title: OpenCv : draw a white filled polygon
body: <p>I'd like to draw a white filled polygon, with arbitrary angle, in a black IplImage. I know there exists function such as createCircle, but I can't find something similar for polygons. 
  I found  <a href="http://opencv.willowgarage.com/documentation/cpp/core_drawing_functions.html?#cv-fillpoly" rel="nofollow">this</a> , but the use of it is awful, I mean I shouldn't have to go into this just to draw one simple white polygon on a black background...!</p>
  
  <p>The example I found on the OpenCV documentation:</p>
  
  <pre><code>void MyPolygon( Mat img )
  {
     int lineType = 8;
  
     /** Create some points */
     Point rook_points[1][20];
     rook_points[0][0] = Point( w/4.0, 7*w/8.0 );
     rook_points[0][1] = Point( 3*w/4.0, 7*w/8.0 );
     rook_points[0][2] = Point( 3*w/4.0, 13*w/16.0 );
     rook_poi /*** blablabla **/
     rook_points[0][19] = Point( w/4.0, 13*w/16.0) ;
  
     const Point* ppt[1] = { rook_points[0] };
     int npt[] = { 20 };
  
     fillPoly( img,
               ppt,
               npt,
               1,
               Scalar( 255, 255, 255 ),
               lineType );
   }
  </code></pre>
  
  <p>Basically, my question is, how do I put a CvBox2D into fillPoly, to get a mask out of it and finally set the "ROI with angle" that I need?</p>