A GdkPixbufModule contains the necessary functions to load and save
images in a certain file format.
If GdkPixbuf has been compiled with GModule support, it can be extended
by modules which can load (and perhaps also save) new image and animation
formats.
The GdkPixbuf 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 GdkPixbuf API. To underline this fact, they are protected by the
GDK_PIXBUF_ENABLE_BACKEND pre-processor symbol.
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.
In order to make format-checking work before actually loading the modules
(which may require calling dlopen to load 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 GdkPixbuf 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 GdkPixbuf
can supply a generic load implementation wrapping the incremental loading.
copy the module file(s) to the loader directory (normally
$libdir/gdk-pixbuf-2.0/$version/loaders, unless overridden by the
environment variable GDK_PIXBUF_MODULEDIR)
call gdk-pixbuf-query-loaders to update the module file (normally
$libdir/gdk-pixbuf-2.0/$version/loaders.cache, unless overridden
by the environment variable GDK_PIXBUF_MODULE_FILE)
A
GdkPixbufModulecontains the necessary functions to load and save images in a certain file format.If
GdkPixbufhas been compiled withGModulesupport, it can be extended by modules which can load (and perhaps also save) new image and animation formats.Implementing modules
The
GdkPixbufinterfaces needed for implementing modules are contained ingdk-pixbuf-io.h(andgdk-pixbuf-animation.hif the module supports animations). They are not covered by the same stability guarantees as the regular GdkPixbuf API. To underline this fact, they are protected by theGDK_PIXBUF_ENABLE_BACKENDpre-processor symbol.Each loadable module must contain a
GdkPixbufModuleFillVtableFuncfunction namedfill_vtable, which will get called when the module is loaded and must set the function pointers of theGdkPixbufModule.In order to make format-checking work before actually loading the modules (which may require calling
dlopento load image libraries), modules export their signatures (and other information) via thefill_infofunction. 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 byGdkPixbufto 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, thefill_vtablefunction will simply not set the corresponding function pointers of theGdkPixbufModulestructure. If a module supports incremental loading (i.e. providesbegin_load,stop_loadandload_increment), it doesn't have to implementload, sinceGdkPixbufcan supply a genericloadimplementation wrapping the incremental loading.Installing modules
Installing a module is a two-step process:
$libdir/gdk-pixbuf-2.0/$version/loaders, unless overridden by the environment variableGDK_PIXBUF_MODULEDIR)gdk-pixbuf-query-loadersto update the module file (normally$libdir/gdk-pixbuf-2.0/$version/loaders.cache, unless overridden by the environment variableGDK_PIXBUF_MODULE_FILE)