PipeWire: Tutorial - Part 6: Binding objects

PipeWire 0.3.37

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;
};
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)
{
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);
}
}
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_VERSION_CLIENT_EVENTS
#define PW_VERSION_CLIENT_EVENTS
Definition: client.h:81
PW_VERSION_REGISTRY_EVENTS
#define PW_VERSION_REGISTRY_EVENTS
Definition: core.h:432
PW_TYPE_INTERFACE_Client
#define PW_TYPE_INTERFACE_Client
Definition: client.h:46
PW_VERSION_CLIENT
#define PW_VERSION_CLIENT
Definition: client.h:48
pw_client_add_listener
#define pw_client_add_listener(c,...)
Definition: client.h:172
pw_context_destroy
void pw_context_destroy(struct pw_context *context)
Destroy a context object.
Definition: context.c:515
pw_context_new
struct pw_context * pw_context_new(struct pw_loop *main_loop, struct pw_properties *properties, size_t user_data_size)
Create a new context object.
Definition: context.c:296
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:401
pw_core_disconnect
int pw_core_disconnect(struct pw_core *core)
disconnect and destroy a core
Definition: core.c:488
PW_VERSION_REGISTRY
#define PW_VERSION_REGISTRY
Definition: core.h:59
pw_main_loop_quit
int pw_main_loop_quit(struct pw_main_loop *loop)
Stop a main loop.
Definition: main-loop.c:131
pw_main_loop_destroy
void pw_main_loop_destroy(struct pw_main_loop *loop)
Destroy a main loop.
Definition: main-loop.c:96
pw_main_loop_run
int pw_main_loop_run(struct pw_main_loop *loop)
Start a main loop.
Definition: main-loop.c:145
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:86
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:119
pw_init
void pw_init(int *argc, char **argv[])
Initialize PipeWire.
Definition: pipewire.c:533
pw_proxy_destroy
void pw_proxy_destroy(struct pw_proxy *proxy)
Destroy a proxy object.
Definition: proxy.c:230
pw_registry_add_listener
#define pw_registry_add_listener(p,...)
Registry.
Definition: core.h:510
spa_zero
#define spa_zero(x)
Definition: defs.h:310
spa_dict_for_each
#define spa_dict_for_each(item, dict)
Definition: utils/dict.h:58
main
int main(int argc, char *argv[])
Definition: media-session.c:2433
props
const char * props
Definition: media-session.c:2383
n
const char unsigned long int n
Definition: pipewire/src/pipewire/i18n.h:35
pipewire.h
client
Definition: access-flatpak.c:67
data
user data to add to an object
Definition: media-session.c:110
data::context
struct pw_context * context
Definition: filter.c:76
item
Definition: impl-metadata.c:49
pw_client_events
Client events.
Definition: client.h:80
pw_client_info
The client information.
Definition: client.h:55
pw_client_info::id
uint32_t id
id of the global
Definition: client.h:56
pw_client_info::props
struct spa_dict * props
extra properties
Definition: client.h:60
pw_registry_events
Registry events.
Definition: core.h:431
registry
Definition: pipewire.c:76
spa_dict_item
Definition: utils/dict.h:41
spa_dict_item::key
const char * key
Definition: utils/dict.h:42
spa_dict_item::value
const char * value
Definition: utils/dict.h:43
spa_dict
Definition: utils/dict.h:48
spa_hook
A hook, contains the structure with functions and the data passed to the functions.
Definition: hook.h:295

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);
/* ... */
}
}

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