[Opensim-users] Scripting: Having fun with C# and UDP

[Jeff Kelley]

That's a thing I was dreaming for years : Linking a physical, real-world
object to an opensim object. You move the object in opensim, the real
object moves. You move the real object, the object in opensim moves. All in
real-time.

Here is a short demo video, in mov and mp4 (H.264) format. If your web
browser can't handle either, download the .mp4 version and open it with
VLC. I don't Youtube, sorry.

http://www.pescadoo.net/tmp/fun_with_udp.mov	(1Mb)
http://www.pescadoo.net/tmp/fun_with_udp.mp4	(1.9Mb)

Right is the familiar Imprudence window. The object with eight yellow bars
is a multi-slider, similar to a mixing desk. Each bar can be clicked and
dragged to the desired value.

Left is a less-familiar window with another application running. The app is
Cycling74' Max/MSP, although that could any app that can animate objects
(graphical or physical) and read/write network sockets.

In this video, i first move the slider in opensim and you see the sliders
in the external app moving. Then I move the sliders in the external app,
and the sliders in opensim move. No delay. Real-time.

But there is more fun. The external app is linked to a physical "control
surface", with motorized sliders. Unfortunately I can't show it in the
video, missing a camcorder. I use a Behringer BCF2000. See it here:

http://www.behringer.com/EN/images/lightboxphotos/BCF2000_P0246_Left_XL.jpg

It is attached to my desktop machine (not the simulator host) via USB/MIDI.
You could as well control lights with DMX, motors with Arduino, a robotic
device, or conversely move an opensim object with a dataglove, or anything
you may imagine.

How does it work?

The opensim object contains two C# script, one for sending and one for
receiving UDP messages using System.Net.Sockets (two scripts are needed
because the receiver runs a forever loop and events can't interrupt). The
simulator host and my desktop machine (both on same LAN) communicate
through UDP messages.

I omit the prim handling script for brevity. It is pure LSL and there is
nothing new here. It reads and writes couples of (track_number, value) via
link messages to the C# sender and receiver. Since i am a beginner in C#,
there is much room for improvement. I was not able to declare a 'use'
clause, so I had to fully qualify each instance and method, making the code
quite ugly.



UDP Sender script
-----------------

//c#

public static void SendUDPPacket (string hostNameOrAddress,
                                  int destinationPort, string data) {

    // Resolve the host name to an IP Address
    System.Net.IPAddress[] ipAddresses
        = System.Net.Dns.GetHostAddresses(hostNameOrAddress);

    // Use the first IP Address in the list
    System.Net.IPAddress destination = ipAddresses[0];
    System.Net.IPEndPoint endPoint
        = new System.Net.IPEndPoint(destination, destinationPort);

    byte[] buffer = System.Text.Encoding.ASCII.GetBytes(data);

    // Send the packet
    System.Net.Sockets.Socket socket = new System.Net.Sockets.Socket
        (System.Net.Sockets.AddressFamily.InterNetwork,
         System.Net.Sockets.SocketType.Dgram,
         System.Net.Sockets.ProtocolType.Udp);

    socket.SendTo(buffer, endPoint);
    socket.Close();
}

int SLIDER_IN  = 101;       // Link Messages input
int SLIDER_OUT = 102;       // Link Messages output

string  remoteAddr = "192.168.0.21";
int     remotePort = 51000;

// Receiving a link message from the sliders

public void default_event_link_message (
    LSL_Types.LSLInteger sender_num,
    LSL_Types.LSLInteger num,
    LSL_Types.LSLString str,    // Channel number
    LSL_Types.LSLString id) {   // Channel value

    // Send the message over UDP

    if (num == SLIDER_OUT)
        SendUDPPacket (remoteAddr, remotePort, str+" "+id);
}



UDP Receiver script
-------------------

//c#

public static System.Net.Sockets.Socket BindUDPSocket (int listenPort) {

    // Local endpoint
    System.Net.IPEndPoint endPoint
        = new System.Net.IPEndPoint(System.Net.IPAddress.Any, listenPort);

    // Create socket
    System.Net.Sockets.Socket socket = new System.Net.Sockets.Socket
        (System.Net.Sockets.AddressFamily.InterNetwork,
         System.Net.Sockets.SocketType.Dgram,
         System.Net.Sockets.ProtocolType.Udp);

    // Bind socket
    socket.Bind(endPoint);
    return socket;
}


int listenPort = 50000;

int SLIDER_IN  = 101;       // Link Messages input
int SLIDER_OUT = 102;       // Link Messages output

public void default_event_state_entry() {
    System.Net.Sockets.Socket socket = BindUDPSocket (listenPort);
    byte[] buffer = new byte[1024];

    // Receiving a message from UDP (loop forever)

    while (true) {
        socket.Receive(buffer);
        string msg = System.Text.ASCIIEncoding.ASCII.GetString(buffer);

        // 1st word is Channel number
        // 2nd word is Channel value

        string[] parse = msg.Split(' ');

        // Send the message using LinkMessage

        llMessageLinked (LINK_THIS, SLIDER_IN, parse[0], parse[1]);

        System.Array.Clear (buffer, 0, 1024);
    }
}


Thanks to Nick Olsen for C# code
http://nickstips.wordpress.com/2010/09/03/c-creating-and-sending-udp-packets/