title: Bordered rounded rectangle in glsl
body: <p>Hello I am trying to get a fast rounded rectangle glsl shader but I've only managed to do it for a filled rectangle using this function (<a href="https://github.com/marklundin/glsl-sdf-primitives/blob/master/udRoundBox.glsl" rel="noreferrer">https://github.com/marklundin/glsl-sdf-primitives/blob/master/udRoundBox.glsl</a>):</p>
  
  <pre><code>float udRoundBox( vec3 p, vec3 b, float r )
  {
    return length(max(abs(p)-b,0.0))-r;
  }
  </code></pre>
  
  <p>I've been trying to find a version of this that does a border rather than a fill, even tried to come up with one, but no luck. Does anyone have a solution to this?</p>