OLA Client API

Note: This refers to the most recent version of OLA [>= 0.3.0]

OLA provides a client library which allows other applications to send/receive DMX as well as control the OLA server. To cater for different application requirements, a SimpleClient helper class is provided which can be used to perform the client setup / management.

Example I: Sending an DMX update

This first client simply connects to the OLA Server and sends one DMX update. It's about as simple as you can get because it requires no callbacks and exits immediately. We use two classes in this example, ola::SimpleClient, and ola::OlaClient.

#include <ola/SimpleClient.h>
 
int main() {
  // some dummy dmx data
  dmx_t dmx_data[] = {0, 128, 255};

  ola::SimpleClient simple_client;
  if (!simple_client.Setup())
    //setup failed
    return -1;

  // Get the underlying OlaClient
  ola::OlaClient *client = simple_client.GetClient();

  // Send the DMX data 
  client->SendDmx(1, dmx_data, sizeof(dmx_data));
}

The main class used to communicate with the LLA Server is OlaClient. For ease of use, the SimpleClient class sets up OlaClient with a connection to an LLA Server running on the localhost:LLA_DEFAULT_PORT. You can call GetClient() on a SimpleClient instance to get a pointer to the underlying OlaClient.

Example II: Sending multiple updates

The previous example only sent a single DMX update before quitting. This next example adds a timeout which sends DMX every 50ms. This introduces a new class SelectServer which is used for registering timeouts.

 #include <ola/network/SelectServer.h>
 #include <ola/SimpleClient.h>
 #include <ola/Closure.h>
 
 // Maximum value of a dmx channel
 static const unsigned int MAX_DMX = 255;
 // How often to send updates
 static const unsigned int TIMEOUT_MS = 50;
 
 class DmxTimeout {
   public:
     DmxTimeout(ola::OlaClient *client): m_tick(0),
                                         m_client(client) {}
 
     // Called on timeout
     int SendDmx() {
       m_dmx_data[0] = MAX_DMX;
       m_dmx_data[1] = m_tick;
       m_dmx_data[2] = MAX_DMX - m_tick;
       m_client->SendDmx(1, m_dmx_data, sizeof(m_dmx_data));
       m_tick++;
       m_tick %= MAX_DMX + 1;
       // we must return 0 else we get canceled
       return 0;
     }
   private:
     unsigned int m_tick;
     dmx_t m_dmx_data[3];
     ola::OlaClient *m_client;
 };
 
 int main() {
   ola::SimpleClient simple_client;
 
   if (!simple_client.Setup())
     return -1;
 
   // Create a timeout and register it
   DmxTimeout timeout(simple_client.GetClient());
   ola::network::SelectServer ss = simple_client.GetSelectServer();
   ss->RegisterTimeout(TIMEOUT_MS,
                       ola::NewClosure(&timeout, &DmxTimeout::SendDmx),
                       true); // we want this to repeat
 
   // Start the main loop
   ss->Run();
 }

In this example we create DmxTimeout class whose SendDmx() method is called every time the timer expires.

The other important part here is the SelectServer. As well as the RegisterTimeout method we've used above, this can also be used to register sockets so we can respond to network activity. The Run() method starts the main event processing loop which will halt if an error occurs or Terminate() is called.

Example III: Receiving DMX data

The third example shows how to listen and respond to event from the LLA server.

#include <ola/SimpleClient.h>

static const unsigned int UNIVERSE = 1;

class OurObserver: public ola::OlaClientObserver {
  public:
    // Called when new DMX values arrive
    void NewDmx(unsigned int universe, unsigned int length,
                dmx_t *data, const std::string &error) {
      printf("received %d channels for universe %d\n",
             length, universe);
    }
};

int main() {
  ola::SimpleClient simple_client;
  OurObserver observer;

  if (!simple_client.Setup())
    return -1;

  ola::OlaClient *client = simple_client.GetClient();
  // Set the observer and register our interest in this universe
  client->SetObserver(&observer);
  client->RegisterUniverse(UNIVERSE, ola::REGISTER);
  simple_client.GetSelectServer()->Run();
}

Here we inherit from the OlaClientObserver class and override the methods we're interested in receiving notification for.

In the main function we set the observer object and register our interest in a universe.

Example IV: More complex client

The above is all well and good but what if the main application has it's own event processing loop? An example of this is a GTK/Glib application which uses GMainLoop.

On the other hand, what if you're not connecting to the LLA Server over TCP? Sometimes it may be desirable to embed the LLA server within the main application.

Bypassing the SimpleClient and using OlaClient directly addresses both these problems.

#include <ola/OlaClient.h>
#include <ola/select_server/SelectServer.h>
#include <ola/select_server/Socket.h>

using ola::select_server::PipeSocket;

int main() {
  // Create the select server
  ola::select_server::SelectServer ss;

  // Create the pipe socket to talk to the server on
  PipeSocket *pipe_socket = new PipeSocket();
  if (!pipe_socket->Init())
    return -1;

  // Remember to add this socket to the SelectServer
  ss.AddSocket(pipe_socket);

  // Setup the OlaClient
  ola::OlaClient client(pipe_socket);
  if (!client.Setup())
    return -1;

  // At this point the client is setup. We then need to setup the LLAServer
  // ...

  // Once that is done we add the pipe as a new connection
  ola_server->NewConnection(m_pipe_socket->OppositeEnd());
}

This example shows how we can create our own instance of a ConnectedSocket (PipeSocket is a subclass of ConnectedSocket) and pass it to the OlaClient to use. This code is very similar to what SimpleClient does under the hood.