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OLA Client API
From wiki.openlighting.org
Contents
Warning: This documentation may be out of date. If in doubt check the code in the ola-examples package.
OLA provides a C++ client library which allows other applications to send/receive DMX as well as control the OLA server. When writing a client application, you have a choice between two client APIs. There was a third API, the OlaClient, but that was deprecated in Feb 2013. It will be removed in a future release and should not be used in new code.
Compiler & Linker Flags
To correctly build and link against libola you'll need to pass the right options to your build system. OLA installs a pkg-config file with the right flags. To get the flags run:
$ pkg-config --cflags --libs libola -I/usr/local/include -L/usr/local/lib -lola -lolacommon -lprotobuf
If you're using autotools, you can add
PKG_PROG_PKG_CONFIG PKG_CHECK_MODULES(libola, [libola >= 0.8.26])
to configure.ac
Different Client APIs
If you want to:
- Only send DMX
- Use StreamingClient.h . This sets up a unidirectional channel between the client and the OLA server.
- Do any of the following send DMX, receive DMX, patch ports, control RDM devices
- Use the OlaCallbackClient which can be setup using the OlaCallbackClientWrapper
OlaClient - DEPRECATED, DO NOT USE
The OlaClient class provides a SetObserver() method which takes an object of type OlaClientObserver. When calls to the OlaClient object complete, the appropriate method is call on the OlaClientObserver object. The following diagrams attempts to show this (the red parts are the bit the client application provides).
class Observer: public ola::OlaClientObserver {
public
Observer() {}:
void ForceRDMDiscoveryComplete(unsigned int universe,
const string &error) {
// something here
}
};
Observer observer();
unsigned int universe = 1;
client->SetObserver(&observer);
client->ForceDiscovery(universe);
OlaCallbackClient
On the other hand, the OlaCallbackClient takes a Callback object whenever a method is called.
void ForceRDMDiscoveryComplete(unsigned int universe, string &error) {
// fill this in
}
unsigned int universe = 1;
client->ForceDiscovery(
universe,
ola::NewSingleCallback(&ForceRDMDiscoveryComplete, universe));
The Callbacks used in OlaCallbackClient are much more flexible than the Observer model in OlaClient. It's recommended that all new code use OlaCallbackClient.
Wrapper Classes
The constructors of both OlaClient and OlaCallbackClient take a pointer to a Connected Socket object. While this is useful for testing, most clients don't care about the details of creating a socket, connecting to the OLA server etc. This is where the client wrapper classes come in. They take care of setting up the connection to the server and provide a way to access the OlaClient* object and the underlying SelectServer object.
#include <ola/OlaClientWrapper.h>
#include <ola/OlaCallbackClient.h>
int main() {
ola::OlaCallbackClientWrapper wrapper;
if (!wrapper.Setup())
//setup failed
return -1;
// Get the underlying OlaCallbackClient object
ola::OlaCallbackClient *client = wrapper.GetClient();
// Get the underlying SelectServer object
ola::network::SelectServer *ss = client->GetSelectServer();
// do stuff here
}
Note that for historical reasons, the OlaClientWrapper class is also referred to as SimpleClient.
Example I: Sending an DMX update using the StreamingClient
The simplest interface to OLA is the StreamingClient which just allows an application to send DMX data to the OLA server
#include <stdlib.h>
#include <ola/DmxBuffer.h>
#include <ola/Logging.h>
#include <ola/StreamingClient.h>
#include <iostream>
using std::cout;
using std::endl;
int main(int argc, char *argv[]) {
unsigned int universe = 1; // universe to use for sending data
unsigned int i;
// turn on OLA logging
ola::InitLogging(ola::OLA_LOG_WARN, ola::OLA_LOG_STDERR);
// Create a new DmxBuffer to hold the data
ola::DmxBuffer buffer;
// set all channels to 0
buffer.Blackout();
// create a new client and set the Error Closure
ola::StreamingClient ola_client;
// Setup the client, this connects to the server
if (!ola_client.Setup()) {
cout << "Setup failed" << endl;
exit(1);
}
// send the data to the ola server
for (i = 0; i < 100; i++) {
buffer.SetChannel(0, i);
if (!ola_client.SendDmx(universe, buffer)) {
cout << "Send DMX failed" << endl;
exit(1);
}
usleep(20000); // sleep for 20ms between updates
}
// close the connection
ola_client.Stop();
return 0;
}
Note there isn't any need to poll for updates from the server in this case because the communication is all one way (client -> server). This also means that you can't receive DMX data or modify state on the server (like port patching and device parameters) when using the StreamingClient.
Also take note of the call to usleep(). Without this you're likely to fill the network socket buffer at which point the client code will detect an error and close the socket (you may need to increase the number of loop iterations to trigger this).
Example II: Sending an DMX update using the SimpleClient
This example connects to the OLA Server and sends one DMX update just like the example above but instead uses OlaClient & OlaClientWrapper. It's about as basic as you can get because it requires no callbacks and exits immediately.
#include <ola/DmxBuffer.h>
#include <ola/Logging.h>
#include <ola/OlaClientWrapper.h>
#include <ola/OlaClient.h>
int main() {
ola::InitLogging(ola::OLA_LOG_WARN, ola::OLA_LOG_STDERR);
ola::DmxBuffer buffer;
buffer.Blackout();
// some dummy dmx data
buffer.SetChannel(0, 255);
ola::OlaClientWrapper wrapper;
if (!wrapper.Setup())
//setup failed
return -1;
// Get the underlying OlaClient object
ola::OlaClient *client = wrapper.GetClient();
// Send the DMX data
client->SendDmx(1, buffer);
}
Example III: Sending multiple updates
The previous example only sent a single DMX update before exiting. 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/DmxBuffer.h>
#include <ola/network/SelectServer.h>
#include <ola/Logging.h>
#include <ola/OlaClient.h>
#include <ola/OlaClientWrapper.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) {
buffer.Blackout();
m_buffer.SetChannel(0, MAX_DMX);
}
// Called on timeout
bool SendDmx() {
m_buffer.SetChannel(1, m_tick)
m_buffer.SetChannel(2, MAX_DMX - m_tick)
m_client->SendDmx(1, buffer);
m_tick++;
m_tick %= MAX_DMX + 1;
// we must return true else we'll get canceled
return true;
}
private:
unsigned int m_tick;
ola::DmxBuffer m_buffer;
ola::OlaClient *m_client;
};
int main() {
ola::InitLogging(ola::OLA_LOG_WARN, ola::OLA_LOG_STDERR);
ola::OlaClientWrapper wrapper;
if (!wrapper.Setup())
return -1;
// Create a timeout and register it
DmxTimeout timeout(wrapper.GetClient());
ola::network::SelectServer ss = wrapper.GetSelectServer();
ss->RegisterRepeatingTimeout(TIMEOUT_MS,
ola::NewClosure(&timeout, &DmxTimeout::SendDmx));
// 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 RegisterRepeatingTimeout 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 IV: Receiving DMX data
The forth example shows how to listen and respond to event from the OLA server.
#include <ola/Logging.h>
#include <ola/OlaCallbackClientWrapper.h>
static const unsigned int UNIVERSE = 1;
void NewDmx(unsigned int universe,
const DmxBuffer &data,
const std::string &error) {
OLA_INFO << "Received " << (int) data.Size() <<
" channels for universe " << (int) universe;
}
int main() {
ola::InitLogging(ola::OLA_LOG_INFO, ola::OLA_LOG_STDERR);
ola::OlaCallbackClient wrapper;
if (!wrapper.Setup())
return -1;
ola::OlaClient *client = simple_client.GetClient();
// Set the observer and register our interest in this universe
client->SetDmxCallback(UNIVERSE, NewCallback(&NewDmx));
client->RegisterUniverse(UNIVERSE, ola::REGISTER);
simple_client.GetSelectServer()->Run();
}
Example V: 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.
