Question

I am a beginner at using openGL.

I have used a program which I found over the internet to draw a cube on the screen and translate, scale and rotate it according to certain keyboard strokes.

Bellow, I have attached the code for doing this:

#define  RADDEG  57.29577951f

float XUP[3] = {1,0,0}, XUN[3] = {-1, 0, 0},
  YUP[3] = {0,1,0}, YUN[3] = { 0,-1, 0},
  ZUP[3] = {0,0,1}, ZUN[3] = { 0, 0,-1},
  ORG[3] = {0,0,0};

GLfloat viewangle = 0, tippangle = 0, traj[120][3];

GLfloat d[3] = {0.1, 0.1, 0.1};

GLfloat  xAngle = 0.0, yAngle = 0.0, zAngle = 0.0;

GLfloat scaleF = 0.2;


//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

//  Use arrow keys to rotate entire scene !!!

void Special_Keys (int key, int x, int y)
{
switch (key) {

   case GLUT_KEY_LEFT :  viewangle -= 5;  break;
   case GLUT_KEY_RIGHT:  viewangle += 5;  break;
   case GLUT_KEY_UP   :  tippangle -= 5;  break;
   case GLUT_KEY_DOWN :  tippangle += 5;  break;

   default: printf ("   Special key %c == %d\n", key, key);
}

glutPostRedisplay();
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

void Keyboard (unsigned char key, int x, int y)
{
switch (key) {

   case 'j' : d[0] += 0.1;  break;
   case 'k' : d[0] -= 0.1;  break;
   case 'n' : d[1] += 0.1; break;
   case 'm' : d[1] -= 0.1; break;
   //case 'l' : d[2] += 0.1;  break;

   case 'z' : xAngle += 5;  break;
   case 'x' : yAngle += 5;  break;
   case 'c' : zAngle += 5;  break;

   case 'q' : scaleF += 0.1; break;
   case 'w' : scaleF -= 0.1; break;

   default: cout<< "Redo a valid keystroke;"<<endl;
}

glutPostRedisplay();
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

void Triad (void)
{
glColor3f (1.0, 1.0, 1.0);

glBegin (GL_LINES);
   glVertex3fv (ORG); glVertex3fv (XUP);
   glVertex3fv (ORG); glVertex3fv (YUP);
   glVertex3fv (ORG); glVertex3fv (ZUP);
glEnd ();

glRasterPos3f (1.1, 0.0, 0.0);
glutBitmapCharacter (GLUT_BITMAP_HELVETICA_18, 'X');

glRasterPos3f (0.0, 1.1, 0.0);
glutBitmapCharacter (GLUT_BITMAP_HELVETICA_18, 'Y');

glRasterPos3f (0.0, 0.0, 1.1);
glutBitmapCharacter (GLUT_BITMAP_HELVETICA_18, 'Z');
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

void Draw_Box (void)
{
glBegin (GL_QUADS);

glColor3f(1,0,0);
    glVertex3f(1,1,1);
    glVertex3f(-1,1,1);
    glVertex3f(-1,-1,1);
    glVertex3f(1,-1,1);

    glColor3f(0,1,1);
    glVertex3f(1,1,-1);
    glVertex3f(-1,1,-1);
    glVertex3f(-1,-1,-1);
    glVertex3f(1,-1,-1);

    glColor3f(0,1,0);
    glVertex3f(1,1,1);
    glVertex3f(1,-1,1);
    glVertex3f(1,-1,-1);
    glVertex3f(1,1,-1);

    glColor3f(1,0,1);
    glVertex3f(-1,1,1);
    glVertex3f(-1,-1,1);
    glVertex3f(-1,-1,-1);
    glVertex3f(-1,1,-1);

    glColor3f(0,0,1);
    glVertex3f(1,1,1);
    glVertex3f(-1,1,1);
    glVertex3f(-1,1,-1);
    glVertex3f(1,1,-1);

    glColor3f(1,1,0);
    glVertex3f(1,-1,1);
    glVertex3f(-1,-1,1);
    glVertex3f(-1,-1,-1);
    glVertex3f(1,-1,-1);

glEnd();
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

void redraw (void)
{
int v;

glClear  (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable (GL_DEPTH_TEST);

glLoadIdentity ();

glTranslatef (0, 0, -3);
glRotatef (tippangle, 1,0,0);  // Up and down arrow keys 'tip' view.
glRotatef (viewangle, 0,1,0);  // Right/left arrow keys 'turn' view.

glDisable (GL_LIGHTING);

Triad ();

glPushMatrix ();
   glTranslatef (d[0], d[1], d[2]);    // Move box down X axis.
   glScalef (scaleF, scaleF, scaleF);
   glRotatef (zAngle, 0,0,1);
   glRotatef (yAngle, 0,1,0);
   glRotatef (xAngle, 1,0,0);
   Draw_Box ();
glPopMatrix ();

glutSwapBuffers();
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

void wait ( int seconds )
{
  clock_t endwait;
  endwait = clock () + seconds * CLOCKS_PER_SEC ;
  while (clock() < endwait) {}
}

int main (int argc, char **argv)
{
glutInit               (&argc, argv);
glutInitWindowSize     (900, 600);
glutInitWindowPosition (300, 300);
glutInitDisplayMode    (GLUT_DEPTH | GLUT_DOUBLE);

glutCreateWindow ("Orbital Font Demo");
glutDisplayFunc  (   redraw   );
glutKeyboardFunc (  Keyboard  );
//glutSpecialFunc  (Special_Keys);



glClearColor (0.1, 0.0, 0.1, 1.0);

glMatrixMode   (GL_PROJECTION);
gluPerspective (60, 1.5, 1, 10);
glMatrixMode   (GL_MODELVIEW);
glutPostRedisplay();

glutMainLoop   ();



return 1;
}

//---+----3----+----2----+----1----+---<>---+----1----+----2----+----3----+----4

The thing is that I want to copy this code into another C++ program where I am using openCV libraries to connect my VGA camera. Based on the movements performed in front of the camera, I am classifying the performed movements using a SVM model.
I want to use the output of the SVM model which is basically a integer value and pass it to the openGL code in order to move the cube in the window.

In the above mentioned code, this procedure is performed by using keystrokes, and implicitly the glKeyboardFunc function. What functions should I use in order to connect the output of the SVM model to the redraw function of the above mentioned code?

Answer 1

You should use glutIdle to check whether there is a new frame. If there is you should update textures with new image using glTexSubImage2D*.

*_{You should use a texture to display a custom image.}