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This guide should give a short introduction in the way zathura's plugin system works and how you can write your own plugin and let zathura use it.

## Introduction

### Plugin system zathura's plugin system is quite simple. At startup zathura searches through a specified directory for shared objects and tries to load them as plugins. Each plugin has to register itself by a name, its version, a special function as well as its supported mimetypes to zathura. After the registration of the plugin zathura will automatically use it to open files with the previous defined mimetypes. That's it.

### A plugin Each plugin has to implement a basic set of functionality so that it can be used in a meaningful way with zathura. For instance it would not make any sense if the plugin was not able to render any page at all. On the contrary the export of images out of the document might not be considered as that important.

We have predefined a certain set of functionality that a plugin can have and that can be used by zathura if it has been implemented by the plugin. When a plugin is loaded, zathura calls a certain function that the plugin must implemented in order to work correctly. This function gets a data structure which has to be filled with function pointers by the plugin, which are then used by the main application.

## Example - A minimalistic PDF plugin In this section we are going to develop a simplified version of the zathura-pdf-poppler plugin. For the sake of simplicity we are not discussing the build process of the plugin because we would recommend you to adapt our Makefiles from existing plugins. In addition we avoid most of the error handling that should be implemented.

### Prerequisites In order to use the following described functions and macros you have to include the plugin-api.h header file:

~~~ {.c} #include ~~~

This automatically loads other header files for the zathura_document_t, zathura_page_t as well as all the other types that are necessary automatically.

### Register the plugin As previously described each plugin has to register itself to zathura so that it can be used properly. Therefore we have introduced a macro called ZATHURA_PLUGIN_REGISTER which expects several parameters:

Plugin name The name of the plugin
Major version The plugins major version
Minor version The plugins minor version
Revision The plugins revision
Open function The open function
Mimetypes A character array of supported mime types

In our case we are going to register our plugin "my plugin" with its version 1.0.1, the register function register_functions and the list of supported mimetypes.

~~~ {.c} ZATHURA_PLUGIN_REGISTER( "plugin-tutorial", 0, 1, 0, register_functions, ZATHURA_PLUGIN_MIMETYPES({ "application/pdf" }) ) ~~~

This macro will automatically generate among others a function called plugin_register which is used to register the plugin to zathura when it has been loaded.

### Register the plugin functions In our macro we have defined that the function register_functions is used to install our functions which will implement a certain functionality in the struct:

~~~ {.c} void register_functions(zathura_plugin_functions_t* functions) { functions->document_open = plugin_document_open; functions->document_free = plugin_document_free; functions->page_init = plugin_page_init; functions->page_clear = plugin_page_clear; functions->page_render_cairo = plugin_page_render_cairo; } ~~~

We are now going to give a short overview about the used functions in the above code snippet. For a complete documentation you should checkout the documentation of zathura_document_functions_t. A document instance consists out of a zathura_document_t document object that contains information about the document itself and a defined number of zathura_page_t page objects. There are several functions defined for those two types and they have to be implemented by the plugin. For our simple plugin which will only be capable of rendering a page we will need one function that is capable of opening the PDF document and setting up all necessary objects for further usage and one function which will clean up all the allocated objects afterwards. In addition we need two of those functions for page objects as well and one function that will actually implement the rendering process.

### Open and closing a document The first thing we have to do when opening a document is to initialize all necessary objects and values that we are going to need for the future use of the plugin. Therefore we have to implement our pdf_document_open function:

~~~ {.c} zathura_error_t plugin_document_open(zathura_document_t document) { / get path and password / const char path = zathura_document_get_path(document); const char* password = zathura_document_get_password(document);

/ create document data / char uri = g_filename_to_uri(path, NULL, NULL); PopplerDocument poppler_document = poppler_document_new_from_file(uri, password, NULL); g_free(uri);

if (poppler_document == NULL) { return ZATHURA_ERROR_UNKNOWN; }

/ save poppler document for further usage / zathura_document_set_data(document, poppler_document);

/ get number of pages / unsigned int number_of_pages = poppler_document_get_n_pages(poppler_document); zathura_document_set_number_of_pages(document, number_of_pages);