Tutorial - Part 6: Binding objects

Tutorial - Part 5: Capturing video frames | Index

In this tutorial we show how to bind to an object so that we can receive events and call methods on the object.

Let take a look at the following application to start.

#include <pipewire/pipewire.h>
struct data {
struct pw_main_loop *loop;
struct pw_context *context;
struct pw_core *core;
struct pw_registry *registry;
struct spa_hook registry_listener;
struct pw_client *client;
struct spa_hook client_listener;
};
/* [client_info] */
static void client_info(void *object, const struct pw_client_info *info)
{
struct data *data = object;
const struct spa_dict_item *item;
printf("client: id:%u\n", info->id);
printf("\tprops:\n");
spa_dict_for_each(item, info->props)
printf("\t\t%s: \"%s\"\n", item->key, item->value);
pw_main_loop_quit(data->loop);
}
static const struct pw_client_events client_events = {
PW_VERSION_CLIENT_EVENTS,
.info = client_info,
};
/* [client_info] */
/* [registry_event_global] */
static void registry_event_global(void *_data, uint32_t id,
uint32_t permissions, const char *type,
uint32_t version, const struct spa_dict *props)
{
struct data *data = _data;
if (data->client != NULL)
return;
if (strcmp(type, PW_TYPE_INTERFACE_Client) == 0) {
data->client = pw_registry_bind(data->registry,
id, type, PW_VERSION_CLIENT, 0);
pw_client_add_listener(data->client,
&data->client_listener,
&client_events, data);
}
}
/* [registry_event_global] */
static const struct pw_registry_events registry_events = {
PW_VERSION_REGISTRY_EVENTS,
.global = registry_event_global,
};
int main(int argc, char *argv[])
{
struct data data;
spa_zero(data);
pw_init(&argc, &argv);
data.loop = pw_main_loop_new(NULL /* properties */ );
data.context = pw_context_new(pw_main_loop_get_loop(data.loop),
NULL /* properties */ ,
0 /* user_data size */ );
data.core = pw_context_connect(data.context, NULL /* properties */ ,
0 /* user_data size */ );
data.registry = pw_core_get_registry(data.core, PW_VERSION_REGISTRY,
0 /* user_data size */ );
pw_registry_add_listener(data.registry, &data.registry_listener,
&registry_events, &data);
pw_main_loop_run(data.loop);
pw_proxy_destroy((struct pw_proxy *)data.client);
pw_proxy_destroy((struct pw_proxy *)data.registry);
pw_core_disconnect(data.core);
pw_context_destroy(data.context);
pw_main_loop_destroy(data.loop);
return 0;
}
PW_TYPE_INTERFACE_Client
#define PW_TYPE_INTERFACE_Client
Definition: client.h:51
PW_VERSION_CLIENT_EVENTS
#define PW_VERSION_CLIENT_EVENTS
Definition: client.h:95
PW_VERSION_CLIENT
#define PW_VERSION_CLIENT
Definition: client.h:54
pw_client_add_listener
#define pw_client_add_listener(c,...)
Definition: client.h:193
pw_context_destroy
void pw_context_destroy(struct pw_context *context)
destroy a context object, all resources except the main_loop will be destroyed
Definition: context.c:434
pw_context_new
struct pw_context * pw_context_new(struct pw_loop *main_loop, struct pw_properties *props, size_t user_data_size)
Make a new context object for a given main_loop.
Definition: context.c:206
pw_context_connect
struct pw_core * pw_context_connect(struct pw_context *context, struct pw_properties *properties, size_t user_data_size)
Connect to a PipeWire instance.
Definition: core.c:402
pw_core_disconnect
int pw_core_disconnect(struct pw_core *core)
disconnect and destroy a core
Definition: core.c:489
PW_VERSION_REGISTRY
#define PW_VERSION_REGISTRY
Definition: core.h:69
pw_core_get_registry
static struct pw_registry * pw_core_get_registry(struct pw_core *core, uint32_t version, size_t user_data_size)
Definition: core.h:405
pw_main_loop_new
struct pw_main_loop * pw_main_loop_new(const struct spa_dict *props)
Create a new main loop.
Definition: main-loop.c:80
pw_main_loop_quit
int pw_main_loop_quit(struct pw_main_loop *loop)
Quit a main loop.
Definition: main-loop.c:125
pw_main_loop_destroy
void pw_main_loop_destroy(struct pw_main_loop *loop)
Destroy a loop.
Definition: main-loop.c:90
pw_main_loop_run
int pw_main_loop_run(struct pw_main_loop *loop)
Run a main loop.
Definition: main-loop.c:139
pw_main_loop_get_loop
struct pw_loop * pw_main_loop_get_loop(struct pw_main_loop *loop)
Get the loop implementation.
Definition: main-loop.c:113
pw_init
void pw_init(int *argc, char **argv[])
Initialize PipeWire.
Definition: pipewire.c:586
pw_proxy_destroy
void pw_proxy_destroy(struct pw_proxy *proxy)
destroy a proxy
Definition: proxy.c:231
PW_VERSION_REGISTRY_EVENTS
#define PW_VERSION_REGISTRY_EVENTS
Definition: core.h:483
pw_registry_bind
static void * pw_registry_bind(struct pw_registry *registry, uint32_t id, const char *type, uint32_t version, size_t user_data_size)
Definition: core.h:571
pw_registry_add_listener
#define pw_registry_add_listener(p,...)
Registry.
Definition: core.h:566
spa_dict_for_each
#define spa_dict_for_each(item, dict)
Definition: dict.h:72
spa_zero
#define spa_zero(x)
Definition: defs.h:385
pipewire.h
pipewire/pipewire.h
pw_client_events
Client events.
Definition: client.h:93
pw_client_info
The client information.
Definition: client.h:63
pw_client_info::id
uint32_t id
id of the global
Definition: client.h:64
pw_client
pw_context
pw_core
pw_main_loop
A main loop object.
pw_proxy
pw_registry_events
Registry events.
Definition: core.h:481
pw_registry
spa_dict_item
Definition: dict.h:51
spa_dict_item::key
const char * key
Definition: dict.h:52
spa_dict_item::value
const char * value
Definition: dict.h:53
spa_dict
Definition: dict.h:59
spa_hook
A hook, contains the structure with functions and the data passed to the functions.
Definition: hook.h:342

To compile the simple test application, copy it into a tutorial6.c file and use:

    gcc -Wall tutorial6.c -o tutorial6 $(pkg-config --cflags --libs libpipewire-0.3)

Most of this is the same as Tutorial - Part 2: Enumerating objects where we simply enumerated all objects on the server. Instead of just printing the object id and some other properties, in this example we also bind to the object.

We use the `pw_registry_bind()` method on our registry object like this:

static void registry_event_global(void *_data, uint32_t id,
uint32_t permissions, const char *type,
uint32_t version, const struct spa_dict *props)
{
struct data *data = _data;
if (data->client != NULL)
return;
if (strcmp(type, PW_TYPE_INTERFACE_Client) == 0) {
data->client = pw_registry_bind(data->registry,
id, type, PW_VERSION_CLIENT, 0);
pw_client_add_listener(data->client,
&data->client_listener,
&client_events, data);
}
}

We bind to the first client object that we see. This gives us a pointer to a `struct pw_proxy` that we can also cast to a `struct pw_client`.

On the proxy we can call methods and listen for events. PipeWire will automatically serialize the method calls and events between client and server for us.

We can now listen for events by adding a listener. We're going to listen to the info event on the client object that is emitted right after we bind to it or when it changes. This is not very different from the registry listener we added before:

static void client_info(void *object, const struct pw_client_info *info)
{
struct data *data = object;
const struct spa_dict_item *item;
printf("client: id:%u\n", info->id);
printf("\tprops:\n");
spa_dict_for_each(item, info->props)
printf("\t\t%s: \"%s\"\n", item->key, item->value);
pw_main_loop_quit(data->loop);
}
static const struct pw_client_events client_events = {
PW_VERSION_CLIENT_EVENTS,
.info = client_info,
};
static void registry_event_global(void *_data, uint32_t id,
uint32_t permissions, const char *type,
uint32_t version, const struct spa_dict *props)
{
/* ... */
pw_client_add_listener(data->client,
&data->client_listener,
&client_events, data);
/* ... */
}

We're also quitting the mainloop after we get the info to nicely stop our tutorial application.

When we stop the application, don't forget to destroy all proxies that you created. Otherwise, they will be leaked:

/* ... */
pw_proxy_destroy((struct pw_proxy *)data.client);
/* ... */
return 0;
}

Tutorial - Part 5: Capturing video frames | Index