digraph G {
    compound=true;
    rankdir=LR;

    gs [label="Game State"];    
    client [label="Client"];
    server [label="Server"];
    physics [label="Physics"];
    graphics [label="Graphics"];
//    internet [label="Teh Internets", shape=polygon];    

    subgraph cluster0 {
        label = "Network";
	{rank=source; client; server;}
	client;
	server;	
	color = black;
    }

    subgraph cluster1 {
        label = "Game Engine";
	{rank=min; gs; physics;}
	gs;
	physics;
	color = black;
    }

    {rank=sink; input; graphics;}
 //   client->server [dir=both];
    client->server;
    server->client;

    gs->physics;	
    physics->graphics [ltail=cluster1];  
    input->gs [lhead=cluster1];    
//   client->internet [ltail=cluster0];
//   internet->server [lhead=cluster0];

    gs->server [lhead=cluster0,dir=both];
}