From e4ff13a75d7acf170f6094db148dc77f380d505a Mon Sep 17 00:00:00 2001
From: Pauli Virtanen <pav@iki.fi>
Date: Sun, 15 Dec 2024 19:27:29 +0200
Subject: [PATCH] module-loopback: support latencyOffsetNsec Prop

Add support for latencyOffsetNsec Prop, which just controls the nsec
part of the ProcessLatency.

This is needed to support latency offset in Pulseaudio apps when using
loopbacks as front-end nodes to underlying sinks.
---
 src/modules/module-loopback.c | 58 ++++++++++++++++++++++++++++++-----
 1 file changed, 51 insertions(+), 7 deletions(-)

diff --git a/src/modules/module-loopback.c b/src/modules/module-loopback.c
index eda5c8230..db3b5725e 100644
--- a/src/modules/module-loopback.c
+++ b/src/modules/module-loopback.c
@@ -423,6 +423,16 @@ static void build_latency_params(struct impl *impl, struct spa_pod_builder *b,
 	params[1] = spa_latency_build(b, SPA_PARAM_Latency, &latency);
 }
 
+static struct spa_pod *build_props(struct impl *impl, struct spa_pod_builder *b,
+		enum spa_direction direction)
+{
+	int64_t nsec = impl->process_latency[direction].ns;
+
+	return spa_pod_builder_add_object(b,
+			SPA_TYPE_OBJECT_Props, SPA_PARAM_Props,
+			SPA_PROP_latencyOffsetNsec, SPA_POD_Long(nsec));
+}
+
 static void param_latency_changed(struct impl *impl, const struct spa_pod *param,
 		struct pw_stream *stream, struct pw_stream *other)
 {
@@ -445,13 +455,28 @@ static void param_latency_changed(struct impl *impl, const struct spa_pod *param
 	impl->recalc_delay = true;
 }
 
+static void emit_process_latency_changed(struct impl *impl,
+		enum spa_direction direction, struct pw_stream *stream)
+{
+	uint8_t buffer[4096];
+	struct spa_pod_builder b;
+	const struct spa_pod *params[4];
+
+	spa_pod_builder_init(&b, buffer, sizeof(buffer));
+	params[0] = spa_process_latency_build(&b, SPA_PARAM_ProcessLatency,
+			&impl->process_latency[direction]);
+	if (stream == impl->capture)
+		params[1] = build_props(impl, &b, SPA_DIRECTION_INPUT);
+	else
+		params[1] = build_props(impl, &b, SPA_DIRECTION_OUTPUT);
+	build_latency_params(impl, &b, &params[2], 2);
+	pw_stream_update_params(stream, params, 4);
+}
+
 static void param_process_latency_changed(struct impl *impl, const struct spa_pod *param,
 		enum spa_direction direction, struct pw_stream *stream)
 {
 	struct spa_process_latency_info info;
-	uint8_t buffer[4096];
-	struct spa_pod_builder b;
-	const struct spa_pod *params[3];
 
 	if (param == NULL)
 		spa_zero(info);
@@ -460,10 +485,23 @@ static void param_process_latency_changed(struct impl *impl, const struct spa_po
 
 	impl->process_latency[direction] = info;
 
-	spa_pod_builder_init(&b, buffer, sizeof(buffer));
-	params[0] = spa_process_latency_build(&b, SPA_PARAM_ProcessLatency, &info);
-	build_latency_params(impl, &b, &params[1], 2);
-	pw_stream_update_params(stream, params, 3);
+	emit_process_latency_changed(impl, direction, stream);
+}
+
+static void param_props_changed(struct impl *impl, const struct spa_pod *param,
+		enum spa_direction direction, struct pw_stream *stream)
+{
+	int64_t nsec;
+
+	if (!param)
+		nsec = 0;
+	else if (spa_pod_parse_object(param,
+					SPA_TYPE_OBJECT_Props, NULL,
+					SPA_PROP_latencyOffsetNsec, SPA_POD_Long(&nsec)) < 0)
+		return;
+
+	impl->process_latency[direction].ns = nsec;
+	emit_process_latency_changed(impl, direction, stream);
 }
 
 static void param_tag_changed(struct impl *impl, const struct spa_pod *param,
@@ -586,6 +624,9 @@ static void capture_param_changed(void *data, uint32_t id, const struct spa_pod
 	case SPA_PARAM_Latency:
 		param_latency_changed(impl, param, impl->capture, impl->playback);
 		break;
+	case SPA_PARAM_Props:
+		param_props_changed(impl, param, SPA_DIRECTION_INPUT, impl->capture);
+		break;
 	case SPA_PARAM_ProcessLatency:
 		param_process_latency_changed(impl, param, SPA_DIRECTION_INPUT, impl->capture);
 		break;
@@ -634,6 +675,9 @@ static void playback_param_changed(void *data, uint32_t id, const struct spa_pod
 	case SPA_PARAM_Latency:
 		param_latency_changed(impl, param, impl->playback, impl->capture);
 		break;
+	case SPA_PARAM_Props:
+		param_props_changed(impl, param, SPA_DIRECTION_OUTPUT, impl->playback);
+		break;
 	case SPA_PARAM_ProcessLatency:
 		param_process_latency_changed(impl, param, SPA_DIRECTION_OUTPUT, impl->playback);
 		break;