Rotating a cone in function of time around its vertex with datas from a txt file

I have a txt file with datas in function of time of the position of the center of mass of a top rotating ( in 3D ). So I would want to represent this top with a cone and the datas i have should represent the center of the basis of cone in time rotating around the vertex.

I have a code representing a cone and I managed working out how to rotate it around the base. However I didn't manage to rotate it around its Vertex . I also have no idea how to move the cone with my datas.

#include <GL\glut.h>

GLfloat xRotated, yRotated, zRotated;
// Cone
GLdouble base=1;
GLdouble height=1.5;
GLint slices =50;
GLint stacks =50;


void displayCone(void)
{
    glMatrixMode(GL_MODELVIEW);
    // clear the drawing buffer.
    glClear(GL_COLOR_BUFFER_BIT);
    // clear the identity matrix.
    glLoadIdentity();
    // traslate the draw by z = -4.0
    // Note this when you decrease z like -8.0 the drawing will looks       far , or smaller.
    glTranslatef(0.0,0.0,-4.5);
    // Red color used to draw.
    glColor3f(0.8, 0.2, 0.1); 
    // changing in transformation matrix.
    // rotation about X axis
    glRotatef(xRotated,1.0,0.0,0.0);
    // rotation about Y axis
    glRotatef(yRotated,0.0,1.0,0.0);
    // rotation about Z axis
    glRotatef(zRotated,0.0,0.0,1.0);
    // scaling transfomation 
    glScalef(1.0,1.0,1.0);
    // built-in (glut library) function , draw you a Cone.

    glutSolidCone(base,height,slices,stacks);
    // Flush buffers to screen

    glFlush();        
    // sawp buffers called because we are using double buffering 
    // glutSwapBuffers();
}


void idleCone(void)
{
    xRotated += 0.1;
    yRotated += 0.1;
    zRotated += 0.1; 

    displayCone();
}


int main (int argc, char **argv)
{
    //Initialize GLUT
    glutInit(&argc, argv);
    //double buffering used to avoid flickering problem in animation
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);  
    // window size
    glutInitWindowSize(400,350);
    // create the window 
    glutCreateWindow("Cone Rotating Animation");
    glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
    xRotated = yRotated = zRotated = 30.0;
    xRotated=33;
    yRotated=40;
    glClearColor(0.0,0.0,0.0,0.0);
    //Assign  the function used in events
    glutDisplayFunc(displayCone);
    glutReshapeFunc(reshapeCone);
    glutIdleFunc(idleCone);
    //Let start glut loop
    glutMainLoop();
    return 0;
}

I already managed to represent the center of mass moving in 3D with Gnuplot but it would be much more beautiful to do it with a cone rotating with OpenGL

Solution

If you want to rotate the cone around its top, then you've to translate the cone in this way, that the top of the cone is in the origin:

glTranslatef(0.0, 0.0, -height);

This has to be done before the rotation and scaling is applied. Since glTranslate (and other matrix transformations) multiply the current matrix by a new transformation matrix, the glTranslate instruction has to be done after the other model transformations like glRotate and glScale:

void displayCone(void)
{
    glMatrixMode(GL_MODELVIEW);
    // clear the drawing buffer.
    glClear(GL_COLOR_BUFFER_BIT);
    // clear the identity matrix.
    glLoadIdentity();
    // traslate the draw by z = -4.0
    // Note this when you decrease z like -8.0 the drawing will looks       far , or smaller.
    glTranslatef(0.0,0.0,-4.5);
    // Red color used to draw.
    glColor3f(0.8, 0.2, 0.1); 
    // changing in transformation matrix.
    // rotation about X axis
    glRotatef(xRotated,1.0,0.0,0.0);
    // rotation about Y axis
    glRotatef(yRotated,0.0,1.0,0.0);
    // rotation about Z axis
    glRotatef(zRotated,0.0,0.0,1.0);

    // scaling transfomation 
    glScalef(1.0,1.0,1.0);
    // built-in (glut library) function , draw you a Cone.

    // move the peak of the cone to the origin
    glTranslatef(0.0, 0.0, -height);

    glutSolidCone(base,height,slices,stacks);
    // Flush buffers to screen

    glFlush();        
    // sawp buffers called because we are using double buffering 
    // glutSwapBuffers();
}

Extension according to the comment:

Could you add a short code snipped to help me understanding what I should do to rotate the cone with the datas stored in the array ?

See how to read a file line by line Read file line by line using ifstream in C++. In the following example, store the data to a std::vector, where each element consists of an std::array of 3 GLfloat:

#include <vector>
#include <array>
#include <fstream>
#include <string>
#include <sstream>

void ReadData( const char *fileName, std::vector<std::array<GLfloat, 3>> &data )
{
    std::ifstream dataFile(fileName);
    std::string line;
    while (std::getline(dataFile, line))
    {
        std::istringstream insstr(line);
        GLfloat x, y, z;
        if (!(insstr >> x >> y >> z))
            break; // reading error

        data.push_back( { x, y, z } );
    }
}

Read the data and access the 3 angles by an index (e.g. j):

std::vector<std::array<GLfloat, 3>> data;

ReadData( "mydata.txt", data );

xRotated = data[j][0];
yRotated = data[j][1];
zRotated = data[j][2];