digraph
{
        //graph [ranksep=1 nodesep=1]
        graph [nodesep=0.5, margin=0]
	fontname="Computer Modern,Arial,sans-serif"
	node [fontname="Helvetica,Arial,sans-serif"]
	edge [fontname="Helvetica,Arial,sans-serif"]
	layout=dot
	labelloc = "t"

        node [shape=plaintext]

        read [label=<<b>read buffer</b>> height=0]
        write [label=<<b>write buffer</b>> height=0]
        shader [label=<<b>fragment shader</b>> height=0]

        particle_stateA [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0" CELLPADDING="4">
  <TR>
    <TD COLSPAN="2" ROWSPAN="2">state </TD>
    <TD BGCOLOR="chartreuse2" PORT="src">a</TD>
  </TR>
  <TR>
    <TD BGCOLOR="azure3">b</TD>
  </TR>
</TABLE>>]

        particle_stateB [label=<
<TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0" CELLPADDING="4">
  <TR>
    <TD BGCOLOR="azure3">a</TD>
    <TD COLSPAN="2" ROWSPAN="2">state</TD>
  </TR>
  <TR>
    <TD BGCOLOR="chartreuse2" PORT="dst">b</TD>
  </TR>
</TABLE>>]

        node [shape=ellipse]
        simulation [label="arbitrary\ncomputation"]

        edge [style=invis]
	rank=same {read -> shader -> write}
	read -> particle_stateA
	shader -> simulation
	write -> particle_stateB

        subgraph program {

	edge [weight=1000 style=dashed]

	// uncomment to hide the grid
	//edge [style=invis]

        //
        // vertex_buffer_copy * 4

	edge [weight=1000 style=solid]

	rank=same {
          particle_stateA:src -> simulation:w
          simulation:e -> particle_stateB:dst
        }

        }
}