refactor and document delayline

libs/ardour/ardour/fixed_delay.h

@@ -26,22 +26,67 @@ namespace ARDOUR {
 
 class ChanCount;
 
+/** Multichannel Audio/Midi Delay Line
+ *
+ * This is an efficient delay line operating directly on Ardour buffers.
+ * The drawback is that there is no thread safety:
+ * All calls need to be executed in the same thread.
+ *
+ * After configuration, the delay can be changed safely up to the maximum
+ * configured delay but doing so flushes the buffer. There is no de-clicking
+ * (see ARDOUR::Delayline for those cases).
+ *
+ * Increasing the delay above the max configured or requesting more
+ * buffers will allocate the required space (not realtime safe).
+ *
+ * All buffers part of the set are treated separately.
+ */
 class LIBARDOUR_API FixedDelay
 {
 public:
 	FixedDelay ();
 	~FixedDelay ();
 
-	void configure (const ChanCount& count, framecnt_t);
-	void set (const ChanCount& count, framecnt_t);
+	/** initial configuration, usually done after instantiation
+	 *
+	 * @param count Channel Count (audio+midi)
+	 * @param max_delay the maximum number of samples to delay
+	 * @param shrink when false already allocated buffers are kept if both channel-count and max-delay requirements are satisified
+	 */
+	void configure (const ChanCount& count, framecnt_t max_delay, bool shrink = true);
 
-	void delay (ARDOUR::DataType, uint32_t, Buffer&, const Buffer&, pframes_t, framecnt_t dst_offset = 0, framecnt_t src_offset = 0);
-	void flush() { _pending_flush = true; }
+	/** set delay time and update active process buffers
+	 *
+	 * This calls configure with shrink = false and sets the current delay time
+	 * if the delay time mismatches, the buffers are silenced (zeroed).
+	 *
+	 * @param count channels to be processed
+	 * @param delay number of audio samples to delay
+	 */
+	void set (const ChanCount& count, framecnt_t delay);
+
+	/** process a channel
+	 *
+	 * Read N samples from the input buffer, delay them by the configured delay-time and write
+	 * the delayed samples to the output buffer at the given offset.
+	 *
+	 * @param dt datatype
+	 * @param id buffer number (starting at 0)
+	 * @param out output buffer to write data to
+	 * @param in input buffer to read data from
+	 * @param n_samples number of samples to process (must be <= 8192)
+	 * @param dst_offset offset in output buffer to start writing to
+	 * @param src_offset offset in input buffer to start reading from
+	 */
+	void delay (ARDOUR::DataType dt, uint32_t id, Buffer& out, const Buffer& in, pframes_t n_samples, framecnt_t dst_offset = 0, framecnt_t src_offset = 0);
+
+	/** zero all buffers */
+	void flush();
 
 private:
 	framecnt_t _max_delay;
+	framecnt_t _buf_size;
 	framecnt_t _delay;
-	bool       _pending_flush;
 	ChanCount  _count;
 
 	struct DelayBuffer {

libs/ardour/fixed_delay.cc

@@ -25,8 +25,8 @@ using namespace ARDOUR;
 
 FixedDelay::FixedDelay ()
 	: _max_delay (0)
+	, _buf_size (0)
 	, _delay (0)
-	, _pending_flush (false)
 {
 	for (size_t i = 0; i < DataType::num_types; ++i) {
 		_buffers.push_back (BufferVec ());
@@ -39,25 +39,6 @@ FixedDelay::~FixedDelay ()
 	clear ();
 }
 
-void
-FixedDelay::configure (const ChanCount& count, framecnt_t max_delay)
-{
-	if (max_delay <= _max_delay || count <= _count) {
-		return;
-	}
-	_max_delay = std::max (_max_delay, max_delay);
-	for (DataType::iterator i = DataType::begin (); i != DataType::end (); ++i) {
-		ensure_buffers (*i, count.get (*i), _max_delay + 1);
-	}
-}
-
-void
-FixedDelay::set (const ChanCount& count, framecnt_t delay)
-{
-	configure (count, delay);
-	_delay = delay;
-}
-
 void
 FixedDelay::ensure_buffers (DataType type, size_t num_buffers, size_t buffer_capacity)
 {
@@ -92,6 +73,47 @@ FixedDelay::clear ()
 	_count.reset ();
 }
 
+void
+FixedDelay::flush()
+{
+	for (std::vector<BufferVec>::iterator i = _buffers.begin (); i != _buffers.end (); ++i) {
+		for (BufferVec::iterator j = (*i).begin (); j != (*i).end (); ++j) {
+			(*j)->buf->silence (_buf_size);
+		}
+	}
+}
+
+void
+FixedDelay::configure (const ChanCount& count, framecnt_t max_delay, bool shrink)
+{
+	if (shrink) {
+		if (max_delay == _max_delay && count == _count) {
+			return;
+		}
+		_max_delay = max_delay;
+	} else if (max_delay <= _max_delay || count <= _count) {
+		return;
+		_max_delay = std::max (_max_delay, max_delay);
+	}
+
+	// max possible (with all engines and during export)
+	static const framecnt_t max_block_length = 8192;
+	_buf_size = _max_delay + max_block_length;
+	for (DataType::iterator i = DataType::begin (); i != DataType::end (); ++i) {
+		ensure_buffers (*i, count.get (*i), _buf_size);
+	}
+}
+
+void
+FixedDelay::set (const ChanCount& count, framecnt_t delay)
+{
+	configure (count, delay, false);
+	if (_delay != delay) {
+		flush ();
+	}
+	_delay = delay;
+}
+
 void
 FixedDelay::delay (
 		ARDOUR::DataType dt, uint32_t id,
@@ -108,25 +130,25 @@ FixedDelay::delay (
 	assert (id < _buffers[dt].size ());
 	DelayBuffer *db = _buffers[dt][id];
 
-	if (db->pos + n_frames > _max_delay) {
-		uint32_t w0 = _max_delay - db->pos;
-		uint32_t w1 = db->pos + n_frames - _max_delay;
+	if (db->pos + n_frames > _buf_size) {
+		uint32_t w0 = _buf_size - db->pos;
+		uint32_t w1 = db->pos + n_frames - _buf_size;
 		db->buf->read_from (in, w0, db->pos, src_offset);
 		db->buf->read_from (in, w1, 0, src_offset + w0);
 	} else {
 		db->buf->read_from (in, n_frames, db->pos, src_offset);
 	}
 
-	uint32_t rp = (db->pos + _max_delay - _delay) % _max_delay;
+	uint32_t rp = (db->pos + _buf_size - _delay) % _buf_size;
 
-	if (rp + n_frames > _max_delay) {
-		uint32_t r0 = _max_delay - rp;
-		uint32_t r1 = rp + n_frames - _max_delay;
+	if (rp + n_frames > _buf_size) {
+		uint32_t r0 = _buf_size - rp;
+		uint32_t r1 = rp + n_frames - _buf_size;
 		out.read_from (*db->buf, r0, dst_offset, rp);
 		out.read_from (*db->buf, r1, dst_offset + r0, 0);
 	} else {
 		out.read_from (*db->buf, n_frames, dst_offset, rp);
 	}
 
-	db->pos = (db->pos + n_frames) % _max_delay;
+	db->pos = (db->pos + n_frames) % _buf_size;
 }