Add a scratch buffer for automation.

Useful as temporary buffer: This allows a controllable to
get a master's automation-curve and combine it with its own
(gain, trim, send) automation buffer.

libs/ardour/ardour/process_thread.h

@@ -51,6 +51,7 @@ public:
 	static gain_t* gain_automation_buffer ();
 	static gain_t* trim_automation_buffer ();
 	static gain_t* send_gain_automation_buffer ();
+	static gain_t* scratch_automation_buffer ();
 	static pan_t** pan_automation_buffer ();
 
 protected:

libs/ardour/ardour/session.h

@@ -1034,6 +1034,7 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	gain_t* gain_automation_buffer () const;
 	gain_t* trim_automation_buffer () const;
 	gain_t* send_gain_automation_buffer () const;
+	gain_t* scratch_automation_buffer () const;
 	pan_t** pan_automation_buffer () const;
 
 	void ensure_buffer_set (BufferSet& buffers, const ChanCount& howmany);

libs/ardour/ardour/thread_buffers.h

@@ -45,6 +45,7 @@ public:
 	gain_t*    gain_automation_buffer;
 	gain_t*    trim_automation_buffer;
 	gain_t*    send_gain_automation_buffer;
+	gain_t*    scratch_automation_buffer;
 	pan_t**    pan_automation_buffer;
 	uint32_t   npan_buffers;
 

libs/ardour/process_thread.cc

@@ -208,6 +208,17 @@ ProcessThread::send_gain_automation_buffer()
 	return g;
 }
 
+gain_t*
+ProcessThread::scratch_automation_buffer()
+{
+	ThreadBuffers* tb = _private_thread_buffers.get();
+	assert (tb);
+
+	gain_t* g = tb->scratch_automation_buffer;
+	assert (g);
+	return g;
+}
+
 pan_t**
 ProcessThread::pan_automation_buffer()
 {

libs/ardour/session.cc

@@ -6301,6 +6301,12 @@ Session::send_gain_automation_buffer() const
 	return ProcessThread::send_gain_automation_buffer ();
 }
 
+gain_t*
+Session::scratch_automation_buffer() const
+{
+	return ProcessThread::scratch_automation_buffer ();
+}
+
 pan_t**
 Session::pan_automation_buffer() const
 {

libs/ardour/thread_buffers.cc

@@ -36,6 +36,7 @@ ThreadBuffers::ThreadBuffers ()
 	, gain_automation_buffer (0)
 	, trim_automation_buffer (0)
 	, send_gain_automation_buffer (0)
+	, scratch_automation_buffer (0)
 	, pan_automation_buffer (0)
 	, npan_buffers (0)
 {
@@ -86,6 +87,8 @@ ThreadBuffers::ensure_buffers (ChanCount howmany, size_t custom)
 	trim_automation_buffer = new gain_t[audio_buffer_size];
 	delete [] send_gain_automation_buffer;
 	send_gain_automation_buffer = new gain_t[audio_buffer_size];
+	delete [] scratch_automation_buffer;
+	scratch_automation_buffer = new gain_t[audio_buffer_size];
 
 	allocate_pan_automation_buffers (audio_buffer_size, howmany.n_audio(), false);
 }