title: glMultiDraw functions and gl_InstanceID
body: <p>When I look at the documentation of <a href="https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glMultiDrawElementsIndirect.xhtml" rel="nofollow noreferrer"><code>glMultiDrawElementsIndirect</code></a> (or in the <a href="https://www.khronos.org/opengl/wiki/GLAPI/glMultiDrawElementsIndirect" rel="nofollow noreferrer">Wiki</a>) it says that a single call to <code>glMultiDrawElementsIndirect</code> is equivalent to repeatedly calling <code>glDrawElementsIndirect</code> (just with different parameters).</p>
  
  <p>Does that mean that <code>gl_InstanceID</code> will reset for each of these "internal" calls? And if so, how am I able to tell all these calls apart in my vertex shader?</p>
  
  <p>Background: I'm trying to draw all my different meshes all at once. But I need some way to know to which mesh the vertex, I'm processing in my vertex shader, belongs.</p>