From a7ed400c81c65a11623418d08cd5c953826754bd Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Tue, 15 Aug 2023 15:46:19 +0200
Subject: [PATCH] Add Audiobuffers::set_channels().

---
 src/lib/audio_buffers.cc   | 19 ++++++++++++++++++
 src/lib/audio_buffers.h    |  2 ++
 test/audio_buffers_test.cc | 41 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+)

diff --git a/src/lib/audio_buffers.cc b/src/lib/audio_buffers.cc
index 119a499b4..4f01146f9 100644
--- a/src/lib/audio_buffers.cc
+++ b/src/lib/audio_buffers.cc
@@ -335,3 +335,22 @@ AudioBuffers::update_data_pointers ()
         }
 }
 
+
+/** Set a new channel count, either discarding data (if new_channels is less than the current
+ *  channels()), or filling with silence (if new_channels is more than the current channels()
+ */
+void
+AudioBuffers::set_channels(int new_channels)
+{
+	DCPOMATIC_ASSERT(new_channels > 0);
+
+	ScopeGuard sg = [this]() { update_data_pointers(); };
+
+	int const old_channels = channels();
+	_data.resize(new_channels);
+
+	for (int channel = old_channels; channel < new_channels; ++channel) {
+		_data[channel].resize(frames());
+	}
+}
+
diff --git a/src/lib/audio_buffers.h b/src/lib/audio_buffers.h
index 4db0fa255..645348aa0 100644
--- a/src/lib/audio_buffers.h
+++ b/src/lib/audio_buffers.h
@@ -65,6 +65,8 @@ public:
 
 	void set_frames (int f);
 
+	void set_channels(int new_channels);
+
 	void make_silent ();
 	void make_silent (int channel);
 	void make_silent (int from, int frames);
diff --git a/test/audio_buffers_test.cc b/test/audio_buffers_test.cc
index 0abd73080..76785d8ec 100644
--- a/test/audio_buffers_test.cc
+++ b/test/audio_buffers_test.cc
@@ -344,3 +344,44 @@ BOOST_AUTO_TEST_CASE (audio_buffers_trim_start)
        }
 }
 
+
+BOOST_AUTO_TEST_CASE(audio_buffers_set_channels_lower)
+{
+	AudioBuffers buffers(9, 9933);
+	srand(4);
+	random_fill(buffers);
+
+	buffers.set_channels(4);
+	BOOST_REQUIRE_EQUAL(buffers.channels(), 4U);
+
+	srand(4);
+	for (int i = 0; i < 9933; ++i) {
+		for (int c = 0; c < 4; ++c) {
+			BOOST_CHECK_EQUAL(buffers.data(c)[i], random_float());
+		}
+		for (int c = 4; c < 9; ++c) {
+			random_float();
+		}
+	}
+}
+
+
+BOOST_AUTO_TEST_CASE(audio_buffers_set_channels_higher)
+{
+	AudioBuffers buffers(9, 9933);
+	srand(4);
+	random_fill(buffers);
+
+	buffers.set_channels(13);
+	BOOST_REQUIRE_EQUAL(buffers.channels(), 13U);
+
+	srand(4);
+	for (int i = 0; i < 9933; ++i) {
+		for (int c = 0; c < 9; ++c) {
+			BOOST_CHECK_EQUAL(buffers.data(c)[i], random_float());
+		}
+		for (int c = 9; c < 13; ++c) {
+			BOOST_CHECK_EQUAL(buffers.data(c)[i], 0);
+		}
+	}
+}
-- 
2.30.2