title: OpenGL, how to use depthbuffer from framebuffer as usual depth buffer
body: <p>I have frame buffer, with depth component and 4 color attachments with 4 textures</p>
  
  <p>I draw some stuff into it and unbind the buffer after, using 4 textures for fragment shader (deferred lighting).
  Later i want to draw some more stuff on the screen, using the depth buffer from my framebuffer, is it possible?</p>
  
  <p>I tried binding the framebuffer again and specifying glDrawBuffer(GL_FRONT), but it does not work.</p>