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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: https://scummvm.svn.sourceforge.net/svnroot/scummvm/scummvm/tags/release-1-0-0rc1/base/plugins.h $
 * $Id: plugins.h 35481 2008-12-22 11:22:15Z jvprat $
 *
 */

#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
 */
00142 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
 */
00157 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>
00186 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.
 */
00201 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.
 */
00272 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

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