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@ -6,7 +6,58 @@ Extending &gdk-pixbuf;
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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If &gdk-pixbuf; has been compiled with GModule support, it can be extended by
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modules which can load (and perhaps also save) new image and animation
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formats. Each loadable module must export a
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#GdkPixbufModuleFillInfoFunc function named <function>fill_info</function> and
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a #GdkPixbufModuleFillVtableFunc function named
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<function>fill_vtable</function>.
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</para>
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<para>
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In order to make format-checking work before actually loading the modules
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(which may require dlopening image libraries), modules export their
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signatures (and other information) via the <function>fill_info</function>
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function. An external utility, <command>gdk-pixbuf-query-loaders</command>, uses
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this to create a text file containing a list of all available loaders and
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their signatures. This file is then read at runtime by &gdk-pixbuf; to obtain
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the list of available loaders and their signatures.
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</para>
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<para>
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Modules may only implement a subset of the functionality available via
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#GdkPixbufModule. If a particular functionality is not implemented, the
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<function>fill_vtable</function> function will simply not set the corresponding
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function pointers of the #GdkPixbufModule structure. If a module supports
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incremental loading (i.e. provides #begin_load, #stop_load and
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#load_increment), it doesn't have to implement #load, since &gdk-pixbuf; can
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supply a generic #load implementation wrapping the incremental loading.
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</para>
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<para>
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Installing a module is a two-step process:
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<itemizedlist>
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<listitem><para>copy the module file(s) to the loader directory (normally
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<filename><replaceable>libdir</replaceable>/gtk-2.0/<replaceable>version</replaceable>/loaders</filename>,
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unless overridden by the environment variable
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<envar>GDK_PIXBUF_MODULEDIR</envar>)
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</para></listitem>
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<listitem><para>call <command>gdk-pixbuf-query-loaders</command> to update the
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module file (normally
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<filename><replaceable>sysconfdir</replaceable>/gtk-2.0/gdk-pixbuf.loaders</filename>,
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unless overridden by the environment variable
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<envar>GDK_PIXBUF_MODULE_FILE</envar>)
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</para></listitem>
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</itemizedlist>
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</para>
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<para>
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The &gdk-pixbuf; interfaces needed for implementing modules are contained in
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<filename>gdk-pixbuf-io.h</filename> (and
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<filename>gdk-pixbuf-animation.h</filename> if the module supports animations).
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They are not covered by the same stability guarantees as the regular
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&gdk-pixbuf; API. To underline this fact, they are protected by
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<literal>#ifdef GDK_PIXBUF_ENABLE_BACKEND</literal>.
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</para>
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<!-- ##### SECTION See_Also ##### -->
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@ -14,7 +65,95 @@ Extending &gdk-pixbuf;
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</para>
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<!-- ##### USER_FUNCTION ModuleFillVtableFunc ##### -->
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<!-- ##### FUNCTION gdk_pixbuf_get_formats ##### -->
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<para>
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</para>
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_format_get_name ##### -->
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<para>
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</para>
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@format:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_format_get_description ##### -->
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<para>
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</para>
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@format:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_format_get_mime_types ##### -->
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<para>
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</para>
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@format:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_format_get_extensions ##### -->
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<para>
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</para>
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@format:
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@Returns:
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<!-- ##### FUNCTION gdk_pixbuf_format_is_writable ##### -->
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<para>
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</para>
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@format:
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@Returns:
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<!-- ##### STRUCT GdkPixbufFormat ##### -->
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<para>
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A #GdkPixbufFormat contains information about the image format accepted by a
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module. Only modules should access the fields directly.
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</para>
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@name: the name of the image format
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@signature: the signature of the module
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@domain: the message domain for the @description
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@description: a description of the image format
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@mime_types: a %NULL-terminated array of MIME types for the image format.
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@extensions: a %NULL-terminated array of typical filename extensions for the
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image format.
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@flags:
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<!-- ##### STRUCT GdkPixbufModulePattern ##### -->
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<para>
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The signature of a module is a set of prefixes. Prefixes are encoded as
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pairs of ordinary strings, where the second string, if not %NULL,
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may contain ' ', '!', 'x', 'z', and 'n' to indicate bytes that must be
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matched, not matched, "don't-care"-bytes, zeros and non-zeros.
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Each prefix has an associated integer that describes the relevance of
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the prefix, with 0 meaning a mismatch and 100 a "perfect match".
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</para>
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<para>
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The signature of a module is stored as an array of
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#GdkPixbufModulePattern<!-- -->s.
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</para>
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@prefix: the prefix for this pattern
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@mask: mask containing bytes which modify how the prefix is matched against
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test data
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@relevance: relevance of this pattern
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<!-- ##### USER_FUNCTION GdkPixbufModuleFillVtableFunc ##### -->
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<para>
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Defines the type of the function used to set the vtable of a
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#GdkPixbufModule when it is loaded.
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@ -23,16 +162,25 @@ Defines the type of the function used to set the vtable of a
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@module: a #GdkPixbufModule.
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<!-- ##### USER_FUNCTION ModuleSizeFunc ##### -->
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<!-- ##### USER_FUNCTION GdkPixbufModuleFillInfoFunc ##### -->
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<para>
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Defines the type of the function used to fill a
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#GdkPixbufFormat structure with information about a module.
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</para>
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@info: a #GdkPixbufFormat.
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<!-- ##### USER_FUNCTION GdkPixbufModuleSizeFunc ##### -->
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<para>
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Defines the type of the function that gets called once the size
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of the loaded image is known is done.
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of the loaded image is known.
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</para>
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<para>
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The function is expected to set @width and @height to the desired
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size to which the image should be scaled. If a module has no efficient
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way to achieve the desired scaling during the loading of the image, it may
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either ignore the size request, or only approximate it -- the loader will
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either ignore the size request, or only approximate it -- &gdk-pixbuf; will
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then perform the required scaling on the completely loaded image.
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</para>
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@ -41,7 +189,7 @@ then perform the required scaling on the completely loaded image.
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@user_data: the loader.
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<!-- ##### USER_FUNCTION ModulePreparedNotifyFunc ##### -->
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<!-- ##### USER_FUNCTION GdkPixbufModulePreparedFunc ##### -->
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<para>
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Defines the type of the function that gets called once the initial
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setup of @pixbuf is done.
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@ -57,7 +205,7 @@ signal.
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@user_data: the loader.
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<!-- ##### USER_FUNCTION ModuleUpdatedNotifyFunc ##### -->
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<!-- ##### USER_FUNCTION GdkPixbufModuleUpdatedFunc ##### -->
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<para>
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Defines the type of the function that gets called every time a region
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of @pixbuf is updated.
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@ -83,17 +231,16 @@ images in a certain file format.
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</para>
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<para>
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A #GdkPixbufModule can be loaded dynamically from a #GModule.
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Each loadable module must contain a #ModuleFillVtableFunc function named
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<function>gdk_pixbuf__<replaceable>module_name</replaceable>_fill_vtable</function>.
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It will get called when the module is loaded and must set the function
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pointers of the #GdkPixbufModule.
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Each loadable module must contain a #GdkPixbufModuleFillVtableFunc function
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named <function>fill_vtable</function>, which will get called when the module
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is loaded and must set the function pointers of the #GdkPixbufModule.
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</para>
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@module_name: the name of the module, usually the same as the
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usual file extension for images of this type, eg. "xpm", "jpeg" or "png".
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@format_check: checks if the given data is the beginning of a valid image
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in the format supported by the module.
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@module_path: the path from which the module is loaded.
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@module: the loaded #GModule.
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@info: a #GdkPixbufFormat holding information about the module.
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@load: loads an image from a file.
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@load_xpm_data: loads an image from data in memory.
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@begin_load: begins an incremental load.
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@ -101,4 +248,10 @@ pointers of the #GdkPixbufModule.
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@load_increment: continues an incremental load.
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@load_animation: loads an animation from a file.
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@save: saves a #GdkPixbuf to a file.
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@_reserved1:
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@_reserved2:
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@_reserved3:
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@_reserved4:
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@_reserved5:
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@_reserved6:
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Matthias Clasen