Module Interface

Module Interface — Extending gdk-pixbuf

Synopsis

#include <gdk-pixbuf/gdk-pixbuf.h>


gboolean    gdk_pixbuf_set_option           (GdkPixbuf *pixbuf,
                                             const gchar *key,
                                             const gchar *value);
GSList*     gdk_pixbuf_get_formats          (void);
gchar*      gdk_pixbuf_format_get_name      (GdkPixbufFormat *format);
gchar*      gdk_pixbuf_format_get_description
                                            (GdkPixbufFormat *format);
gchar**     gdk_pixbuf_format_get_mime_types
                                            (GdkPixbufFormat *format);
gchar**     gdk_pixbuf_format_get_extensions
                                            (GdkPixbufFormat *format);
gboolean    gdk_pixbuf_format_is_writable   (GdkPixbufFormat *format);
gboolean    gdk_pixbuf_format_is_scalable   (GdkPixbufFormat *format);
gboolean    gdk_pixbuf_format_is_disabled   (GdkPixbufFormat *format);
void        gdk_pixbuf_format_set_disabled  (GdkPixbufFormat *format,
                                             gboolean disabled);
gchar*      gdk_pixbuf_format_get_license   (GdkPixbufFormat *format);
            GdkPixbufFormat;
enum        GdkPixbufFormatFlags;
            GdkPixbufModulePattern;
void        (*GdkPixbufModuleFillVtableFunc)
                                            (GdkPixbufModule *module);
void        (*GdkPixbufModuleFillInfoFunc)  (GdkPixbufFormat *info);
void        (*GdkPixbufModuleSizeFunc)      (gint *width,
                                             gint *height,
                                             gpointer user_data);
void        (*GdkPixbufModulePreparedFunc)  (GdkPixbuf *pixbuf,
                                             GdkPixbufAnimation *anim,
                                             gpointer user_data);
void        (*GdkPixbufModuleUpdatedFunc)   (GdkPixbuf *pixbuf,
                                             int x,
                                             int y,
                                             int width,
                                             int height,
                                             gpointer user_data);
            GdkPixbufModule;

            GdkPixbufAnimationClass;
            GdkPixbufAnimationIterClass;

Description

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.

Details

gdk_pixbuf_set_option ()

gboolean    gdk_pixbuf_set_option           (GdkPixbuf *pixbuf,
                                             const gchar *key,
                                             const gchar *value);

Attaches a key/value pair as an option to a GdkPixbuf. If key already exists in the list of options attached to pixbuf, the new value is ignored and FALSE is returned.

pixbuf : a GdkPixbuf
key : a nul-terminated string.
value : a nul-terminated string.
Returns : TRUE on success.

Since 2.2


gdk_pixbuf_get_formats ()

GSList*     gdk_pixbuf_get_formats          (void);

Obtains the available information about the image formats supported by GdkPixbuf.

Returns : A list of GdkPixbufFormats describing the supported image formats. The list should be freed when it is no longer needed, but the structures themselves are owned by GdkPixbuf and should not be freed.

Since 2.2


gdk_pixbuf_format_get_name ()

gchar*      gdk_pixbuf_format_get_name      (GdkPixbufFormat *format);

Returns the name of the format.

format : a GdkPixbufFormat
Returns : the name of the format.

Since 2.2


gdk_pixbuf_format_get_description ()

gchar*      gdk_pixbuf_format_get_description
                                            (GdkPixbufFormat *format);

Returns a description of the format.

format : a GdkPixbufFormat
Returns : a description of the format.

Since 2.2


gdk_pixbuf_format_get_mime_types ()

gchar**     gdk_pixbuf_format_get_mime_types
                                            (GdkPixbufFormat *format);

Returns the mime types supported by the format.

format : a GdkPixbufFormat
Returns : a NULL-terminated array of mime types which must be freed with g_strfreev() when it is no longer needed.

Since 2.2


gdk_pixbuf_format_get_extensions ()

gchar**     gdk_pixbuf_format_get_extensions
                                            (GdkPixbufFormat *format);

Returns the filename extensions typically used for files in the given format.

format : a GdkPixbufFormat
Returns : a NULL-terminated array of filename extensions which must be freed with g_strfreev() when it is no longer needed.

Since 2.2


gdk_pixbuf_format_is_writable ()

gboolean    gdk_pixbuf_format_is_writable   (GdkPixbufFormat *format);

Returns whether pixbufs can be saved in the given format.

format : a GdkPixbufFormat
Returns : whether pixbufs can be saved in the given format.

Since 2.2


gdk_pixbuf_format_is_scalable ()

gboolean    gdk_pixbuf_format_is_scalable   (GdkPixbufFormat *format);

Returns whether this image format is scalable. If a file is in a scalable format, it is preferable to load it at the desired size, rather than loading it at the default size and scaling the resulting pixbuf to the desired size.

format : a GdkPixbufFormat
Returns : whether this image format is scalable.

Since 2.6


gdk_pixbuf_format_is_disabled ()

gboolean    gdk_pixbuf_format_is_disabled   (GdkPixbufFormat *format);

Returns whether this image format is disabled. See gdk_pixbuf_format_set_disabled().

format : a GdkPixbufFormat
Returns : whether this image format is disabled.

Since 2.6


gdk_pixbuf_format_set_disabled ()

void        gdk_pixbuf_format_set_disabled  (GdkPixbufFormat *format,
                                             gboolean disabled);

Disables or enables an image format. If a format is disabled, gdk-pixbuf won't use the image loader for this format to load images. Applications can use this to avoid using image loaders with an inappropriate license, see gdk_pixbuf_format_get_license().

format : a GdkPixbufFormat
disabled : TRUE to disable the format format

Since 2.6


gdk_pixbuf_format_get_license ()

gchar*      gdk_pixbuf_format_get_license   (GdkPixbufFormat *format);

Returns information about the license of the image loader for the format. The returned string should be a shorthand for a wellknown license, e.g. "LGPL", "GPL", "QPL", "GPL/QPL", or "other" to indicate some other license.

format : a GdkPixbufFormat
Returns : a string describing the license of format.

Since 2.6


GdkPixbufFormat

typedef struct {
  gchar *name;
  GdkPixbufModulePattern *signature;
  gchar *domain;
  gchar *description;
  gchar **mime_types;
  gchar **extensions;
  guint32 flags;
  gboolean disabled;
  gchar *license;
} GdkPixbufFormat;

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.

gchar *name;the name of the image format.
GdkPixbufModulePattern *signature;the signature of the module.
gchar *domain;the message domain for the description.
gchar *description;a description of the image format.
gchar **mime_types;a NULL-terminated array of MIME types for the image format.
gchar **extensions;a NULL-terminated array of typical filename extensions for the image format.
guint32 flags;a combination of GdkPixbufFormatFlags.
gboolean disabled;a boolean determining whether the loader is disabled.
gchar *license;a string containing license information, typically set to shorthands like "GPL", "LGPL", etc.

Since 2.2


enum GdkPixbufFormatFlags

typedef enum /*< skip >*/
{
  GDK_PIXBUF_FORMAT_WRITABLE = 1 << 0,
  GDK_PIXBUF_FORMAT_SCALABLE = 1 << 1,
  GDK_PIXBUF_FORMAT_THREADSAFE = 1 << 2
} GdkPixbufFormatFlags;

Flags which allow a module to specify further details about the supported operations.

GDK_PIXBUF_FORMAT_WRITABLEthe module can write out images in the format.
GDK_PIXBUF_FORMAT_SCALABLEthe image format is scalable
GDK_PIXBUF_FORMAT_THREADSAFEthe module is threadsafe. If this flag is not set, gdk-pixbuf will use a lock to prevent multiple threads from using this module at the same time. (Since 2.6)

Since 2.2


GdkPixbufModulePattern

typedef struct {
	unsigned char *prefix;
	unsigned char *mask;
	int relevance;
} GdkPixbufModulePattern;

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.
unsigned char *prefix;the prefix for this pattern
unsigned char *mask;mask containing bytes which modify how the prefix is matched against test data
int relevance;relevance of this pattern

Since 2.2


GdkPixbufModuleFillVtableFunc ()

void        (*GdkPixbufModuleFillVtableFunc)
                                            (GdkPixbufModule *module);

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

module :a GdkPixbufModule.

Since 2.2


GdkPixbufModuleFillInfoFunc ()

void        (*GdkPixbufModuleFillInfoFunc)  (GdkPixbufFormat *info);

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

info :a GdkPixbufFormat.

Since 2.2


GdkPixbufModuleSizeFunc ()

void        (*GdkPixbufModuleSizeFunc)      (gint *width,
                                             gint *height,
                                             gpointer 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 gdk_pixbuf_get_file_info() efficiently.

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


GdkPixbufModulePreparedFunc ()

void        (*GdkPixbufModulePreparedFunc)  (GdkPixbuf *pixbuf,
                                             GdkPixbufAnimation *anim,
                                             gpointer 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.

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


GdkPixbufModuleUpdatedFunc ()

void        (*GdkPixbufModuleUpdatedFunc)   (GdkPixbuf *pixbuf,
                                             int x,
                                             int y,
                                             int width,
                                             int height,
                                             gpointer 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.

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


GdkPixbufModule

typedef struct {
	char *module_name;
	char *module_path;
	GModule *module;
	GdkPixbufFormat *info;
	
        GdkPixbuf *(* load) (FILE    *f,
                             GError **error);
        GdkPixbuf *(* load_xpm_data) (const char **data);

        /* Incremental loading */

        gpointer (* begin_load)     (GdkPixbufModuleSizeFunc size_func,
                                     GdkPixbufModulePreparedFunc prepare_func,
                                     GdkPixbufModuleUpdatedFunc update_func,
                                     gpointer user_data,
                                     GError **error);
        gboolean (* stop_load)      (gpointer context,
                                     GError **error);
        gboolean (* load_increment) (gpointer      context,
                                     const guchar *buf,
                                     guint         size,
                                     GError      **error);

	/* Animation loading */
	GdkPixbufAnimation *(* load_animation) (FILE    *f,
                                                GError **error);

        /* Saving */
        gboolean (* save) (FILE      *f,
                           GdkPixbuf *pixbuf,
                           gchar    **param_keys,
                           gchar    **param_values,
                           GError   **error);

        gboolean (*save_to_callback) (GdkPixbufSaveFunc save_func,
				      gpointer user_data,
				      GdkPixbuf *pixbuf,
				      gchar **option_keys,
				      gchar **option_values,
				      GError **error);
} GdkPixbufModule;

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.

char *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".
char *module_path;the path from which the module is loaded.
GModule *module;the loaded GModule.
GdkPixbufFormat *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.
save_to_callback ()

GdkPixbufAnimationClass

typedef struct {
        GObjectClass parent_class;


        gboolean                (*is_static_image)  (GdkPixbufAnimation *anim);

        GdkPixbuf*              (*get_static_image) (GdkPixbufAnimation *anim);
        
        void                    (*get_size) (GdkPixbufAnimation *anim,
                                             int                 *width,
                                             int                 *height);
        
        GdkPixbufAnimationIter* (*get_iter) (GdkPixbufAnimation *anim,
                                             const GTimeVal     *start_time);
} GdkPixbufAnimationClass;

Modules supporting animations must derive a type from GdkPixbufAnimation, providing suitable implementations of the virtual functions.

GObjectClass 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.

GdkPixbufAnimationIterClass

typedef struct {
        GObjectClass parent_class;


        int        (*get_delay_time)   (GdkPixbufAnimationIter *iter);

        GdkPixbuf* (*get_pixbuf)       (GdkPixbufAnimationIter *iter);

        gboolean   (*on_currently_loading_frame) (GdkPixbufAnimationIter *iter);

        gboolean   (*advance)          (GdkPixbufAnimationIter *iter,
                                        const GTimeVal         *current_time);
} GdkPixbufAnimationIterClass;

Modules supporting animations must derive a type from GdkPixbufAnimationIter, providing suitable implementations of the virtual functions.

GObjectClass 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.