title: How to install libX11-dev on mac os x sierra
body: <p>I am working on facial landmarks and therefore I have installed dlib on my mac. When I try to execute a program in Xcode from learnopencv.com, the compiler says:</p>
  
  <pre><code>error "DLIB_NO_GUI_SUPPORT is defined so you can't use the GUI code. Turn DLIB_NO_GUI_SUPPORT off if you want to use it."
  error "Also make sure you have libx11-dev installed on your system"
  </code></pre>
  
  <p>I already installed XQuartz. I don't know what to do anymore. Can anyone help me out here? </p>