rework panning -- Squashed commit of the following:

commit 6f4f4f161b00cb36252727f67ecc4913eb944fd7
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 22:13:09 2014 +0100

    fix panner plugin discovery (prev commit)

commit 26e514f4a80af9192cae3cbd62fde0ae95474dfc
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 18:56:59 2014 +0100

    update panner plugin discovery

    * recurse dirs in 'PANNER_PATH' and 'panner_dir_name' up to 1 level.
    * don't look in ardour_dll_directory() -- no panners are supposed to be in there
    * use .dylib on OSX exclusively.

commit a514c3f1c425dccf3d42eee9d2b183b44fd26a03
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:48:34 2014 +0100

    remove debug/devel printf()s

commit d863742ddc69af493ee6a8817bc778968d9b0800
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:17:13 2014 +0100

    panner-type: session backward/forward compatibility

commit 25d5e4c663ada34129451b0f9045ab047d6cc2f0
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 16:09:07 2014 +0100

    update URIs -> URLs

commit 00a606a43d9456cfbaf43cae4fb598549326ba71
Merge: 0f1cec1 382eb0f
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 03:29:45 2014 +0100

    Merge branch 'master' into panning

commit 0f1cec19babae538c9697eed4be5d6ddc851b013
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 02:41:15 2014 +0100

    switch panner ID to URI

commit 575282b412c3ae1cd8219cf75f00a1a4239e2813
Author: Robin Gareus <robin@gareus.org>
Date:   Wed Jan 8 00:50:15 2014 +0100

    prepare API for panner URI

commit ea62cd049308859782a7bb16e4f18169d8638b46
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 19:57:06 2014 +0100

    update development doc relating to panner selection

commit 586d7de2392e26b9d7f597b1a00b98dfaa42ecdc
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 19:56:24 2014 +0100

    clean up PanShell::set_user_selected_panner_type() API

commit 99077886a5a1cacece908d87c29c3be12903027e
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 04:46:22 2014 +0100

    panner bypass: visualize & [in]sensitivity

commit 46d688d216f0e67d672376a607157af02b359fb2
Merge: 4e67573 c4cdf61
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 02:18:54 2014 +0100

    Merge branch 'master' into panning

commit 4e67573517b3d60ddf65729783687b16cfb2adb7
Author: Robin Gareus <robin@gareus.org>
Date:   Tue Jan 7 01:05:17 2014 +0100

    don't call configure_io() for merely swapping panners

commit d32a4c51f6967f48f7680554866f1f7b311ccde1
Merge: a3226d4 cec3116
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 23:49:55 2014 +0100

    Merge branch 'master' into panning

commit a3226d46b598afae54a65ac69320eca84669f347
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:52:38 2014 +0100

    add notes about panner re-design

commit d1ae2366024605f22b05572a81ee249e6fdbcd2f
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 15:06:40 2014 +0100

    add simple stereo-balance panner for testing

commit e0ddd256ff2288b8d8cfad3ad485a916964ce5b5
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:02:52 2014 +0100

    add frontend/GUI for panner selection

commit 2cb8f846755eb5aea8a2620d31ea981c446c4041
Author: Robin Gareus <robin@gareus.org>
Date:   Mon Jan 6 17:02:20 2014 +0100

    prepare backend for panner selection

7 files changed, 463 insertions, 2 deletions

diff --git a/libs/panners/1in2out/panner_1in2out.cc b/libs/panners/1in2out/panner_1in2out.cc
index 4524ed560b..b7ca5ce914 100644
--- a/libs/panners/1in2out/panner_1in2out.cc
+++ b/libs/panners/1in2out/panner_1in2out.cc
@@ -63,6 +63,8 @@ using namespace PBD;
 
 static PanPluginDescriptor _descriptor = {
         "Mono to Stereo Panner",
+        "http://ardour.org/plugin/panner_1in2out",
+        "http://ardour.org/plugin/panner_1in2out#ui",
         1, 2, 
         Panner1in2out::factory
 };
@@ -332,6 +334,8 @@ XMLNode&
 Panner1in2out::get_state ()
 {
 	XMLNode& root (Panner::get_state ());
+	root.add_property (X_("uri"), _descriptor.panner_uri);
+	/* this is needed to allow new sessions to load with old Ardour: */
 	root.add_property (X_("type"), _descriptor.name);
 	return root;
 }
diff --git a/libs/panners/2in2out/panner_2in2out.cc b/libs/panners/2in2out/panner_2in2out.cc
index a316b764c7..43cf4840a1 100644
--- a/libs/panners/2in2out/panner_2in2out.cc
+++ b/libs/panners/2in2out/panner_2in2out.cc
@@ -63,6 +63,8 @@ using namespace PBD;
 
 static PanPluginDescriptor _descriptor = {
         "Equal Power Stereo",
+        "http://ardour.org/plugin/panner_2in2out",
+        "http://ardour.org/plugin/panner_2in2out#ui",
         2, 2,
         Panner2in2out::factory
 };
@@ -464,6 +466,8 @@ XMLNode&
 Panner2in2out::get_state ()
 {
 	XMLNode& root (Panner::get_state ());
+	root.add_property (X_("uri"), _descriptor.panner_uri);
+	/* this is needed to allow new sessions to load with old Ardour: */
 	root.add_property (X_("type"), _descriptor.name);
 	return root;
 }
diff --git a/libs/panners/stereobalance/panner_balance.cc b/libs/panners/stereobalance/panner_balance.cc
new file mode 100644
index 0000000000..18bda54b18
--- /dev/null
+++ b/libs/panners/stereobalance/panner_balance.cc
@@ -0,0 +1,332 @@
+/*
+    Copyright (C) 2004-2011 Paul Davis
+    adopted from 2in2out panner by Robin Gareus <robin@gareus.org>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#include <inttypes.h>
+
+#include <cmath>
+#include <cerrno>
+#include <fstream>
+#include <cstdlib>
+#include <string>
+#include <cstdio>
+#include <locale.h>
+#include <unistd.h>
+#include <float.h>
+#include <iomanip>
+
+#include <glibmm.h>
+
+#include "pbd/cartesian.h"
+#include "pbd/convert.h"
+#include "pbd/error.h"
+#include "pbd/failed_constructor.h"
+#include "pbd/xml++.h"
+#include "pbd/enumwriter.h"
+
+#include "evoral/Curve.hpp"
+
+#include "ardour/audio_buffer.h"
+#include "ardour/audio_buffer.h"
+#include "ardour/buffer_set.h"
+#include "ardour/pan_controllable.h"
+#include "ardour/pannable.h"
+#include "ardour/runtime_functions.h"
+#include "ardour/session.h"
+#include "ardour/utils.h"
+#include "ardour/mix.h"
+
+#include "panner_balance.h"
+
+#include "i18n.h"
+
+#include "pbd/mathfix.h"
+
+using namespace std;
+using namespace ARDOUR;
+using namespace PBD;
+
+static PanPluginDescriptor _descriptor = {
+	"Stereo Balance",
+	"http://ardour.org/plugin/panner_balance",
+	"http://ardour.org/plugin/panner_balance#ui",
+	2, 2,
+	Pannerbalance::factory
+};
+
+extern "C" { PanPluginDescriptor* panner_descriptor () { return &_descriptor; } }
+
+Pannerbalance::Pannerbalance (boost::shared_ptr<Pannable> p)
+	: Panner (p)
+{
+	if (!_pannable->has_state()) {
+		_pannable->pan_azimuth_control->set_value (0.5);
+	}
+
+	update ();
+
+	/* LEFT SIGNAL */
+	pos_interp[0] = pos[0] = desired_pos[0];
+	/* RIGHT SIGNAL */
+	pos_interp[1] = pos[1] = desired_pos[1];
+
+	_pannable->pan_azimuth_control->Changed.connect_same_thread (*this, boost::bind (&Pannerbalance::update, this));
+}
+
+Pannerbalance::~Pannerbalance ()
+{
+}
+
+double
+Pannerbalance::position () const
+{
+	return _pannable->pan_azimuth_control->get_value();
+}
+
+	void
+Pannerbalance::set_position (double p)
+{
+	if (clamp_position (p)) {
+		_pannable->pan_azimuth_control->set_value (p);
+	}
+}
+
+	void
+Pannerbalance::thaw ()
+{
+	Panner::thaw ();
+	if (_frozen == 0) {
+		update ();
+	}
+}
+
+void
+Pannerbalance::update ()
+{
+	if (_frozen) {
+		return;
+	}
+
+	float const pos = _pannable->pan_azimuth_control->get_value();
+
+	if (pos == .5) {
+		desired_pos[0] = 1.0;
+		desired_pos[1] = 1.0;
+	} else if (pos > .5) {
+		desired_pos[0] = 2 - 2. * pos;
+		desired_pos[1] = 1.0;
+	} else {
+		desired_pos[0] = 1.0;
+		desired_pos[1] = 2. * pos;
+	}
+}
+
+bool
+Pannerbalance::clamp_position (double& p)
+{
+	p = max (min (p, 1.0), 0.0);
+	return true;
+}
+
+pair<double, double>
+Pannerbalance::position_range () const
+{
+	return make_pair (0, 1);
+}
+
+void
+Pannerbalance::distribute_one (AudioBuffer& srcbuf, BufferSet& obufs, gain_t gain_coeff, pframes_t nframes, uint32_t which)
+{
+	assert (obufs.count().n_audio() == 2);
+
+	pan_t delta;
+	Sample* dst;
+	pan_t pan;
+
+	Sample* const src = srcbuf.data();
+
+	dst = obufs.get_audio(which).data();
+
+	if (fabsf ((delta = (pos[which] - desired_pos[which]))) > 0.002) { // about 1 degree of arc
+
+		/* we've moving the pan by an appreciable amount, so we must
+			 interpolate over 64 frames or nframes, whichever is smaller */
+
+		pframes_t const limit = min ((pframes_t) 64, nframes);
+		pframes_t n;
+
+		delta = -(delta / (float) (limit));
+
+		for (n = 0; n < limit; n++) {
+			pos_interp[which] = pos_interp[which] + delta;
+			pos[which] = pos_interp[which] + 0.9 * (pos[which] - pos_interp[which]);
+			dst[n] += src[n] * pos[which] * gain_coeff;
+		}
+
+		/* then pan the rest of the buffer; no need for interpolation for this bit */
+
+		pan = pos[which] * gain_coeff;
+
+		mix_buffers_with_gain (dst+n,src+n,nframes-n,pan);
+
+	} else {
+
+		pos[which] = desired_pos[which];
+		pos_interp[which] = pos[which];
+
+		if ((pan = (pos[which] * gain_coeff)) != 1.0f) {
+
+			if (pan != 0.0f) {
+
+				/* pan is 1 but also not 0, so we must do it "properly" */
+
+				//obufs.get_audio(1).read_from (srcbuf, nframes);
+				mix_buffers_with_gain(dst,src,nframes,pan);
+
+				/* mark that we wrote into the buffer */
+
+				// obufs[0] = 0;
+
+			}
+
+		} else {
+			/* pan is 1 so we can just copy the input samples straight in */
+			mix_buffers_no_gain(dst,src,nframes);
+		}
+	}
+}
+
+void
+Pannerbalance::distribute_one_automated (AudioBuffer& srcbuf, BufferSet& obufs,
+                                         framepos_t start, framepos_t end, pframes_t nframes,
+                                         pan_t** buffers, uint32_t which)
+{
+	assert (obufs.count().n_audio() == 2);
+
+	Sample* dst;
+	pan_t* pbuf;
+	Sample* const src = srcbuf.data();
+	pan_t* const position = buffers[0];
+
+	/* fetch positional data */
+
+	if (!_pannable->pan_azimuth_control->list()->curve().rt_safe_get_vector (start, end, position, nframes)) {
+		/* fallback */
+		distribute_one (srcbuf, obufs, 1.0, nframes, which);
+		return;
+	}
+
+	for (pframes_t n = 0; n < nframes; ++n) {
+
+		float const pos = position[n];
+
+		if (which == 0) { // Left
+			if (pos > .5) {
+				buffers[which][n] = 2 - 2. * pos;
+			} else {
+				buffers[which][n] = 1.0;
+			}
+		} else { // Right
+			if (pos < .5) {
+				buffers[which][n] = 2. * pos;
+			} else {
+				buffers[which][n] = 1.0;
+			}
+		}
+	}
+
+	dst = obufs.get_audio(which).data();
+	pbuf = buffers[which];
+
+	for (pframes_t n = 0; n < nframes; ++n) {
+		dst[n] += src[n] * pbuf[n];
+	}
+
+	/* XXX it would be nice to mark the buffer as written to */
+}
+
+Panner*
+Pannerbalance::factory (boost::shared_ptr<Pannable> p, boost::shared_ptr<Speakers> /* ignored */)
+{
+	return new Pannerbalance (p);
+}
+
+	XMLNode&
+Pannerbalance::get_state ()
+{
+	XMLNode& root (Panner::get_state ());
+	root.add_property (X_("uri"), _descriptor.panner_uri);
+	/* this is needed to allow new sessions to load with old Ardour: */
+	root.add_property (X_("type"), _descriptor.name);
+	return root;
+}
+
+std::set<Evoral::Parameter>
+Pannerbalance::what_can_be_automated() const
+{
+	set<Evoral::Parameter> s;
+	s.insert (Evoral::Parameter (PanAzimuthAutomation));
+	return s;
+}
+
+string
+Pannerbalance::describe_parameter (Evoral::Parameter p)
+{
+	switch (p.type()) {
+		case PanAzimuthAutomation:
+			return _("L/R");
+		default:
+			return _pannable->describe_parameter (p);
+	}
+}
+
+string
+Pannerbalance::value_as_string (boost::shared_ptr<AutomationControl> ac) const
+{
+	/* DO NOT USE LocaleGuard HERE */
+	double val = ac->get_value();
+
+	switch (ac->parameter().type()) {
+		case PanAzimuthAutomation:
+			/* We show the position of the center of the image relative to the left & right.
+				 This is expressed as a pair of percentage values that ranges from (100,0)
+				 (hard left) through (50,50) (hard center) to (0,100) (hard right).
+
+				 This is pretty wierd, but its the way audio engineers expect it. Just remember that
+				 the center of the USA isn't Kansas, its (50LA, 50NY) and it will all make sense.
+
+				 This is designed to be as narrow as possible. Dedicated
+				 panner GUIs can do their own version of this if they need
+				 something less compact.
+				 */
+
+			return string_compose (_("L%1R%2"), (int) rint (100.0 * (1.0 - val)),
+					(int) rint (100.0 * val));
+
+		default:
+			return _pannable->value_as_string (ac);
+	}
+}
+
+void
+Pannerbalance::reset ()
+{
+	set_position (0.5);
+	update ();
+}
diff --git a/libs/panners/stereobalance/panner_balance.h b/libs/panners/stereobalance/panner_balance.h
new file mode 100644
index 0000000000..f381340888
--- /dev/null
+++ b/libs/panners/stereobalance/panner_balance.h
@@ -0,0 +1,83 @@
+/*
+    Copyright (C) 2004-2014 Paul Davis
+    adopted from 2in2out panner by Robin Gareus <robin@gareus.org>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#ifndef __ardour_panner_balance_h__
+#define __ardour_panner_balance_h__
+
+#include <cmath>
+#include <cassert>
+#include <vector>
+#include <string>
+#include <iostream>
+
+#include "pbd/stateful.h"
+#include "pbd/controllable.h"
+#include "pbd/cartesian.h"
+
+#include "ardour/automation_control.h"
+#include "ardour/automatable.h"
+#include "ardour/panner.h"
+#include "ardour/types.h"
+
+namespace ARDOUR {
+
+class Pannerbalance : public Panner
+{
+	public:
+	Pannerbalance (boost::shared_ptr<Pannable>);
+	~Pannerbalance ();
+
+	ChanCount in() const { return ChanCount (DataType::AUDIO, 2); }
+	ChanCount out() const { return ChanCount (DataType::AUDIO, 2); }
+
+	void set_position (double);
+	bool clamp_position (double&);
+	std::pair<double, double> position_range () const;
+	double position () const;
+
+	std::set<Evoral::Parameter> what_can_be_automated() const;
+
+	static Panner* factory (boost::shared_ptr<Pannable>, boost::shared_ptr<Speakers>);
+
+	std::string describe_parameter (Evoral::Parameter);
+	std::string value_as_string (boost::shared_ptr<AutomationControl>) const;
+
+	XMLNode& get_state ();
+
+	void reset ();
+	void thaw ();
+
+	protected:
+	float pos[2];
+	float desired_pos[2];
+	float pos_interp[2];
+
+	void update ();
+
+	private:
+	void distribute_one (AudioBuffer& srcbuf, BufferSet& obufs, gain_t gain_coeff, pframes_t nframes, uint32_t which);
+	void distribute_one_automated (AudioBuffer& srcbuf, BufferSet& obufs,
+			framepos_t start, framepos_t end, pframes_t nframes,
+			pan_t** buffers, uint32_t which);
+};
+
+} // namespace
+
+#endif /* __ardour_panner_balance_h__ */
diff --git a/libs/panners/stereobalance/wscript b/libs/panners/stereobalance/wscript
new file mode 100644
index 0000000000..75eccca419
--- /dev/null
+++ b/libs/panners/stereobalance/wscript
@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+from waflib.extras import autowaf as autowaf
+import os
+
+# Library version (UNIX style major, minor, micro)
+# major increment <=> incompatible changes
+# minor increment <=> compatible changes (additions)
+# micro increment <=> no interface changes
+LIBARDOUR_PAN2IN2OUT_LIB_VERSION = '1.0.0'
+
+# Mandatory variables
+top = '.'
+out = 'build'
+
+def options(opt):
+    autowaf.set_options(opt)
+
+def configure(conf):
+    autowaf.configure(conf)
+
+def build(bld):
+    obj = bld(features = 'cxx cxxshlib')
+    obj.source = [ 'panner_balance.cc' ]
+    obj.export_includes = ['.']
+    obj.cxxflags     = '-DPACKAGE="libardour_panbalance"'
+    obj.includes     = ['.']
+    obj.name         = 'libardour_panbalance'
+    obj.target       = 'panbalance'
+    obj.use          = 'libardour libardour_cp libpbd'
+    obj.vnum         = LIBARDOUR_PAN2IN2OUT_LIB_VERSION
+    obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardour3', 'panners')
+
+def shutdown():
+    autowaf.shutdown()
diff --git a/libs/panners/vbap/vbap.cc b/libs/panners/vbap/vbap.cc
index 1cef98fc7d..83095cf7b8 100644
--- a/libs/panners/vbap/vbap.cc
+++ b/libs/panners/vbap/vbap.cc
@@ -46,6 +46,8 @@ using namespace std;
 
 static PanPluginDescriptor _descriptor = {
         "VBAP 2D panner",
+        "http://ardour.org/plugin/panner_vbap",
+        "http://ardour.org/plugin/panner_vbap#ui",
         -1, -1,
         VBAPanner::factory
 };
@@ -392,7 +394,9 @@ VBAPanner::distribute_one_automated (AudioBuffer& /*src*/, BufferSet& /*obufs*/,
 XMLNode&
 VBAPanner::get_state ()
 {
-        XMLNode& node (Panner::get_state());
+	XMLNode& node (Panner::get_state());
+	node.add_property (X_("uri"), _descriptor.panner_uri);
+	/* this is needed to allow new sessions to load with old Ardour: */
 	node.add_property (X_("type"), _descriptor.name);
 	return node;
 }
diff --git a/libs/panners/wscript b/libs/panners/wscript
index aec57eb40f..f3ce6e6f19 100644
--- a/libs/panners/wscript
+++ b/libs/panners/wscript
@@ -6,7 +6,7 @@ import os
 top = '.'
 out = 'build'
 
-panners = [ '2in2out', '1in2out', 'vbap' ]
+panners = [ '2in2out', '1in2out', 'vbap', 'stereobalance' ]
 
 def options(opt):
     autowaf.set_options(opt)