/* This file is part of Magnum. Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Vladimír Vondruš Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */ namespace Magnum { /** @page plugins Loading and using plugins @brief Extending Magnum with additional functionality @tableofcontents @m_footernavigation @m_keywords{Plugins} The base Magnum libraries contain math support, scene graph implementation and are able to interact with graphics and audio hardware. However, they don't provide any functions for dealing with specific file formats on their own, as there are simply too many formats to include all of them directly. Instead, the libraries provide plugin APIs using which you can load a plugin that's able to understand a particular file format. Plugins are distributed as additional libraries and loaded either dynamically from the filesystem or, in case of embedded systems that don't support dynamic loading, built statically into the executable. Depending on the target platform requirements, different set of plugins can be deployed for different platforms. The @ref building "core Magnum repository" contains a few basic plugins for opening simple formats, such as TGA images or WAV audio files. These plugins are included because the file formats are so simple that no 3rd party libraries are needed for loading their contents and thus they are suitable for quick demos and prototyping without needing to deal with additional dependencies. Additional plugins (such as importers for PNG and JPEG images, glTF scenes, TrueType fonts etc.) are available in the @ref building-plugins "Magnum Plugins" repository. Majority of these plugins depends on external libraries, thus not all of them might be available on all platforms. @section plugins-types Plugin interfaces Plugin functionality is exposed via an interface that's common for all plugins of given type. Magnum provides these plugin interfaces: - @ref Trade::AbstractImporter --- importers for general 2D and 3D scene, mesh, material, texture and image data. See `*Importer` classes in the @ref Trade namespace for available importer plugins. - @ref Trade::AbstractImageConverter --- conversion among various image formats. See `*ImageConverter` classes in the @ref Trade namespace for available image converter plugins. - @ref Text::AbstractFont --- font loading and glyph layout. See `*Font` classes in the @ref Text namespace for available font plugins. - @ref Text::AbstractFontConverter --- font and glyph cache conversion. See `*FontConverter` classes in the @ref Text namespace for available font converter plugins. - @ref Audio::AbstractImporter --- importers for audio formats. See `*Importer` classes in the @ref Audio namespace for available audio importer plugins. @section plugins-loading Loading and instantiating plugins To load a plugin, you need to instantiate @ref Corrade::PluginManager::Manager for given plugin interface, for example for the @ref Trade::AbstractImporter. In order to find plugins on the filesystem, plugin interfaces have a bunch of plugin search paths hardcoded --- see documentation of the @ref Trade::AbstractImporter::pluginSearchPaths() "pluginSearchPaths()" functions provided by each plugin interface. It usually just works, but you can also pass a plugin directory to the manager constructor explicitly. Once the plugin manager is instantiated, you can start creating instances of particular plugins. Keep in mind that the manager instance has to exist for whole lifetime of all plugin instances created using it. @snippet plugins.cpp loading @section plugins-dependencies Plugin dependencies Some plugins have dependencies, for example the @ref Trade::TinyGltfImporter "TinyGltfImporter" plugin uses @ref Trade::AnyImageImporter "AnyImageImporter" to load texture data. The dependency loading is done automatically, but in some cases it's across plugin types (for example the @ref Text::MagnumFont "MagnumFont" plugin depends on the @ref Trade::TgaImporter "TgaImporter" plugin, which is of a different type) --- there you need to create manager instances for all required plugin interfaces: @snippet plugins.cpp dependencies @section plugins-static Static plugins By default, on desktop systems at least, all plugins are built as dynamic ones, i.e. they are a separate binary which gets linked in at runtime. This is good for reducing memory consumption, as the code is loaded in memory only for the time it is actually needed. However, if you need to port to a platform which does not support dynamic linking or you simply want to have the plugin loaded at all times, you can use static plugins. The plugins are built as static if the `BUILD_PLUGINS_STATIC` CMake parameter is enabled (see @ref building and @ref building-plugins for more information). The actual usage in the code is basically the same as above, but you need to explicitly find the plugin and link it into the executable. If you use CMake, it would look like this: @code{.cmake} find_package(MagnumPlugins REQUIRED TinyGltfImporter StbTrueTypeFont) add_executable(my-app my-app.cpp) target_link_libraries(my-app PRIVATE MagnumPlugins::TinyGltfImporter MagnumPlugins::StbTrueTypeFont) @endcode The only user-visible behavioral change in the code will be that @ref Corrade::PluginManager::AbstractManager::load() "PluginManager::Manager::load()" will return @ref Corrade::PluginManager::LoadState::Static "PluginManager::LoadState::Static" instead of @ref Corrade::PluginManager::LoadState::Loaded "PluginManager::LoadState::Loaded", but there is no need to change the above code, as it will work for both dynamic and static case. The static plugin needs to be explicitly registered so the plugin manager is aware it's there. If you use CMake, it's done automatically. Otherwise, you can achieve the same if you explicitly @cpp #include @ce the static plugin import file (named `importStaticPlugin.cpp`, residing in plugin's include directory) in a source file that gets compiled into your main application. The static import file contains just a simple call to @ref CORRADE_PLUGIN_IMPORT(), see its documentation for further information. @snippet plugins.cpp static-import @section plugins-aliases Plugin aliases and "any" plugins There's usually more than one plugin available to achieve a particular goal --- for example in order to open a PNG file, you can choose among @ref Trade::PngImporter "PngImporter", @ref Trade::StbImageImporter "StbImageImporter" or @ref Trade::DevIlImageImporter "DevIlImageImporter" plugins. Rather than this being an unnecessary redundancy, it allows you to pick a particular performance / portability / feature tradeoff --- a plugin with no external dependencies for a web build or, on the other hand, the fastest possible implementation for a tool that does heavy image processing. To make this simpler in the code and defer the decision to the buildsystem or app deployment, all plugins that support a particular format provide a common *alias* --- in case of PNG images, you can just load a @cpp "PngImporter" @ce plugin and if @ref Trade::PngImporter "PngImporter" is not available, it will pick up any of the other candidates. For greater control you can also use @ref Corrade::PluginManager::AbstractManager::setPreferredPlugins() "setPreferredPlugins()", giving a prioritized candidate list for a particular alias. This is especially useful in case of font plugins, where you can get advanced layout capabilities if the @ref Text::HarfBuzzFont "HarfBuzzFont" plugin is available or at least a faster and smoother glyph rendering if you can get the @ref Text::FreeTypeFont "FreeTypeFont" plugin. If none of the suggestions is available, it falls back to whatever is left (which can be, for example, the @ref Text::StbTrueTypeFont "StbTrueTypeFont" plugin). @snippet plugins.cpp aliases To make your life even simpler, there are various "any format" plugins --- these detect format based on file extension, map it to a plugin alias and then proxy the rest of the work to a corresponding plugin: @snippet plugins.cpp anyimporter Besides convenience for the end user, this allows for example the scene importer plugins to load any image formats without needing to have a knowledge about them or having an explicit dependency on multitude of image importer plugins. So far, the following plugins have the "any format" ability: - @ref Trade::AnyImageImporter "AnyImageImporter" --- imports any image format - @ref Trade::AnyImageConverter "AnyImageConverter" --- converts to any image format - @ref Trade::AnySceneImporter "AnySceneImporter" --- imports any scene format - @ref Audio::AnyImporter "AnyImporter" --- imports any audio format @section plugins-configuration Plugin-specific configuration Because it's not possible for a general statically typed plugin API to expose all possible knobs and switches that a file format could support, the plugins have a possibility to supply additional configuration via the @ref Corrade::PluginManager::AbstractPlugin::configuration() "configuration()" function. For example, in the @ref Trade-AssimpImporter-configuration "AssimpImporter" plugin you can toggle various postprocessing steps that are applied to loaded scene files: @snippet plugins.cpp configuration Besides affecting a single plugin instance, you can also change the configuration globally via @ref Corrade::PluginManager::PluginMetadata::configuration() "PluginManager::PluginMetadata::configuration()". That will affect all plugin instances created after. Resetting the global configuration back to the initial state can be done by recreating the plugin manager. @section plugins-direct Direct usage of plugins @todoc and also check that this is not already mentioned above @section plugins-develop Developing your own plugins See class documentation of particular plugin interfaces for more information about subclassing. The Corrade's @ref plugin-management "plugin management tutorial" contains more information about plugin compilation and registering. */ }