Module Interface
Extending &gdk-pixbuf;
If &gdk-pixbuf; has been compiled with GModule support, it can be extended by
modules which can load (and perhaps also save) new image and animation
formats. Each loadable module must export a
#GdkPixbufModuleFillInfoFunc function named fill_info and
a #GdkPixbufModuleFillVtableFunc function named
fill_vtable.
In order to make format-checking work before actually loading the modules
(which may require dlopening image libraries), modules export their
signatures (and other information) via the fill_info
function. An external utility, gdk-pixbuf-query-loaders,
uses this to create a text file containing a list of all available loaders and
their signatures. This file is then read at runtime by &gdk-pixbuf; to obtain
the list of available loaders and their signatures.
Modules may only implement a subset of the functionality available via
#GdkPixbufModule. If a particular functionality is not implemented, the
fill_vtable function will simply not set the corresponding
function pointers of the #GdkPixbufModule structure. If a module supports
incremental loading (i.e. provides #begin_load, #stop_load and
#load_increment), it doesn't have to implement #load, since &gdk-pixbuf; can
supply a generic #load implementation wrapping the incremental loading.
Installing a module is a two-step process:
copy the module file(s) to the loader directory (normally
libdir/gtk-2.0/version/loaders,
unless overridden by the environment variable
GDK_PIXBUF_MODULEDIR)
call gdk-pixbuf-query-loaders to update the
module file (normally
sysconfdir/gtk-2.0/gdk-pixbuf.loaders,
unless overridden by the environment variable
GDK_PIXBUF_MODULE_FILE)
The &gdk-pixbuf; interfaces needed for implementing modules are contained in
gdk-pixbuf-io.h (and
gdk-pixbuf-animation.h if the module supports animations).
They are not covered by the same stability guarantees as the regular
&gdk-pixbuf; API. To underline this fact, they are protected by
#ifdef GDK_PIXBUF_ENABLE_BACKEND.
@pixbuf:
@key:
@value:
@Returns:
@Returns:
@format:
@Returns:
@format:
@Returns:
@format:
@Returns:
@format:
@Returns:
@format:
@Returns:
A #GdkPixbufFormat contains information about the image format accepted by a
module. Only modules should access the fields directly, applications should
use the gdk_pixbuf_format_* functions.
@name: the name of the image format.
@signature: the signature of the module.
@domain: the message domain for the @description.
@description: a description of the image format.
@mime_types: a %NULL-terminated array of MIME types for the image format.
@extensions: a %NULL-terminated array of typical filename extensions for the
image format.
@flags: a combination of #GdkPixbufFormatFlags.
@Since: 2.2
Flags which allow a module to specify further details about the supported
operations.
@GDK_PIXBUF_FORMAT_WRITABLE: the module can write out images in the format.
@Since: 2.2
The signature of a module is a set of prefixes. Prefixes are encoded as
pairs of ordinary strings, where the second string, if not %NULL, must be
of the same length as the first one and may contain ' ', '!', 'x', 'z',
and 'n' to indicate bytes that must be matched, not matched,
"don't-care"-bytes, zeros and non-zeros.
Each prefix has an associated integer that describes the relevance of
the prefix, with 0 meaning a mismatch and 100 a "perfect match".
The signature of a module is stored as an array of
#GdkPixbufModulePatterns. The array is terminated by a pattern
where the @prefix is %NULL.
GdkPixbufModulePattern *signature[] = {
{ "abcdx", " !x z", 100 },
{ "bla", NULL, 90 },
{ NULL, NULL, 0 }
};
The example matches e.g. "auud\0" with relevance 100, and "blau" with
relevance 90.
@prefix: the prefix for this pattern
@mask: mask containing bytes which modify how the prefix is matched against
test data
@relevance: relevance of this pattern
@Since: 2.2
Defines the type of the function used to set the vtable of a
#GdkPixbufModule when it is loaded.
@module: a #GdkPixbufModule.
@Since: 2.2
Defines the type of the function used to fill a
#GdkPixbufFormat structure with information about a module.
@info: a #GdkPixbufFormat.
@Since: 2.2
Defines the type of the function that gets called once the size
of the loaded image is known.
The function is expected to set @width and @height to the desired
size to which the image should be scaled. If a module has no efficient
way to achieve the desired scaling during the loading of the image, it may
either ignore the size request, or only approximate it -- &gdk-pixbuf; will
then perform the required scaling on the completely loaded image.
@width: pointer to a location containing the current image width
@height: pointer to a location containing the current image height
@user_data: the loader.
@Since: 2.2
Defines the type of the function that gets called once the initial
setup of @pixbuf is done.
#GdkPixbufLoader uses a function of this type to emit the
"area_prepared"
signal.
@pixbuf: the #GdkPixbuf that is currently being loaded.
@anim: if an animation is being loaded, the #GdkPixbufAnimation, else %NULL.
@user_data: the loader.
@Since: 2.2
Defines the type of the function that gets called every time a region
of @pixbuf is updated.
#GdkPixbufLoader uses a function of this type to emit the
"area_updated"
signal.
@pixbuf: the #GdkPixbuf that is currently being loaded.
@x: the X origin of the updated area.
@y: the Y origin of the updated area.
@width: the width of the updated area.
@height: the height of the updated area.
@user_data: the loader.
@Since: 2.2
A #GdkPixbufModule contains the necessary functions to load and save
images in a certain file format.
A #GdkPixbufModule can be loaded dynamically from a #GModule.
Each loadable module must contain a #GdkPixbufModuleFillVtableFunc function
named fill_vtable, which will get called when the module
is loaded and must set the function pointers of the #GdkPixbufModule.
@module_name: the name of the module, usually the same as the
usual file extension for images of this type, eg. "xpm", "jpeg" or "png".
@module_path: the path from which the module is loaded.
@module: the loaded #GModule.
@info: a #GdkPixbufFormat holding information about the module.
@load: loads an image from a file.
@load_xpm_data: loads an image from data in memory.
@begin_load: begins an incremental load.
@stop_load: stops an incremental load.
@load_increment: continues an incremental load.
@load_animation: loads an animation from a file.
@save: saves a #GdkPixbuf to a file.
Modules supporting animations must derive a type from
#GdkPixbufAnimation, providing suitable implementations of the
virtual functions.
@parent_class:
@is_static_image: returns whether the given animation is just a static image.
@get_static_image: returns a static image representing the given animation.
@get_size: fills @width and @height with the frame size of the animation.
@get_iter: returns an iterator for the given animation.
Modules supporting animations must derive a type from
#GdkPixbufAnimationIter, providing suitable implementations of the
virtual functions.
@parent_class:
@get_delay_time: returns the time in milliseconds that the current frame
should be shown.
@get_pixbuf: returns the current frame.
@on_currently_loading_frame: returns whether the current frame of @iter is
being loaded.
@advance: advances the iterator to @current_time, possibly changing the
current frame.