title: How do I call line or cv::line with OpenCV 3.1?
body: <p>The tutorial I'm following has code like the following:</p>
  
  <pre><code>line( img_matches, ..., ..., Scalar( 0, 255, 0), 4 );
  </code></pre>
  
  <p>where img_matches is just a Mat, the next two arguments are points and then there's a color and a width. I have figured out everything else that changed in OpenCV 3.1 for this tutorial but I cannot figure out how to draw lines. The documentation seems to imply it will simply be cv::line(...), but that is not defined in my namespace, and there's a cvLine in scope, but it is expecting something other than a Mat it seems like.</p>
  
  <p>I'm no kind of C++ programmer, so this may be something basic.</p>
  
  <p>As requested, here are my headers:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;iostream&gt;
  #include "opencv2/core.hpp"
  #include "opencv2/features2d.hpp"
  #include "opencv2/highgui.hpp"
  #include "opencv2/calib3d.hpp"
  #include "opencv2/xfeatures2d.hpp"
  </code></pre>
  
  <p>My code is 99% what's in this tutorial here: <a href="http://docs.opencv.org/3.0-beta/doc/tutorials/features2d/feature_homography/feature_homography.html" rel="nofollow">http://docs.opencv.org/3.0-beta/doc/tutorials/features2d/feature_homography/feature_homography.html</a></p>