scummvm/base/plugins.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL$
 * $Id$
 *
 */

#ifndef BASE_PLUGINS_H
#define BASE_PLUGINS_H

#include "common/error.h"
#include "common/singleton.h"
#include "common/util.h"

namespace Common {
	class FSList;
	class FSNode;
}


/**
 * @page pagePlugins An overview of the ScummVM plugin system
 * This is a brief overview of how plugins (dynamically loadable code modules)
 * work in ScummVM. We will explain how to write plugins, how they work internally,
 * and sketch how porters can add support for them in their ports.
 *
 * \section secPluginImpl Implementing a plugin
 * TODO
 *
 * \section secPluginUse Using plugins
 * TODO
 *
 * \section secPluginInternals How plugins work internally
 * TODO
 *
 * \section secPluginBackend How to add support for dynamic plugins to a port
 * TODO
 */



// Plugin versioning

/** Global Plugin API version */
#define PLUGIN_VERSION 1

enum PluginType {
	PLUGIN_TYPE_ENGINE = 0,
	PLUGIN_TYPE_MUSIC,
	/* PLUGIN_TYPE_SCALER, */	// TODO: Add graphics scaler plugins

	PLUGIN_TYPE_MAX
};

// TODO: Make the engine API version depend on ScummVM's version
// because of the backlinking (posibly from the SVN revision)
#define PLUGIN_TYPE_ENGINE_VERSION 1
#define PLUGIN_TYPE_MUSIC_VERSION 1

extern int pluginTypeVersions[PLUGIN_TYPE_MAX];


// Plugin linking

#define STATIC_PLUGIN 1
#define DYNAMIC_PLUGIN 2

#define PLUGIN_ENABLED_STATIC(ID) \
	(ENABLE_##ID && !PLUGIN_ENABLED_DYNAMIC(ID))

#define PLUGIN_ENABLED_DYNAMIC(ID) \
	(ENABLE_##ID && (ENABLE_##ID == DYNAMIC_PLUGIN) && DYNAMIC_MODULES)

/**
 * REGISTER_PLUGIN_STATIC is a convenience macro which is used to declare
 * the plugin interface for static plugins. Code (such as game engines)
 * which needs to implement a static plugin can simply invoke this macro
 * with a plugin ID, plugin type and PluginObject subclass, and the correct
 * wrapper code will be inserted.
 *
 * @see REGISTER_PLUGIN_DYNAMIC
 */
#define REGISTER_PLUGIN_STATIC(ID,TYPE,PLUGINCLASS) \
	PluginType g_##ID##_type = TYPE; \
	PluginObject *g_##ID##_getObject() { \
		return new PLUGINCLASS(); \
	} \
	void dummyFuncToAllowTrailingSemicolon()

#ifdef DYNAMIC_MODULES

/**
 * REGISTER_PLUGIN_DYNAMIC is a convenience macro which is used to declare
 * the plugin interface for dynamically loadable plugins. Code (such as game engines)
 * which needs to implement a dynamic plugin can simply invoke this macro
 * with a plugin ID, plugin type and PluginObject subclass, and the correct
 * wrapper code will be inserted.
 *
 * @see REGISTER_PLUGIN_STATIC
 */
#define REGISTER_PLUGIN_DYNAMIC(ID,TYPE,PLUGINCLASS) \
	extern "C" { \
		PLUGIN_EXPORT int32 PLUGIN_getVersion() { return PLUGIN_VERSION; } \
		PLUGIN_EXPORT int32 PLUGIN_getType() { return TYPE; } \
		PLUGIN_EXPORT int32 PLUGIN_getTypeVersion() { return TYPE##_VERSION; } \
		PLUGIN_EXPORT PluginObject *PLUGIN_getObject() { \
			return new PLUGINCLASS(); \
		} \
	} \
	void dummyFuncToAllowTrailingSemicolon()

#endif // DYNAMIC_MODULES


// Abstract plugins

/**
 * Abstract base class for the plugin objects which handle plugins
 * instantiation. Subclasses for this may be used for engine plugins
 * and other types of plugins.
 *
 * FIXME: This class needs better documentation, esp. how it differs from class Plugin
 */
class PluginObject {
public:
	virtual ~PluginObject() {}

	/** Returns the name of the plugin. */
	virtual const char *getName() const = 0;
};

/**
 * Abstract base class for the plugin system.
 * Subclasses for this can be used to wrap both static and dynamic
 * plugins.
 *
 * FIXME: This class needs better documentation, esp. how it differs from class PluginObject
 */
class Plugin {
protected:
	PluginObject *_pluginObject;
	PluginType _type;

public:
	Plugin() : _pluginObject(0) {}
	virtual ~Plugin() {
		//if (isLoaded())
			//unloadPlugin();
	}

//	virtual bool isLoaded() const = 0;	// TODO
	virtual bool loadPlugin() = 0;	// TODO: Rename to load() ?
	virtual void unloadPlugin() = 0;	// TODO: Rename to unload() ?

	PluginType getType() const;
	const char *getName() const;
};

/** List of Plugin instances. */
typedef Common::Array<Plugin *> PluginList;

/**
 * Convenience template to make it easier defining normal Plugin
 * subclasses. Namely, the PluginSubclass will manage PluginObjects
 * of a type specified via the PO_t template parameter.
 */
template<class PO_t>
class PluginSubclass : public Plugin {
public:
	PO_t *operator->() const {
		return (PO_t *)_pluginObject;
	}

	typedef Common::Array<PluginSubclass *> List;
};

/**
 * Abstract base class for Plugin factories. Subclasses of this
 * are responsible for creating plugin objects, e.g. by loading 
 * loadable modules from storage media; by creating "fake" plugins
 * from static code; or whatever other means.
 */
class PluginProvider {
public:
	virtual ~PluginProvider() {}

	/**
	 * Return a list of Plugin objects. The caller is responsible for actually
	 * loading/unloading them (by invoking the appropriate Plugin methods).
	 * Furthermore, the caller is responsible for deleting these objects
	 * eventually.
	 *
	 * @return a list of Plugin instances
	 */
	virtual PluginList getPlugins() = 0;
};

#ifdef DYNAMIC_MODULES

/**
 * Abstract base class for Plugin factories which load binary code from files.
 * Subclasses only have to implement the createPlugin() method, and optionally
 * can overload the other protected methods to achieve custom behavior.
 */
class FilePluginProvider : public PluginProvider {
public:
	/**
	 * Return a list of Plugin objects loaded via createPlugin from disk.
	 * For this, a list of directories is searched for plugin objects:
	 * The current dir and its "plugins" subdirectory (if present), a list
	 * of custom search dirs (see addCustomDirectories) and finally the 
	 * directory specified via the "pluginspath" config variable (if any).
	 *
	 * @return a list of Plugin instances
	 */
	virtual PluginList getPlugins();

protected:
	/**
	 * Create a Plugin instance from a loadable code module with the specified name.
	 * Subclasses of FilePluginProvider have to at least overload this method.
	 * If the file is not found, or does not contain loadable code, 0 is returned instead.
	 *
	 * @param node	the FSNode of the loadable code module
	 * @return	a pointer to a Plugin instance, or 0 if an error occurred.
	 */
	virtual Plugin *createPlugin(const Common::FSNode &node) const = 0;

	/**
	 * Check if the supplied file corresponds to a loadable plugin file in
	 * the current platform. Usually, this will just check the file name.
	 *
	 * @param node	the FSNode of the file to check
	 * @return	true if the filename corresponds to a plugin, false otherwise
	 */
	virtual bool isPluginFilename(const Common::FSNode &node) const;

	/**
	 * Optionally add to the list of directories to be searched for
	 * plugins by getPlugins().
	 *
	 * @param dirs	the reference to the list of directories to be used when
	 * 		searching for plugins.
	 */
	virtual void addCustomDirectories(Common::FSList &dirs) const;
};

#endif // DYNAMIC_MODULES

/**
 * Singleton class which manages all plugins, including loading them,
 * managing all Plugin class instances, and unloading them.
 */
class PluginManager : public Common::Singleton<PluginManager> {
	typedef Common::Array<PluginProvider *> ProviderList;
private:
	PluginList _plugins[PLUGIN_TYPE_MAX];
	ProviderList _providers;

	bool tryLoadPlugin(Plugin *plugin);

	friend class Common::Singleton<SingletonBaseType>;
	PluginManager();

public:
	~PluginManager();

	void addPluginProvider(PluginProvider *pp);

	void loadPlugins();
	void unloadPlugins();
	void unloadPluginsExcept(PluginType type, const Plugin *plugin);

	const PluginList &getPlugins(PluginType t) { return _plugins[t]; }
};

#endif