title: What's the behavior of overlaping Image Barriers?
body: <p>Standard usage of Barriers is relatively straightforward, but I was wondering what is the behavior of two (or more) overlapping Image Barriers (especially with respect to their side effect -- the layout transition). E.g. (pseudocode):</p>
  
  <pre><code>begin( commandBuffer );
  1: write( image );
  2: imageBarrier(
       image,
       src=STAGE_FRAGMENT(from the write at 1:),
       dst=STAGE_FRAGMENT(intended for read in FS of read at 4:),
       appropriate src and dst access flags,
       newLayout=A
     );
  3: imageBarrier(
       image,
       src=STAGE_FRAGMENT(from the write at 1:),
       dst=STAGE_TRANSFER(intended for read by transfer of readT at 5:),
       appropriate src and dst access flags,
       newLayout=B
     );
  4: read( image ); // through vkCmdDraw -- expects layout A
  5: readT( image ); // different kind of read through Transfer -- expects layout B
  end( commandBuffer );
  </code></pre>
  
  <ol>
  <li>Is this even legal? (can you back it up by spec quote?)</li>
  <li>What is the image layout at each point of the program?</li>
  <li>For completeness, what is the proper/best way to write this (one producer, two consumers situation)? (Swap lines 3: and 4: and make it Read-Read dependency?)</li>
  </ol>