width;
  this->uistate.rect[0].height = buf_height;

  this->ui0.spacing = mjui_themeSpacing(this->spacing);
  this->ui0.color = mjui_themeColor(this->color);
  this->ui0.predicate = UiPredicate;
  this->ui0.rectid = 1;
  this->ui0.auxid = 0;

  this->ui1.spacing = mjui_themeSpacing(this->spacing);
  this->ui1.color = mjui_themeColor(this->color);
  this->ui1.predicate = UiPredicate;
  this->ui1.rectid = 2;
  this->ui1.auxid = 1;

  // set GUI adapter callbacks
  this->uistate.userdata = this;
  this->platform_ui->SetEventCallback(UiEvent);
  this->platform_ui->SetLayoutCallback(UiLayout);

  // populate uis with standard sections, open some sections initially
  this->ui0.userdata = this;
  this->ui1.userdata = this;
  mjui_add(&this->ui0, defFile);
  mjui_add(&this->ui0, this->def_option);
  mjui_add(&this->ui0, this->def_simulation);
  this->ui0.sect[0].state = 1;
  this->ui0.sect[1].state = 1;
  this->ui0.sect[2].state = 1;
  mjui_add(&this->ui0, this->def_watch);
  UiModify(&this->ui0, &this->uistate, &this->platform_ui->mjr_context());
  UiModify(&this->ui1, &this->uistate, &this->platform_ui->mjr_context());

  // set VSync to initial value
  this->platform_ui->SetVSync(this->vsync);

  frames_ = 0;
  last_fps_update_ = mj::Simulate::Clock::now();

  // run event loop
  while (!this->platform_ui->ShouldCloseWindow() && !this->exitrequest.load()) {
    {
      const MutexLock lock(this->mtx);

      // load model (not on first pass, to show "loading" label)
      if (this->loadrequest==1) {
        this->LoadOnRenderThread();
      } else if (this->loadrequest == 2) {
        this->loadrequest = 1;
      }

      // poll and handle events
      this->platform_ui->PollEvents();

      // upload assets if requested
      bool upload_notify = false;
      if (hfield_upload_ != -1) {
        mjr_uploadHField(m_, &platform_ui->mjr_context(), hfield_upload_);
        hfield_upload_ = -1;
        upload_notify = true;
      }
      if (mesh_upload_ != -1) {
        mjr_uploadMesh(m_, &platform_ui->mjr_context(), mesh_upload_);
        mesh_upload_ = -1;
        upload_notify = true;
      }
      if (texture_upload_ != -1) {
        mjr_uploadTexture(m_, &platform_ui->mjr_context(), texture_upload_);
        texture_upload_ = -1;
        upload_notify = true;
      }
      if (upload_notify) {
        cond_upload_.notify_all();
      }

      // update scene, doing a full sync if in fully managed mode
      if (!this->is_passive_) {
        Sync();
      } else {
        scnstate_.data.warning[mjWARN_VGEOMFULL].number += mjv_updateSceneFromState(
            &scnstate_, &this->opt, &this->pert, &this->cam, mjCAT_ALL, &this->scn);
      }
    }  // MutexLock (unblocks simulation thread)

    // render while simulation is running
    this->Render();

    // update FPS stat, at most 5 times per second
    auto now = mj::Simulate::Clock::now();
    double interval = Seconds(now - last_fps_update_).count();
    ++frames_;
    if (interval > 0.2) {
      last_fps_update_ = now;
      fps_ = frames_ / interval;
      frames_ = 0;
    }
  }

  const MutexLock lock(this->mtx);
  mjv_freeScene(&this->scn);
  if (is_passive_) {
    mjv_freeSceneState(&scnstate_);
  }

  this->exitrequest.store(2);
}

// add state to history buffer
void Simulate::AddToHistory() {
  if (history_.empty()) {
    return;
  }

  // circular increment of cursor
  history_cursor_ = (history_cursor_ + 1) % nhistory_;

  // add state at cursor
  mjtNum* state = &history_[state_size_ * history_cursor_];
  mj_getState(m_, d_, state, mjSTATE_INTEGRATION);
}

// inject Brownian noise
void Simulate::InjectNoise() {
  // no noise, return
  if (ctrl_noise_std <= 0) {
    return;
  }

  // convert rate and scale to discrete time (Ornstein–Uhlenbeck)
  mjtNum rate = mju_exp(-m_->opt.timestep / ctrl_noise_rate);
  mjtNum scale = ctrl_noise_std * mju_sqrt(1-rate*rate);

  for (int i=0; i<m_->nu; i++) {
    mjtNum bottom = 0, top = 0, midpoint = 0, halfrange = 1;
    if (m_->actuator_ctrllimited[i]) {
      bottom = m_->actuator_ctrlrange[2*i];
      top = m_->actuator_ctrlrange[2*i+1];
      midpoint =  0.5 * (top + bottom);  // target of exponential decay
      halfrange = 0.5 * (top - bottom);  // scales noise
    }

    // exponential convergence to midpoint at ctrl_noise_rate
    d_->ctrl[i] = rate * d_->ctrl[i] + (1-rate) * midpoint;

    // add noise
    d_->ctrl[i] += scale * halfrange * mju_standardNormal(nullptr);

    // clip to range if limited
    if (m_->actuator_ctrllimited[i]) {
      d_->ctrl[i] = mju_clip(d_->ctrl[i], bottom, top);
    }
  }
}

void Simulate::UpdateHField(int hfieldid) {
  MutexLock lock(this->mtx);
  if (!m_ || hfieldid < 0 || hfieldid >= m_->nhfield) {
    return;
  }
  hfield_upload_ = hfieldid;
  cond_upload_.wait(lock, [this]() { return hfield_upload_ == -1; });
}

void Simulate::UpdateMesh(int meshid) {
  MutexLock lock(this->mtx);
  if (!m_ || meshid < 0 || meshid >= m_->nmesh) {
    return;
  }
  mesh_upload_ = meshid;
  cond_upload_.wait(lock, [this]() { return mesh_upload_ == -1; });
}

void Simulate::UpdateTexture(int texid) {
  MutexLock lock(this->mtx);
  if (!m_ || texid < 0 || texid >= m_->ntex) {
    return;
  }
  texture_upload_ = texid;
  cond_upload_.wait(lock, [this]() { return texture_upload_ == -1; });
}
}  // namespace mujoco