title: openGL GLSL Shader: Draw a Circle on a flat polygon
body: <p>I'm looking for a way to draw something similar to these "knobs" with an GLSL shader</p>
  
  <p><img src="https://i.stack.imgur.com/fQ5OL.jpg" alt="alt text"></p>
  
  <p>I only want to draw the coloured circles, and my application is not for a knob rather a funky progress meter. Is it possible to draw circles (or more specifically arcs) on a flat polygon just by using a shader? And how would one start the process?</p>