title: fill rectangle and apply nonzero winding rule in opengl
body: <p>this is simple rectangle drawing code in opengl..i want to fill the rectangle with some color and want to apply non-zero winding rule to tell the user whether rectangle is filled for inside or outside...how can i achieve this???</p>
  
  <pre><code>#include &lt;cstdlib&gt;
  #include &lt;iostream&gt;
  #include&lt;GL/glut.h&gt;
  
  using namespace std;
  
  #include &lt;GL/glut.h&gt;
  
  void display(void)
  {
     glClear (GL_COLOR_BUFFER_BIT);
  
  
     glColor3f (1.0, 1.0, 1.0);
     glBegin(GL_POLYGON);
        glVertex3f (0.25, 0.25, 0.0);
        glVertex3f (0.75, 0.25, 0.0);
        glVertex3f (0.75, 0.75, 0.0);
        glVertex3f (0.25, 0.75, 0.0);
     glEnd();
  
  
     glFlush ();
  }
  
  void init (void) 
  {
  
     glClearColor (0.0, 0.0, 0.0, 0.0);
  
  
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
  }
  
  
  int main(int argc, char** argv)
  {
     glutInit(&amp;argc, argv);
     glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
     glutInitWindowSize (250, 250); 
     glutInitWindowPosition (100, 100);
     glutCreateWindow ("hello");
     init ();
     glutDisplayFunc(display); 
     glutMainLoop();
     return 0;  
  }
  </code></pre>