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

8 files changed, 154 insertions, 20 deletions

diff --git a/libs/ardour/ardour/panner.h b/libs/ardour/ardour/panner.h
index b30b1859a3..fa72b236f7 100644
--- a/libs/ardour/ardour/panner.h
+++ b/libs/ardour/ardour/panner.h
@@ -174,6 +174,8 @@ protected:
 extern "C" {
 struct PanPluginDescriptor {
 	std::string name;
+	std::string panner_uri;
+	std::string gui_uri;
 	int32_t in;
 	int32_t out;
 	ARDOUR::Panner* (*factory)(boost::shared_ptr<ARDOUR::Pannable>, boost::shared_ptr<ARDOUR::Speakers>);
diff --git a/libs/ardour/ardour/panner_manager.h b/libs/ardour/ardour/panner_manager.h
index 016ba56ce3..7b52c65c0a 100644
--- a/libs/ardour/ardour/panner_manager.h
+++ b/libs/ardour/ardour/panner_manager.h
@@ -49,7 +49,8 @@ public:
 	void discover_panners ();
 	std::list<PannerInfo*> panner_info;
 
-	PannerInfo* select_panner (ChanCount in, ChanCount out);
+	PannerInfo* select_panner (ChanCount in, ChanCount out, std::string const uri = "");
+	PannerInfo* get_by_uri (std::string uri);
 
 private:
 	PannerManager();
diff --git a/libs/ardour/ardour/panner_shell.h b/libs/ardour/ardour/panner_shell.h
index dba5826370..f798e0da97 100644
--- a/libs/ardour/ardour/panner_shell.h
+++ b/libs/ardour/ardour/panner_shell.h
@@ -36,6 +36,7 @@
 namespace ARDOUR {
 
 class Session;
+class Route;
 class Panner;
 class BufferSet;
 class AudioBuffer;
@@ -70,11 +71,23 @@ public:
 	bool bypassed () const;
 	void set_bypassed (bool);
 
+	std::string current_panner_uri() const { return _current_panner_uri; }
+	std::string user_selected_panner_uri() const { return _user_selected_panner_uri; }
+	std::string panner_gui_uri() const { return _panner_gui_uri; }
+
   private:
+	friend class Route;
 	void distribute_no_automation (BufferSet& src, BufferSet& dest, pframes_t nframes, gain_t gain_coeff);
+	bool set_user_selected_panner_uri (std::string const uri);
+
 	boost::shared_ptr<Panner> _panner;
 	boost::shared_ptr<Pannable> _pannable;
 	bool _bypassed;
+
+	std::string _current_panner_uri;
+	std::string _user_selected_panner_uri;
+	std::string _panner_gui_uri;
+	bool _force_reselect;
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/ardour/route.h b/libs/ardour/ardour/route.h
index 83605d7413..0d200ae44c 100644
--- a/libs/ardour/ardour/route.h
+++ b/libs/ardour/ardour/route.h
@@ -255,6 +255,7 @@ class Route : public SessionObject, public Automatable, public RouteGroupMember,
 	int remove_processor (boost::shared_ptr<Processor>, ProcessorStreams* err = 0, bool need_process_lock = true);
 	int remove_processors (const ProcessorList&, ProcessorStreams* err = 0);
 	int reorder_processors (const ProcessorList& new_order, ProcessorStreams* err = 0);
+	void set_custom_panner_uri (std::string const panner_uri);
 	void disable_processors (Placement);
 	void disable_processors ();
 	void disable_plugins (Placement);
diff --git a/libs/ardour/panner_manager.cc b/libs/ardour/panner_manager.cc
index 94e8d4ff2f..b62f36b355 100644
--- a/libs/ardour/panner_manager.cc
+++ b/libs/ardour/panner_manager.cc
@@ -24,7 +24,8 @@
 
 #include "pbd/error.h"
 #include "pbd/compose.h"
-#include "pbd/file_utils.h"
+#include "pbd/pathscanner.h"
+#include "pbd/stl_delete.h"
 
 #include "ardour/debug.h"
 #include "ardour/panner_manager.h"
@@ -59,25 +60,30 @@ PannerManager::instance ()
 	return *_instance;
 }
 
+static bool panner_filter (const string& str, void */*arg*/)
+{
+#ifdef __APPLE__
+	return str[0] != '.' && (str.length() > 6 && str.find (".dylib") == (str.length() - 6));
+#else
+	return str[0] != '.' && (str.length() > 3 && str.find (".so") == (str.length() - 3));
+#endif
+}
+
 void
 PannerManager::discover_panners ()
 {
-	vector<std::string> panner_modules;
-
-	Glib::PatternSpec so_extension_pattern("*.so");
-	Glib::PatternSpec dylib_extension_pattern("*.dylib");
+	PathScanner scanner;
+	std::vector<std::string *> *panner_modules;
+	std::string search_path = panner_search_path().to_string();
 
-	find_matching_files_in_search_path (panner_search_path (),
-	                                    so_extension_pattern, panner_modules);
+	DEBUG_TRACE (DEBUG::Panning, string_compose (_("looking for panners in %1\n"), search_path));
 
-	find_matching_files_in_search_path (panner_search_path (),
-	                                    dylib_extension_pattern, panner_modules);
+	panner_modules = scanner (search_path, panner_filter, 0, false, true, 1, true);
 
-	DEBUG_TRACE (DEBUG::Panning, string_compose (_("looking for panners in %1"), panner_search_path().to_string()));
-
-	for (vector<std::string>::iterator i = panner_modules.begin(); i != panner_modules.end(); ++i) {
-		panner_discover (*i);
+	for (vector<std::string *>::iterator i = panner_modules->begin(); i != panner_modules->end(); ++i) {
+		panner_discover (**i);
 	}
+	vector_delete (panner_modules);
 }
 
 int
@@ -97,7 +103,7 @@ PannerManager::panner_discover (string path)
 
 		if (i == panner_info.end()) {
 			panner_info.push_back (pinfo);
-			DEBUG_TRACE (DEBUG::Panning, string_compose(_("Panner discovered: \"%1\" in %2"), pinfo->descriptor.name, path));
+			DEBUG_TRACE (DEBUG::Panning, string_compose(_("Panner discovered: \"%1\" in %2\n"), pinfo->descriptor.name, path));
 		}
 	}
 
@@ -138,12 +144,21 @@ PannerManager::get_descriptor (string path)
 }
 
 PannerInfo*
-PannerManager::select_panner (ChanCount in, ChanCount out)
+PannerManager::select_panner (ChanCount in, ChanCount out, std::string const uri)
 {
 	PanPluginDescriptor* d;
 	int32_t nin = in.n_audio();
 	int32_t nout = out.n_audio();
 
+	/* look for user-preference -- check if channels match */
+	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
+		d = &(*p)->descriptor;
+		if (d->panner_uri != uri) continue;
+		if (d->in != nin && d->in != -1) continue;
+		if (d->out != nout && d->out != -1) continue;
+		return *p;
+	}
+
 	/* look for exact match first */
 
 	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
@@ -188,3 +203,15 @@ PannerManager::select_panner (ChanCount in, ChanCount out)
 
 	return 0;
 }
+
+PannerInfo*
+PannerManager::get_by_uri (std::string uri)
+{
+	PannerInfo* pi = NULL;
+	for (list<PannerInfo*>::iterator p = panner_info.begin(); p != panner_info.end(); ++p) {
+		if ((*p)->descriptor.panner_uri != uri) continue;
+		pi = (*p);
+		break;
+	}
+	return pi;
+}
diff --git a/libs/ardour/panner_search_path.cc b/libs/ardour/panner_search_path.cc
index 63802ffc4e..49ca786182 100644
--- a/libs/ardour/panner_search_path.cc
+++ b/libs/ardour/panner_search_path.cc
@@ -35,9 +35,7 @@ SearchPath
 panner_search_path ()
 {
 	SearchPath spath(user_config_directory ());
-	spath += ardour_dll_directory ();
 	spath.add_subdirectory_to_paths(panner_dir_name);
-
 	spath += SearchPath(Glib::getenv(panner_env_variable_name));
 	return spath;
 }
diff --git a/libs/ardour/panner_shell.cc b/libs/ardour/panner_shell.cc
index 1aeb94eb7e..a25cb49ab5 100644
--- a/libs/ardour/panner_shell.cc
+++ b/libs/ardour/panner_shell.cc
@@ -63,6 +63,10 @@ PannerShell::PannerShell (string name, Session& s, boost::shared_ptr<Pannable> p
 	: SessionObject (s, name)
 	, _pannable (p)
 	, _bypassed (false)
+	, _current_panner_uri("")
+	, _user_selected_panner_uri("")
+	, _panner_gui_uri("")
+	, _force_reselect (false)
 {
 	set_name (name);
 }
@@ -82,7 +86,7 @@ PannerShell::configure_io (ChanCount in, ChanCount out)
 	   the config hasn't changed, we're done.
 	*/
 
-	if (_panner && (_panner->in().n_audio() == nins) && (_panner->out().n_audio() == nouts)) {
+	if (!_force_reselect && _panner && (_panner->in().n_audio() == nins) && (_panner->out().n_audio() == nouts)) {
 		return;
 	}
 
@@ -90,17 +94,21 @@ PannerShell::configure_io (ChanCount in, ChanCount out)
 		/* no need for panning with less than 2 outputs or no inputs */
 		if (_panner) {
 			_panner.reset ();
+			_current_panner_uri = "";
+			_panner_gui_uri = "";
 			Changed (); /* EMIT SIGNAL */
 		}
 		return;
 	}
 
-	PannerInfo* pi = PannerManager::instance().select_panner (in, out);
+	PannerInfo* pi = PannerManager::instance().select_panner (in, out, _user_selected_panner_uri);
 	if (!pi) {
 		cerr << "No panner found: check that panners are being discovered correctly during startup.\n";
 		assert (pi);
 	}
 
+	DEBUG_TRACE (DEBUG::Panning, string_compose (_("select panner: %1\n"), pi->descriptor.name.c_str()));
+
 	boost::shared_ptr<Speakers> speakers = _session.get_speakers ();
 
 	if (nouts != speakers->size()) {
@@ -116,6 +124,8 @@ PannerShell::configure_io (ChanCount in, ChanCount out)
 	// boost_debug_shared_ptr_mark_interesting (p, "Panner");
 	_panner.reset (p);
 	_panner->configure_io (in, out);
+	_current_panner_uri = pi->descriptor.panner_uri;
+	_panner_gui_uri = pi->descriptor.gui_uri;
 
 	Changed (); /* EMIT SIGNAL */
 }
@@ -126,6 +136,7 @@ PannerShell::get_state ()
 	XMLNode* node = new XMLNode ("PannerShell");
 
 	node->add_property (X_("bypassed"), _bypassed ? X_("yes") : X_("no"));
+	node->add_property (X_("user-panner"), _user_selected_panner_uri);
 
 	if (_panner) {
 		node->add_child_nocopy (_panner->get_state ());
@@ -146,12 +157,29 @@ PannerShell::set_state (const XMLNode& node, int version)
 		set_bypassed (string_is_affirmative (prop->value ()));
 	}
 
+	if ((prop = node.property (X_("user-panner"))) != 0) {
+		_user_selected_panner_uri = prop->value ();
+	}
+
 	_panner.reset ();
 	
 	for (niter = nlist.begin(); niter != nlist.end(); ++niter) {
 
 		if ((*niter)->name() == X_("Panner")) {
 
+			if ((prop = (*niter)->property (X_("uri")))) {
+				PannerInfo* p = PannerManager::instance().get_by_uri(prop->value());
+				if (p) {
+					_panner.reset (p->descriptor.factory (_pannable, _session.get_speakers ()));
+					_current_panner_uri = p->descriptor.panner_uri;
+					_panner_gui_uri = p->descriptor.gui_uri;
+					if (_panner->set_state (**niter, version) == 0) {
+						return -1;
+					}
+				}
+			}
+
+			else /* backwards compatibility */
 			if ((prop = (*niter)->property (X_("type")))) {
 
 				list<PannerInfo*>::iterator p;
@@ -166,6 +194,8 @@ PannerShell::set_state (const XMLNode& node, int version)
 						*/
 
 						_panner.reset ((*p)->descriptor.factory (_pannable, _session.get_speakers ()));
+						_current_panner_uri = (*p)->descriptor.panner_uri;
+						_panner_gui_uri = (*p)->descriptor.gui_uri;
 
 						if (_panner->set_state (**niter, version) == 0) {
 							return -1;
@@ -347,3 +377,19 @@ PannerShell::bypassed () const
 {
 	return _bypassed;
 }
+
+/* set custom-panner config
+ *
+ * This function is intended to be only called from
+ * Route::set_custom_panner()
+ * which will trigger IO-reconfigutaion if this fn return true
+ */
+bool
+PannerShell::set_user_selected_panner_uri (std::string const uri)
+{
+	if (uri == _user_selected_panner_uri) return false;
+	_user_selected_panner_uri = uri;
+	if (uri == _current_panner_uri) return false;
+	_force_reselect = true;
+	return true;
+}
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index c032b77eff..951a4ff30c 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -51,6 +51,7 @@
 #include "ardour/midi_port.h"
 #include "ardour/monitor_processor.h"
 #include "ardour/pannable.h"
+#include "ardour/panner.h"
 #include "ardour/panner_shell.h"
 #include "ardour/plugin_insert.h"
 #include "ardour/port.h"
@@ -1574,6 +1575,51 @@ Route::remove_processors (const ProcessorList& to_be_deleted, ProcessorStreams*
 }
 
 void
+Route::set_custom_panner_uri (std::string const panner_uri)
+{
+	if (!_main_outs->panner_shell()->set_user_selected_panner_uri(panner_uri)) {
+		DEBUG_TRACE (DEBUG::Panning, string_compose (_("Route::set_custom_panner_uri '%1 '%2' -- no change needed\n"), name(), panner_uri));
+		/* no change needed */
+		return;
+	}
+
+	DEBUG_TRACE (DEBUG::Panning, string_compose (_("Route::set_custom_panner_uri '%1 '%2' -- reconfigure I/O\n"), name(), panner_uri));
+
+	if (_in_configure_processors) {
+		DEBUG_TRACE (DEBUG::Panning, string_compose (_("Route::set_custom_panner_uri '%1' -- called while in_configure_processors\n"), name()));
+		return;
+	}
+
+	/* reconfigure I/O */
+	{
+		Glib::Threads::RWLock::WriterLock lm (_processor_lock);
+		ProcessorState pstate (this);
+		if (panner())
+		{
+			/* there is already a panner it can just be re-configured in-place */
+			Glib::Threads::Mutex::Lock lm (AudioEngine::instance()->process_lock ());
+			ChanCount in = panner()->in();
+			ChanCount out = panner()->out();
+			_main_outs->panner_shell()->configure_io(in, out);
+			_main_outs->panner_shell()->pannable()->set_panner(panner());
+		}
+		else
+		{
+			Glib::Threads::Mutex::Lock lm (AudioEngine::instance()->process_lock ());
+
+			if (configure_processors_unlocked (0)) {
+				pstate.restore ();
+				configure_processors_unlocked (0); // it worked before we tried to add it ...
+				return;
+			}
+		}
+	}
+
+	processors_changed (RouteProcessorChange ()); /* EMIT SIGNAL */
+	_session.set_dirty ();
+}
+
+void
 Route::reset_instrument_info ()
 {
 	boost::shared_ptr<Processor> instr = the_instrument();