in the producing shader
                invocation and call memoryBarrier() after the last write.  The consuming
                shader invocation should also use coherent variables.</p>
            </li>
            <li class="listitem">
              <p>Data written to image variables in one rendering pass and read by the
                shader in a later pass need not use coherent variables or
                memoryBarrier().  Calling MemoryBarrier() with the
                SHADER_IMAGE_ACCESS_BARRIER_B