Draw point by point 3D scatter plot with MathGL in C

Question

I am building a particle simulation, and I want to display each particle's position as a dot in a 3D scatter plot using MathGL in C (not C++!). I am having trouble with the C interface.

So far I found two interesting examples:

1. A C++ example that seems to be close to what I want: http://mathgl.sourceforge.net/doc_en/Dots-sample.html (but this is in C++, I have been unable to find the C-equivalent)

2. This is a piece of C code that constructs a 3D surf plot with dots.

   #include <mgl2/mgl_cf.h>
   int main()
   {
           HMGL gr = mgl_create_graph(600,400);
   
           HMDT a,x,y;
           a = mgl_create_data_size(30,40,1);
           x = mgl_create_data_size(30,1,1);
           y = mgl_create_data_size(40,1,1);
           mgl_data_modify(a,"pi*(1-2*x)*exp(-4*y^2-4*(2*x-1)^2)",0);
           mgl_data_fill(x,-1.,1.,'x');
           mgl_data_fill(y,0.,1.,'x');
           mgl_rotate(gr,40.,60.,0.);
           mgl_set_light(gr,1);
           mgl_box(gr,1);
           mgl_surf_xy(gr,x,y,a,".","");
           mgl_delete_data(a);
           mgl_delete_data(y);
           mgl_delete_data(x);
   
           mgl_write_frame(gr,"test.png","");
           mgl_delete_graph(gr);
           return 0;
   }
   

The example 2 is close to what I want to do, but it is annoying that a is not a linear array of just N particles. It also has to take a function to evaluate the values for a (z-axis) whereas I just want to pass the z-coordinate manually for each dot).

My data is just a 1D array of structs, similar to this:

struct particle {
    double x, y, z, velocity;
};

How do I plot these particles as dots in a 3D (scatter) plot with MathGL in C? I guess I have to use mgl_dots, but how does it read from my array of values? (I could use velocity as color coding, but that is optional)

Answer 1

I was right about using mgl_dots, and the data can be prepared using mgl_create_data_sizeand mgl_data_put_val, e.g.:

HMDT z,x,y;
int N = 1000;
x = mgl_create_data_size(N,1,1);
z = mgl_create_data_size(N,1,1);
y = mgl_create_data_size(N,1,1);

for(int i=0; i < N; i++) {
        // Set position of particle[i]
        printf("%lf\n", i/(double) N);
        mgl_data_put_val(x, i/(double) N, i, 0, 0);
        mgl_data_put_val(y, i/(double) N, i, 0, 0);
        mgl_data_put_val(z, i/(double) N, i, 0, 0);
}