Plotting of data using mjvFigure

[Sraobot]

How to create a plot of data generated using simulation like qpos or qvel in C/C++ using mjvFigure?

Till now, I have been writing the data to a file and when the simulation finishes, I use matplotlib to plot the data.
There was this discussion #298 regarding live plotting but it is python.
I tried this

#include <cstdio>
#include <cstring>
#include <GLFW/glfw3.h>
#include <mujoco/mujoco.h>

int main(int argc, const char **argv)
{
    mjrContext con;   

    // init GLFW
    if (!glfwInit()) {
        mju_error("Could not initialize GLFW");
    }

    mjr_defaultContext(&con);

    mjvFigure fig; 
    mjv_defaultFigure(&fig);

    strcpy(fig.title, "Trying to Plot");
    strcpy(fig.xlabel, "X");

    fig.linepnt[0] = mjMAXLINEPNT; // Points in line 0

    // Writing the data to the line. I understood maybe first point is for x and the just next one for y. Maybe, I don't know about this properly. Someone could clarify about this.
    for (int i=0; i<2*mjMAXLINEPNT; i=i+2) {
        fig.linedata[0][i] = -i;   // x
        fig.linedata[0][i+1] = -i; // y
    }

    mjrRect viewport = {0, 0, 300,200};
    
    mjr_figure(viewport, &fig, &con); // I get a segmentation fault(Core dumped) here.

    // To stop going further
    int c;
    while(scanf("%d",&c))
    {
        printf("breaking while loop");
        break;
    }

    mjr_freeContext(&con);
    
    glfwTerminate();
    return 0;
}

Please consider helping.

[yuvaltassa]

Are you familiar with our MJPC project?

This is an example of a C++ application based on MuJoCo with lots of custom plotting. Check out the associated video to see the kind of plots that we use.

[Sraobot]

No. I am not familiar. I will check that out.
Also, can this be made to work?

[Sraobot]

@yuvaltassa I am getting a segmentation fault in glDisable(GL_NORMALIZE) in init2D() function in mjr_figure() function in src/render/render_gl2.c. Any pointers or suggestions regarding that?

[nimrod-gileadi]

I can see a couple of issues with the code above.

1. No GLFW window is created.
   Replace your existing glfwInit call with something like:

  if (glfwInit() != GLFW_TRUE) {
    mju_error("Could not initialize GLFW");
  }
  GLFWwindow* window = glfwCreateWindow(300, 200, "Render", nullptr, nullptr);
  if (!window) {
    mju_error("Could not create GLFW window");
  }
  glfwMakeContextCurrent(window);

2. I think that mjr_makeContext is required after mj_defaultContext. It requires an mjModel but you can use an empty one. Add a function like:

namespace {
mjModel* LoadModelFromString(std::string_view xml) {
  static constexpr char file[] = "filename.xml";
  // mjVFS structs need to be allocated on the heap, because it's ~2MB
  auto vfs = std::make_unique<mjVFS>();
  mj_defaultVFS(vfs.get());
  mj_makeEmptyFileVFS(vfs.get(), file, xml.size());
  int file_idx = mj_findFileVFS(vfs.get(), file);
  memcpy(vfs->filedata[file_idx], xml.data(), xml.size());
  mjModel* m = mj_loadXML(file, vfs.get(), nullptr, 0);
  mj_deleteFileVFS(vfs.get(), file);
  return m;
}
}  // namespace

Then in your main function:

  mjrContext con;
  mjr_defaultContext(&con);
  mjModel* model = LoadModelFromString("<mujoco/>");
  mjr_makeContext(model, &con, mjFONTSCALE_100);

[Sraobot]

Actually, I was using basic.cc as provided in the sample. In trying to figure out the problem, I stripped the code too much which lead to seg fault like issues.
Can you take a look at this code. I get the GLFW "Demo" window but not the plot --

#include <cstdio>
#include <cstring>
#include <GLFW/glfw3.h>
#include <mujoco/mujoco.h>

int main(int argc, const char **argv)
{
    char error[1000] = "Could not load binary model";

    char filename[] = "double_pendulum.xml";

    mjModel* m = NULL;  // model
    mjData* d = NULL;     // data
   
    m = mj_loadXML(filename, 0, error, 1000);
    d = mj_makeData(m);

    // init GLFW
    if (!glfwInit()) {
        mj_deleteModel(m);
        mj_deleteData(d);
        mju_error("Could not initialize GLFW");
    }

    GLFWwindow *window = glfwCreateWindow(1200, 900, "Demo", NULL, NULL);
    glfwMakeContextCurrent(window);

    mjrContext con;    // custom GPU context
    mjvFigure fig; 

    mjr_defaultContext(&con);
    mjv_defaultFigure(&fig);

    mjr_makeContext(m,&con, mjFONTSCALE_300);

    strcpy(fig.title, "Trying to Plot");
    strcpy(fig.xlabel, "X");

    fig.range[0][0] = -5;
    fig.range[0][1] = 30;
    fig.range[1][0] = -5;
    fig.range[1][1] = 30;
    
    fig.linepnt[0] = 20; // Points in the line 0
    
    // Writing the data to the line.
    for (int i=0; i<2*fig.linepnt[0]; i=i+2) {
        fig.linedata[0][i] = i;   // x
        fig.linedata[0][i+1] = i; // y
    }

    mjrRect viewport = {0, 0, 600,300};
    mjr_figure(viewport, &fig, &con);

    // To stop going further
    int c;
    printf("Enter an integer to exit\n");
    while(scanf("%d",&c))
    {
        printf("breaking while loop\n");
        break;
    }

    mjr_freeContext(&con);

    mj_deleteData(d);
    mj_deleteModel(m);

    glfwTerminate();
    return 0;
}

[Sraobot]

@nimrod-gileadi Any suggestions with the code shared?

[huihuishen]

Actually, I was using basic.cc as provided in the sample. In trying to figure out the problem, I stripped the code too much which lead to seg fault like issues. Can you take a look at this code. I get the GLFW "Demo" window but not the plot --

#include <cstdio>
#include <cstring>
#include <GLFW/glfw3.h>
#include <mujoco/mujoco.h>

int main(int argc, const char **argv)
{
    char error[1000] = "Could not load binary model";

    char filename[] = "double_pendulum.xml";

    mjModel* m = NULL;  // model
    mjData* d = NULL;     // data
   
    m = mj_loadXML(filename, 0, error, 1000);
    d = mj_makeData(m);

    // init GLFW
    if (!glfwInit()) {
        mj_deleteModel(m);
        mj_deleteData(d);
        mju_error("Could not initialize GLFW");
    }

    GLFWwindow *window = glfwCreateWindow(1200, 900, "Demo", NULL, NULL);
    glfwMakeContextCurrent(window);

    mjrContext con;    // custom GPU context
    mjvFigure fig; 

    mjr_defaultContext(&con);
    mjv_defaultFigure(&fig);

    mjr_makeContext(m,&con, mjFONTSCALE_300);

    strcpy(fig.title, "Trying to Plot");
    strcpy(fig.xlabel, "X");

    fig.range[0][0] = -5;
    fig.range[0][1] = 30;
    fig.range[1][0] = -5;
    fig.range[1][1] = 30;
    
    fig.linepnt[0] = 20; // Points in the line 0
    
    // Writing the data to the line.
    for (int i=0; i<2*fig.linepnt[0]; i=i+2) {
        fig.linedata[0][i] = i;   // x
        fig.linedata[0][i+1] = i; // y
    }

    mjrRect viewport = {0, 0, 600,300};
    mjr_figure(viewport, &fig, &con);

    // To stop going further
    int c;
    printf("Enter an integer to exit\n");
    while(scanf("%d",&c))
    {
        printf("breaking while loop\n");
        break;
    }

    mjr_freeContext(&con);

    mj_deleteData(d);
    mj_deleteModel(m);

    glfwTerminate();
    return 0;
}

Did you solve the problem? I'm working on the same problem recentlly.