gdk-pixbuf-Module-Interface: Module Interface
In RGtk2: R Bindings for Gtk 2.8.0 and Above

Description Methods and Functions Detailed Description Structures User Functions Author(s) References

Extending

gdkPixbufSetOption(object, key, value)
gdkPixbufGetFormats()
gdkPixbufFormatGetName(object)
gdkPixbufFormatGetDescription(object)
gdkPixbufFormatGetMimeTypes(object)
gdkPixbufFormatGetExtensions(object)
gdkPixbufFormatIsWritable(object)
gdkPixbufFormatIsScalable(object)
gdkPixbufFormatIsDisabled(object)
gdkPixbufFormatSetDisabled(object, disabled)
gdkPixbufFormatGetLicense(object)

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 fillInfo and a GdkPixbufModuleFillVtableFunc function named fillVtable.

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 fillInfo 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 fillVtable 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’, unless overridden by the environment variable GDK_PIXBUF_MODULEDIR)
call gdk-pixbuf-query-loaders to update the module file (normally ‘sysconfdir’, 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.

GdkPixbufFormat

A GdkPixbufFormat contains information about the image format accepted by a module. Only modules should access the fields directly, applications should use the gdkPixbufFormat* functions. Since 2.2

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 list of MIME types for the image format.
extensions: a list of typical filename extensions for the image format.
flags: a combination of GdkPixbufFormatFlags.
disabled: a boolean determining whether the loader is disabled.
license: a string containing license information, typically set to shorthands like "GPL", "LGPL", etc.

GdkPixbufModuleFillVtableFunc(module)

Defines the type of the function used to set the vtable of a GdkPixbufModule when it is loaded. Since 2.2

module: a GdkPixbufModule.

GdkPixbufModuleFillInfoFunc(info)

Defines the type of the function used to fill a GdkPixbufFormat structure with information about a module. Since 2.2

info: a GdkPixbufFormat.

GdkPixbufModuleSizeFunc(width, height, user.data)

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.

If the function sets width or height to zero, the module should interpret this as a hint that it will be closed soon and shouldn't allocate further resources. This convention is used to implement gdkPixbufGetFileInfo efficiently. Since 2.2

width: pointer to a location containing the current image width
height: pointer to a location containing the current image height
user.data: the loader.

GdkPixbufModulePreparedFunc(pixbuf, anim, user.data)

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. Since 2.2

pixbuf: the GdkPixbuf that is currently being loaded.
anim: if an animation is being loaded, the GdkPixbufAnimation, else NULL.
user.data: the loader.

GdkPixbufModuleUpdatedFunc(pixbuf, x, y, width, height, user.data)

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. Since 2.2

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.