void display()
{
    glClearColor(0,0,0,0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glTranslatef(1.5f+X, 0.0f+Z, -7.0f+Y);
    glRotatef(r,0.0f,1.0f,0.0f);
    //cube
    glBegin(GL_QUADS);
     //top
    glColor3f(1.0f,0.0f,0.0f);     //red
     glVertex3d(1.0f  ,1.0f ,1.0f);
     glVertex3d(-1.0f ,1.0f ,1.0f);
     glVertex3d(1.0f  ,1.0f ,-1.0f);
     glVertex3d(-1.0f ,1.0f ,-1.0f);
    //bot
    glColor3f(0.0f,0.0f,1.0f);     //blue
     glVertex3d(1.0f  ,-1.0f ,1.0f);
     glVertex3d(-1.0f ,-1.0f ,1.0f);
     glVertex3d(1.0f  ,-1.0f ,-1.0f);
     glVertex3d(-1.0f ,-1.0f ,-1.0f);
    //left
    glColor3f(0.0f,1.0f,0.0f);     //green
     glVertex3d(-1.0f ,1.0f  ,1.0f);
     glVertex3d(-1.0f ,-1.0f ,1.0f);
     glVertex3d(-1.0f ,1.0f  ,-1.0f);
     glVertex3d(-1.0f ,-1.0f ,-1.0f);
     //right
    glColor3f(1.0f,1.0f,0.0f);     //yellow
     glVertex3d(1.0f  ,1.0f  ,1.0f);
     glVertex3d(1.0f  ,-1.0f ,1.0f);
     glVertex3d(1.0f  ,1.0f  ,-1.0f);
     glVertex3d(1.0f  ,-1.0f ,-1.0f);
     //front
    glColor3f(1.0f,0.0f,1.0f);     //purple
     glVertex3d(1.0f  ,1.0f  ,1.0f);
     glVertex3d(-1.0f ,1.0f  ,1.0f);
     glVertex3d(1.0f  ,-1.0f ,1.0f);
     glVertex3d(-1.0f ,-1.0f ,1.0f);
     //back
    glColor3f(1.0f,1.0f,1.0f);     //white
     glVertex3d(1.0f  ,1.0f  ,-1.0f);
     glVertex3d(-1.0f ,1.0f  ,-1.0f);
     glVertex3d(1.0f  ,-1.0f ,-1.0f);
     glVertex3d(-1.0f ,-1.0f ,-1.0f);
    glEnd();

    glutSwapBuffers();
}