title: How to draw part of a circle(Opengl/GLFW)
body: <p>I'm trying to draw only a <strong>sector/part</strong> of a 3d circle - 2 angles are given(start,end), the coordinates of the center, the radius and the width of the circle.
  I painted in Photoshop what The result must be like. 
  <img src="https://i.imgur.com/uhOE2Wd.png" alt="sector of a circle"></p>
  
  <p>Could you help me to do that (2d examples, with 1 simple curved line, works too)? Just want to understand how to do it...</p>
  
  <p>p.s.Sorry for the bad English</p>