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Working with Peers

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Every participant in the session — devices and applications alike — is a peer. The peer API lets your application answer "who is here?", present itself well, and react to arrivals and departures. (Concept: The QAROS World.)

info

The C# snippets on this page are illustrative — they track the Qar binding surface but are not yet compiled from a published sample project.

Presenting your application​

Your own peer's metadata is set at onboarding time via QarPeerPresentation (display name, app version, custom info string) and can be updated live:

qar_peer_update_display_name(session, "My CAD Tool — Assembly B");

The app_custom_peer_info field is yours: put a JSON blob or tag there to coordinate between instances of your own application across the session.

Enumerating peers​

In C this is a count-then-fetch, like every enumeration in the API. In C# the same enumeration returns a ready-made array:

size_t count = 0;
qar_result_log_if_error(qar_query_peer_specs_count(session, &count));

QarPeerSpec** specs = malloc(count * sizeof(*specs));
qar_result_log_if_error(
    qar_query_peer_specs(session, specs, count, &count));

for (size_t i = 0; i < count; ++i)
{
    char name[128];
    qar_peer_spec_get_display_name(specs[i], name, sizeof(name));
    /* also: _get_app_version, _get_app_custom_peer_info,
             _get_app_state, _get_version_id, _get_room_tag,
             _get_id */
    qar_peer_spec_handle_destroy(specs[i]);
}
free(specs);

Useful fields:

  • app state — QAR_APP_STATE_INITIALIZING / RUNNING / SHUTTING_DOWN / UNKNOWN: distinguish a peer that is present-but-loading from one that is live.
  • room tag — which physical room the peer is in; lets multi-room deployments group peers.
  • qar_session_get_my_spec — your own peer's spec (e.g. to learn your assigned peer ID).

Reacting to changes​

static void on_peer_update(/* peer update info */ ..., void* state)
{
    /* peer joined / left / changed presentation or app state */
}

qar_peer_subscribe_updates(session, on_peer_update, NULL);

Typical uses: refresh a "participants" panel, start a render stream when a target device appears, or pause expensive rendering when the last viewer leaves. Callback threading rules apply as everywhere: see API Conventions.