title: How to acquire mapbox-gl-js z-buffer
body: <p>I'm developing webgl application, where I draw detailed building on top of mapbox-gl-js.</p>
  
  <p>Everything goes fine except one detail, I don't know how to acquire depth buffer of every drawn frame. </p>
  
  <p>In some cases my overlay is drawn over extruded by mapbox-gl-js style buildings, but it must be behind it. </p>
  
  <p><a href="https://i.stack.imgur.com/c9p9u.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/c9p9u.png" alt="enter image description here"></a></p>
  
  <p>I see only one possibility to do this correctly - acquire depth buffer from mapbox-gl-js and pass it in to my shader as texture and compare with my actual depth buffer values. </p>
  
  <p>As in deferred rendering technique.</p>
  
  <p>Any possibility to do that? </p>