Introduce PluginFactory class

This singleton class handles management of plugin search paths and plugin
discovery. Search paths are (if they exist):
  * <lmms-exe-dir>/../lib/lmms: This is the common location on Unixoids
    (Not included in Windows builds)
  * <lmms-exe-dir>/plugins: For portable and Windows installations
  * The path given by the compile define LMMS_PLUGIN_DIR
  * Environment variable LMMS_PLUGIN_DIR if given

This commit also tweaks the build script to output built plugins to
"${CMAKE_BINARY_DIR}/plugins". This way lmms can find plugins during
development without the need to use `make install`.

Plugin::getDescriptorsOfAvailPlugins and ConfigManager::pluginDir were
removed.

include/ConfigManager.h

@@ -120,11 +120,6 @@ public:
 		return m_dataDir + LOCALE_PATH;
 	}
 
-	const QString & pluginDir() const
-	{
-		return m_pluginDir;
-	}
-
 	const QString & vstDir() const
 	{
 		return m_vstDir;
@@ -202,7 +197,6 @@ private:
 	QString m_workingDir;
 	QString m_dataDir;
 	QString m_artworkDir;
-	QString m_pluginDir;
 	QString m_vstDir;
 	QString m_flDir;
 	QString m_ladDir;

include/EffectSelectDialog.h

@@ -55,7 +55,6 @@ protected slots:
 private:
 	Ui::EffectSelectDialog * ui;
 
-	Plugin::DescriptorList m_pluginDescriptors;
 	EffectKeyList m_effectKeys;
 	EffectKey m_currentSelection;
 

include/Plugin.h

@@ -137,9 +137,8 @@ public:
 		SubPluginFeatures *subPluginFeatures;
 
 	} ;
-
 	// typedef a list so we can easily work with list of plugin descriptors
-	typedef QList<Descriptor> DescriptorList;
+	typedef QList<Descriptor*> DescriptorList;
 
 	// contructor of a plugin
 	Plugin( const Descriptor* descriptor, Model* parent );
@@ -177,9 +176,6 @@ public:
 	// if specified plugin couldn't be loaded, it creates a dummy-plugin
 	static Plugin * instantiate( const QString& pluginName, Model *parent, void * data );
 
-	// fills given list with descriptors of all available plugins
-	static void getDescriptorsOfAvailPlugins( DescriptorList& pluginDescriptors );
-
 	// create a view for the model 
 	PluginView* createView( QWidget* parent );
 

include/PluginBrowser.h

@@ -55,9 +55,6 @@ class PluginDescList : public QWidget
 	Q_OBJECT
 public:
 	PluginDescList(QWidget* parent);
-
-private:
-	Plugin::DescriptorList m_pluginDescriptors;
 };
 
 

include/PluginFactory.h

@@ -0,0 +1,84 @@
+/*
+ * PluginFactory.h
+ *
+ * Copyright (c) 2015 Lukas W <lukaswhl/at/gmail.com>
+ *
+ * This file is part of LMMS - http://lmms.io
+ *
+ * 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 (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef PLUGINFACTORY_H
+#define PLUGINFACTORY_H
+
+#include <QtCore/QFileInfo>
+#include <QtCore/QList>
+
+#include "Plugin.h"
+
+class QLibrary;
+
+class PluginFactory
+{
+public:
+	struct PluginInfo
+	{
+		QFileInfo file;
+		QLibrary* library;
+		Plugin::Descriptor* descriptor;
+
+		bool isNull() const {return library == 0;}
+	};
+	typedef QList<PluginInfo> PluginInfoList;
+
+	PluginFactory();
+	~PluginFactory();
+
+	/// Returns the singleton instance of PluginFactory. You won't need to call
+	/// this directly, use pluginFactory instead.
+	static PluginFactory* instance();
+
+	/// Returns a list of all found plugins' descriptors.
+	const Plugin::DescriptorList descriptors() const;
+
+	/// Returns a list of all found plugins' PluginFactory::PluginInfo objects.
+	const PluginInfoList& pluginInfos() const;
+
+	/// Returns the PluginInfo object of the plugin with the given name.
+	/// If the plugin is not found, an empty PluginInfo is returned (use
+	/// PluginInfo::isNull() to check this).
+	const PluginInfo pluginInfo(const char* name) const;
+
+	/// When loading a library fails during discovery, the error string is saved.
+	/// It can be retrieved by calling this function.
+	QString errorString(QString pluginName) const;
+
+public slots:
+	void discoverPlugins();
+
+private:
+	Plugin::DescriptorList m_descriptorList;
+	PluginInfoList m_pluginInfos;
+
+	QHash<QString, QString> m_errors;
+
+	static PluginFactory* s_instance;
+};
+
+#define pluginFactory PluginFactory::instance()
+
+#endif // PLUGINFACTORY_H