annotate vamp-sdk/hostext/PluginLoader.h @ 74:64d45f526afc

* strengthen imprecations against doing heavy lifting in plugin constructor

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Vamp

    An API for audio analysis and feature extraction plugins.

    Centre for Digital Music, Queen Mary, University of London.
    Copyright 2006-2007 Chris Cannam and QMUL.
  
    Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
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    of the Software, and to permit persons to whom the Software is
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    The above copyright notice and this permission notice shall be
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    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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    Except as contained in this notice, the names of the Centre for
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*/

#ifndef _VAMP_PLUGIN_LOADER_H_
#define _VAMP_PLUGIN_LOADER_H_

#include <vector>
#include <string>
#include <map>

#include "PluginWrapper.h"

namespace Vamp {

class Plugin;

namespace HostExt {

/**
 * Vamp::HostExt::PluginLoader is a convenience class for discovering
 * and loading Vamp plugins using the typical plugin-path, library
 * naming, and categorisation conventions described in the Vamp SDK
 * documentation.  This class is intended to greatly simplify the task
 * of becoming a Vamp plugin host for any C++ application.
 * 
 * Hosts are not required by the Vamp specification to use the same
 * plugin search path and naming conventions as implemented by this
 * class, and are certainly not required to use this actual class.
 * But it's recommended, for sound practical reasons.
 */

class PluginLoader
{
public:
    /**
     * PluginLoader is a singleton class.  This function returns a
     * pointer to the single instance of it.  Use this to obtain your
     * loader object.
     */
    static PluginLoader *getInstance();

    /**
     * PluginKey is a string type that is used to identify a plugin
     * uniquely within the scope of "the current system".  It consists
     * of the lower-cased base name of the plugin library, a colon
     * separator, and the identifier string for the plugin.  It is
     * only meaningful in the context of a given plugin path (the one
     * returned by PluginHostAdapter::getPluginPath()).
     *
     * Use composePluginKey to construct a plugin key from a known
     * plugin library name and identifier.
     *
     * Note: the fact that the library component of the key is
     * lower-cased implies that library names are matched
     * case-insensitively by the PluginLoader class, regardless of the
     * case sensitivity of the underlying filesystem.  (Plugin
     * identifiers _are_ case sensitive, however.)  Also, it is not
     * possible to portably extract a working library name from a
     * plugin key, as the result may fail on case-sensitive
     * filesystems.  Use getLibraryPathForPlugin instead.
     */
    typedef std::string PluginKey;

    /**
     * PluginKeyList is a sequence of plugin keys, such as returned by
     * a plugin lookup function.
     */
    typedef std::vector<PluginKey> PluginKeyList;

    /**
     * PluginCategoryHierarchy is a sequence of general->specific
     * category names, as may be associated with a single plugin.
     * This sequence describes the location of a plugin within a
     * category forest, containing the human-readable names of the
     * plugin's category tree root, followed by each of the nodes down
     * to the leaf containing the plugin.
     */
    typedef std::vector<std::string> PluginCategoryHierarchy;

    /**
     * Search for all available Vamp plugins, and return a list of
     * them in the order in which they were found.
     */
    PluginKeyList listPlugins();

    /**
     * AdapterFlags contains a set of values that may be OR'd together
     * to indicate in which circumstances PluginLoader should use a
     * plugin adapter to make a plugin easier to use for a host that
     * does not want to cater for complex features.
     *
     * The available flags are:
     * 
     * ADAPT_INPUT_DOMAIN - If the plugin expects frequency domain
     * input, wrap it in a PluginInputDomainAdapter that automatically
     * converts the plugin to one that expects time-domain input.
     * This enables a host to accommodate time- and frequency-domain
     * plugins without needing to do any conversion itself.
     *
     * ADAPT_CHANNEL_COUNT - Wrap the plugin in a PluginChannelAdapter
     * to handle any mismatch between the number of channels of audio
     * the plugin can handle and the number available in the host.
     * This enables a host to use plugins that may require the input
     * to be mixed down to mono, etc., without having to worry about
     * doing that itself.
     * 
     * See PluginInputDomainAdapter and PluginChannelAdapter for more
     * details of the classes that the loader may use if these flags
     * are set.
     */
    enum AdapterFlags {
        ADAPT_INPUT_DOMAIN  = 0x01,
        ADAPT_CHANNEL_COUNT = 0x02,
        ADAPT_ALL           = 0xff
    };

    /**
     * Load a Vamp plugin, given its identifying key.  If the plugin
     * could not be loaded, returns 0.
     *
     * adapterFlags is a bitwise OR of the values in the AdapterFlags
     * enum, indicating under which circumstances an adapter should be
     * used to wrap the original plugin.  See AdapterFlags for more
     * details.  If adapterFlags is 0, no optional adapters will be
     * used.
     *
     * The returned plugin should be deleted (using the standard C++
     * delete) after use.
     */
    Plugin *loadPlugin(PluginKey key,
                       float inputSampleRate,
                       int adapterFlags = 0);

    /**
     * Given a Vamp plugin library name and plugin identifier, return
     * the corresponding plugin key in a form suitable for passing in to
     * loadPlugin.
     */
    PluginKey composePluginKey(std::string libraryName,
                               std::string identifier);

    /**
     * Return the category hierarchy for a Vamp plugin, given its
     * identifying key.  See PluginCategoryHierarchy documentation for
     * more details.
     *
     * If the plugin has no category information, return an empty
     * hierarchy.
     */
    PluginCategoryHierarchy getPluginCategory(PluginKey plugin);

    /**
     * Return the file path of the dynamic library from which the
     * given plugin will be loaded (if available).
     */
    std::string getLibraryPathForPlugin(PluginKey plugin);

protected:
    PluginLoader();
    virtual ~PluginLoader();

    class Impl;
    Impl *m_impl;

    static PluginLoader *m_instance;
};

}

}

#endif