Using glut, how do I make it so I can move an object around in a scene by clicking and dragging it around?

I have written a program that creates a room that currently contains a triangle. I want to make more objects like this triangle, but I also want to add functionality that allows me to move the objects by clicking on them and dragging them. I am thinking the best way would be to create some sort of template/prototype etc. etc. that has the geometric data passed via a constructor but has a function for moving it around by mouse, but I am unsure if I have it right, and I am not entirely sure about what I actually need to do to get this working like that. Here is my current code, it allows rotation of scene using direction keys, but I am unsure how to make it so I can click on an object and drag it at this point (I have the beginnings of something I was trying for this commented out because I don't think it would work, but if it will let me know how):

#include <stdio.h>
#include <stdarg.h>
#include <math.h>
#include <stdlib.h>
#include <GL/glut.h>


void display();
void viewButtons();

//const double ZoomSTEP = 0.2;
//const double zoomFactor = 1.03;
double rotationY = 0;
double rotationX = 0;
// Mouse positions, normalized to [0,1].
//double xMouse = 0.5;
//double yMouse = 0.5;

//GLdouble startView = 2.0;

void display()
{
//Clear the screen and clear z-buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Reset transformations
glLoadIdentity();

// Rotate when user changes rotate_x and rotate_y
glRotatef(rotationX, 1.0, 0.0, 0.0);
glRotatef(rotationY, 0.0, 1.0, 0.0);
glBegin(GL_POLYGON);
//Vertices and colors
glColor3f(1.0, 0.0, 0.0);     
glVertex3f(0.5, -0.5, 0.5);      // P1 is red
glColor3f(0.0, 1.0, 0.0);    
glVertex3f(0.5, 0.5, 0.5);      // P2 is green
glColor3f(0.0, 0.0, 1.0);     
glVertex3f(-0.5, 0.5, 0.5);      // P3 is blue
glColor3f(1.0, 0.0, 1.0);     
glVertex3f(-0.5, -0.5, 0.5);      // P4 is purple

glEnd();

/*// White side - BACK
glBegin(GL_POLYGON);
glColor3f(1.0, 1.0, 1.0);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glEnd();*/

// Purple side - RIGHT
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 1.0);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, -0.5, 0.5);
glEnd();

// Green side - LEFT
glBegin(GL_POLYGON);
glColor3f(0.0, 1.0, 0.0);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, 0.5, 0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, -0.5, -0.5);
glEnd();

// Blue side - TOP
glBegin(GL_POLYGON);
glColor3f(0.0, 0.0, 1.0);
glVertex3f(0.5, 0.5, 0.5);
glVertex3f(0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, -0.5);
glVertex3f(-0.5, 0.5, 0.5);
glEnd();

// Red side - BOTTOM
glBegin(GL_POLYGON);
glColor3f(1.0, 0.0, 0.0);
glVertex3f(0.5, -0.5, -0.5);
glVertex3f(0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, 0.5);
glVertex3f(-0.5, -0.5, -0.5);
glEnd();

glBegin(GL_POLYGON);
glColor3f(0.5, 0.6, 0.3);
glVertex3f(0.3, 0.1, 0.5);
glVertex3f(0.4, 0.1, 0.5);
glVertex3f(0.2, -0.2, 0.1);
glEnd();

glFlush();
glutSwapBuffers();


}

void viewButtons(int button, int x, int y)
{
if (button == GLUT_KEY_RIGHT)
    rotationY += 5;

else if (button == GLUT_KEY_LEFT)
    rotationY -= 5;

else if (button == GLUT_KEY_UP)
    rotationX += 5;

else if (button == GLUT_KEY_DOWN)
    rotationX -= 5;

//update display
glutPostRedisplay();
}

int main(int argc, char **argv) {

// init GLUT and create window

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);

glutInitWindowPosition(100, 100);
glutInitWindowSize(720, 640);
glutCreateWindow("Room with objects");

// register callbacks
glutDisplayFunc(display);
glutSpecialFunc(viewButtons);
glEnable(GL_DEPTH_TEST);
// enter GLUT event processing cycle
glutMainLoop();

return 1;
}