title: How to draw transparent polygon?
body: <p>I want to draw a transparent polygon (triangle in this case). But I'm unable to find any examples by searching the web. </p>
  
  <pre><code>// Create image
  Mat image = Mat::zeros( 400, 400, CV_8UC3 );
  
  // Draw a circle 
  /** Create some points */
  Point Treangle_points[1][20];
  Treangle_points[0][0] = Point( 150, 100 );
  Treangle_points[0][1] = Point( 275, 350 );
  Treangle_points[0][2] = Point( 50, 20 );
  
  const Point* ppt[1] = { Treangle_points[0] };
  int npt[] = { 3 };
  
  fillPoly( image, ppt, npt, 1, Scalar( 255, 255, 255 ), 8 );
  imshow("Image",image);
  </code></pre>