OpenGL: retrieve raw vertex and index buffer from displayed objects in OpenGL

Question

My apologies for the long code sample. Here is my sample code:

#include <iostream>
#include <cstdlib>
#include <GL/glut.h>
using namespace std;


//#include "glutint.h"

/* Rim, body, lid, and bottom data must be reflected in x and
   y; handle and spout data across the y axis only.  */

static int patchdata[][16] =
{
    /* rim */
  {102, 103, 104, 105, 4, 5, 6, 7, 8, 9, 10, 11,
    12, 13, 14, 15},
    /* body */
  {12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
    24, 25, 26, 27},
  {24, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36,
    37, 38, 39, 40},
    /* lid */
  {96, 96, 96, 96, 97, 98, 99, 100, 101, 101, 101,
    101, 0, 1, 2, 3,},
  {0, 1, 2, 3, 106, 107, 108, 109, 110, 111, 112,
    113, 114, 115, 116, 117},
    /* bottom */
  {118, 118, 118, 118, 124, 122, 119, 121, 123, 126,
    125, 120, 40, 39, 38, 37},
    /* handle */
  {41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52,
    53, 54, 55, 56},
  {53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64,
    28, 65, 66, 67},
    /* spout */
  {68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
    80, 81, 82, 83},
  {80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91,
    92, 93, 94, 95}
};
/* *INDENT-OFF* */

static float cpdata[][3] =
{
    {0.2, 0, 2.7}, {0.2, -0.112, 2.7}, {0.112, -0.2, 2.7}, {0,
    -0.2, 2.7}, {1.3375, 0, 2.53125}, {1.3375, -0.749, 2.53125},
    {0.749, -1.3375, 2.53125}, {0, -1.3375, 2.53125}, {1.4375,
    0, 2.53125}, {1.4375, -0.805, 2.53125}, {0.805, -1.4375,
    2.53125}, {0, -1.4375, 2.53125}, {1.5, 0, 2.4}, {1.5, -0.84,
    2.4}, {0.84, -1.5, 2.4}, {0, -1.5, 2.4}, {1.75, 0, 1.875},
    {1.75, -0.98, 1.875}, {0.98, -1.75, 1.875}, {0, -1.75,
    1.875}, {2, 0, 1.35}, {2, -1.12, 1.35}, {1.12, -2, 1.35},
    {0, -2, 1.35}, {2, 0, 0.9}, {2, -1.12, 0.9}, {1.12, -2,
    0.9}, {0, -2, 0.9}, {-2, 0, 0.9}, {2, 0, 0.45}, {2, -1.12,
    0.45}, {1.12, -2, 0.45}, {0, -2, 0.45}, {1.5, 0, 0.225},
    {1.5, -0.84, 0.225}, {0.84, -1.5, 0.225}, {0, -1.5, 0.225},
    {1.5, 0, 0.15}, {1.5, -0.84, 0.15}, {0.84, -1.5, 0.15}, {0,
    -1.5, 0.15}, {-1.6, 0, 2.025}, {-1.6, -0.3, 2.025}, {-1.5,
    -0.3, 2.25}, {-1.5, 0, 2.25}, {-2.3, 0, 2.025}, {-2.3, -0.3,
    2.025}, {-2.5, -0.3, 2.25}, {-2.5, 0, 2.25}, {-2.7, 0,
    2.025}, {-2.7, -0.3, 2.025}, {-3, -0.3, 2.25}, {-3, 0,
    2.25}, {-2.7, 0, 1.8}, {-2.7, -0.3, 1.8}, {-3, -0.3, 1.8},
    {-3, 0, 1.8}, {-2.7, 0, 1.575}, {-2.7, -0.3, 1.575}, {-3,
    -0.3, 1.35}, {-3, 0, 1.35}, {-2.5, 0, 1.125}, {-2.5, -0.3,
    1.125}, {-2.65, -0.3, 0.9375}, {-2.65, 0, 0.9375}, {-2,
    -0.3, 0.9}, {-1.9, -0.3, 0.6}, {-1.9, 0, 0.6}, {1.7, 0,
    1.425}, {1.7, -0.66, 1.425}, {1.7, -0.66, 0.6}, {1.7, 0,
    0.6}, {2.6, 0, 1.425}, {2.6, -0.66, 1.425}, {3.1, -0.66,
    0.825}, {3.1, 0, 0.825}, {2.3, 0, 2.1}, {2.3, -0.25, 2.1},
    {2.4, -0.25, 2.025}, {2.4, 0, 2.025}, {2.7, 0, 2.4}, {2.7,
    -0.25, 2.4}, {3.3, -0.25, 2.4}, {3.3, 0, 2.4}, {2.8, 0,
    2.475}, {2.8, -0.25, 2.475}, {3.525, -0.25, 2.49375},
    {3.525, 0, 2.49375}, {2.9, 0, 2.475}, {2.9, -0.15, 2.475},
    {3.45, -0.15, 2.5125}, {3.45, 0, 2.5125}, {2.8, 0, 2.4},
    {2.8, -0.15, 2.4}, {3.2, -0.15, 2.4}, {3.2, 0, 2.4}, {0, 0,
    3.15}, {0.8, 0, 3.15}, {0.8, -0.45, 3.15}, {0.45, -0.8,
    3.15}, {0, -0.8, 3.15}, {0, 0, 2.85}, {1.4, 0, 2.4}, {1.4,
    -0.784, 2.4}, {0.784, -1.4, 2.4}, {0, -1.4, 2.4}, {0.4, 0,
    2.55}, {0.4, -0.224, 2.55}, {0.224, -0.4, 2.55}, {0, -0.4,
    2.55}, {1.3, 0, 2.55}, {1.3, -0.728, 2.55}, {0.728, -1.3,
    2.55}, {0, -1.3, 2.55}, {1.3, 0, 2.4}, {1.3, -0.728, 2.4},
    {0.728, -1.3, 2.4}, {0, -1.3, 2.4}, {0, 0, 0}, {1.425,
    -0.798, 0}, {1.5, 0, 0.075}, {1.425, 0, 0}, {0.798, -1.425,
    0}, {0, -1.5, 0.075}, {0, -1.425, 0}, {1.5, -0.84, 0.075},
    {0.84, -1.5, 0.075}
};

static float tex[2][2][2] =
{
  { {0, 0},
    {1, 0}},
  { {0, 1},
    {1, 1}}
};

/* *INDENT-ON* */

static void
teapot(GLint grid, GLdouble scale, GLenum type)
{
  float p[4][4][3], q[4][4][3], r[4][4][3], s[4][4][3];
  long i, j, k, l;

  glPushAttrib(GL_ENABLE_BIT | GL_EVAL_BIT);
  glEnable(GL_AUTO_NORMAL);
  glEnable(GL_NORMALIZE);
  glEnable(GL_MAP2_VERTEX_3);
  glEnable(GL_MAP2_TEXTURE_COORD_2);
  glPushMatrix();
  glRotatef(270.0, 1.0, 0.0, 0.0);
  glScalef(0.5 * scale, 0.5 * scale, 0.5 * scale);
  glTranslatef(0.0, 0.0, -1.5);
  for (i = 0; i < 10; i++) {
    for (j = 0; j < 4; j++) {
      for (k = 0; k < 4; k++) {
        for (l = 0; l < 3; l++) {
          p[j][k][l] = cpdata[patchdata[i][j * 4 + k]][l];
          q[j][k][l] = cpdata[patchdata[i][j * 4 + (3 - k)]][l];
          if (l == 1)
            q[j][k][l] *= -1.0;
          if (i < 6) {
            r[j][k][l] =
              cpdata[patchdata[i][j * 4 + (3 - k)]][l];
            if (l == 0)
              r[j][k][l] *= -1.0;
            s[j][k][l] = cpdata[patchdata[i][j * 4 + k]][l];
            if (l == 0)
              s[j][k][l] *= -1.0;
            if (l == 1)
              s[j][k][l] *= -1.0;
          }
        }
      }
    }
    glMap2f(GL_MAP2_TEXTURE_COORD_2, 0, 1, 2, 2, 0, 1, 4, 2,
      &tex[0][0][0]);
    glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
      &p[0][0][0]);
    glMapGrid2f(grid, 0.0, 1.0, grid, 0.0, 1.0);
    glEvalMesh2(type, 0, grid, 0, grid);
    glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
      &q[0][0][0]);
    glEvalMesh2(type, 0, grid, 0, grid);
    if (i < 6) {
      glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
        &r[0][0][0]);
      glEvalMesh2(type, 0, grid, 0, grid);
      glMap2f(GL_MAP2_VERTEX_3, 0, 1, 3, 4, 0, 1, 12, 4,
        &s[0][0][0]);
      glEvalMesh2(type, 0, grid, 0, grid);
    }
  }
  glPopMatrix();
  glPopAttrib();
}

/* CENTRY */
void APIENTRY 
_glutSolidTeapot(GLdouble scale)
{
  teapot(14, scale, GL_FILL);
}

void APIENTRY 
_glutWireTeapot(GLdouble scale)
{
  teapot(10, scale, GL_LINE);
}

// function prototypes
void disp(void);
void keyb(unsigned char key, int x, int y);


// window identifier
static int win;

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

    //////////
    // INIT //
    //////////

    // initialize glut
    glutInit(&argc, argv);

    // specify the display mode to be RGB and single buffering 
    // we use single buffering since this will be non animated
    glutInitDisplayMode(GLUT_RGBA | GLUT_SINGLE);

    // define the size
    glutInitWindowSize(500,500);

    // the position where the window will appear
    glutInitWindowPosition(100,100);


    // if we would want fullscreen:
    // glutFullScreen();

    // create the window, set the title and keep the 
    // window identifier.
    win = glutCreateWindow("Yet another teapot");

    //////////////
    // CALLBACK //
    //////////////

    glutDisplayFunc(disp);
    glutKeyboardFunc(keyb);

    ////////////
    // OPENGL //
    ////////////

    // define the color we use to clearscreen 
    glClearColor(0.0,0.0,0.0,0.0);



    // enter the main loop
    glutMainLoop();

    return 0;
}


void disp(void){

    // do  a clearscreen
    glClear(GL_COLOR_BUFFER_BIT);

    // draw something

    _glutWireTeapot(0.5);
    // glutSolidTeapot(0.5);
    // glutWireSphere(0.5,100,100);
    // glutSolidSphere(0.5,100,100);
    // glutWireTorus(0.3,0.5,100,100);
    // glutSolidTorus(0.3,0.5,100,100);
    // glutWireIcosahedron();
    // glutSolidIcosahedron();
    // glutWireDodecahedron();
    // glutSolidDodecahedron();
    // glutWireCone(0.5,0.5,100,100);
    // glutSolidCone(0.5,0.5,100,100);
    // glutWireCube(0.5);
    // glutSolidCube(0.5);
}

void keyb(unsigned char key, int x, int y){
    cout << "Pressed key " << key << " on coordinates (" << x << "," << y << ")";
    cout << endl;
    if(key == 'q'){
        cout << "Got q,so quitting " << endl;
        glutDestroyWindow(win);
        exit(0);
    }
}

http://mindfuck.de-brauwer.be/articles/glut/

http://www.it.freebsd.org/pub/Unix/NetBSD/NetBSD-current/xsrc/external/mit/MesaGLUT/dist/src/glut/beos/glut_teapot.c

Are relevant references.

Thank you Misha Koshelev

Answer 1

I'm guessing you want the feedback functionality.